IStructE
The operation and maintenance of bridge access gantries and runways Second edition
Gantries are complex machines as well as major structures. Complexity of design can increase the opportunities for error and complex operational procedures can lead to misunderstanding and mistakes. Gantries often have substantial electronic control gear and all parts are required to operate safely in very severe environments. The design of gantries is a specialist business and the work should not be undertaken lightly. This new edition of the Guide builds on the industry's experience following the first edition, and provides best practice guidance to all parties involved in the management of works of inspection, maintenance, refurbishment and strengthening of bridges where travelling gantries are to be employed. It is relevant to bridge owners, bridge operators, contractors undertaking works on bridges and their specialist subcontractors, utility companies working on bridges and their contractors and inspecting and testing houses. Furthermore the Guide is commended to designers considering the performance, function, serviceability, and maintenance of new or replacement gantries. All gantries require the same standard of operational safety, management responsibility, and performance. This Guide makes no distinction between permanently installed gantries, gantries which are moved from bridge to bridge, or temporary gantries – the same standards apply to all.
The operation and maintenance of bridge access gantries and runways
Bridge gantries, whether used for access or for works, can be a cause of real danger. Despite considerable efforts to improve design, manufacture and management of gantries, failures have still occurred, and have resulted in fatalities and serious injury.
The operation and maintenance of bridge access gantries and runways Second edition
Those who manage gantries are responsible for the safety of those who use them. It is considered vital that procedures are properly thought through, understood and followed, that vigilance is not relaxed and that changes are not made without detailed analysis of all the risks involved.
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Second edition
The Institution of Structural Engineers
October 2007
October 2007
The operation and maintenance of bridge access gantries and runways Second edition
IStructE The operation and maintenance of bridge access gantries and runways
Constitution of Task Group
Professor W J Harvey BSc PhD CEng FIStructE FICE (Bill Harvey Associates Ltd) Chairman Dr C Bird BSc MEng PhD CEng FIMechE (M G Bennett & Associates Ltd) B R Colford BSc CEng MICE (Forth Estuary Transport Authority) A J Clayton BSc CEng MICE (Network Rail) B H G Cresswell Riol BEng MICE (IStructE) R A Evans BSc CEng FICE MASCE (Consultant) K Herbert (Apollo Cradles Ltd) B Hill BSc(Eng) CEng MICE (Highways Agency) I E Hunter MA CEng FICE FIHT MIMechE (I E Hunter Associates) S J Matthews MSc DIC CEng FIStructE MICE (WSP Civils UK) M Reed BSc CEng MICE (Tractel, Chairman of SAEMA) G Neilson BSc CEng FIMechE (GN3D Engineering) D A B Thomas MSc BSc(Eng) CEng AKC FICE CFIOSH (William Hare Ltd, previously Health & Safety Executive) A H Tricklebank FRSA BSc(Eng) CEng FIStructE FICE FCIWEM (Gifford & Partners Ltd)
Corresponding members G T Bessant BSc CEng AMIStructE FICE MCIT (Transport for London) D K Doran BSc(Eng) DIC FCGI CEng FIStructE FICE (Consultant) A Hudson BSc CEng MIMechE IMarEng (Severn River Crossings) Dr J B Menzies BSc(Eng) PhD DipCU FREng FIStructE (Consultant) J D Parsons BSc CEng MIStructE MICE (Cass Hayward & Partners) D Thomas (Pembrokeshire County Council) B Valentine BSc MSc CEng MICE (Transport Scotland, Scottish Executive)
Consultant to the Task Group J A Gill MA CEng MICE (Jolyon Gill Consultancy Ltd) Acknowledgement The preparation of this Guide was in part funded by the Highways Agency whose support is greatly appreciated.
Published by The Institution of Structural Engineers, International HQ, 11 Upper Belgrave Street, London SW1X 8BH ISBN 978-1-906335-00-7 © 2007 The Institution of Structural Engineers The Institution of Structural Engineers and the members who served on the Task Group that produced this Guide have endeavoured to ensure the accuracy of its contents. However, the guidance and recommendations given should always be reviewed by those using the Guide in the light of the facts of their particular case and any specialist advice. No liability for negligence or otherwise in relation to this Guide and its contents is accepted by the Institution, the members of the Task Group, their servants or agents. Any person using this Guide should pay particular attention to the provisions of this Condition. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means without prior permission of the Institution of Structural Engineers, who may be contacted at 11 Upper Belgrave Street, London, SW1X 8BH.
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IStructE The operation and maintenance of bridge access gantries and runways
CONTENTS
glossary
vi
Foreword
ix
1
Introduction
1
1.1 1.2 1.3 1.4 1.5
2 2 3 3 4
Introduction Scope Use of gantries Outline process Use of this Guide
2 Review of existing access gantry facilities 2.1 2.2
2.3
3
Introduction Gantries and cradles 2.2.1 Gantry structure 2.2.2 Runways and their supports 2.2.3 Power systems 2.2.4 Bogies and wheels 2.2.5 Crabbing of gantries 2.2.6 Control equipment Walkways, platforms and ladders
5 6 6 6 8 9 9 10 11 11
Management and operation of bridge access gantries
12
3.1 3.2
13 13 13 13 14 14 14 15 15 15 15 16 17 17 17 18 18 19 19 19 20
3.3
3.4 3.5
3.6
Introduction Management system 3.2.1 Scope of management procedures for gantries 3.2.2 Organisation and responsibilities 3.2.3 Manuals Managing gantries 3.3.1 Planning 3.3.2 Control of gantry operation 3.3.3 Planning for emergencies 3.3.4 Working with interested third parties 3.3.5 Particular hazards 3.3.6 Phases of gantry operation Operating gantries Arrangements for working with contractors 3.5.1 Working relationship 3.5.2 Minor tasks 3.5.3 Major tasks 3.5.4 Runway beam and gantry replacement Records and review 3.6.1 Reporting and records 3.6.2 Review
IStructE The operation and maintenance of bridge access gantries and runways
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4 Training, Certification and Competence 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10
5
Introduction Legislative Requirements Certification Competence Assessment Training Course Training materials Post Training General Safety Induction Training for the use of existing gantries
22 22 22 23 23 23 23 23 24 24
Inspection and maintenance
26
5.1 5.2 5.3 5.4 5.5 5.6 5.7
27 27 28 28 28 28 28
Introduction The inspection and maintenance programme Inspections – levels and frequency Qualifications of inspectors Preventative maintenance Reactive maintenance Reporting and records
6 Testing and commissioning 6.1 6.2 6.3
6.4
6.5
6.6
Introduction Commissioning Load testing 6.3.1 Use of load testing 6.3.2 Gantry proof load test 6.3.3 Runway proof load test 6.3.4 Secondary load effects Mechanical testing 6.4.1 Use of mechanical testing 6.4.2 Gantry operation 6.4.3 Component testing Electrical testing 6.5.1 Verification 6.5.2 Certification and reporting Reporting and records
7 Refurbishment, retrofitting, replacement, re-commissioning and change of use 7.1 7.2 7.3 7.4 7.5
Introduction Refurbishment Retrofitting Replacement Re-commissioning
References
iv
21
30 31 31 32 32 32 33 33 34 34 34 35 35 35 35 36
37 38 38 38 38 39
41
IStructE The operation and maintenance of bridge access gantries and runways
Appendix A Safety legislation, codes and standards relevant to the UK
43
Appendix B Gantry life cycle
47
Appendix C Operational and safety procedures A typical example of relevant matters to be covered
49
Appendix D Gantry incidents, concerns and ‘near hits’ over recent years – Examples
Appendix E Gantry design – some considerations
52 54
Appendix F Gantry and runway inspections and maintenance
– more detailed guidance
63
Appendix G Gantry operation and maintenance manuals
– contents
IStructE The operation and maintenance of bridge access gantries and runways
69
glossary
Access A route by which part of a bridge superstructure is approached for inspection and maintenance purposes. Bogie A mechanism (with multiple wheels) which travels on the runway and is part of a gantry (see Figures Gl.1 and Gl.2).
Figure Gl.1 Bogie removed from runway during Principal Inspection of gantry
Bridge access gantry A mobile structure, which may be manually driven or powered, carrying platforms and/or cradles giving authorised personnel access to parts of a bridge for inspection or maintenance purposes. Principal members are usually constructed of steel or aluminium (see Figure Gl.3).
Figure Gl.3 Bridge access gantry
Bridge Operator The organisation which operates and maintains the bridge and its access systems for the owner. The bridge operator may be the owner. Crabbing An undesirable alignment of a gantry in skewed mode such that it is not in true alignment with its runway. It results from the bogies on one runway moving in advance of those on the other. This can result in large lateral loads being applied to the system and may result in bogies leaving the runway or structural failure of part of the supporting system. Cradle A platform (e.g. suspended access equipment) suspended on ropes giving access to parts of a bridge for inspection or maintenance purposes. This document does not provide specific guidance for cradles (see Figure Gl.4). Figure Gl.2 One of a pair of bogies
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IStructE The operation and maintenance of bridge access gantries and runways
to demonstrate load-carrying capability. Proof load tests are carried out during gantry commissioning or after refurbishment, prior to erection on the bridge and, in the case of the supporting elements, after erection. Rated Load (sometimes referred to as Safe Working Load or SWL). The maximum load, comprising personnel, equipment and materials, which the gantry is designed to carry for normal operational use and may include consideration of partial or unevenly distributed loads (see proof load test). Figure Gl.4 Cradle
Driver A competent person trained and responsible for driving a particular gantry.
Runway A generic term describing the path on which the wheels of a gantry bogie travel either on a bridge member or on a dedicated runway beam (see Figure Gl.5).
Gantry See bridge access gantry. Gantry Manager A competent and trained engineer appointed by the bridge operator to manage the whole process of continuous care for and use of gantries on a bridge. Legally the position can be referred to as the ‘Person in Control of the Premises’ (PCP) or the ‘Duty Holder’. Gantry Supervisor A competent and trained person appointed by the bridge operator to organise and control the day to day maintenance, operation and use of gantries. Longitudinal A dimension measured along the bridge. Manuals Documents held by management of supervisory staff which, among other things, set out procedures for the maintenance, care and use of gantries. The manuals also contain detailed specifications of all the equipment and structure. Owner The authority owning the bridge. The owner may also be the bridge operator.
Figure Gl.5 Runway beam
Runway beam A rolled steel section or builtup beam which is fixed to the permanent bridge structure and provides the runway for a gantry bogie (see Figure Gl.5).
Principal Inspection A close up and hands-on visual structural inspection of all gantry components at six-yearly intervals.
Scaffold A temporary framework supporting a fixed working p1atform. This document does not provide specific rules/standards for the provision and use of scaffolds which is given elsewhere.
Proof load test The application of a specific test load or several different loads (which have a more severe effect than the rated load) to a gantry
Spotter A trained, competent and formally appointed person assisting a gantry driver to manoeuvre a gantry safely and to observe and check its behaviour.
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Superimposed Dead Load (SDL) The load arising from fixed equipment, e.g. fixed ladders, engines, etc. Track The deck edge, girder flange or upstand attached to the girder of a bridge which provides the runway for a gantry (see Figure Gl.6).
Figure Gl.6 Track
viii
Transverse A dimension measured across the bridge width. Walkway A permanent pedestrian access to a part of a bridge (see Figure Gl.7).
Figure Gl.7 Permanent walkway
IStructE The operation and maintenance of bridge access gantries and runways
Foreword
I always wanted to be a bridge engineer. As a young man I worked on a number of big bridges and experienced a wide range of erection gantries. Most of them were a challenge to my comfort. Despite moving out of bridges and into academia 30 years ago, I have retained an interest in big bridges and I was very pleased to be asked to steer this Guide into a second edition. Bridge gantries, whether used for access or for works, can be a cause of real danger. Despite considerable efforts to improve design, manufacture and management of gantries, failures still occur and people are still killed. It may seem strange that the first message in a volume about gantries should be, “don’t use them unless you have to, and if you think you have to, think again”. Other forms of access are always being developed and even an existing gantry may be more difficult to use and more dangerous than a modern, flexible system. Of course, there are bridges where nothing else will do, where a gantry is truly essential, but even there, making a complex gantry that can reach into difficult corners may not be justified. The second message is, “complexity kills”. Complex designs have increased opportunities for error and complex operational procedures lead to misunderstanding and mistakes. Consider, for example, the accident at the M5 Avonmouth Bridge in the UK in 1999. The contractors involved pleaded guilty to a prosecution brought by the Health and Safety Executive after four people had been thrown from a gantry and killed. Gantries are complex machines as well as major structures. They often have substantial electronic control gear and all these parts operate in very severe environments. The design of gantries is a specialist business and the work should not be undertaken lightly. Be sure to have, or at least have ready access to, all the skills needed. There was considerable debate about including the appendix on design issues because some felt that it might encourage people to think it was sufficient. It isn’t, it is merely there to sound a warning. We worked from a very solid base in the first edition of this Guide (1996) and recognise the hard work put in by that Task Group. The present working group, listed inside the front cover, gave a great deal of time and energy to discussion and redrafting of this document. We all hope that the effort was worthwhile and that you find the new Guide as useful as the old and suitably in tune with current needs. We would also like to extend our gratitude to the Highways Agency for their financial support which allowed the appointment of a consultant to assist the Task Group. A final note. Those who manage gantries are responsible for the safety of those who use them. It is vital that procedures are properly thought through, understood and followed, that vigilance is not relaxed, that changes are not made without due consideration of all the risks involved.
Bill Harvey Chairman
IStructE The operation and maintenance of bridge access gantries and runways
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IStructE The operation and maintenance of bridge access gantries and runways
1 Introduction
Glossary of terms
1
Introduction • Scope • Use of gantries • Outline process • Use of this Guide
2
Review of existing access gantry facilities • Gantries and cradles • Walkways, platforms and ladders
3
Management and operation of bridge access facilities • Management systems • Managing gantries • Operating gantries • Arrangements for working with contractors • Records and review
4
Training, certification and competence • Legislative requirements • Certification • Competence • Assessment • Training course • Training materials • Post training • General safety induction • Training for older gantries
5
Inspection and maintenance • The inspection and maintenance programme • Inspections – levels and frequency • Qualifications of inspectors • Preventative maintenance • Reactive maintenance • Reporting and records
6
Testing and commissioning • Commissioning • Load testing • Mechanical testing • Electrical testing • Reporting and records
7
Refurbishment, retrofitting, replacement, re-commissioning and change of use • Refurbishment • Retrofitting • Replacement • Re-commissioning
References
Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F Appendix G
Safety legislation, codes and standards relevant to the UK Gantry life cycle – key considerations and flow chart Operational and safety procedures – A typical example of relevant matters Gantry incidents, concerns and ‘near hits’ over recent years – examples Gantry design – some considerations Gantry and runway inspections and maintenance – more detailed guidance Gantry operation and maintenance manuals – contents
The flow chart provides the full contents of this document.
IStructE The operation and maintenance of bridge access gantries and runways
Chapter one
1.1
Introduction
Bridge access gantries provide a particular solution to the problems of servicing the underside of bridge. They can be integral to a bridge from the outset or be devised to undertake a specific major strengthening or protective treatment project. They comprise moving carriages mounted on tracks or runway beams, permanently attached to the structure, with access systems to reach them from deck level or the substructures. Bridges can generally remain open to traffic whilst gantries are in use. Managing health and safety requires the use of industry best practice in the operation, maintenance and use of bridge access gantries because: • they are machines operated in a civil engineering environment, but they have to be operated and maintained as befits machinery • they are not covered in explicit and detailed terms by regulations as is, for example, other mechanical plant used on bridges such as cranes and lifting equipment • their use may involve organisations and personnel who have little or no previous experience of them • if not managed competently, their use can result in very serious accidents (some examples of gantry incidents are summarised in Appendix D).
Figure 1.1 Main cable access gantry
Chapter one
All gantries require the same standard of operational safety, management responsibility, and performance so this Guide makes no distinction between permanently installed gantries, gantries which are moved from bridge to bridge, or temporary gantries; the same standards apply to all. The guidance has been prepared by a Task Group of the Institution of Structural Engineers, comprising senior engineers with substantial personal experience of all aspects of gantries, drawing on information on current practice and experience provided by bridge owners, operators and others.
1.2
Scope
This new edition of the Guide provides best practice guidance to all parties involved in the management of works of inspection, maintenance, refurbishment and strengthening of bridges using all types of travelling gantries. It is relevant to: • bridge owners • bridge operators • contractors undertaking works on bridges and their specialist subcontractors • utility companies and their contractors working on bridges • inspecting and testing houses. It updates the guidance for the operation and maintenance of bridge access gantries, and builds on the industry’s experience of health and safety including the Construction (Design and Management) Regulations1 since their inception. The Guide is commended to designers considering the performance, function, serviceability, and maintenance of new or replacement gantries. It will also assist in their assessment of the effects on bridges imposed by gantries supported from them. The Guide is not intended to provide comprehensive or sufficient guidance on the design of gantries. Gantry design should only be undertaken by design organisations with strong relevant experience in the structural and mechanical engineering disciplines (see Appendix E). The guidance does not cover other mechanical equipment used on bridges such as erection gantries, cradle hoist systems, or suspension bridge main cable access gantries (see Figure 1.1), though they present some similar management and technical challenges.
IStructE The operation and maintenance of bridge access gantries Chapter and runways one
1.3 Use of gantries Prospective users of gantries have to take account of their particular characteristics: • they are of great variety, usually tailor-made for each bridge • as machines, they have to be kept in commission by systematic inspection, testing and maintenance • their electrical and mechanical components are much more vulnerable to the elements than the gantry structure or the bridge • the lack of systematic maintenance renders them unusable without comprehensive re-commissioning • they are used intermittently and often for short periods • they require safe access for personnel, equipment, services and material for the planned work • their use is limited by defined rated loads and their distribution, and to the extent that they provide safe access for work to be done • they provide a remote, isolated and exposed work place at height • in the event of mechanical failure, the occupants can be marooned • they provide an unfamiliar work environment for general operatives, tradesmen and specialist technical staff • they must be operated only by trained competent gantry drivers • they require the use of documented safe systems of work for any task to be carried out with or from a gantry • the consequences of accidents, as with cranes, can be very serious • the risk of unplanned incidents and actions must be considered high. The circumstances in which gantries are used vary widely and include: • regular use on long span bridges with an established team for routine inspection and maintenance • infrequent use by bridge operators for routine inspection and maintenance using their own personnel • provision of access to a specialist contractor for minor works • use of installed gantries by a main contractor to carry out substantial works with specialist subcontractors • use of project-specific gantries provided by a main contractor to carry out substantial works • installation of replacement runway beams or gantries.
Each set of circumstances requires a systematic planned approach from the outset to manage risk, define responsibilities, and ensure that all personnel are trained and competent to fulfil those responsibilities. Procurement processes must demonstrably show this is done effectively. The use, operation and serviceability of gantries is dependent in the first instance on the quality of the original design; a specialised activity requiring an integrated approach from the mechanical, electrical and structural disciplines to the gantry and runway system. During the life of each bridge, design and engineering input in relation to the use of gantries is required for: • providing structural and mechanical information about the gantry and the bridge to users • a written protocol for commissioning and recommissioning • assessment of users’ proposals for tasks involving gantries including effects on runway beams, on the bridge itself and on operation of the bridge • design of replacement gantries and runway beams • design and assessment of project specific gantries. Designers undertaking this work require an informed appreciation of the detail and condition of the bridge, and all that is involved in carrying out the planned work with the gantries (for more consideration relating to design issues, see Appendix E). A procurement process, which seeks competent management of risks by the whole supply chain, must provide sufficient time for familiarisation and realistic pricing of the risks: an informed balance between quality and price should be maintained. When complex operations or new gantries are required, the procurement plan and process must allow sufficient time for all the parties to communicate, interact and carry out their work planning, designing, checking supply and commissioning as well as training for gantry use. This will be particularly significant for powered gantries which incorporate complex mechanisms and control systems.
1.4 Outline process Ownership of a bridge access gantry brings with it responsibilities which continue from its inception and initial commissioning of the gantry throughout the whole of its operational life until it is finally disposed of. Appendix B gives an indicative, but not exhaustive, summary of a typical gantry life cycle with key considerations and a flow chart.
IStructE The operation and maintenance of bridge access gantries and runways
Chapter one
The responsibilities of gantry ownership can only be fulfilled through a continuous process of care and maintenance, operational control and management. The process may extend to twenty or thirty years for a permanent installation before the gantry is upgraded or replaced. For a contractor charged with the use of a gantry, those responsibilities will last for the duration of the specific project. The process is potentially subject to change in the condition of the bridge and the gantry system, in the use and environment of the bridge, in the regulatory regime and advancing technology, and in organisation and personnel. After initial installation and commissioning, the process includes: • maintaining the gantry system • ensuring the gantry remains safe to use • ensuring the gantry is used safely all the time • enabling contractors to make use of the gantry effectively and safely • design and engineering input (as described in Section 1.3) • managing costs to ensure best value • replacing components, carriages and runways • and, possibly, re-commissioning after extended periods out of use, or damage, accident or neglect. The key responsibility for the bridge operator in managing the process is to maintain continuously a comprehensive, documented knowledge base. That will comprise: • original design data for the gantry (and the bridge where appropriate) • commissioning, operational and signed service records (to establish responsibility) • operation, maintenance and training manuals • risk assessments and method statements for safe systems of work using the gantry • survey and inspection reports. Nowadays this information should form part of the bridge health and safety file. Just as significant to the process is the personal knowledge of the bridge managers, their staff, and any third party service organisation; so maintaining continuity of experience and expertise is essential too.
Chapter one
The bridge operator should manage the gantry process by appointing an appropriately experienced chartered engineer to take responsibility for ensuring that all work on and with gantries by the bridge operator or contractor undertaking works on the superstructure are carried out in an informed, planned and controlled safe manner. If a gantry is used only infrequently (and there are other means of practicable access available), then the investment necessary to sustain the whole process for a gantry system may outweigh the advantages of using a dedicated gantry. Bridge operators would then need to carry out thorough whole life costing of their options and take account of the installation, use, replacement or scrapping of a gantry system – supported of course by strict assessment of the risk to health and safety.
1.5 Use of this Guide The Institution of Structural Engineers has produced this report as a summary of current best practice and, as such, it is only intended for use as a guide. It is not intended to provide the definitive approach in any situation, as in all circumstances the party best placed to decide on the appropriate course of action will be the bridge operator undertaking the particular project. Where this Guide is used as a basis for a specification of goods, materials, tests, qualifications, certificates, etc. in the United Kingdom, users should ensure that they fulfil their legal obligations to consider and use equivalents sourced from elsewhere. Nothing in this Guide should be construed so as to suggest that an equivalent may not be used unless, exceptionally, such use would be unlawful. Current good practice in management and operation, training, inspection and maintenance, testing, refurbishment and re-commissioning is set out in Chapters 3, 4, 5, 6 and 7 of this Guide following a review of existing facilities in Chapter 2. Chapters 1, 2 and 3 are intended to be most useful to those responsible for the management of bridge access gantries. Chapters 4, 5, 6 and 7 give guidance that is targeted at the general operation and maintenance of gantries. The Appendices give more specific details. The flow chart illustrating the full content of this document highlights at the beginning of each chapter the material about to be presented.
IStructE The operation and maintenance of bridge access gantries and runways
2 Review of existing access gantry facilities
Glossary of terms
1
Introduction • Scope • Use of gantries • Outline process • Use of this Guide
2
Review of existing access gantry facilities • Gantries and cradles • Walkways, platforms and ladders
3
Management and operation of bridge access facilities • Management systems • Managing gantries • Operating gantries • Arrangements for working with contractors • Records and review
4
Training, certification and competence • Legislative requirements • Certification • Competence • Assessment • Training course • Training materials • Post training • General safety induction • Training for older gantries
5
Inspection and maintenance • The inspection and maintenance programme • Inspections – levels and frequency • Qualifications of inspectors • Preventative maintenance • Reactive maintenance • Reporting and records
6
Testing and commissioning • Commissioning • Load testing • Mechanical testing • Electrical testing • Reporting and records
7
Refurbishment, retrofitting, replacement, re-commissioning and change of use • Refurbishment • Retrofitting • Replacement • Re-commissioning
References
Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F Appendix G
Safety legislation, codes and standards relevant to the UK Gantry life cycle – key considerations and flow chart Operational and safety procedures – A typical example of relevant matters Gantry incidents, concerns and ‘near hits’ over recent years – examples Gantry design – some considerations Gantry and runway inspections and maintenance – more detailed guidance Gantry operation and maintenance manuals – contents
IStructE The operation and maintenance of bridge access gantries and runways
Chapter two
2.1
Introduction
2.2.1 Gantry structure Underdeck gantries in their simplest forms usually consist of a main structure spanning transversely across the underdeck space (whole or part) and supported by bogies on runway beams or tracks (see Figure 2.1). The runways are usually continuous and fixed to the bridge deck structure (see Figure 2.2). Several gantries running in parallel along the bridge may be used to give access to the whole underdeck.
Typically gantry structures are made of steel or aluminium, frame a working platform and span between the supporting bogies. A gantry of space frame construction may consist of a single, double or multiple platform structures which are supported on two runways fixed to the bridge (see Figure 2.3). An upper platform may give access to a cantilever soffit and the top of the adjacent webs of the bridge beams. A lower platform may be able to be rotated horizontally, or slewed, through 180° to give access to the soffit of the bridge and, when positioned longitudinally, to allow travel past pier locations. It may also be adjustable in height using a lowering/ raising mechanism (see Figure 2.4). More usually underdeck gantries, spanning transversely, include means to reduce their transverse length to enable travel along the bridge past piers,
Figure 2.1 Underdeck gantry
Figure 2.3 Two platform structure
Figure 2.2 Runways fixed to deck
Figure 2.4 Slewing gantry
The number of permanently installed existing bridge access gantries in the UK is not precisely known but it is believed to be about a hundred. The following paragraphs give an overview of the considerable variation in type.
2.2
Gantries and cradles
Chapter two
IStructE The operation and maintenance of bridge access gantries and runways
or to extend their working platforms to reach, for example, the soffits of a cantilevered carriageway or access to the outside of main girders. Alternatively, the working platform may be suspended on bogies directly from the gantry with the bogies travelling from one end of the gantry to the other across the bridge width to give access to different parts of the underdeck (see Figure 2.5). Special gantries on larger suspension and cable stayed bridges are used to give access to the cables (see Figure 2.6). Some travel along the cables on wheels, often running on the cable handstrands. (Although cable gantries are not specifically covered by this document and especially not by the inspection and testing recommendations, much of the best practice presented in this document may be relevant). Gantries may also carry cradles (not covered by this document) suspended from a single gantry or
spanning between two gantries. These facilities are used in particular to give access to the faces of piers. Cradles are also used on the larger suspension and cable stayed bridges to give access to the towers and to cable hangers. Scissor lifts or other forms of elevating work platforms are sometimes mounted on the platform (also on cradles) to allow access to the gantry and/or inspection/maintenance of surfaces (sides of girders, soffits or deck) above the gantry platform, (see Figure 2.7). Gantries may carry permanent scaffolds for the same purposes. Generally gantries are permanently in place on their runways and, when not in use, are parked in the span of the bridge (sometimes with additional supports to reduce local loading or for storm protection) or in a ‘garage’ at an abutment. In a few cases gantries are demountable and stored off-site when not in use.
Figure 2.5 Platform suspended from gantry
Figure 2.6 Cable access gantry
IStructE The operation and maintenance of bridge access gantries and runways
Figure 2.7 Scissor lift
Chapter two
Proprietary access systems are also available which can provide underdeck gantries and other access facilities as and when required (see Figure 2.8). 2.2.2 Runways and their supports Runway beams for underdeck gantries and their supports are usually made of steel I sections which are bolted or welded to the bridge superstructure (see Figure 2.2). The gantry wheels either run on the top flange of the steel section or on both sides of the bottom flange. Some gantry systems have moveable runway beams. This can allow the gantry system to pass between the bridge piers. The use of an upper frame, consisting of a pair of I beams spanning transversely across the bridge, allows the working platform to be not as wide as the bridge. The upper frame can travel along the length of the bridge, being supported from primary runway beams welded to the bottom flange of the main bridge girders. The work platform is slung below the upper frame, and can traverse the upper frame, in similar manner to the crab unit of an overhead crane. The wheels of the work platform
are set in from its ends. Thus when the platform is travelled to one end of the upper frame, the scissor lift at the end of the platform can be raised outside of the main bridge girder. When the platform is centralised on the upper frame the whole gantry system can travel along the bridge between the bridge piers. (see Figure 2.9). These gantry systems, as with all gantries, can be prone to misuse and should be subject to rigorous risk assessment and suitably robust management procedures. The bridge structure can serve as a runway in some cases. This can be the deck edge (in concrete or steel), the girder flange or an upstand continuously welded to the flanges. This arrangement usually has less scope for adjustment and levelling of the runway. However, where such an arrangement is possible (see Figure 2.10) it can lead to a very effective solution because it avoids the need to provide separate runway beams, which are expensive and difficult to inspect and maintain. Special cable gantries used for access to the cables of suspension bridges will usually use the cable handstrands as their runways.
Figure 2.9 Moveable runway beams
Figure 2.8 Proprietary access system Courtesy of Facelift Access Hire (www.facelift.co.uk)
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Figure 2.10 Deck edge runway (runway beams not required)
IStructE The operation and maintenance of bridge access gantries and runways
The supports for runways generally need to carry horizontal lateral loads from the bogies (e.g. from wind or gantry crabbing actions) and to provide lateral restraint to the bogie wheels to ensure that they remain in their correct position on the runway. Where runways are included on parts of a bridge which incorporate a movement joint, the runway may also need a movement joint feature to ensure the runway remains continuous for all bridge positions (see Figure 2.11). It should be noted that traversing movement joints in a running system is a high risk activity. Special attention should be given to the procedure in the operating instructions. 2.2.3 Power systems Power for driving gantries may be manual but is more usually provided by a diesel, petrol, or gas engine mounted on the gantry or placed nearby on or below the bridge or by mains electrical supply or compressed air. Non-powered platforms are sometimes provided on the runways and used with self-propelled gantries to give larger working platform areas. Power may be transmitted to driving wheels (the most usual method for underdeck gantries) or the gantry may be pulled along its tracks using wire ropes and motorised pulling equipment. Driving wheels may be driven by electric, compressed air or hydraulic motors. Power systems are generally arranged to enable a soft start to gantry travel and usually have a low maximum speed (e.g. up to 20 m/minute, which is a very slow walking speed). 2.2.4 Bogies and wheels The wide diversity of gantry forms leads to a large variety of mounting arrangements. Gantries are usually supported by one or more mounting carriages bearing upon the runways. The carriage to gantry connection may be rigid or may include an articulated linkage which can accommodate vertical variations in runway alignment. Overslung gantries may have a rigid connection, with a single rigid-frame carriage on wheels (see Figure 2.12). Most underslung gantries comprise a frame spanning between bogies running on two runway beams, although monorail systems are also in use. A balanced configuration is usual. The bogies themselves may be mounted on outrigger arms which reduce the length to breadth ratio, stabilising the movements of the gantry and reducing any tendency to crab. The bogies usually house both
Figure 2.11 Movement joint in runway
Figure 2.12 Overslung gantry
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Figure 2.13 Bogie wheel arrangement
vertically loaded running wheels and horizontal guide wheels (see Figure 2.13). A symmetrical wheel arrangement with horizontal guide wheels running on either the beam web or edges of the flange will provide some resistance to lateral movement, but will not prevent crabbing. Motive power may be supplied by driving all or some of the running wheels. A few underslung gantries span between vertical support frames, situated just clear of each parapet. The tops of the frames house projecting axles which carry the gantry running wheels. These traverse the top of the bridge deck either directly or on rails. This arrangement has the advantage of providing for access ladders to the underdeck gantries. Most climbing gantries are cable mounted although some are mounted on racks. For gantries which can only travel vertically the winches, racks or screws carry out the functions of both support and raising/lowering. Gantries giving access to suspension bridge cables travel both horizontally and vertically. The gantry ‘car’ is suspended from a cable trolley, usually running on the handstrand cables. The power is often provided by winching on auxiliary drive cables. Symmetric mounting arrangements may be used for the trolley, drive and brake wheels. The working platform is usually provided with a pivot to ensure the platform is horizontal anywhere on the cable.
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2.2.5 Crabbing of gantries Crabbing is a possible phenomenon, often when the wheel base is short compared with the span, or as a result of the drive wheel arrangement. It can lead to large side loads on the wheels which may cause damage, such as de-bonding of polyurethane tyres from wheels. Crabbing forces can sometimes be minimised (at the design stage) by articulation of the bogie assembly about the vertical axis allowing bogies to move longitudinally relative to each other up to predetermined limits. Anti-crabbing devices vary in sophistication. There may be no provision for limiting crabbing or, if provision is made, it may consist of side rollers only. Crabbing is often limited in operation by the manual intervention of the gantry driver in adjusting the drive. The ideal situation is one in which the design of the gantry is such that even if it were crabbed to the fullest limit of its geometry no damage or derailment would be caused. Sophisticated (anti-crabbing) control systems should only be needed where this ideal situation cannot be achieved. In such a case, gantries may be equipped with sensors which detect crabbing and input to a control system which adjusts the motor drives to keep crabbing movement within pre-set limits. However, it is necessary to provide some manual override controls to permit correction.
IStructE The operation and maintenance of bridge access gantries and runways
2.2.6 Control equipment Some gantries are equipped with proximity sensors (e.g. mechanical limit switches, doppler sonic or infra-red sensors, photocell incline sensors) to prevent movement beyond safe limits. In particular, sensors are used to prevent collision with bridge piers or other obstructions and to prevent the gantry becoming inclined beyond safe limits. Sensors may also be used to initiate automatic speed control systems. In all cases the design of the system should ensure that any sensor failure leaves the gantry in a safe condition. Proximity sensors may also be fitted to gantrymounted equipment, e.g. scissor lifts, to prevent collision with the bridge structure. They should be fitted by specialists and should only be replaced by experts fully conversant with their operating limits. Gantries which have extendable platforms, slewing or height adjustment usually have anticollision sensors to limit all motions. Other types of ‘cut out’ arrangements are found. For example, bogies may be fitted with mechanical switches which cut out the drive to the bogies if the wheels rise off the runway. Where the width of the gantry is adjustable to permit access to a splayed or wider section of deck, the design and operation of the interlock system, which should only be operated by an authorised and trained gantry driver under a permit, is extremely
critical. It must be ensured that the span of the gantry is locked into its ‘normal’ moving position after operation on the overwidth location. Emergency stop switches are fitted on some gantries. These switches are hand operated or they may be connected to a tensioned wire placed so that an operator would lean against it and trigger the cut out if stretching over the platform barrier or trapped between the barrier and superstructure as the gantry moves along.
2.3 Walkways, platforms and ladders These facilities may be fixed or moveable parts of the bridge access system. They may be part of a toolkit designed to be used in a defined way on specific parts of the gantry to provide access to the bridge structure and services for inspection and maintenance and/or to give access to gantries and cradles (see Figure 2.14). Walkways and platforms generally have open mesh flooring and are provided with barriers and handrails. Permanent ladders generally have hooped safety cages. Removable or extending ladders are sometimes employed (but their use is strongly discouraged) where permanent ones are not practicable or have been removed for security reasons. They are generally open ladders and in some cases their deployment is such that the use of personnel fall protection equipment is required for safety.
Figure 2.14 Access to gantry from roadway
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3 Management and operation of bridge access gantries
Glossary of terms
1
Introduction • Scope • Use of gantries • Outline process • Use of this Guide
2
Review of existing access gantry facilities • Gantries and cradles • Walkways, platforms and ladders
3
Management and operation of bridge access facilities • Management systems • Managing gantries • Operating gantries • Arrangements for working with contractors • Records and review
4
Training, certification and competence • Legislative requirements • Certification • Competence • Assessment • Training course • Training materials • Post training • General safety induction • Training for older gantries
5
Inspection and maintenance • The inspection and maintenance programme • Inspections – levels and frequency • Qualifications of inspectors • Preventative maintenance • Reactive maintenance • Reporting and records
6
Testing and commissioning • Commissioning • Load testing • Mechanical testing • Electrical testing • Reporting and records
7
Refurbishment, retrofitting, replacement, re-commissioning and change of use • Refurbishment • Retrofitting • Replacement • Re-commissioning
References
Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F Appendix G
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Safety legislation, codes and standards relevant to the UK Gantry life cycle – key considerations and flow chart Operational and safety procedures – A typical example of relevant matters Gantry incidents, concerns and ‘near hits’ over recent years – examples Gantry design – some considerations Gantry and runway inspections and maintenance – more detailed guidance Gantry operation and maintenance manuals – contents
IStructE The operation and maintenance of bridge access gantries and runways
3.1
Introduction
The process of managing gantries continuously throughout their lifespan involves a wide range of activities and a variety of skill and expertise. The objective is to ensure that gantries are safe to use and used safely in all circumstances. Bridge operators use management systems developed from their Health and Safety Policy which cover all aspects of their responsibilities; for health and safety and quality with proper regard for the environment. Procedures should be fully documented, promulgated throughout the organisation, systematically reviewed and maintained; they must comply with current health and safety regulations. Provision of proper access to carry out any task on a working bridge is fundamental to the efficiency and safety of that bridge; it is an integral part of bridge management. Access with gantries presents particular challenges to bridge operators especially as most are used intermittently, sometimes with long periods of inactivity. Therefore the procedures for gantries must be robust to ensure continuity in managing them, and in the training of the people who make use of them. This applies throughout all types of change and over long periods of disuse, not only when the gantries are about to be used. This Chapter outlines the main areas of a management system for bridge access gantries and details procedures for gantry operation, and for their use by bridge operators and contractors. Gantries may be simple or complex, bridges may be large or small, use may be spasmodic or regular, but the principles of gantry management are common to all. The bridge operator or a contractor should apply them as part of their own procedures and safe systems of work to suit their particular circumstances.
3.2
Management system
3.2.1 Scope of management procedures for gantries On any bridge where gantries are to be used, the bridge operator’s management system should provide arrangements for: • their management as a continuous process • maintaining an up-to-date knowledge base • keeping gantries in commission or in a planned out-of-use state • maintaining trained supervisors, maintenance staff and gantry drivers • safeguarding bridge users, third parties and the environment
• • • • • • • • • •
establishing relationships with contractors using gantries control of access to and use of gantries ensuring that only designated trained gantry drivers operate them induction and training for all personnel on gantries clear documented work instructions for supervisors, maintenance staff and gantry drivers safe systems of work for all tasks involving gantries operational communication emergencies monitoring performance continuous improvement through reporting, feedback and review.
Helpful guidance is also provided in HSG 65, Successful health and safety management2. 3.2.2 Organisation and responsibilities The bridge operator is responsible for the safety of all works and operations on a bridge (whether carried out by permanently employed staff or by separately employed contractors), which must be carried out in accordance with all relevant statutory provisions. The principal Regulations are summarised in Appendix A. The bridge operator should take overall responsibility for training all personnel working with gantries on the bridge. Safe operation of gantries depends on managers, supervisors and operatives working together with a clear understanding of their responsibilities, their authority, and the controls to be respected. The bridge operator’s organisation chart should show a clear chain of command and the relationships with the executive responsible for the Policy and with health and safety officers. Job descriptions should define the duties and responsibilities for each role unequivocally. The bridge operator should appoint a gantry manager to carry through the whole process of caring for, operating, using, repairing and replacing gantries on the bridge: this role is best filled by a chartered engineer with the knowledge and understanding to resource, integrate and oversee all the activities envisaged in 3.2.1. The gantry manager should keep a register of trained supervisors, maintenance personnel and gantry drivers. The role of the gantry supervisor is to organise and control the maintenance, operation and use of the gantry in compliance with procedures and work instructions and in particular to: • oversee the preparations before a new phase of gantry operation
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• • • • •
carry out the prescribed controls on access, personnel and use brief gantry drivers and personnel working on the gantry monitor operations and work, and instigate corrective action maintain communications and coordinate the response to emergencies manage gantry records on a day to day basis.
It must be clear who the driver of a gantry is at any time. The designated trained gantry driver should report to the gantry manager and is responsible for safe operation of the gantry and for the personnel on it. Only the gantry driver should operate it and should be responsible for: • carrying out the daily check before use, including the loading • operating the gantry strictly in accordance with work instructions and as required by the safe systems of work for tasks carried out on or from the gantry • observing the running condition and behaviour of the gantry and reporting defects, malfunctions, mishaps or accidents • completing a log book at the end of each operating shift. 3.2.3 Manuals It should be noted that for clarity in giving guidance, the text refers to separate Operations, Maintenance, Training and Drivers’ Manuals, indicating the scope of the document under consideration. These may be separate manuals or parts of one larger manual according to the needs of the particular bridge. Management procedures define how the gantry manager deals with the overall process, whereas supervisors and operatives require clear, logically presented, and unambiguous detailed work instructions to maintain the gantries and to operate them. These are provided in the form of Manuals designed specifically for their use: Gantry Operations and Maintenance (O&M) Manuals should: • refer to the manufacturer’s inspection and maintenance instructions (or manuals) and be consistent with them and the designer’s intentions • be prepared before commissioning so as to be available for commissioning, training and operations at initial handover • be reviewed and kept up to date by the gantry manager
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•
•
include emergency procedures and provide for the safety of everyone in the vicinity of gantry activities, as well as the personnel directly involved be promulgated to all gantry personnel by formal regular training according to their duties.
A full set of manufacturer’s as-built drawings for the gantry and runway system should be available with the original design documentation. Should they not be available for an existing gantry, an engineering appraisal should be carried out with inspections, surveys and material testing where appropriate: otherwise, worst case assumptions should be made for materials and specifications. Guidance on the content of the Operations Manual is given in 3.4 and Appendix G; it should include a gantry drivers’ Manual giving the detailed operating instructions for routine use. An example of operational and safety procedures used on one particular bridge is given in Appendix C. Inspection, maintenance and testing practice is covered in Chapters 5 and 6. Personnel providing training should be trained and competent to do so and they should use Training Manuals, developed from the management procedures and O&M Manuals, to maintain consistency of content and scope (see Chapter 4). The distinction should be drawn between the routine activity covered by the Manuals, and the provision of safe systems of work for tasks carried out using gantries. The safe systems of work require risk assessment, the development of methods, and method statements to cover the whole of the task whilst continuing to operate the bridge safely, of which operating the gantry will be but a part.
3.3
Managing gantries
3.3.1 Planning The resume of the key Regulations in Appendix A sets out the framework within which all managers and supervisors responsible for bridge gantries and their use fulfil their duties. They must know and understand these Regulations and how to apply them. All activities have to be planned, so that resources can be used efficiently and economically whilst demonstrating that they are safe. All systems of work, methods and work instructions must be based on risk assessments which identify the hazards involved and set out actions to eliminate and/or reduce risk; systems of work must be communicated clearly and be understood by the personnel carrying them out.
IStructE The operation and maintenance of bridge access gantries and runways
Keeping gantries in commission and safe to use, and using them safely, needs to be systematic. They should be included explicitly in the bridge operator’s overall management programme for the bridge. Gantry inspections, testing and maintenance should be planned; training, and retraining of staff, should maintain a sufficient cadre of supervisors, gantry drivers and maintenance staff. Phases of gantry operations should be prepared for efficiently and closed out carefully.
manager should anticipate: • incapacity of the gantry driver • accident or injury to personnel on the gantry • mechanical breakdown • loss of traction • fire involving gantry machinery or work processes • fumes or dust • electrocution • unplanned overloading.
3.3.2 Control of gantry operation Trespass and unauthorised access and use must be prevented. This should be anticipated in the design, but it can be affected, depending on the bridge layout, by: • removal of access ladders • locking gates or manholes on access routes • removing the carriage from the bridge to store • removal or immobilisation of the drive control or power source • parking at an inaccessible location.
Each operating gantry must carry the appropriate safety and first aid equipment. Discussions should be held with the local emergency services to establish the procedures to be followed, although it may not always be possible to rely on the emergency services to effect escape. Escape from the gantry carriage should be possible at any position on the bridge, and preferably a choice of safe routes should be available. On highway bridges without walkways, measures to protect personnel from traffic are essential. Planned emergency traffic management arrangements are required for rescue and recovery vehicles. Training and procedure rehearsals with the emergency services should be considered.
Access to gantries should be restricted to authorised personnel needed to operate and separately to work on them for planned tasks, all of whom must have relevant training and competence. Occasional visits by engineering staff or prospective contractors must be preceded by formal induction covering gantry movements, personal safety, and escape procedures. Occasional visitors will usually need to be accompanied by a competent person. The bridge operator should assess the risks to health and determine whether prospective gantry personnel should be subject to fitness and health checks. Measures should be in place to prevent the movement of gantries when authorised gantry drivers are not available. Every use of a gantry requires some measure of planning, preparation and checking before the start: control is essential so use of a permit-to-work procedure should be considered, operated by the supervisor and authorised by the gantry manager. The procedure should suit the circumstances of the particular bridge, the organisation and the work to be done; it may involve strict control of the issue and return of keys for access or to power systems. 3.3.3 Planning for emergencies Emergency procedures have to be planned for all reasonably foreseeable emergencies which may occur on the bridge. For work with gantries the gantry
3.3.4 Working with interested third parties The bridge may pass over footpaths, roads, railways, navigable waters or shipping channels; it may adjoin residential, commercial or industrial properties; the bridge serves the public going about their business. The bridge operator has to safeguard the interests of all who may be affected by work on the bridge, and not prejudice the responsibilities of the authorities involved. Gantry movement and work on gantries requires consultation with interested parties and agreement on the measures to be adopted. They may well put constraints on gantry operation. Protocols should be agreed with the relevant bodies with details to cover emergencies and routine contact. For some activities it may be appropriate to provide information to road users and local residents as part of good customer care. 3.3.5 Particular hazards Of the variety of hazards that may have to be considered by the gantry manager or contractor in planning work with and on gantries, measures commonly have to be taken to deal with the following: Working at height – although gantries are often at considerable height and exposed, the edge protection
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of gantry platforms means that personal fall protection equipment should not be required except where a task may require an individual to move above or reach beyond the platform. Whenever practicable, and certainly in designing new facilities, the access routes to gantries and for escape in emergency should eliminate the risk of falling. Working over water – the risk of falling into water
should be eliminated in the same way. Where that is not reasonably practicable, the bridge operator should consider whether inflatable life-jackets should be worn and, except where tides or currents are hazardous, whether a recovery vessel is necessary (there are hazards associated with operating boats which may outweigh the risks associated with falls into the water). Otherwise special rescue equipment should be provided. Manual handling – access to gantries under a
bridge deck is often not straightforward or direct, so transferring tools, equipment and materials between transport and gantry may be difficult and involve extensive manual handling of heavy or bulky items. Planning must consider the use of mechanical devices and trolleys to minimise lifting. Where practicable, hatches should be provided to lower items directly on to the gantry. Lifting and other equipment may be required on the gantry itself. Moving machinery – relative movement between
a gantry and the bridge structure, and the movement of wheels, trolleys, bogies and drive systems present the risk of injury due to impact, entanglement or entrapment. Notwithstanding passive measures and guards built into the equipment, personnel need to be aware of the hazards and should be positioned in safe areas during gantry travel or movement. Exposure to bridge traffic – even if personnel
can get to and from the gantry from footways on the bridge, there will sometimes be situations where they may be exposed to traffic on the deck; for access for material, equipment or plant, or for emergency access and rescue. Pre-planned traffic management arrangements should be agreed with the police and highway authority, which can be implemented to agreed timetables. The intent would be that vehicles and people should be kept separate. Falling objects – the gantry design should eliminate
the risk of tools, equipment or material, including
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waste and water, from falling from the gantry or access routes during normal operation of the gantry – protecting people and property below the bridge. Emissions – exhaust fumes from internal combustion
engines powering a gantry can become a hazard in certain conditions, e.g. between girders, so extraction equipment may be necessary. Planning for tasks to be carried out on, or from, the gantry must assess the risks arising from fumes, dust or other emissions from the process and provide protective measures. Gantry overload – the systems of work for tasks
on the gantry need to take account of the loads from personnel, materials, and process on the gantry so that there is no risk of exceeding the rated load or its distribution. The rated load should be displayed clearly and permanently on the gantry platform together with the name of the competent person authorised to permit its use. Strict control of processes may be required, for example, continuous removal of grit from blasting or water from cleaning. It is best practice to clear the gantry of all waste and loose items at the end of each shift. Contractor’s proposals may need design checks and approvals. Effects of wind – wind on exposed bridge gantries
poses a hazard which has to be considered. In winter, wind-chill can be a serious hazard to the health and performance of personnel. Strong winds may affect gantry travel and can blow gantries uphill; strong winds can cause local overload of the gantry or runway beams especially if temporary screening has been fixed to the gantry. The gantry manager, taking expert advice if necessary, should set limiting wind speeds for gantry operation and maintain a procedure for accurate weather forecasts and wind speed measurement at the bridge. The deployment and removal of temporary screening should be strictly controlled by written procedure. 3.3.6 Phases of gantry operation Utilisation of gantries is typically low, so it cannot be assumed that they are ready for use at short notice even when properly maintained. All phases of gantry operation need planning. The time needed will depend on how the particular gantry is managed and the task to be undertaken. The gantry manager needs to: • check that maintenance, inspection and testing will be up to date at the date required • check that trained staff will be available for
IStructE The operation and maintenance of bridge access gantries and runways
• • • •
supervision and driving contact third parties and agree arrangements arrange training of personnel using the gantry for the task arrange for the documented safe system of work for the task implement requirements of the CDM Regulations1 if applicable, e.g. Health & Safety Plan.
Further considerations arise when contractors are using the gantry (see 3.5). When a phase of gantry use is complete, actions are needed to: • shut down the gantry for security, safety and protection from the weather • debrief the supervisor and gantry driver • review gantry behaviour, records, and procedures • consider and implement follow-up actions.
3.4 Operating gantries The scope of the Operations Manual (see 3.2.3) should cover the necessary and sufficient work instructions for supervisors, gantry drivers and other personnel to access and operate a fully serviced gantry in commission safely, in accordance with the designer’s intentions and manufacturer’s instructions. The gantry manager is responsible for the preparation, review and updating of the instructions based on risk assessment of gantry operations. The safe systems of work should be devised to eliminate and/or reduce risk. The work instructions should reflect: • the nature and configuration of the gantry • the form and location of the bridge • the proximity of the maintenance yard • the requirements of third parties • the environmental constraints • the duties of all involved for health and safety. A check list for the range of work instructions which may be required in the Operation and Maintenance Manual is set out in Appendix G.
3.5 Arrangements for working with contractors 3.5.1 Working relationship Contractors and personnel from other organisations will carry out a variety of tasks on a bridge using existing gantries or gantries they provide. They may include: • engineers and specialists for survey and inspections
• • • • •
contractors for minor works utilities attending to services carried on the bridge contractors for planned refurbishment, repairs and strengthening protective treatment contractors project management for major works.
In the UK, many of these tasks will fall within the scope of the CDM Regulations1 and all will require planned safe systems of work based on risk assessment. The bridge operator has primary responsibility for establishing the relationship with the particular contractor, a relationship which should be characterised by: • realistic project planning by the bridge operator • introduction of the gantry manager to the contractor’s staff at an appropriate level • provision of all necessary information about gantry and bridge • competence of the contractor, contractor’s personnel and supply chain for the particular task • realistic programming of the work by the contractor • cooperation between all parties in managing safety • adherence to planned systems of work • appropriate technical support (design and engineering) • monitoring of the contractor’s performance in the context of ongoing use of the bridge • feedback and responsive actions. When the CDM Regulations1 apply, the bridge operator, in the role of client, must: • appoint a competent CDM Coordinator • provide pre-construction information to designers and contractors • appoint a principal contractor • make sure that the construction phase does not start unless there are suitable welfare facilities, and that a construction plan is in place. The approach taken by the bridge operator to procuring the services of a contractor must be appropriate to the scale of the task; e.g. for strengthening or modification works there may be substantial surveys and design to manage as well.
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3.5.2 Minor tasks Before minor tasks of any kind are carried out by a contractor using the bridge gantries, the gantry manager must identify the hazards presented by the work to be done and assess the risks. It may be appropriate that the bridge operator be the principal contractor and therefore be responsible for the planning, management and coordination of the health and safety aspects of the work during the construction phase. It is not a requirement that the ‘main contractor’ be the principal contractor. This role should be undertaken by the party best equipped, and competent, to fulfil the role of ensuring that risks are properly controlled. Given the rarity of gantries and the scarcity of contractors’ expertise with them, it is absolutely essential that the parties cooperate and that responsibilities are defined, understood and adhered to. Operation of the gantry must be by a designated competent trained gantry driver and in accordance with the Operations Manual. If the bridge operator permits the contractor to operate the gantry, the gantry manager must train the contractor’s designated staff to supervise gantry operations and to drive it, as set out in the Training Manual. In any event the bridge operator must provide induction or training as appropriate for all the contractor’s staff who manage, supervise, travel or work on, any gantry. The contractor’s risk assessment and safe system of work must be documented and used to brief personnel and the gantry driver. For all but the smallest simple tasks, the contractor should prepare a comprehensive method statement covering the management, technical and safety aspects of the task. It may include: • control of, and issue of permits to work • sequence and method of work • coordination of work with gantry operation • emergency procedures • getting equipment and services on and off the gantry • communications • traffic management • measures to deal with hazards to safety and the environment. The contractor should give the method statement to the bridge operator for review, with sufficient time to allow for amendment or revision, before starting work. The contractor is responsible for carrying out the task as planned, but the bridge operator should also monitor the work.
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3.5.3 Major tasks When a bridge requires repainting, refurbishment, strengthening or modification, many engineers and tradesmen will work under the deck continuously for many months, if not years. They will be carrying out familiar activities in an unfamiliar, hazardous and relatively inaccessible workplace where safety depends on continuous and rigorous attention to detail. Existing gantries may not be the whole solution for the workplace but probably they would have an important role. Work platforms or purpose-made gantries suspended from the permanent runway beams may be the best solution. The main contractor, who may be the principal contractor, will manage the project but most of the work will be done by subcontractors e.g. for steelwork, protective treatment and traffic management. Gantry design and a separate gantry supplier may also be required. The combined expertise should cover the work scope but each participant’s experience will be but partial, and there may be very little previous experience of gantry working. The bridge operator should anticipate this scenario in preparing for and scheduling major works on the bridge and address each of the essential characteristics listed in 3.5.1. The procurement may well require expert input from bridge engineers and possibly specialist contractors, and certainly from the Coordinator, required by CDM Regulations1, who should be familiar with gantry operations and experienced with the type of works to be done. The overall project programme should allocate sufficient time: • for tenderers to work up the access logistics and determine a viable approach to the work • for meaningful participation of the supply chain in tendering • after contract award for working platform or gantry design, manufacture, installation and commissioning before construction if required • for the work to be done within all the logical and environmental constraints. For some projects early contractor involvement or formal partnering could be the best course for managing safety as well as value. The contractor along with the team of subcontractors has to be competent to undertake the work: the bridge operator must be satisfied that is so before letting the contract. A combined historic experience record from a tenderer and their supply chain is unlikely, on its own, to be sufficient to demonstrate that their approach would be competent.
IStructE The operation and maintenance of bridge access gantries and runways
The bridge operator should require a quality submission from each tenderer defining their approach with method statements, detailed programming, and the proposed key personnel from all the tenderer’s team. Particular attention should be paid to prospective work with gantries. The bridge operator must first be satisfied that the tenderer understands precisely what is to be done, and the hazards faced, and is able to be successful in all respects; then and only then should price be considered. Work under the bridge deck is likely to involve all parties on the site; the performance and safety of all the contractors’ personnel will be interdependent. All the contractors are required to cooperate on matters of safety, but the principal contractor should adopt an integrated approach to all planning and progress involving the key managers and supervisors involved; teamwork is essential to maintaining safety in such a workplace. Where existing bridge gantries are not designed for large scale tasks e.g. blast-cleaning and painting, the bridge operator should assess whether they should be used by the contractor. The key consideration should be whether their use would eliminate or reduce particular areas of risk in the contractor’s approach compared with other options. Of course, the gantries would have to be in commission to be available, or returned to commission for the project. The permanent runway beams may be used for support of work platforms or contractor’s gantries, so the bridge operator should be sure of their condition and provide the contractor with details of their design and of the bridge as necessary. Correspondingly, the contractor must provide details of their gantries and their load effects on the runway beams and the bridge, including wind loading generated by safety or environmental screening fixed to the gantry. Particular risks arise and have to be addressed if the contractor elects to use temporary runway beams. As part of the construction phase Health & Safety Plan, the contractor must provide, as described for minor tasks in 3.5.2, method statements and risk assessments for review before starting work. The arrangements for training all personnel, for operation of gantries only by designated authorised gantry drivers, for regular briefing of all personnel working below deck on the safe systems of work, and for emergency procedures, must be documented. Measures for maintaining a disciplined approach to gantry management are essential and must be enforced by managers and supervisors.
(Note: The preparation and review of method statements for such works requires skill, expertise and experience from each party as well as time. Guidance Note GN7.08 (Method Statements)3 gives guidance for writers and reviewers.) If existing gantries are taken over by the contractor, the contractor’s gantry manager should operate and maintain them as prescribed by the Manuals. Formal handover and return procedures should take place supported by inspection, defect schedules, and relevant records. The principles of gantry operation and maintenance apply equally to contractor’s gantries. The designer and manufacturer should provide detailed instructions for the contractor to prepare the manuals to be used on site and for training site personnel. 3.5.4 Runway beam and gantry replacement When the time comes to replace runway beams or gantries on a working bridge, the bridge operator faces a potentially complex procurement process for work which is inherently hazardous. The whole process needs to be undertaken by all involved with informed action and care as described in Chapter 7.
3.6 Records and review 3.6.1 Reporting and records Responsibility for gantries on a bridge will pass through the hands of a sequence of gantry managers during their operational life and they may be used only intermittently. Careful reports and records should be kept for continuity and to provide the current gantry manager with essential information to: • assess performance • verify the gantry is in commission • review maintenance schedules • assess the need for refurbishment, retrofitting or replacement • undertake risk assessments for future operations and tasks. The Operation and Maintenance Manuals should define the reports and records to be maintained and the recording methods. All gantry operations should be recorded and a daily gantry drivers’ logbook must be kept. Understanding the pattern and frequency of minor incidents can be very helpful in predicting the possibility of mechanical deterioration or further incidents and allow preventative measures to be
IStructE The operation and maintenance of bridge access gantries and runways
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19
taken in good time. A record of man-hours worked on the gantry may help to determine realistic incident rates. The performance history should include reports of all untoward incidents, whether they resulted in accidents or not. All personnel on an operating gantry should be required to report anything abnormal they observe to the gantry driver or gantry supervisor. Training records should be strictly maintained so that there is no doubt who has been trained for what roles and when, and when retraining is required. 3.6.2 Review Regular critical review and assessment is an essential part of the gantry management process to: • reflect changing circumstances • learn from experience • keep up to date with regulations • seek continuous improvement.
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The bridge operator is required to review the Health and Safety Policy periodically. It is recommended that this should be at least annually, to ensure that the management procedures are effective, reflect the current organisation and responsibilities, and comply with developing health and safety legislation. The gantry manager should review and update the Manuals: • at least every two years • after any substantial change to gantries, runways or methods • as part of the Principal Inspection. The gantry manager should review annually the emergency procedures with the respective services. When a contractor is working on the bridge with continuous extended gantry use, the gantry’s operation and performance should be reviewed and minuted explicitly at regular monthly site safety meetings.
IStructE The operation and maintenance of bridge access gantries and runways
4 Training, Certification and Competence
Glossary of terms
1
Introduction • Scope • Use of gantries • Outline process • Use of this Guide
2
Review of existing access gantry facilities • Gantries and cradles • Walkways, platforms and ladders
3
Management and operation of bridge access facilities • Management systems • Managing gantries • Operating gantries • Arrangements for working with contractors • Records and review
4
Training, certification and competence • Legislative requirements • Certification • Competence • Assessment • Training course • Training materials • Post training • General safety induction • Training for older gantries
5
Inspection and maintenance • The inspection and maintenance programme • Inspections – levels and frequency • Qualifications of inspectors • Preventative maintenance • Reactive maintenance • Reporting and records
6
Testing and commissioning • Commissioning • Load testing • Mechanical testing • Electrical testing • Reporting and records
7
Refurbishment, retrofitting, replacement, re-commissioning and change of use • Refurbishment • Retrofitting • Replacement • Re-commissioning
References
Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F Appendix G
Safety legislation, codes and standards relevant to the UK Gantry life cycle – key considerations and flow chart Operational and safety procedures – A typical example of relevant matters Gantry incidents, concerns and ‘near hits’ over recent years – examples Gantry design – some considerations Gantry and runway inspections and maintenance – more detailed guidance Gantry operation and maintenance manuals – contents
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4.1
Introduction
The operation of a bridge access gantry is a potentially hazardous task. It affects the safety of those using the gantry as well as those located nearby. Training to promote awareness, understanding and full open communication is key to successful operation of bridge access gantries. The extent and nature of training for operating and using gantries may be as varied as the range of different types of bridge gantries. However, the same general principles involved in providing suitable training are common to all gantries. Procedures for training should be included in the bridge operator’s documented management system.
4.2 Legislative Requirements The legislative requirements relating to training are briefly outlined as follows: Health and Safety at Work Act etc. 19744 Under Section 2(2)(c) it is the employer’s duty to provide information, instruction, training and supervision to ensure the health and safety of employees, with the usual caveat of being reasonably practicable. Section 4 of the Act; General duties of persons concerned with premises to persons other than their employees; covers the safety of those not directly employed. The Management of Health and Safety at Work Regulations 1999 (MHSWR)5 Regulation 13(2) reinforces the employer’s duty to provide “adequate health and safety training”. Regulation 13(3) requires that training is repeated periodically. The Provision and Use of Work Equipment Regulations 1998 (PUWER)6 The requirement for adequate training for users is further reinforced by Regulation 9(1) of PUWER. Regulation 9(2) of PUWER amplifies training requirements in respect of supervisors. The bridge operator or contractor involved with bridge gantries should determine and define the scope of ‘adequate training’ for a particular gantry, taking into account the general competencies of the personnel intended for operating and using a gantry as well as the nature of the work involved. In tandem with requirements for training are requirements for the provision of information concerning safe use: i.e. Regulation 8 of PUWER
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and Regulation 10 of MHSWR. Requirements for Operating and Maintenance Manuals are covered in Chapter 3 of this Guide, but any training shall, by implication, be based on information contained in the Operating and Maintenance Manual for the particular gantry system. The Work at Height Regulations 2005 (WAHR)7 There are no explicit requirements in WAHR for training. Regulation 5 concerns competence and the requirement on employers to ensure that persons engaged in work at height are competent to do so. The provision of suitable gantry training could assist in satisfying the bridge operator’s duties with respect to competence. The operation and use of gantries invariably involves work at height, which is a further factor in considering the extent and nature of the training to be provided (BS 84548 is the code of practice covering the provision of training for work at height). The process of determining the scope of training should be included in the overall risk assessment for the use of the gantries; training may be a factor in mitigating particular risks. Lifting Operations and Lifting Equipment Regulations 1998 (LOLER)9 These regulations are also relevant to bridge access gantries. For more details regarding the regulations see Appendix A.
4.3
Certification
The requirements for certification of trainees are not explicitly defined in legislative terms. However there is a duty on employers to keep records of training. The provision of certificates is a practice adopted in some industries and the significance of such certificates can vary from simply verifying that a trainee attended to certifying that the trainee achieved satisfactory performance following assessment. Some types of training can be generic and transferable between employers and even industries: e.g. training in the operation of mobile elevating work platforms. Given the bespoke nature of bridge gantries, driver certification is unlikely to be transferable to other gantries or bridges, without further training. The provision of certificates of competency should be determined by the bridge operator, in line with the bridge operator’s general health and safety policies and training policies, and with consideration to the nature of the particular gantry.
IStructE The operation and maintenance of bridge access gantries and runways
4.4
Competence
The bridge operator must take account of the general competence of potential gantry supervisors, gantry drivers and spotters. A degree of judgement is required as specific criteria for competence are rarely defined Minimum attributes for gantry drivers and spotters should include: • not susceptible to vertigo • physically fit with particular regard to eyesight, hearing and reflexes. Basic agility is required if ladders and other access equipment involved • ability to judge distances, heights and clearances • demonstrate a reliable and mature attitude to work and carry out duties in a responsible manner. The bridge operator should appoint competent personnel to carry out the required training and retraining of gantry staff. As well as the general ability to train staff well, the trainer should have technical knowledge, familiarity with the particular bridge and gantry system, and personal experience of operating and maintaining it; matching the scale and complexity of the gantry. In some cases this may require a qualified mechanical engineer or technician.
4.5 Assessment Training in the operation of gantries affords an opportunity to assess the competence of gantry drivers and a simple assessment may be included as part of the training. Any assessment will depend on the nature of the particular gantry, but at the very least should involve the trainee operating the gantry under supervision. Where gantries have complex controls involving sensors, limit/proximity switches etc. then hands-on operation should include the simulation of ‘fault’ conditions, provided it is safe to do so, and trainees should be tasked to investigate and resolve the fault, under supervision. Simple written tests (e.g. multiple choice) may be considered as a supplement to hands-on assessment particularly where the gantry is complex. The accent on such tests should be simplicity, but should determine whether a trainee has appreciated specific key aspects of the gantry and its operation. Where such assessments are carried out, consideration should be given to providing and encouraging the trainees to utilise the gantry manuals to complete the assessment.
4.6 Training Course Content for a gantry training course may include the topics outlined in the schedule below. In structuring a training course for gantry operation some prerequisites may have to be assumed. In particular it may be expected that operatives had previous experience of work at height, of use of PPE associated with fall prevention/fall arrest (see BS 843710) (if the use of such PPE were a requirement of gantry use) and an appreciation of typical construction or industrial equipment and machinery; e.g. scaffolding, ladders, generators, etc. The structure of the training course would depend on the nature of the particular gantry, but the training should include a hands-on element on the gantry. A classroom session prior to this may be appropriate, depending on the nature of the gantry and the site arrangements. A suggested schedule is given in Table 4.1.
4.7 Training materials It is generally good practice to provide trainees with some form of training material, covering the training they receive, although it is unlikely that it will be practical to provide each driver with a full copy of the gantry manuals. A short form version of the operating instructions, a Driver’s Manual, covering key information likely to be required on a day-to-day basis may be provided for retention by the drivers. Any such document must be reviewed and updated in line with any review and update of the gantry manuals. A register of the recipients should be maintained, to ensure that all are made aware of any amendments to gantry operational procedures. No copies of the issued sets should be made.
4.8 Post Training Gantry drivers should have the opportunity to practise their skills of driving and operating the gantry. If possible gantry crews should include experienced and novice users. If there are a large number of gantry drivers and spotters, rotation of crews should be considered to ensure that all gantry drivers maintain familiarity with the gantry. Depending on the usage pattern of the gantry, refresher training may be required annually. If the gantry is out of use for long periods, refresher training would be essential prior to bringing the gantry back into use.
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4.9
General Safety Induction
Occasionally, bridge access gantries may be used by inspectors, engineers or other personnel not trained in their use. It is unlikely that they would be trained in the operation and use of the gantry, but given the unusual nature of gantries they must receive some form of induction to highlight particular hazards and other key requirements. A typical ‘general safety induction for gantry visitors’ is shown in Table 4.2
4.10 Training for the use of existing gantries Gantries of different ages will have had different rules, regulations and legal requirements in force at the time of their original fabrication and commissioning. Training for the use of these gantries will need to take account of this historical perspective.
Table 4.1 Schedule for a typical gantry training course Subject
Details
Introduction Training objectives Legislation and guidance
Briefly outline relevant items including WAHR7, LOLER9 and IStructE Guide with the aim of reinforcing the serious and dangerous aspects of gantry use
Personnel
Outline the duties and responsibilities of the various personnel involved (gantry supervisor, gantry drivers, gantry spotters) ensuring that trainees are aware of the role they are being trained to undertake
General description
Of particular gantry system, include access/egress, gantry self-weight
Safety/emergency procedures
Emergency evacuations, power failure, personal injury, monitor wind speed, monitor loading, PPE requirements, safety equipment on gantry
Risk assessment and hazards
Familiarise trainees with key elements from the risk assessment
Operating parameters
Rated Loading including different loading configurations if applicable, wind speed and temperature restrictions
Gantry controls and operation
Highlight controls, emergency stop, outline interlocks where applicable, fault finding/trouble shooting, common faults, re-fuelling
Parking and storm rigging
24
Inspection
Pre-use checks, weekly checks, intermediate checks, six monthly thorough examinations (LOLER9), Principal Inspection. It may be appropriate to outline some of the commissioning tests carried out if the gantry is new or has been re-commissioned
Maintenance
Outline maintenance requirements (may not be directly relevant to drivers and spotters, but an appreciation of what must be carried out may prove useful to drivers in identifying faults)
Manuals
Review the gantry manuals, highlighting where copies are retained
Demonstration
Operation of gantry
Hands-on
Opportunity for trainees to operate the gantry, under supervision
Records
Reports and Driver’s log book
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IStructE The operation and maintenance of bridge access gantries and runways
Table 4.2 Typical safety induction for gantry visitors General safety induction for gantry visitors These notes are intended to provide a brief reminder of the general hazards associated with the gantry and they are aimed at visitors/untrained personnel going onto the gantry for the first time 1
The gantry must only be operated by a competent, trained driver appointed in writing by the gantry manager. The driver shall be assisted by spotter(s). Visitors on the gantry must follow any advice or instructions given by the gantry driver
2
Visitors must wear PPE as advised
3
The access provided by the gantry is considered safe under normal conditions. Visitors must remain within the main areas, which are protected by handrails
4
There are wind speed restrictions on the use of the gantry – wind speed is monitored by the gantry drivers and shore based staff. The gantry must not be used in wind speeds exceeding xx mph
5
Under normal operating conditions, the weight of all plant, equipment and personnel on board the gantry must not exceed the ‘Rated Load’ of the gantry. The Rated Load of the gantry is XXXXX kg distributed as indicated
6
Visitors should be aware that the gantry is subject to a regime of safety inspections ~ (e.g. on a daily, weekly and six monthly basis) and access/use is via a ‘permit to work’
7
There are general hazards present when the gantry is in use and they are summarised as follows: Hazard
Action Required
High level working/falls from height
Fall arrest equipment including body harness may occasionally be required, particularly during access egress
Falling objects/materials and head bump hazards
Hard hats to be worn
Moving Machinery/Mechanical Hazards
When the gantry is travelling along the bridge, visitors shall remain on the main/upper platform, at a safe distance from the trolleys and brake mechanisms. Visitors must be aware of relative movement between the gantry and bridge structure and shall take care to avoid contact with the bridge. Visitors must not hold onto parts of the bridge while the gantry is moving
Open Floor Hatches
Visitors must remain aware of floor hatches (floor hatches shall be closed when they are not required for access to other gantries or parts of the gantry)
Emergencies
Visitors should be briefed on emergency procedures
A more comprehensive risk assessment is contained in the gantry’s O&M Manual
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5 Inspection and maintenance
Glossary of terms
1
Introduction • Scope • Use of gantries • Outline process • Use of this Guide
2
Review of existing access gantry facilities • Gantries and cradles • Walkways, platforms and ladders
3
Management and operation of bridge access facilities • Management systems • Managing gantries • Operating gantries • Arrangements for working with contractors • Records and review
4
Training, certification and competence • Legislative requirements • Certification • Competence • Assessment • Training course • Training materials • Post training • General safety induction • Training for older gantries
5
Inspection and maintenance • The inspection and maintenance programme • Inspections – levels and frequency • Qualifications of inspectors • Preventative maintenance • Reactive maintenance • Reporting and records
6
Testing and commissioning • Commissioning • Load testing • Mechanical testing • Electrical testing • Reporting and records
7
Refurbishment, retrofitting, replacement, re-commissioning and change of use • Refurbishment • Retrofitting • Replacement • Re-commissioning
References
Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F Appendix G
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Chapter five
Safety legislation, codes and standards relevant to the UK Gantry life cycle – key considerations and flow chart Operational and safety procedures – A typical example of relevant matters Gantry incidents, concerns and ‘near hits’ over recent years – examples Gantry design – some considerations Gantry and runway inspections and maintenance – more detailed guidance Gantry operation and maintenance manuals – contents
IStructE The operation and maintenance of bridge access gantries and runways
5.1
Introduction
This Chapter covers inspection, preventative maintenance and reactive maintenance of the structural, mechanical and electrical elements of gantries and runways. Reliable and safe operation of gantries is achieved by: • design and construction to current good practice or, in the case of existing gantries whose original design is unknown or based on outdated codes, an engineering assessment using inspection information, records and material sampling and testing where appropriate (see Section 1.3) • acceptance and commissioning procedures in which the manufacturer provides the bridge operator with details of the design, construction and recommended inspection and maintenance, and demonstrates that the gantry meets the performance specification through commissioning tests and operation on the bridge over its full specified range (see Chapter 6) • a detailed inspection and maintenance programme carried out by competent people and based upon a thorough examination of all gantry and support components taking into account loading, fatigue, wear, deterioration, criticality and vulnerability (see Section 5.2) • safe operational methods (see Chapter 3). Access gantries are essentially machines composed of structural elements together with mechanical (including hydraulic) and electrical systems. The maintenance of this total system, whose various parts can deteriorate at different rates and can be subjected to changes in imposed loading during its lifetime, is essential to ensure safe operation. The combined use of structural, mechanical and electrical engineering disciplines is necessary for this purpose. A summary of relevant safety legislation, codes and standards is presented in Appendix A. Particular reference should be made to LOLER9 and PUWER6.
5.2 The inspection and maintenance programme This section is relevant for gantries that are used on a frequent and regular basis. Inspection and maintenance requirements should be set by the bridge operator taking into account the recommendations of the gantry manufacturer and supplier, assessment of the gantry installation and the results of commissioning and acceptance procedures.
The frequency of inspection should take account of frequency of use and environmental conditions. A programme of inspection and maintenance should be formulated taking into consideration the following (see also Table 5.1): • inspection and maintenance of gantries and runways should be seen as a coherent set of interrelated activities. To maintain safe operation a combination of preventative and reactive maintenance is required • a principal inspection is required every 6 years when all gantries should be fully inspected. However, when a number of similar gantries are installed, much inspection and maintenance work can be carried out with advantage in a 6-year cycle programme, e.g. if 6 gantries of a similar type are installed then at least one gantry should be inspected each year. Any inherent problems can thus be identified and dealt with at an earlier stage than would be the case with an inspection regime based strictly on commissioning date anniversary • depending on the gantry complexity, bridge operators may consider additional intermediate inspections, particularly where gantry usage is intensive • the maintenance schedule for mechanical and electrical systems should include inspection and replacement of parts when worn or after fixed periods of service. These systems should be considered to have a finite life which, depending on the extent of gantry use and the conditions of exposure, may be 10-15 years, but could be shorter. Complete replacement should be scheduled for the end of the system life and may conveniently be a part of a total gantry refurbishment or retrofit. Where a gantry structure is articulated by means of pinned joints, these joints should be included as part of the mechanical system • gantries and runways should be considered to have a finite life depending on design, use and environment. During this lifetime, they should be subject to 6-yearly principal inspections. They may require partial or complete refurbishment at intervals during their life • inspections should be carried out under the direction of the gantry manager or an appropriately qualified chartered engineer appointed by him • as an alternative to gantries being out of use for long periods it may be economic to operate a gantry, say, once every quarter, whether work is carried out or not.
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5.3
Inspections – levels and frequency
Recommended levels and frequency of inspections for gantries and runways in frequent use are summarised in Table 5.1. This illustrates the importance of a coordinated approach to inspection. More details are given in Appendix F1. If the schedule of inspections is followed it is envisaged that structural testing would not be undertaken as part of the verification process for a gantry unless: • the gantry has been refurbished (see Chapter 7) • the gantry has had a change of use which involves a more onerous loading regime (e.g. for a specific task or activity) • the gantry has been involved in an accident/ incident, jamming of wheels, extreme crabbing, hit by falling material, paint spill on, say, winding gear etc. (see Appendix F1.3). Where gantries are used intermittently, an appropriate level of inspection and testing should be carried out before use commences. Pre-use inspections should look for any signs of vandalism. When gantries used at long intervals are inspected and maintained less frequently than recommended, the bridge operator should consider re-commissioning (see Chapter 7) before use. After long periods of disuse and neglect, re-commissioning is considered absolutely essential.
5.4
• •
•
approved Contractors on the Roll of the Inspection Council for Electrical Installation Contracting members of the Electrical Contractors Association or Electrical Contractors Association of Scotland incorporated Engineers who are Corporate Members of the Institution of Electronics & Electrical Engineers Chartered Electrical Engineers.
Special inspections should only be carried out under the direction of a Chartered Engineer. Before accessing a gantry, inspectors should be briefed on procedures and safety.
5.5 Preventative maintenance Preventative maintenance is defined as any operation undertaken to ensure that the installation remains safe and operable for its design life, short of replacement or repair to a damaged item. An essential prerequisite for preventative maintenance is an authoritative Maintenance Manual together with a full set of ‘as-built’ drawings, relevant calculations, and specifications and for all structural, mechanical, and electrical systems (see Appendix G). Recommended levels and frequencies of maintenance for gantries are shown in Table 5.2 Some details for structural, mechanical and electrical preventative maintenance are given in Appendix F2.
Qualifications of inspectors
Inspections should be carried out by competent persons under the direction of the gantry manager. Competency requirements are met mainly through technical knowledge and experience. They differ depending on the type of inspection to be undertaken. Pre-use inspections of a frequently used gantry may be carried out by the gantry driver who has passed a test of competence. Whilst gantry drivers may not hold a technical qualification, they should have been trained in the inspection of the gantry and its runways. Weekly, intermediate, six-monthly and 6-yearly inspections should be carried out by suitably experienced technician engineers supervised by appropriate chartered engineers. Recognised bridge inspectors, nondestructive testing (NDT) technicians and insurance inspectors may have the relevant technical knowledge and experience and could be used. The Institution’s view is that suitably competent persons for carrying out electrical inspections should be selected by relevant qualification and experience for each inspection and may include:
28
•
Chapter five
5.6 Reactive maintenance Reactive maintenance is defined as the replacement of any items that have failed in service, or the execution of repairs to any aspect of the installation following an inspection. Some details for structural, mechanical and electrical reactive maintenance are given in Appendix F.
5.7 Reporting and records All inspections and maintenance work should be reported and recorded. Appropriate log books and report forms should be used to facilitate the work. Maintenance records may conveniently be stored on a suitable computer database with back up facilities. Computerised maintenance records should be subject to a system of password control and unalterable storage to prevent unauthorised revision. The procedures should be defined in the manuals. It is recommended that the methods of record keeping and defect classification detailed in Appendix F are adopted.
IStructE The operation and maintenance of bridge access gantries and runways
Table 5.1 Recommended inspections for gantries and runways in frequent and regular use (For typical scope of each inspection see Appendix F) Type of inspection
Carried out by
Gantry and moveable runway inspection
Inspection of fixed runways
Pre-use
Gantry driver
Needed particularly for all moving parts (M & E)
Visual check of runway to be travelled on during particular day
Weekly inspection
Gantry supervisor or driver if competent to do so
Needed particularly to check for any effects that the moving parts may have had upon the structural elements
May not be necessary – dependent on particular gantry and extent of usage since last inspection
Special inspection
Gantry supervisor or competent person
Needed after any severe weather or other unusual conditions (the scope of the inspection to be decided by the gantry manager/supervisor/ engineer as appropriate)
Needed after any severe weather or other unusual conditions (the scope of the inspection to be decided by the gantry manager/ supervisor/engineer as appropriate)
Intermediate M&E inspection
A suitably qualified engineer or competent person
Where considered necessary – an inspection of the mechanical and electrical systems of the gantry to encompass a visual examination, tests and checking of lubrication in accordance with the manufacturers instructions
May not be necessary – dependent on particular gantry and extent of usage since last inspection
Six-monthly inspection
A suitably qualified engineer or competent person
Can form part or all of the LOLER9 inspection. In addition this may include non-destructive testing (NDT) (e.g. checking for loose or missing bolts)
Can form part or all of the LOLER inspection and should cover the full length of the runways. In addition this may include NDT. Can be carried out from the gantries or other suitable means of access
Principal
A suitably qualified engineer or competent person
Similar to the P.I. carried out on the bridge structure and should include NDT. However, if NDT has been included in every six-monthly inspection in the previous 6 years, there is no need to perform a P.I. for the gantry structure
Similar to the P.I. carried out on the bridge structure and should include NDT. If the sixmonthly inspections have included NDT and they have covered the full extent of the runways in a rolling programme of inspection over the previous 6 years, there is no need to perform a P.I. for the runways
inspection
Inspection (6 yearly)
Table 5.2 Supervision and Frequency limits for Maintenance Intermediate maintenance procedure
Yearly maintenance procedure
Six-yearly maintenance procedure
Maximum interval between services when in use
Not exceeding 6 months
Not exceeding 14 months
Not exceeding 76 months
Service required if out of use for a period of
6-12 months
24-48 months
Work to be carried out
Intermediate maintenance procedure
Intermediate, 6-month and 12-month maintenance procedure
Intermediate, 6-month, 12 -month and 72-month maintenance procedure
Check spare parts schedule Work to be supervised by
Bridge supervisor
Technician Engineer, Chartered Mechanical Engineer or Insurance Company Inspector
Chartered Mechanical Engineer or other suitably qualified Chartered Engineer
Documentation
Inspection report
Inspection report
Inspection report
Re-issue defects report
Test report
Test report
Re-order consumed spares
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6 Testing and commissioning
Glossary of terms
1
Introduction • Scope • Use of gantries • Outline process • Use of this Guide
2
Review of existing access gantry facilities • Gantries and cradles • Walkways, platforms and ladders
3
Management and operation of bridge access facilities • Management systems • Managing gantries • Operating gantries • Arrangements for working with contractors • Records and review
4
Training, certification and competence • Legislative requirements • Certification • Competence • Assessment • Training course • Training materials • Post training • General safety induction • Training for older gantries
5
Inspection and maintenance • The inspection and maintenance programme • Inspections – levels and frequency • Qualifications of inspectors • Preventative maintenance • Reactive maintenance • Reporting and records
6
Testing and commissioning • Commissioning • Load testing • Mechanical testing • Electrical testing • Reporting and records
7
Refurbishment, retrofitting, replacement, re-commissioning and change of use • Refurbishment • Retrofitting • Replacement • Re-commissioning
References
Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F Appendix G
30
Chapter six
Safety legislation, codes and standards relevant to the UK Gantry life cycle – key considerations and flow chart Operational and safety procedures – A typical example of relevant matters Gantry incidents, concerns and ‘near hits’ over recent years – examples Gantry design – some considerations Gantry and runway inspections and maintenance – more detailed guidance Gantry operation and maintenance manuals – contents
IStructE The operation and maintenance of bridge access gantries and runways
6.1
Introduction
Testing is a fundamental part of the commissioning of a new gantry system; and, throughout the life of the system it supplements inspection and maintenance in the continual assessment of the safety and reliability of the gantries and runways. Tests of structure and of mechanical and electrical systems should be chosen and planned with discrimination: they should be relevant, necessary, have clear objectives and comply with applicable Regulations. Methods of testing should be formulated on the basis of technical risk assessment, and they should be designed not to cause material damage. Management of health and safety during testing and commissioning must recognise the hazards, assess the risks and plan testing accordingly. Methods which introduce risks greater than those which would remain if the testing were not undertaken should be avoided; they should present no greater risk than those arising in normal gantry operation. No personnel on or near a gantry under test must be put at risk should the test fail. The gantry manager is responsible for planning routine testing and for initiating testing in response to unusual behaviour of the gantry system, or following repairs or replacement of components. Routine testing during service should be described with clear work instructions in the Maintenance Manual. Other instructions for incidental testing, and re-commissioning works (Chapter 7) must be planned and documented with the supporting risk assessments. It should be noted that load testing during service is generally of no great benefit when assurance is given by proper gantry management as described in 6.3.1. A gantry system that is in regular use and subject to a full programme of inspection followed up with relevant maintenance (Chapter 5), is likely to have no need for further load testing after successfully completing its initial proof load test during commissioning.
6.2
Commissioning
The final phase of procurement of a new gantry, in most cases, requires the manufacturer to commission it successfully before it is accepted by the bridge operator and put into service. The commissioning process of a gantry system is vital to ensuring the integrity of the gantry and its safe operation, so it is important to • specify the requirements for commissioning in procuring its supply, based on risk assessment • prepare a detailed plan and programme for the process
• •
• •
establish safe methods of testing based on risk assessment involve the designer, contractor, gantry manager and bridge operator’s staff as appropriate in witnessing tests trial the operating procedures prepare a commissioning report including observations and measurements from the various tests and activities.
The purposes of commissioning are: • to validate the structural design by proof load testing • to assemble the gantry drive and control systems and verify their performance under load • to enable final adjustment and settings • to verify accuracy of runway beam or track construction and clearances • to prove operation, including secondary mechanisms, throughout the whole working range on the bridge • to confirm operating procedures • to provide familiarisation and initial training to the gantry manager and other personnel • to hand over manufacturer’s manuals and data • to secure acceptance and handover. The process should normally be carried out in two phases as proof load testing is safer done close to ground level; depending on the novelty of the design or the complexity of the gantry, the first phase may be undertaken on the bridge site or at the manufacturer’s works: • for the first phase, it is preferable to assemble the completed gantry on representative runway track or beams so that both gantry and runway can be proof load tested with some approximation to the dynamic loads generated by their interaction • for the second phase, the completed gantry system is put through a set of operational tests and trials at its Rated Load. Generally, as discussed in Section 6.3.3, it is not necessary or desirable to proof load the full length of runways during commissioning. The gantry manager takes responsibility for the gantry when the process, including documentation, is completed satisfactorily and it is formally handed over. Commissioning provides an initial opportunity for the bridge operator and the gantry manager to gain a valuable insight into the characteristics and behaviour of the gantry system.
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Re-commissioning and testing of a gantry system will usually be required after: • refurbishment, substantial repair, or alteration • a significant increase in rated loading has been decided • significant deterioration in condition requiring reevaluation of the design calculations • significant periods without full routine inspection and servicing. The scope of the re-commissioning and testing in these circumstances should be determined by the gantry manager or a suitably qualified and experienced chartered engineer appointed by him (see Chapter 7).
•
• •
6.3 Load testing 6.3.1 Use of load testing Load testing of a well maintained gantry system during its service life is generally of no great benefit. The gantry manager needs to have substantial grounds before deciding to undertake it, as the integrity of the gantry or runway beams can be assured by other measures. Load testing is limited to simulating primary loads by practical constraints although some unquantifiable dynamic load effects can occur and be scrutinised in rolling load testing (see Section 6.3.4). It is not easy to arrange an effective means of load testing a gantry in-situ and it is potentially hazardous. The designers, manufacturers and constructors of a new gantry system must be competent and experienced in their works and should use quality management systems rigorously in compliance with BS EN ISO 900111. For a gantry, assurance in service is provided by: • the commissioning which, validates the structural design and the specified mechanical performance • structural inspection, particularly at the six-yearly principal inspection, and subsequent cleaning, refurbishment and protective treatment • systematic inspection, servicing and maintenance of the mechanical and electrical systems • replacement of components before they reach the end of their serviceable life. The required resistance of runways to service loads is assured primarily through the design. Further assurance that the runway support system is adequate and safe may be provided by: • redundancy and adequate margins in the design of the runway to cover unknown transient effects,
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corrosion, wear, etc. It is recommended that the runway design should include a special (and additional) partial load factor, typically in the region of 1.25 to suit the chosen design code, in order to introduce a degree of overdesign to the runways and their connections to the bridge (see Appendix E3) laboratory load testing as part of the design process, which can explore global and local behaviour under vertical load, significant axial and lateral loads, and dynamic effects. Specialist advice should be sought for such tests proof load testing of a representative runway assembly at ground level before erection replacement of the whole or part lengths of the runway system and bolt assemblies, or repairing welded connections where inspections reveal unacceptable deterioration, or where runways or connections are deemed to have reached the end of their safe life exceptionally, proof loading sections of runway in-situ.
Accordingly it is recommended that load testing of a gantry system is limited to: • proof load testing each gantry during commissioning at ground level • proof load testing of a representative length of runway beam at commissioning, preferably using the gantry, but not in-situ • load testing of secondary mechanisms (such as scissor-lifts, telescopic arms, or cradles) as part of commissioning and the six-yearly principal inspections (and in accordance with the manufacturer’s recommendations). It should be noted that proof load testing, or any load test, is no substitute for thorough inspection and essential maintenance to justify use of an out-ofcommission gantry. 6.3.2 Gantry proof load test As part of the acceptance and commissioning of a new or refurbished gantry, proof load tests should be made at the factory or at ground level on site on a test track prior to erection. The test track should replicate the bridge runways and their supports, incorporating joints, connections and movement joints: the tracks should be set at the maximum operating gradient on the bridge. Runway supports must have adequate resistance to dynamic load effects generated during rolling tests under power, braking or impact.
IStructE The operation and maintenance of bridge access gantries and runways
The test arrangement should be conceived, located and detailed so that risk to health and safety from any possible failure mode is minimal, and the gantry system is left in a safe position (e.g. very limited vertical drop). Arrangements for loading, control and observation should be such that essential personnel close to the gantry for observation are not put at risk, and where possible there are no personnel on the gantry. It is probable that the requisite test load material needs to be relocated between proof load tests of various parts of the system. The load should be applied in pre-determined discrete increments for each load case; the gantry should be operated at each increment of load so that if necessary the test can be suspended pending remedial action. The test weight, and weight distributions, applied to the gantry during the proof load test should be determined from an appraisal of the design: for a new or retrofitted gantry, they should be defined on the drawings by the designer. Generally an appropriate proof load would be the Rated Load modified by the relevant partial factors used in the design for loads and materials. The manufacturer, or the gantry manager when recommissioning, should document the planned method for the proof load test following risk assessment with a detailed stage by stage method statement, including prepared report forms for observations, measurements and comments. The conduct of the test must be under the direction and control of an appointed competent chartered engineer, with appropriate personnel designated to monitor the behaviour of the gantry system, to observe, measure and record. It is desirable for a new gantry that the designers of structure and mechanisms participate in the test. 6.3.3 Runway proof load test Where possible the runway proof load test is best incorporated with the gantry proof load test, as described in 6.3.2. This allows the runway beams to be observed under a combination of measured vertical loads, and the significant representative but unquantifiable dynamic loads from gantry movement, braking, impact of bogies at joints, and deliberate crabbing of the gantry under power. The total proof load for a runway beam should be the combination of the maximum effect of distribution of the Rated Load on the gantry, for that beam, modified by the relevant partial factors for loads and materials used in the gantry system. If a runway beam is to be tested independently,
then a representative section should be set up with details and supports as described in 6.3.2 but with the runway beam horizontal. A test load arrangement has to be devised to be suspended from a bogey, or set of bogies, identical to the gantry bogies: arrangements to apply static transverse loads to the bogie, representing wind or crabbing effects, could be provided. The independent test requires an accurate gantry self-weight to evaluate the test load (this could be calculated or determined by weighing to confirm information that should be shown on the design drawings). The approach to planning, method, documentation and conduct of the test should be as described for the gantry proof load test. In particular the bogies should be positioned at various points along the runway beam to maximise bending effects and deflections in the beam, and effects at joints and connections to supports. Observations and measurements should be made at each position. In exceptional circumstances, for example where it is not physically possible safely to replace support components which are suspect, proof load testing of small sections of runway beam may be considered as a means of extending useful life. For safety such tests would require that: • a proof load could be applied to the runway directly without using the gantry, e.g. with a specially constructed trolley and haulage system • the behaviour of the runway under load can be observed remotely by instrumentation of points of interest or by CCTV. 6.3.4 Secondary load effects Secondary static and dynamic loads may occur in gantry systems which cannot be simulated readily or precisely during load testing. Some may be present so close observation by test witnesses and assessment of their effects is part of load testing. These and other load effects may occur in the gantry system in service; they should be diagnosed as action may be necessary to minimise them or eliminate the risk of damage. Travelling of the gantry All vertical load carrying wheels of the gantry carriage should stay in contact with the runway at all times. Impact loading may occur during gantry operation, particularly at joints. Horizontal (along the line of the bridge) loads will arise as a gantry starts to move or stop either by braking or running into its end stops or an obstruction.
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It should be noted that the distortion caused by a small lateral load applied to a relatively deep RSJ or UB section with a thin web can be substantial. Hangers supporting runways may also have little resistance to horizontal, longitudinal or lateral forces. Crabbing of the gantry induces horizontal transverse reactions between the runway and the gantry itself, which can be large when under power. Anti-crabbing devices may reduce these loads and observation should aim to determine their effectiveness. Assessment should evaluate the efficacy of the devices, and consider the effects should they fail to operate. Wind loads Wind can produce horizontal and vertical loads on a gantry which are difficult to replicate during load testing. Prior to a load test, the loads arising from wind speeds at the limit for gantry operation should be calculated. Specialist advice may be required. Precise calculation is not easy. The calculated wind loads provide input to determining the test load to be applied during the proof load test. Further advice may be needed if temporary screening is to be fitted to the gantry (see Section 3.3.5). Vibration A gantry structure may vibrate due to wind effects, the travelling of the gantry or movement of the bridge itself under: traffic and wind actions. Measurement of vibration should seek to determine the magnitudes of movement under different conditions. Where the vibration is sustained and possibly significant structurally, (human sensitivity to acceleration is high and very small movements of little structural significance can cause concern) the magnitude, modes and frequencies of vibration of the gantry and the bridge should be recorded. Such measurement provides a basis for the evaluation of the risk of resonance and fatigue, and it allows the gantry manager to determine whether the specified operating conditions will keep vibrations within acceptable limits, whether differential or not. If resonance occurs, fatigue damage will become more likely. Some gantries vibrate even when parked, being excited by wind or traffic effects. Consideration should be given to the installation of simple damping devices (such as screw props resting on the bridge structure) to guard against fatigue of components).
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6.4
Mechanical testing
6.4.1 Use of mechanical testing The most exhaustive range of mechanical testing is carried out during the manufacture and commissioning of a new gantry system, it comprises testing of all aspects of gantry operation and testing of separate components and mechanisms. In service such tests are an aid to diagnosis of abnormal behaviour or defects of the gantry. They should be used as well with care and discrimination, on the basis of risk assessment, to verify the quality of workmanship in inspection, servicing and repairs. 6.4.2 Gantry operation Operation of the gantry and its subsidiary mechanisms should be tested thoroughly during the initial commissioning. Tests in the first phase under proof load should include: • travelling along a runway including joints and movement joints • travelling up the maximum gradient • braking uphill, downhill and emergency stop • induced crabbing and recovery • operation of any mechanisms to change gantry configuration (e.g. slewing, telescoping or lowering of platforms) • operation of scissor lifts or telescopic arms. In the second phase these tests should be repeated on the completed gantry system, within the rated load, as well as the following tests: • travelling the full range to verify runway beam geometry, setting of runway joints and movement joints, and clearances between gantry and structure • docking at access platforms to verify safe access for personnel and material • testing operation of limit switches on movements • manual operation of the gantry under power failure conditions • operation of end stops and storm anchors. For use in service, for diagnosis or after inspection and maintenance, the Operations and Maintenance Manuals should include schedules and detailed instructions for the conduct and application of each operational test under light or normal loading. Where appropriate, clear acceptance criteria should be defined, or quantified.
IStructE The operation and maintenance of bridge access gantries and runways
When it is necessary to re-commission a gantry (Chapter 7) the gantry manager, with appropriate technical advice, should determine which operational tests should be carried out and which, if any, should be carried out under proof load. Proof load testing for re-commissioning should be carried out as for the first phase of commissioning. 6.4.3 Component testing Mechanical testing requirements for all individual mechanical components and: equipment, for example engines, motors, hydraulic cylinders and bogies, are: • before delivery, it is desirable that, where practicable, all new components should be tested at the suppliers or the manufacturer’s site where measurement, adjustment or modification can be more readily and more safely carried out • full testing during commissioning of the installed gantry system • retesting of all mechanical components as part of the six yearly principal inspection • retesting of some or all of the mechanical components after any of the major assemblies has been replaced, or after a substantial modification of access platforms or the method of operation, the extent of testing should be determined with regard to the effect of the changes on other mechanical components, and should be specified by the gantry manager or the appointed chartered engineer supervising the testing.
6.5
Electrical testing
6.5.1 Verification The initial verification of a new electrical installation is substantially different from the requirements for periodic inspection and testing. It is most important to carry out a comprehensive inspection of the electrical installation at regular intervals. The purpose of testing is to verify the findings of the inspection procedure. Testing should be undertaken in accordance with the requirements of BS 767112 and relevant guidance notes, using well maintained and regularly calibrated test instruments. Specifications for the test instruments to be used and details of the main tests required to ensure electrical safety are stated in Part 7 of BS 767112 and explained in I.E.E. Guidance Note 313. These can be summarized as tests to verify: • the effectiveness of earthing • the integrity of conductors • the operation of safety devices • freedom of movement of moving parts.
The manufacturers of specific items of equipment which need testing should be consulted to ascertain any special requirements, including precautions to be taken to prevent damage whilst testing electronic components and the like. The gantry manuals should be consulted. The manuals should explain the required safety procedures for that gantry and its recommendations should be followed. The general requirements of BS 767112 should be adopted in the manuals. Tests should be carried out in the following sequence: • external earth fault loop impedance (as appropriate) • earth electrode resistance (as appropriate) • continuity of protective conductors (earth wires) • polarity – including correct connection of switches, socket outlets and lampholders • earth fault loop impedance at furthest points of utilisation • insulation resistance • physical operation of devices for isolation and switching • operation of residual current devices (RCDs) • continuity of ring circuit conductors • manual operation of circuit breakers • electrical separation of circuits (low voltage, extra low voltage etc.). The physical operation of switches, circuit breakers, limit switches, proximity detectors, etc. is required to verify, as far as is reasonably practicable, that the equipment is in good working order, that mechanical linkages and micro-switches are operating correctly, and that all sensors, both electronic and mechanical, are correctly aligned. 6.5.2 Certification and reporting The Completion and Inspection Certificate for the original gantry electrical installation, together with all subsequent Periodic Inspection and Test Reports, should be kept in the gantry log books. At the time of the first intermediate inspection after a new gantry has been installed, the Completion and Inspection Certificate should be made available to the person carrying out the electrical inspection. At all subsequent periodic inspections the most recent Inspection and Test Report documents should be available. Failure to provide previous test results to the Inspector may result in a much more detailed inspection procedure being carried out than would otherwise be necessary.
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Suitable forms for the certification of new electrical installations, small additions to an electrical installation and the reporting of periodic inspection and test results, are contained in Appendix 6 of BS 767112. Certificates should include the date when the next inspection is due.
6.6 Reporting and records The original commissioning report, and any recommissioning reports, should be kept with the gantry service records for reference during subsequent testing. The results of all tests and inspections should be reported and records maintained in compliance with procedures defined in the Operation and Maintenance
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Manuals. For scheduled tests appropriate log books and report forms should be used to facilitate the implementation of the test procedure. On satisfactory completion of testing, the chartered engineer supervising the tests should issue to the gantry manager a Certificate of Test stating the list of tests undertaken and the results obtained. A copy of the Certificate of Test should be retained in the gantry log books. If the results are unsatisfactory, a Rejection Certificate should be issued. Newly supplied gantries (and significantly modified gantries) should also be CE marked as required by the Supply of Machinery (Safety) Regulations 199214 (and as amended).
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7 Refurbishment, retrofitting, replacement, re-commissioning and change of use Glossary of terms
1
Introduction • Scope • Use of gantries • Outline process • Use of this Guide
2
Review of existing access gantry facilities • Gantries and cradles • Walkways, platforms and ladders
3
Management and operation of bridge access facilities • Management systems • Managing gantries • Operating gantries • Arrangements for working with contractors • Records and review
4
Training, certification and competence • Legislative requirements • Certification • Competence • Assessment • Training course • Training materials • Post training • General safety induction • Training for older gantries
5
Inspection and maintenance • The inspection and maintenance programme • Inspections – levels and frequency • Qualifications of inspectors • Preventative maintenance • Reactive maintenance • Reporting and records
6
Testing and commissioning • Commissioning • Load testing • Mechanical testing • Electrical testing • Reporting and records
7
Refurbishment, retrofitting, replacement, re-commissioning and change of use • Refurbishment • Retrofitting • Replacement • Re-commissioning
References
Appendix A Appendix B Appendix C Appendix D Appendix E Appendix F Appendix G
Safety legislation, codes and standards relevant to the UK Gantry life cycle – key considerations and flow chart Operational and safety procedures – A typical example of relevant matters Gantry incidents, concerns and ‘near hits’ over recent years – examples Gantry design – some considerations Gantry and runway inspections and maintenance – more detailed guidance Gantry operation and maintenance manuals – contents
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7.1
Introduction
The structural, mechanical and electrical systems of gantries deteriorate at different rates. Reliability and safety may decrease over time despite diligent inspection and maintenance. The need for refurbishment or retrofitting of the systems or replacement of the gantry and its runways should be determined on the basis of reports of inspections, operational observations, structural assessments and maintenance records and future operational requirements. It is recommended that this technical audit and the subsequent design and specification of refurbishment, retrofitting or replacement of gantries should be carried out by a multi-disciplinary team under the control of one designated organisation. In addition all planning for such works must take account of relevant health and safety legislation. If a gantry has been dismantled, refurbished or had a change of use resulting in a more onerous loading regime the gantry and its runways should be tested in accordance with Chapter 6.
7.2 Refurbishment Refurbishment and retrofitting of part or the whole of a permanent gantry may be undertaken, in some circumstances, whilst on the bridge, but it will generally be more convenient to carry out this work after removing the gantry from the bridge. Refurbishment may be required after periods in use of, perhaps, 12-18 years. The mechanical and electrical components of gantries have a finite life, perhaps 10-15 years. Some of the structural components, e.g. runway beams or gantry floor framework, may have an appreciably shorter life than the bridge due to wear and corrosion. An assessment should be made whether refurbishment of existing equipment represents a safer or best value option in the light of current Health and Safety legislation or technological improvements. Retrofitting may be the better option. Whether refurbishing or retrofitting, any changes to control software should be made by suitably qualified personnel in a manner consistent with the method described in Appendix E.
7.3 Retrofitting Retrofitting, i.e. the replacement of an existing system by one of different design and specification, may often be preferred to refurbishment, depending on the performance of the existing system. One of the key drivers to retrofit may be legislative or
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health and safety developments. Gantries provide most severe conditions for both electrical and mechanical equipment. They may stand unused for long periods in a damp corrosive environment. Thrust bearings indent, self-lubricating bearings stick and may then tear, wheels in the upper half of a gearbox rust, sensors with moving parts seize. Many of these problems can be overcome by correct specification and selection during retrofitting. Retrofitting provides an opportunity to improve the performance, reliability and safety of an existing gantry and to take advantage of newer equipment and technology. For example, existing emergency electrical systems, i.e. the push-buttons, sensors and limit switches, used to limit crabbing, over-running, collision with piers and to avoid personal injury from contact with moving parts, should be arranged such that any failure will leave them in a safe position. However, the use of fail-safe devices can create a hazard, for example. On some gantries, when an electricity supply failure occurs, the brakes are applied to the wheels of the gantry and cannot be released until power is restored: it is then almost impossible to recover the gantry to a location from which the gantry driver and others can escape by normal means. The emergency evacuation procedure may have to be followed. The retrofitting of simple mechanical brake override devices would make evacuation and recovery of such gantries much safer and easier.
7.4 Replacement Gantries and runways and their supports which have been in service in the region of 20-35 years should be considered to have reached the end of their finite life unless their continued use is supported by valid inspection and valid assessment of their components. This recommendation is made principally from consideration of structural safety. Mechanical and electrical components will have their own replacement criteria. Gantries, when not in use, are seldom parked in a protected environment. In addition, gantry structures and runways experience dynamic stresses which may be significant from a fatigue point of view. These stresses arise whilst gantries are: • parked out of use – they arise from wind action and to vibration of the supporting bridge structure under traffic and wind loads. The resulting vibrating movements of the gantries may be continuous
IStructE The operation and maintenance of bridge access gantries and runways
•
in use – they are due to the effects described above together with those arising from the operation of the gantry. The transient stresses on parts of the gantry structure and runways due to operations, such as travelling, starting, stopping, etc. may be significant.
The structural systems of gantries and their runways generally have a low degree of redundancy, although it is recognised that good design has built-in reserves in the structures, their supports and connections in many cases. They may have a relatively low capability to remain safe following a local failure of a component or connection. This consideration combined with the risks of minor structural damage being undetected in service, of the unknown effects of dynamic stresses and of the damp environment suggest that it is prudent to replace gantries and also runways when they have reached the end of their finite life in service. When it is decided to replace the gantry carriages, the bridge operator should consider what improvements or changes should be made to the design, particularly the drive and control system, in the light of experience, technological advances and applicable regulations. New gantries will be subject to CE marking. Identifying and appointing a supplier for design and manufacture is often not straightforward. It should be remembered that while most gantries may have simple, easy to fabricate, structures, the performance of the gantry depends very much on the quality of the mechanical components and machinery; in detail design and specification, in articulation, and in manufacture and technical support. Design and supply is probably best let to a competent mechanical engineering company who may sublet the fabrication of the carriage to a small fabricator, the lead contractor then controls the key engineering directly and the programme to supply, commission and provide manuals. (Should the bridge operator have difficulty in identifying suitable companies, enquiries to other large bridge owners may provide help). Depending on the complexity of the gantry and the order of design changes, works running trials on representative runway beams should be considered in addition to the proof testing (described in Chapter 6 of this document) to prove the design performance and minimise work at height in installation and commissioning. The gantry supplier should prepare
a method statement for the replacement operation and for running trials before delivery. The condition of runways will deteriorate with wear to the running surfaces and joints, and from corrosion. The integrity of any bolted or welded connections to the bridge must remain assured. Operations to replace runway beams or refurbish connections raise further hazards for gantry operation. A gantry should never be used for any task on runway beams with open ends: where necessary robust stopends must be provided, fitted and removed to strictly controlled procedures. The bridge operator and contractor must take particular care, in view of the consequences of failure, to ensure that the risk assessments are thorough, the methods are inherently fail safe, and that the safe system of work is followed rigorously.
7.5 Re-commissioning If a gantry and its runways are in regular use and are subject to a full inspection programme and maintained as set out in Chapter 5, there should be no need for any further load testing after the initial Proof Load Test has been performed satisfactorily. If a gantry and/or its runways have been out of use for a significant period of time (e.g. the six monthly LOLER9 inspection has not been undertaken) then it is recommended that they are only brought back into use following a thorough review of the risks associated with their use and any controls necessary for the safe operation of the system. The degree of inspection and assessment required will depend on the complexity of the gantry and the runway. For example, motorised multi-functional gantries are likely to need more extensive assessment than simple hand operated systems. Before it is brought into regular use the gantry and the runways should have a principal inspection, a structural assessment and any mechanical or electrical equipment should be inspected by a competent person, and if appropriate, tested for use. The rated load should be checked or reclassified by structural assessment, and it is recommended that this is clearly displayed on the gantry together with the name of the authorising person for its use. The structural assessment should take into account the duty, the self weight, live and other imposed loading on the gantry and runway beams. The risks, requirement and the benefit of carrying out a proof load test should be considered as part of the structural assessment. The risks associated with the proof load test should be designed to be negligible
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and every effort should be made to avoid permanent damage to the structure. Particular attention should be paid to the inspection and re-validation of the runways to ensure there are sufficient reserves of strength. The risks associated with crabbing and derailment need to be reassessed and appropriate work carried out if required. It is also recommended that the opportunity is taken to consider improvements to the gantry system when re-commissioning. These could include improvement to:
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emergency egress arrangements walkway surfaces and handrails braking systems and retraining arrangements.
These improvements may need to reflect changes in legislation since the gantry was last commissioned. It is recommended that the gantry and any systems associated with it are operated along the whole length of the runway by the recommissioning team before the gantry is handed over for regular use.
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References
1
2
3
4 5
6
7
9
10
11 12
13
14
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Construction (Design and Management) Regulations 2007. London: The Stationery Office, 2007 (SI 2007/320) Health and Safety Executive. Successful health and safety management. HSG65. London: HSE, 1997 Evans, J.E. and Iles, D.C. Guidance notes on best practice in steel bridge construction. P185. 4th Issue. Ascot: SCI, 2006 Health and Safety at Work, etc. Act 1974: Chapter 37. London: HMSO, 1974 Management of Health and Safety at Work Regulations 1999. London: The Stationery Office, 1999 (SI 1999/3242) Provision and Use of Work Equipment Regulations 1998. London: The Stationery Office, 1998 (SI 1992/2932) Work at Height Regulations 2005. London: The Stationery Office, 2005 (SI 2005/735) BS 8454: 2006: Code of practice for the delivery of training and education for work at height and rescue. London: BSI, 2006 Lifting Operations and Lifting Equipment Regulations 1998. London: The Stationery Office, 1998 (SI 1998/2307) BS 8437: 2005: Code of practice for selection, use and maintenance of personal fall protection systems and equipment for use in the workplace. London: BSI, 2005 BS EN ISO 9001: Quality management systems. Requirements. London: BSI, 2000 BS 7671: 2001: Requirements for electrical installations. IEE Wiring Regulations. 16th ed. London: BSI, 2001 IEE. 16th Edition of the Wiring Regulations. Guidance Note 3: inspection and testing. 4th ed. London: IEE, 2001 Supply of Machinery (Safety) Regulations 1992. London: The Stationery Office, 1992 (1992/3073) Health and Safety Executive. Management of health and safety at work. L21. London: HSE, 2000 Health and Safety Executive. Managing health and safety in construction. Construction (Design and Management Regulations 2007. Approved Code of Practice. L144. London: HSE, 2007
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22
23
24 25
26
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Health and Safety Executive. Health and safety in construction. HSG150. London: HSE, 2006 Health and Safety Executive. The Work at Height Regulations 2005 (as amended): a brief guide. INDG401. London: HSE, 2007 Health and Safety Commission. Safe use of lifting equipment. Lifting Operations and Lifting Equipment Regulations 1998. L113. London: HSE, 1998 Personal Protective Equipment at Work Regulations 1992. London: The Stationery Office, 1992 (SI 1992/2966) Health and Safety Executive. Personal protective equipment at work. L25. 2nd ed. London: HSE, 2005 Health and Safety Commission. Safe use of work equipment. Provision and Use of Work Equipment Regulations 1998. L22. London: HSE, 1998 Directive 98/37/EC of the European Parliament and of the Council of 22 June 1998 on the approximation of the laws of the Member States relating to machinery as amended by Directive 98/79/EC Health and Safety Executive. Five steps to risk assessment. INDG 163. London: HSE, 2006 Workplace (Health, Safety and Welfare) Regulations 1992. London: The Stationery Office, 1992 (SI 1998/2306) Electrical Equipment (Safety) Regulations 1994. London: The Stationery Office, 1994 (SI 1994/3260) Electromagnetic Compatibility Regulations 1992. London: The Stationery Office, 1992 (SI 1992/2372) Product standards: Machinery. Guidance notes on the UK regulations.URN 95/650. London: DTI, 1995 Health and Safety Executive. Supplying new machinery. INDG270. London: HSE, 1998 Control of Substances Hazardous to Health Regulations 2002. London: The Stationery Office, 2002 (SI 2002/2677) Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 1995. London: The Stationery Office, 1995 (SI 1995/3163)
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References
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3
39
42
BS 5400: Steel, concrete and composite bridges [various parts] BS EN 1993: Eurocode 3. Design of steel structures [various parts] BS 2853: 1957: Specification for the design and testing of steel overhead runway beams. London: BSI, 1957 National Access and Scaffolding Confederation. Guide to good practice for scaffolding with tubes and fittings. TG20:05. London: NASC, 2005 BS 5974: 1990: Code of practice for temporarily installed suspended scaffolds and access equipment. London: BSI, 1990 BS 6037-1: 2003: Code of practice for the planning, design, installation and use of permanently installed access equipment. Suspended access equipment. London: BSI, 2003 BS 7171: 1989: Specification for mobile elevating work platforms. London: BSI, 1989 BS EN 1808: 1999: Safety requirements on suspended access equipment. Design calculations, stability criteria, construction. Tests. London: BSI, 1999
References
40
41
42
43 44
45
46
BS 5395-3: 1985: Stairs, ladders and walkways. Code of practice for the design of industrial type stairs, permanent ladders and walkways. London: BSI, 1985 BS EN ISO 14122-4: 2004: Safety of machinery. Permanent means of access to machinery. Fixed ladders. London: BSI, 2006 Highways Agency and others. Design manual for roads and bridges. Vol 1: Highway structures: Approval procedures and general design. Section 1: Approval procedures. Part 1: Technical approval of highway structures. BD 2/05. London: The Stationery Office, 2005 BS EN 13001: 2004: Crane safety. General design. London: BSI, 2004 [2 parts] BS EN 60529: 1992: Specification for degrees of protection provided by enclosures (IP code). London: BSI, 1992 BS 7608: 1993: Code of practice for fatigue design and assessment of steel structures. London: BSI, 1993 BS EN 61508: 2002: Functional safety of electrical/electronic/programmable electronic safety-related systems. London: BSI, 2002 [7 parts]
IStructE The operation and maintenance of bridge access gantries and runways
Appendix A Safety legislation, codes and standards relevant to the UK
A1
General
Attention is drawn to the following acts and regulations, and HSE approved codes of practice (ACoP) and guidance, which are seen to be most relevant. These are then summarised in the subsequent sections. • Health and Safety at Work etc. Act 19744. •
Management of Health and Safety at Work Regulations 19995 (MHSW) and ACoP
Management of health and safety at work (HSE L21)15. •
Construction (Design and Management) Regulations 20071 (CDM), ACoP Managing
construction for health and safety (L144)16 and guidance Health and safety in construction (HSG150)17. •
Work at Height Regulations 20057 (WAHR)
and guidance; The Work at Height Regulations 2005; A brief guide (INDG401)18. •
Lifting Operations and Lifting Equipment Regulations 19989 (LOLER) and ACoP and
guidance; Safe use of lifting equipment 1998 (HSE L113)19. •
Personal Protective Equipment at Work Regulations 199220 (PPE) and guidance;
Personal protective equipment at work 1992 (HSE L25)21. •
Provision and Use of Work Equipment Regulations 19986 (PUWER) and ACoP Safe
use of work equipment (HSE L22)22. •
The Supply of Machinery (Safety) Regulations 199214 and European Machinery
Directive23. The relationship between these documents is summarized graphically in Figure A.1.
A2
Synopsis of regulations
A2.1 The Health and Safety at Work etc. Act 19744 The basis of British health and safety law is the Health and Safety at Work etc Act 1974. The Act sets out the general duties which employers have towards employees and members of the public, and employees have to themselves and to each other. These duties are qualified in the Act by the principle of ‘so far as is reasonably practicable’. In other words, an employer does not have to take measures to avoid or reduce the risk if they are technically impossible or
if the time, trouble or cost of the measures would be grossly disproportionate to the risk. Regulations, for example the Management of Health and Safety at Work Regulations 19995, have been made under the Act. These often bring into force the requirements of EC Directives. A2.2 The Management of Health and Safety at Work Regulations 19995 The Management of Health and Safety at Work Regulations 1999 generally make more explicit what employers are required to do to manage health and safety under the Health and Safety at Work Act. Like the Act, they apply to every work activity. The main requirement on employers is to carry out a risk assessment. Employers with five or more employees need to record the significant findings of the risk assessment. The HSE leaflet Five steps to risk assessment24 provides more information. Besides carrying out a risk assessment, employers also need to: • make arrangements for implementing the health and safety measures identified as necessary by the risk assessment • appoint competent people (often themselves or company colleagues) to help them to implement the arrangements • set up emergency procedures • provide clear information and training to employees • work together with other employers sharing the same workplace. A2.3 Construction (Design and Management) Regulations 20071 (CDM) The Construction (Design and Management) Regulations 2007 are aimed at improving the overall management and co-ordination of health, safety and welfare throughout all stages of a construction project. They place duties on all those who can contribute to the health and safety of a construction project: clients, designers, contractors and coordinators. They require the production of certain documents, including the construction phase plan and the health and safety file. Industry-produced guidance for CDM 2007 is available from CITB-ConstructionSkills at www.citb/cdm.
IStructE The operation and maintenance of bridge access gantries and runways
Appendix A
43
A2.4 The Work at Height Regulations 20057 The Work at Height Regulations require that all that is reasonably practicable should be done to prevent anyone falling. They set out a simple hierarchy for managing and selecting equipment for work at height: • avoid work at height where possible • use work equipment or other measures to prevent falls where working at height cannot be avoided • where the risk of a fall cannot be eliminated, use work equipment or other measures to minimise the distance and consequences of a fall should one occur. The Regulations require duty holders to ensure: • all work at height is properly planned and organised • all work at height takes account of weather conditions that could endanger health and safety • those involved in work at height are trained and competent • the place where work at height is done is safe • equipment for work at height is appropriately inspected • the risks from fragile surfaces are properly controlled • the risks from falling objects are properly controlled. A2.5 The Lifting Operations and Lifting Equipment Regulations 19989 Generally, the Lifting Operations and Lifting Equipment Regulations 1998 (LOLER) require that lifting equipment provided for use at work is: • sufficiently strong, stable and suitable for the proposed use. Similarly, the load and anything attached (e.g. timber pallets, lifting points) must be suitable • positioned or installed to prevent the risk of injury, e.g. from the equipment or the load falling or striking people • visibly marked with any appropriate information to be taken into account for its safe use, e.g. rated loads. Accessories, e.g. slings, clamps etc, should be similarly marked • used safely, i.e. lifting operations are planned, supervised and carried out in a safe manner by people who are competent • subject to ongoing thorough examination and, where appropriate, inspection by competent people.
44
Appendix A
Lifting equipment includes any equipment used at work for lifting or lowering loads, including attachments used for anchoring, fixing or supporting it. The Regulations cover a wide range of equipment including, cranes, forklift trucks, lifts, hoists, mobile elevating work platforms, and vehicle inspection platform hoists. The definition also includes lifting accessories such as chains, slings, eyebolts etc. LOLER does not apply to escalators; these are covered by more specific legislation, e.g. the Workplace (Health, Safety and Welfare) Regulations 199225. If employees are allowed to provide their own lifting equipment, then this too is covered by the Regulations. It should be ensured that in using any lifting equipment the requirements of LOLER are met. Additionally, it should be ensured that: • where equipment is used for lifting people it is marked accordingly, and it should be safe for such a purpose, e.g. all necessary precautions have been taken to eliminate or reduce any risk • where appropriate, before lifting equipment (including accessories) is used for the first time, it is thoroughly examined. Lifting equipment may need to be thoroughly examined in use at periods specified in the Regulations (i.e. at least six-monthly for accessories and equipment used for lifting people and, at a minimum, annually for all other equipment) or at intervals laid down in an examination scheme drawn up by a competent person. All examination work should be performed by a competent person • following a thorough examination or inspection of any lifting equipment, a report is submitted by the competent person to the employer to take the appropriate action. A2.6 The Personal Protective Equipment at Work Regulations 199220 The main requirement of the PPE at Work Regulations 1992 is that personal protective equipment is to be supplied and used at work wherever there are risks to health and safety that cannot be adequately controlled in other ways. The Regulations also require that PPE: • is properly assessed before use to ensure it is suitable • is maintained and stored properly • is provided with training and instructions on how to use it safely • is used correctly by employees.
IStructE The operation and maintenance of bridge access gantries and runways
A2.7 The Provision and Use of Work Equipment Regulations 19986 In general terms, the Regulations require that equipment provided for use at work be: • suitable for use, and for the purpose and conditions in which it is used • maintained in a safe condition for use so that people’s health and safety is not at risk • used only by people who have received adequate information, instruction and training • accompanied by suitable safety measures, e.g. protective devices, markings, warnings • inspected in certain circumstances to ensure that it is, and continues to be, safe for use. Any inspection should be carried out by a competent person (this could be an employee if they have the necessary competence to perform the task) and a record kept until the next inspection. It should also be ensured that risks, created by the use of the equipment, are eliminated where possible or controlled by: • taking appropriate ‘hardware’ measures, e.g. providing suitable guards, protection devices, markings and warning devices, system control devices (such as emergency stop buttons) and personal protective equipment • taking appropriate ‘software’ measures such as following safe systems of work (e.g. ensuring maintenance is only performed when equipment is shut down etc), and providing adequate information, instruction and training. A combination of these measures may be necessary depending on the requirements of the work, the assessment of the risks involved, and the practicability of such measures. A2.8 Supply of new machinery The supply of new machinery should, wherever possible, use proprietary equipment that is fully CE marked. It is also important to note that there are several relevant pieces of law on supplying new machinery, including: • the Supply of Machinery (Safety) Regulations 199214, which implement the European Machinery Directive23, and which contain detailed requirements for manufacturing safe new machinery • the Health and Safety at Work etc. Act 19744, which contains general requirements for the manufacture and supply of safe workplace
•
machinery (including second-hand machinery) other regulations, which implement other European Directives, such as those on the supply of electrical equipment or on gas appliances, which are important for many suppliers of machinery.
A2.8.1 The Supply of Machinery (Safety) Regulations 199214 (sometimes referred to as the
‘Machinery Directive’) apply to all new machinery manufactured or supplied in the UK, wherever it is to be used in the European Economic Area (EEA). The term ‘machinery’ is broadly defined and includes what is generally understood by the term. The Regulations require all UK manufacturers and suppliers of new machinery to make sure that the machinery that they supply is safe. They also require manufacturers to make sure that: • machinery meets relevant essential health and safety requirements (listed in detail in the Regulations), which include the provision of sufficient instructions • a technical file for the machinery has been drawn up, and in certain cases, the machinery has been type-examined by a notified body • there is a ‘declaration of conformity’ (or in some cases a ‘declaration of incorporation’) for the machinery, which should be issued with it • there is CE marking affixed to the machinery (unless it comes with a declaration of incorporation) • identify the health and safety hazards (trapping, crushing, electrical shock, dust or fumes, noise, vibration, etc) that are likely to be present when the machinery is used • assess the likely risks • eliminate the risks, or if that is not possible • provide safeguards (e.g. guarding dangerous parts of the machinery, providing noise enclosures) or, if that is not possible • provide information about any residual risks and place signs on the machinery to warn of risks that cannot be reduced in other ways (e.g. ‘noisy machine’ signs). A2.8.2 The Supply of Machinery (Safety) Regulations 199214 only apply to the first supply
of machinery into the EEA, and only if this took place after 1 January 1993. Therefore, if second-hand machinery is supplied that was first in use before 1993, without substantially refurbishing it, the machinery does not need to comply with these Regulations.
IStructE The operation and maintenance of bridge access gantries and runways
Appendix A
45
Also, if CE-marked machinery is re-supplied, these Regulations do not apply. However, all machinery should be maintained in a safe state, and Section 6 of the Health and Safety at Work etc Act 19744 will apply to the re-sale (in Great Britain) of all second-hand workplace machinery, however old it is. Section 6 of the Health and Safety at Work etc Act 19744 places a duty on ‘any person who designs, manufactures, imports or supplies any article for use at work... to ensure, so far as is reasonably practicable, that the article is so designed and constructed that it will be safe and without risks to health...’ Adequate information about the use for which the article is designed is also required. Suppliers of all types of workplace machinery must meet these requirements, whether the machinery is new or second-hand. But the drawing up of a technical file, type-examination, the issuing of a declaration of conformity and affixing CE marking are not required under this Act. Other laws that will often apply to the supply of machinery are: • Electrical Equipment (Safety) Regulations 199426, which apply to most electrically powered machinery used in workplaces • Electromagnetic Compatibility Regulations 199227 which cover equipment likely to
cause electromagnetic disturbance, or whose performance is likely to be affected by electromagnetic disturbance. Machinery must satisfy the essential health and safety requirements of the law, i.e. the Supply of Machinery (Safety) Regulations 199214 in the UK. But there are an increasing number of harmonised European Standards that will help manufacturers to do this. The use of these standards is voluntary, and manufacturers can design and manufacture their machinery in accordance with other national or international standards if they wish, so long as the essential health and safety requirements of the law are satisfied. CE marking is not a quality mark and affixing it on machinery is only one of the several requirements that the manufacturer has to meet. By affixing CE marking to machinery, the manufacturer is claiming that all relevant legal requirements have been met, but that does not remove the obligation on the purchaser to still make sure as far as is possible that the machinery is safe. Further guidance is available in Product standards: Machinery: Guidance Notes on UK Regulations28 and Supplying new machinery29.
Directives
The Supply of Machinery (Safety) Regulations 199214
British and European Standards
Acts
Health and Safety at Work Act 19744
Regulations Safety
MHSW5 CDM1 WAHR7 LOLER9 PPE20 PUWER6 COSH30 RIDDOR31
BRIDGE ACCESS GANTRIES
BS 540032 BS EN 199333 BS 285334 TG 2035 BS 597436 BS 767112 BS 603737 BS 717138 BS 180839
Design
Industry guidance
ACoPs
HSE L2115 HSE L2222
IStructE Guide IEE: Guidance Note 313
Guidance
HSG 15017 INDG 40118 HSG L11319 HSE L2521
Figure A.1 Brief graphical summary of some relevant legislation, standards, codes and guidance documents
46
Appendix A
IStructE The operation and maintenance of bridge access gantries and runways
Appendix B Gantry Life Cycle
Structure and maintenance scheme conceptual design
Gantry construction
Gantry commissioning
Gantry operation
Gantry maintenance
Gantry removal
Structural design regulations Electrical design regulations Mechanical design regulations Operating and storage conditions Relevant legislation, regulations, standards, codes and guidance Intended use Maintenance cycle Industry guidance (IStructE guide) Escape and safety systems Environmental considerations related to materials used for construction Environmental considerations related to use (collection of spent shot, blast etc.) Materials for construction Power systems and delivery Lubrication systems Installation scheme for runway and carriage Vandal proofing and storage Proofloading of whole gantry system Operating procedures Operator competence and training User competence and training Operating criteria Acceptance criteria Operating and procedure manuals Pre-operations checks and briefing Go/no go criteria Control systems and override capability Limits for operation Cut-out devices Reporting and usage logs Ownership and responsibility during operation Inspection cycle Maintenance cycle Repair and refurbishment operations Go/no go limits for condition Conditions for storage Indicative procedure for gantry removal included as part of H&S file Effects on structure to be noted Environmental considerations related to materials
Figure B.1 . Gantry life cycle – key considerations
IStructE The operation and maintenance of bridge access gantries and runways
Appendix B
47
Figure B.2 . A typical gantry detailed life cycle – Flow Chart
48
Appendix B
IStructE The operation and maintenance of bridge access gantries and runways
Gantry usage
Detailed design of structure
CONCEPT
Consult bridge operator
Maintenance and inspections not performed
Remove existing gantry
Decommission and make safe existing gantry
N
Should a gantry be part of the solution to bridge maintenance access?
Follow operational procedures
Y
Check operator and user safety induction
N
Competence OK?
Y
N
DO NOT use gantry
Use gantry
Gantry fit for use?
Y
Complete session log
Follow close down and security procedures
Functional check of gantry operation
Commissioning
Check against relevant legislation regulations, standards, codes and guidance
Pre-use inspection of gantry and runway
Y
Check against structural, electrical mechanical reqts.
Maintenance and inspection procedures without use of gantry
Acceptable
N
Identify significant hazards
Identify significant hazards
Detailed examination and proof load testing if required
N
Y
Proof testing and load adjustment & Operator training
Design structure and gantry in parallel
Maintenance checks up to date?
Operator retraining
Construction of structure and gantry & Produce operating and maintenance manuals
Should a gantry be part of Y the solution to bridge maintenance access?
Review by bridge operator. Complete Y maintenance and inspections. Re-commission if required
N
Design complete
Maintenance strategy
Gantry used and maintained in accordance with procedures
Details design of gantry and runways
Structure conceptual design
N
Design structure with maintenance provision (no gantry)
Gantry fit to use?
N
Inspection, maintenance and repair procedures operative
N
Design concept acceptable?
Y
Y
Appendix C Operational and safety procedures A typical example of relevant matters to be covered
The following illustrates some procedures for a particular bridge and its specific access system. They are not directly applicable in general and are not necessarily appropriate for other bridges and access systems.
Preparation • No person will attempt to gain access to an underdeck gantry for the purpose of operating it in any way, unless they personally have been fully trained and are accompanied by at least one other person who has also been fully trained. Fully trained personnel will be in possession of a certificate of competency issued by the gantry manager. • One of the operating personnel will be a qualified first-aider wherever possible. • A defined set of equipment will be taken onto the gantry. Typical items are: – a ladder, which will be used for access and egress – a first-aid box – torches – two functional radio sets – a whistle – two first-aid thermal blankets carried in a pre-prepared haversack – two fire extinguishers of powder types coloured blue and preferably of stainless steel – rope ties for the ladder – a can of petrol or diesel – a bar for storm anchor bottle screws – two portable tirfors as stand-by. • Each person going on to the gantry will wear a safety harness, a safety helmet, appropriate protective and easily visible clothing, and industrial footwear. • Prior to leaving for the bridge, a check will be made in the Control Room or office of the existing and forecast wind speeds for the period when the gantries are to be occupied. Gantries will not be moved in a wind speed typically of more than 30mph (50km/h) and work will cease on gantries and they will immediately be vacated when the wind speed exceeds typically 50mph (80km/h).
•
If gantries over water are to be used, in addition to the previous procedures, a safety boat should be employed on the river and the River Authority should be informed.
Access to gantries • Access to gantries may be over the bridge parapet and down a portable ladder, onto the cantilevered top deck of the gantry; alternatively via permanent access platforms outside the parapet onto the gantry. • Where temporary access ladders are used, they will be placed at the bridge parapet and lashed securely to the walkway handrail. Safety harnesses will be secured to the bridge structure before any move is made, and following each move, the harnesses will be re-secured as appropriate. The first person to go down the ladder will tie the bottom end of the ladder to the gantry deck. When all personnel are on the gantry a radio check will be made to the control or supervising engineer. The ladder will be left in place until the pre-use checks are completed, see below. Operation of gantries Pre-use checks (maintained equipment) • Remove covers from hydraulic power pack and drive units and check fluid level. • Check hydraulic hoses and connections for leaks, check any electrical connections and limit switches. • Check that all hydraulic valves are in the correct position • Check engine oil level and fuel level. • Start engine and confirm satisfactory running. • Confirm operation of drive units by operating one control lever at a time. If the drive unit is of a rope haulage type use the slack in the cable, and observe that the cable moves smoothly in both directions.
IStructE The operation and maintenance of bridge access gantries and runways
Appendix C
49
•
• • •
• •
• • •
Slacken the bottle screws on the storm anchors which are at the rear of the gantry (depending on direction of travel). To remove the storm anchor hook from the cross-girder will require the fitter to lean out over the edge of the gantry. A safety harness must be worn and be secured to the gantry before removing the storm anchor hook. Remove both rear edge storm anchors and lay them on the gantry. Other gantries may be anchored differently, although a similar procedure will be required. Confirm that the gantry upper deck is clear of all equipment, except the ladder. Ensure that the loading on the gantry does not exceed the rated load. In the interests of health and safety, ensure that the gantry is in a tidy condition and that only essential materials and equipment are on board. Confirm that the locking pins securing platform extensions in the retracted position are fitted. Ensure floor access hatches are closed and ladders retracted if necessary, before moving the gantry. Ensure that access tower platforms are retracted before moving the gantry. Confirm the operation of the emergency stop controls. Check access ladders are secure.
Moving the gantry • No gantry will be moved without the authority of the gantry manager. Their signature must be obtained on the work order or written procedure. • Remove the rope ties from the ladder and stow the ladder on the lower deck. • Station one person on each side of the gantry whose duty is to monitor the movement of the gantry and inform the gantry driver if crabbing or snagging is likely. This person must not go on to the upper deck unless so directed by the gantry driver. • Operate one control lever and take up all the slack in the cable. Operate the other control lever and take up all the slack in the other cable. Operate both levers together to move the gantry. On gantries where drive units power trolley wheels directly a similar operation is required. • Move the gantry approximately 0.5m then STOP. Unhook the storm anchors from the cross-girder
50
Appendix C
• •
at the front edge and lay them on the deck. Confirm that the upper deck is clear, and that the two assistants are back in place on the steps. Drive the gantry to the required position.
For the gantries which operate on the centre span, the procedure is: • The towing cable is suspended from hooks. When the hook is within reach STOP the gantry. Direct the assistants to go on to the upper deck and unhook the cable. • Check that the assistants are back on the steps then move the gantry forward again until the hook is past the winch. STOP the gantry again and direct the assistants to go on to the upper deck and hook the cable back on. • Check that the assistants are back on the steps then move the gantry forward as required. • Under no circumstances will personnel stand on the upper deck whilst the gantry is in motion. Parking the gantry at the required work position Permitted locations and procedures for parking: • the only authorised parking position is between the cross girders. Under no circumstance whatsoever may the gantry be parked elsewhere • as soon as the gantry is in the correct position, rig the ladder to the walkway handrail and tie it top and bottom • if the gantry is to be parked for a significant period or if wind speed rises then rig all four storm anchors to the cross-girders. The gantry and runway beams should be inspected during the gantry travel for signs of untoward movement, deformation, running of wheels off-line, wear of wheels or beams, misalignment at runway beam joints, or structural defects. The driver should note a log of any unusual occurrences or deterioration during the use of the gantry. These will be subsequently reviewed by the supervisor who should produce recommendations for maintenance action. Communications • Two of the operating personnel on the gantry (the driver and one other) will carry a radio
IStructE The operation and maintenance of bridge access gantries and runways
• •
handset, using a belt attachment and lapel clip. A radio check will be made to control or the supervising engineer every 30 minutes. When personnel are on gantries, the duty controller or supervising engineer will notify them by radio if the (gust) wind speed reaches 30mph (50km/h). In such a case the gantry will immediately be secured by use of storm anchors. The duty controller or supervising engineer will continue to keep gantry personnel updated with wind speeds if above 30mph (50km/h), and if 50mph (80km/h) is reached will specifically notify them, and the gantry will be immediately vacated.
•
Rated load • Rated load notices should be displayed on all gantries. No more than 6 persons in each cantilever at any time, i.e. no more than 12 persons in total. • No more than 550kg of materials on each cantilever and the central span, distributed over not less than 3m on each blue area, or 3400kg on bearers spanning 1250mm across each red painted area, plus 550kg distributed over not less than 3m confined to the central span. Egress from gantries • If possible, the gantry is to be returned to its normal stowed position, i.e. against a pier. If this is not possible, or work is to continue over a period of time the gantry may remain in a parked position. • The drive units, drive ropes, control console and the suspension trolleys will be covered by tarpaulin. • The storm anchors will be placed in position. • Any wind sheeting installed for work purposes will be removed. • The portable ladder will be placed in the egress position and secured at top and bottom. Emergency procedures • Emergencies may take the form of an accident involving the gantry and/or personnel; a sudden illness amongst the personnel; a fire; an inability to move the gantry to an accessible egress
•
•
point, either because of mechanical or electrical malfunction, or because of high winds. Immediately an emergency occurs, the controller or supervising engineer will be notified by radio, and given the location of the gantry. The controller or supervising engineer will immediately telephone the local fire brigades by means of direct line if available or a mobile phone and inform them of the emergency on the gantry; requesting the attendance of an aerial appliance for rescue purposes. If a traffic lane is not already closed the controller or supervising engineer will then close a lane utilising traffic management signs; and will despatch patrol vehicles to the scene who will station themselves in a ‘fend-off’ position to protect the fire brigade when they arrive. The controller or supervising engineer will call an ambulance if there is any suggestion of personal injury or illness, and will notify the police. If there is personal injury or illness and there is no qualified first-aider on the gantry, the controller or supervising engineer will despatch a first-aider to the scene as quickly as possible. The first-aider, if volunteering to go onto the gantry, will require all protective clothing including a harness (the latter is carried on each patrol vehicle). The duty controller will notify the bridge owner and operator. Providing all personnel are capable of vacating the gantry, this should be done as a matter of priority. Personnel should only remain on the gantry if egress is not immediately possible or if there is personal injury or illness preventing evacuation. In the latter case, sufficient personnel should remain to provide whatever assistance may be required to comfort and assist in evacuating the disabled person. In any case where personnel need to be rescued from the gantry, or where the gantry is in such a position that the normal method of egress via a ladder is not possible, the fire officer in charge will be responsible for organising the rescue. In such situations, personnel at the scene will place themselves under the command of the fire officer, and should be prepared to render whatever assistance is required.
IStructE The operation and maintenance of bridge access gantries and runways
Appendix C
51
Appendix D Gantry incidents, concerns and ‘near hits’ over recent years – Examples
This Appendix lists some real examples of gantry incidents. Study of this table may inspire the use of procedures that will help prevent further incidents. End use of gantry
Use of gantry when incident occurred
Description of incident
Injuries to Personnel
Erection gantry for in-situ segmental construction
Moving forward for next segment during construction
Gantry rolled downhill off end of partially completed structure
Construction workers – two killed, one seriously injured
Temporary works gantry for the erection of deck box sections
Erection of sections
Lifting crane fell off while One person gantry being moved to next injured position
Designed concurrently with bridge deck to service inspection/maintenance of
Use by contractor to paint box girder
Moving of gantry along from its station to position of work. Gantry geometry
Two construction workers killed on going down with
was intended to have been locked but previous misuse had left it in an un-locked mode
the platform; one injured
None
the permanent works (steel box girder)
52
Temporary supports to units
Positioning of 2000tonne units
Punching shear failure through previously constructed unit
Erection gantry for pre-cast segmental construction
Erection of a 350tonne segment
Segment suspended from None runway trolley ran onto cantilever arm designed only for the unloaded trolley causing segment to crash through already completed deck
Retrofitting of a pair of gantries to service permanent works
During painting/ maintenance
Access door fell from gantry onto public area below
None
Construction gantry travelling on runway beams designed for a permanent works inspection gantry
Strengthening works to the bridge superstructure and replacement of the existing permanent gantry runway beams; decision to combine these two operations
The front hangers were running on old runway beams with the rear hangers suspended from sections of newly installed runway beams. At the time of the accident there was a gap of approximately 3.5 metres between the ends of the new and the end of one of the old runway beams
Four construction workers killed on being thrown from platform
Designed concurrently with bridge deck to service inspection/maintenance of the permanent works (steel box girder)
Moving of gantry from its parked position to end of structure to allow for its servicing
Previous inspection had shown runway beams to be corroded and some of its holding up bolts to be fractured
None
Appendix D
IStructE The operation and maintenance of bridge access gantries and runways
Specific details relating to the cause of the gantry incident have been removed. However, each of the following causes may have been relevant to at least one of the incidents in the previous table. • Possibly unauthorised modification of agreed operating procedures • Local failure of cable system used to move gantry • Complexity of management requirements • General failure to plan, organise, train, control, monitor and review the wider temporary gantry operation when used by multi-organisations • Operator error • Automatic stop mechanism not provided • Operating procedures inadequate • Electronic safety systems were overridden regularly to facilitate use of gantries in an unauthorised and unsafe configuration • Unsatisfactory hardware and unsafe working practices • Ineffective restraints on beams to prevent longitudinal movement of gantries
• •
•
•
No provision of end stops as a ‘fail safe’ in the event of restraints not working effectively General failure to plan, organise, control, monitor and review the wider temporary gantry operation Driving of gantry along defective beams without consideration of previously identified and documented defects Possible absence of clear management procedures by either operator/owner or/and maintenance company
The fact of these failures is a matter of record but the causes of many have never been made public. One striking element of concern, though, is the regularity with which complex systems for moving gantries lead to accidents. This seems to be chiefly because the users become familiar with the system and then careless, but a large proportion of the fault lies with a design that is not appropriate to the circumstances in which it will be used
IStructE The operation and maintenance of bridge access gantries and runways
Appendix D
53
Appendix E Gantry design – some considerations
E1
Introduction
It should be emphasised that the quality of the original design can have a profound effect on the safety, functionality and economy of the gantry and therefore some reference to design in this manual is appropriate. The preparation and revision of this Guide revealed a vast amount of hidden experience. As a result some key points relating to the design of gantries and gantry systems are given for the assistance of designers. Feedback on experience should be channelled to the Institution of Structural Engineers. E1.1 Scope There is unfortunately very limited literature available covering specifically the design of bridge access gantries. It is outside the scope of this publication to fill this gap. In view of these limitations, this Appendix should not be regarded as providing comprehensive guidance. The opportunity is taken nevertheless to set out some important design considerations and issues with the intention of assisting and stimulating designers in their thinking about gantry facilities. Study of the whole publication is similarly commended to designers. E1.2 The designer Projects involving the design and supply of new bridge access gantries are relatively infrequent, and there is insufficient work of this nature to support a large body of general bridge designers with recent direct experience. It is therefore important that this is recognised in the selection of an engineer/engineering firm to undertake such work. In such circumstances particular care should be taken in the appointment to establish that there is: • relevant experience of equipment and systems involving similar technical disciplines and operating regimes • a proper appreciation of the general nature of the design task, a clearly defined approach to understanding the requirement and a process to develop a safe and economic design solution • an adequate strategy to address any lack of direct relevant experience of bridge access gantries to ensure proper involvement of the required range of technical disciplines and expertise • an understanding of the procurement process overall and strategies to ensure that proper control of the design process can be maintained throughout.
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E1.3 The design process in relation to procurement For gantries, particularly those incorporating more complex mechanical and control systems, the design process is likely to continue into the contract for the supply and installation (which in itself may be part of an overall contract for constructing or modifying the bridge concerned). The specialist electrical, mechanical and control design may need substantial development by specialist supplier/designers which in turn may require some adjustment of the primary structure or configuration. The supervision, management and programming of the procurement phase needs to take proper account of this. The guidance given in Section 1.3 is relevant to this.
E2
General considerations
E2.1 The general requirement for access Access is ideally required to all parts of the superstructure of a bridge for inspection and maintenance purposes. This requirement may generally be said to be necessary to ensure the long-term safety and serviceability of the bridge. The range of work may include: • general, special or principal inspections of the structure • inspection of services, drainage and statutory undertakers apparatus and utilities which may be carried across the bridge • painting of steelwork, repairs to reinforced concrete, repairs/replacement of bearings, handrails, joints, platforms, ladders, drainage pipes, etc. Access may also be required for work in connection with major ‘refit’ activities including major repair and refurbishment, strengthening, deck widening etc. Such work is likely to be carried out under a different management and contractual regime to that applying to routine inspection and maintenance. E2.2 General means of providing access For small bridges access is often relatively straightforward. Ladders, temporary scaffolds or mobile access vehicles with extending work platforms can be used to give access to the few parts which are not directly accessible from the bridge deck or from the area around or beneath the bridge.
IStructE The operation and maintenance of bridge access gantries and runways
For larger bridges access for inspection and maintenance generally becomes more difficult and may require dedicated and/or purpose-built arrangements. For large bridges access might be provided by equipment brought onto site for the specific occasion or by permanently installed equipment. Such equipment may include gantries, cradles, walkways and platforms in addition to the methods appropriate for small bridges. E2.3 Determining the appropriate means of providing access The circumstances requiring the provision of a new gantry will generally arise from a project for constructing a new bridge structure, repairing/ strengthening an existing bridge or because of the need for replacement of an existing gantry for operational/ safety reasons. Even where some form of gantry appears to be the obvious candidate for the provision of access it is recommended that explicit and documented consideration is given to the options available to meet the circumstances. Such consideration should be based on a clear definition of the functional requirements for inspection, maintenance and any other duties over the life cycle of the bridge and the gantry itself. This option study may be a relatively straightforward task or in the case of a large or complex bridge structure, may require careful consideration of interactions between the bridge design and the access design both at overall and detailed levels. These may involve such things as the consequences of different maintenance regimes, structural interactions, dynamic and aerodynamic interactions. Initial work would be essentially strategic, and would consider possible trade-offs between different aspects over the life-cycle of the bridge. As the design process moves forward the assumptions on which any conclusions are based may need to be reviewed in order to check the continuing validity of the conclusions. Access arrangement options to be considered, either singly or in combination, might include: • bridge access gantries of various types, configurations, and capabilities • inspection cradles • remotely operated systems or fixed installations (involving specialist vehicles, cameras or other sensors)) for inspection • road vehicle-mounted articulated-arm systems providing manned access platforms for underdeck inspection
• • • •
•
fixed walkways platforms/ladders abseiling/lightweight rope-harnessed access methods scaffolding/purpose-erected fixed structure to be erected and dismantled on an occasional basis as required other methods.
In effect this study would form a significant part of the development of a complete maintenance and access strategy for the whole bridge. The selected option should be chosen on the basis of a broad life-cycle view of costs and not simply on first-cost estimates of equipment provision or direct task-based operational costs. Thus consideration also needs to be given to the costs of procurement, operational management, staffing and training, maintenance of the access facilities and other relevant costs. The costs of providing and keeping a team of staff fully trained and rehearsed to operate the facility safely when required as well as to undertake the primary functional tasks need to be considered very carefully. Proper account should also be taken of the effort required to sustain management responsibility for safety. Similarly maintaining gantry /access equipment in safe operational order may involve more complexity than maintaining the bridge itself and these costs need to be taken fully into account. These life-cycle costs are likely to have more influence on the scheme selection in-situations where access for the primary tasks is only required infrequently. In such cases the effort required for maintaining gantry equipment, operational staff preparedness and safety training may be disproportionate and it may be more satisfactory to provide, for instance, anchorage points for scaffolds or just to provide rails for the attachment of a (temporary) gantry or cradle deployed for those occasions when it is specifically required. It is important when considering such alternatives to make proper allowance for the provision of high levels of management, technical competence and trained operator availability to ensure high standards of safety. On no account should ‘temporary’ situations be regarded as justifying lower standards than those applying to permanent installations. For large steel bridges, underdeck access may be required for major repainting at intervals during the life of the bridge. A gantry designed principally for inspection and general maintenance work may not adapt well to such operations. A more extensive work platform area and/or improved mobility may
IStructE The operation and maintenance of bridge access gantries and runways
Appendix E
55
be necessary to serve a major repainting programme. Whilst it may be possible to design a suitable gantry for this purpose, initial provision for use at some distant and uncertain future date may not be cost effective. Similarly such investment may be in jeopardy to the envisaged requirement changing once the actual circumstances of the work come into view. Consideration should given to later upgrade or replacement of the gantry, or alternatively to the use of purpose-designed relocatable work platforms. In the situation where the bridge deck is deep a permanent deck soffit enclosure system may be feasible and economic.
E2.4
General design issues for gantries
E2.4.1 Operating environment Bridge access gantries generally operate in an exposed and difficult environment subject to high local wind speeds and turbulence. In many cases they may have to be parked in this environment for long periods between operations. This environment not only affects the hardware but also affects the conditions in which gantry operators or maintenance staff may have to work. Clearly reliability of the gantry and its operating system is of great importance, but at the same time effort in maintaining and operating it needs to be sensibly minimised. Durability and robustness are essential qualities of all exposed component parts. E2.4.2 Simple or complex systems As a general guide gantries should be as simple as possible and consistent with fulfilling their function. Complex systems increase the risk of loss of availability, are more likely to require high skill levels to operate and maintain, and may lead to more complex maintenance and inspection requirements. It is difficult to be categoric about complexity since even for complex systems high reliabilities and straightforward in-situ routine maintenance tasks can be achieved through good design and engineering allied to careful manufacture. However given the significant prototypical content of a typical gantry design and the nature of the operating environment, the maxim of simplicity should be applied where possible. E2.4.3 System design approach A bridge access gantry is a moving structure, often involving powered mechanical, electrical and electronic equipment, which is associated with a large static structure namely the bridge. The design and engineering regime which prevails for projects involving the design and procurement of gantries
56
Appendix E
is usually dominated or strongly influenced by that applying to the bridge itself. This regime may not always be inherently sensitive to the technical and functional issues peculiar to gantries. In these circumstances it is particularly important to recognise and define the gantry system as an entity that needs full consideration as part of the design and procurement process. The system boundary may be defined to embrace the behaviours of physical elements alone (possibly including the bridge itself) or be extended to encompass the human/operational features according to the level or type of design being undertaken. This implies some form of modelling of the various elements and their interaction as part of the design process. This approach is perhaps most valuable for more complex systems but even simple systems are likely to benefit from explicit and thorough consideration of the features, interactions and interfaces that are involved in the system. The system design approach naturally links to a whole life-cycle view which again helps to focus attention on key questions affecting design. E2.4.4 Bridge and gantry The design of the access gantry and the design of the bridge itself are clearly linked. The importance of this linkage will depend on the nature and design of the bridge, the gantry requirement and the point in the bridge’s life-cycle that the gantry design is being undertaken. For a major new long span bridge the interactions could be profound and of strategic importance to the design. It may be possible at the early design stage to conFigure the bridge to achieve simple gantry geometry or operation or to engineer the bridge structure or key details in a way that eliminates or reduces the need for regular maintenance using gantry access. For long bridges a number of gantries may be needed. It may be possible to minimise the number required by, for instance, providing space/openings at intermediate piers for the passage of gantries from one span to another. Where a gantry is required it may impose loading conditions that could have an important effect on, say, girder strength, key edge details or even overall behaviour. The local interactions at the detailed level also have to be considered carefully even on less sensitive or complex structures. Where gantries are to be provided for an existing bridge then there will be much less scope for engineering the interactions to advantage and there will be constraints on gantry configuration and design
IStructE The operation and maintenance of bridge access gantries and runways
determined by the original bridge design basis and the current operating circumstances. Any significant departure from any original allowance for gantry provision will require careful and knowledgeable assessment since what is significant may depend upon the type and design of the bridge itself. E2.4.5 Life cycle considerations A terminology for the gantry life cycle is included in Appendix B. The key life cycle phases are characterised by the overall processes and key process stages that they encompass. These are illustrative and may be structured and described differently in particular situations. They do help to illustrate the potential complexity and depth of process that may be involved in gantry design and procurement. As well as the question of the basic design life of the gantry, consideration of the life cycle of the gantry in relation to the life-cycle needs of the bridge may identify particular conditions or patterns of operation which should be allowed for in the design. For example: • typically the design service life for a gantry system should be 20-35 years, after which time it should be assessed for its suitability and upgraded or replaced as appropriate • the likely pattern of operation during the life of the bridge should be considered and any assumptions affecting the design/operation/maintenance, should be recorded as part of the design basis. For instance: – are there likely to be significant lay-up/ hibernation periods within the life cycle? – typically a six-yearly principal inspection and thorough overhaul of the gantry and its runway beams will be needed. Does the design of the gantry justify /require a different pattern of inspection? – has a planned refit/retrofit at gantry mid-life or prior to a major bridge refurbishment been allowed for in the design arrangements? E2.4.6 Environmental considerations Examine the possible requirements for safe working and for the containment and safe disposal of wastes from paint blasting and other contaminants from surface preparation and coatings application. • Consider precautions and issues relating to leakage of hydraulic fluid, lubricating oils or fuel from tanks, power units, drive motors and actuation gear etc. • Where a gantry can enter a confined space,
adequate ventilation should be provided. Gantries powered by internal combustion engines should not be used under such circumstances. E2.4.7 General arrangement of the gantry • The range and diversity of existing gantry configurations is illustrated in Chapter 2. The basic arrangement may be quite simple or may need to have adaptable geometry to meet variable plan or under-deck profiles, or to by-pass bridge piers or other local obstructions within the length of the bridge. • The gantry configuration will also depend upon the specific duties and performance that are defined for it, and may be strongly influenced by the means of support/guidance for travel along the bridge. • The gantry may run on track suspended from the main bridge structure or on runways which themselves form part of the bridge deck. The bogies/wheels may be captured by the track or held by wheel flanges, or may be effectively prevented from departure from the track by the overall geometry of the gantry structure. There is a general preference for systems which do not rely purely on overall geometry for adherence to the track. However for certain types of bridge it may not be practical to achieve such arrangements because of constraints on, for instance, the introduction of continuous upstands or downstands to the deck profile. In such situations particular care needs to be taken to ensure that the construction tolerances and possible distortion of the bridge/gantry structure under load or from secondary effects does not remove the necessary geometrical containment. • Similarly if the gantry is required to change its support mode or articulation for travel into certain areas of the bridge, extreme care is required to ensure that clear and reliable safeguards are incorporated to avoid a catastrophic failure from a failure in transition mechanisms/procedures. Such arrangements are not recommended and are only justifiable if there is no practical alternative and then only with the highest level of attention to the engineering and operations management to assure safe operation. A thorough review of the bridge design can usually remove the need for such arrangements. • Endstops should be provided at the ends of runways and may also be required at other positions. Where practical the design of endstops should be
IStructE The operation and maintenance of bridge access gantries and runways
Appendix E
57
•
•
•
•
•
58
capable of safely arresting a run-away gantry, and occasionally to allow straightening of a crabbed gantry by running onto the endstops. Consideration into the use of shock absorbing buffers forming part of the endstops may be necessary in such cases and impact forces need to be taken into account. Alternative means of arresting a run-away gantry may include additional braking systems. Account should be taken of the gradients on the gantry track and of wind forces that can add momentum to a gantry. The durability and reliability of the track/runway, any local brackets or support structure and all associated structural fixings is of great importance as access for close inspection and maintenance may be difficult. In the circumstances where the gantry has been out of action for a long period, it may prove difficult to justify re-use of the track without a careful and close prior inspection unless the design can be shown to be robust and such that it can be reliably inspected by remote means. Consideration should be given to the provision of significant excess load capacity to a vulnerable structure particularly the fixings, to the avoidance of corrosion traps and to detail arrangements which allow easy replacement of the most vulnerable elements. Reference should be made to Chapters 5 and 6 of this Guide. The provision of protective enclosures on a gantry should be considered for bridge inspection or maintenance work to meet requirements for safety and environmental protection. In the design of the bridge a lockable, weathertight shelter for the gantry should be integrated or provision made for easy removal of the gantry to ground level or off-site when it is not needed. Provision should be made for the gantries to be fully inspectable. This could be achieved by arranging that gantries can be lowered to the ground or by providing a means of gaining temporary access around the gantries while they are in position on the bridge or by designing the gantry such that it can be inspected from the gantry. If the gantry is to be inspected while in position on the bridge provision probably needs to be made to provide an alternative load path so that key components can be dismantled during the inspection. Even if the gantry is not lowered to the ground for inspection it will have to be lowered when it eventually needs replacing (see Section 7.4). Means of evacuating the personnel should be considered at all positions.
Appendix E
•
•
•
Any vertical access (over 75° to the horizontal) more than 3m high should be carefully considered. Safety lines, harnesses or (less preferable) back hoops may be required. Assistance can be found in the codes of practice for the design of ladders (e.g. BS 5395-340 or BS EN ISO 14122-441). Any sloping access, (30° – 75° to the horizontal) should have handrails and be provided with antislip bars. Side protection should be totally enclosed and at least 1.1m off a horizontal working surface. Suitable toe boards should be provided with a minimum height of 150mm.
E2.4.8 Design Process The detailed design process must ensure that all the relevant codes and standards are met. As with any major facility it must be designed to provide the required functionality with economy and to achieve as far as reasonably practicable safety by design. • Hazard identification and risk assessment should be a fundamental part of the design process for decisions on design and on commissioning, operation, maintenance, inspection and testing procedures. • The designer should communicate to all parties involved in following operations and life-cycle phases the particular importance of continued attention to the aspects of design that are prerequisites of continuing safe operation. • A Failure Mode and Effect Analysis should be prepared at the design stage to highlight any potential problems for consideration and action before the completion of design. Account should be taken of the effects of mishandling, long term effects and the effects of lack of maintenance to check and avoid undue sensitivity to these circumstances. • The key design documents including the design basis, design/maintenance manuals, hazard and risk assessments and the FME analysis report should remain available throughout the life of the gantry and be updated as necessary including feedback from the maintainer/operator linked to inspection/incident reports. • A third party calculation and operation check should be performed of the equipment before being taken into use. It should also be noted that the UK Highways Agency Design Manual for Roads and Bridges – Technical Approval of Highway Structures42, requires that Access Gantries are subject to Category 3 checking.
IStructE The operation and maintenance of bridge access gantries and runways
E3 Particular design considerations E3.1 Structure • The design should take account of horizontal loads due to gantry operation and wind effects. In the absence of precise information a notional horizontal load, determined as a percentage of the gantry self-weight, applied to the structure (laterally and longitudinally simultaneously) at the level where the carriage wheels are in contact with the runway beam may be considered for design. (Guidance is given in BS EN 1300143.) • Consider the need to minimize side forces on wheels due to crabbing. For example, this can be achieved by articulation of bogie assemblies with respect to the gantry structure about a vertical axis. This allows one bogie to be in advance of the other thereby minimizing the motion control requirements. • Many gantries are supported from bogies with pairs of wheels running on the lower flanges of rolled steel section runway beams. The interface between the precise mechanical arrangement of the bogie wheels and the structure (which is anything but precise in mechanical terms), presents problems for the designer at concept and detail stages; it is very significant for the serviceability and performance of the gantry, and for local stressing and wear of components. • The permissible, and commercially unavoidable, tolerances for rolling, for fabrication, and for erection, mean that the bogie arrangement has to cope with variations in beam dimensions, inclination of webs and flanges, and gaps and misalignment at joints. So, for example, if all bogie wheels are to remain in contact with the running surfaces on a flange either the beam must twist or the bogie must be free to rotate about its longitudinal axis. Wheels, for example, must be able to negotiate joints without undue impact. • Care and attention, commencing in design and through manufacture and installation can reduce the detrimental effects of the variations at the interface. If the phenomenon is overlooked problems at commissioning and in service are inevitable. • Vibration of gantry systems needs careful consideration at the design stage (see Section 6.3.4). • For many gantry systems, particularly on long bridges, the maintenance of the runway beams has proved to be much more onerous and expensive than maintenance of the gantries themselves.
•
•
•
•
•
A design which avoids the need for runway beams, say by supporting the gantries from soft-tyred wheels running directly on the bridge deck, is likely to have considerable long term advantages. Runways, and their attachments to the bridge structure, can often be the weakest element in the gantry system and can be difficult to inspect and maintain. For this reason it is recommended that their design should include an additional special partial load factor over and above the normal partial factors adopted in the design code (see also Section 6.3.1). This additional factor should be typically in the region of 1.25 and chosen to suit the code that has been adopted for runway design. The bridge operator may decide to modify the magnitude of this additional partial load factor to suit the characteristics of the gantry system (or systems). The application of this additional factor has the effect of introducing a degree of overdesign to the runway and its fixings to the bridge. (Note that this additional partial factor should be used only in the theoretical design of the runway. It should not be included in the calculation for the loading to be applied in any physical proof load test). The design of the connections between runway and bridge need careful attention to ensure that they are not susceptible to fatigue effects (e.g. bolted attachments should be prestressed to prevent reversals of stress under any load conditions). Runway beams should be designed so that they can be replaced. Where gantries run directly on the bridge deck they should not cause wear/ damage or overloading to the bridge structure. Consideration should be given to the provision of redundancy in the primary means of support. This may seem obviously desirable but it can be difficult in some circumstances to reconcile with fatigue considerations or with simplicity and reliability in terms of the impact on the design of the mechanism. Alternative load-paths might be provided by other means, for instance those, such as tethers, which come into play only in extreme circumstances to avoid or limit catastrophic collapse. All primary means of support should be readily inspectable. The design should take careful account of the durability and corrosion resistance of all elements affecting the safety and reliability of the gantry. Contact between dissimilar metals should be avoided.
IStructE The operation and maintenance of bridge access gantries and runways
Appendix E
59
E3.2 Mechanics • A simple hand-propelled gantry which can pass ‘through’ or around specially designed supports may require less maintenance and may therefore be preferable. Manually operated gantries should be designed to require no more than 25kg effort per person to move them. • If the bridge structure is large or complex, it may be relevant to consider a more sophisticated powered gantry. Such gantries may require other control systems proximity sensing equipment, speed control, braking, overload warning, etc. There are no insurmountable safety problems with the provision of an electrical supply which is a prerequisite for the deployment of such systems. • However, it is emphasised that such gantries need to be designed by a multidisciplinary team and that, while complex control systems can be engineered, the extreme conditions imposed on gantries can make such systems unreliable, at best troublesome, and at worst dangerous, if they have not been fully tested and all fault conditions simulated. • Consider the need to remove the load from wheels with polyurethane tyres when the gantry is parked. Polyurethane (and similar) tyres may flatten when left under load for several hours/days, especially if the tyres were warm from running prior to the gantry being parked. The ‘flats’ on the wheels can inhibit running and may require more power for initial running. • Gantry components should be suitably protected against the ingress of dirt and robust enough to resist damage caused by the envisaged bridge maintenance activities, e.g. blasting and painting. • The design should take account of wear and possible vibration and fatigue effects. Clear guidance should be given to the Operator on vibration limits and on measures required to minimise fatigue. The recommended service life for any components which may be susceptible to wear or the effects of fatigue should be specified. • A failsafe mechanism should be provided for the circumstance of wheel derailment. It is preferable where design circumstances allow for bogies to run along tracks with captive wheels which bear against all enclosing surfaces. • Moving parts, e.g. wheels and bogies, should be designed for ease of inspection and replacement. • Speed limiters that cannot be over-ridden without specialist tools should be fitted.
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•
Any hydraulic tank should be the subject of a suitable risk assessment with regard to possible leakages with resulting fire, safety and environmental hazards.
E3.3 Electrics • Motors should be operated from one location except where local operation may be desirable in an emergency. • An assessment should be made of the security of electrical equipment enclosures. Using the coding system of British Standard BS EN 6052944, the degree of protection against the possible ingress of water or dirt may be assessed. It is recommended that a minimum rating of IP 55 be insisted upon for all such enclosures in general use. A higher rating may be necessary in some cases. All components should be suitable for the environment in which they are to be used. • If Programmable Logic Controllers (PLCs) are used a hardwire recovery system or a fully manual mode shall be available. • Field devices (proximity switches, limit switches, encoders etc) can be a major source of problems with control systems. It is recommended that sophisticated devices of this type (distance measuring etc) should be avoided. Sophisticated design should be ‘designed out by suitable mechanical design. • Any hand tools powered from the gantry should be 110V (55V centre tap to earth). • Consideration should be given to the provision of a 110V lighting system. • All control voltages should be 24Vdc. • Where a PLC is used it should at the completion of the design stage have a 25% capacity for input/output and memory for future development or changes in control. E3.4 Logical control software (additions and modifications) Dependent upon the complexity of the gantry various interlocks, either mechanical or electrical, may form a significant part of the design for its safe operation. Unqualified persons shall not undertake any change to any interlocks. A special case exists for gantries that are controlled by a Programmable Logic Controller (PLC). Due to the complex control arrangements and potential fatal consequences, any changes to the software must be performed in a controlled way and the following matters should be considered:
IStructE The operation and maintenance of bridge access gantries and runways
• • • • • • • •
high level security password required to change software electronic copy of software to be obtained before any changes are undertaken risk assessment to examine potential hazards and the implementation of risk reduction strategies development of a disaster recovery strategy simulation testing of software any automatic sequences to be manually stepped through until software proved software log to be maintained detailing all changes with incorporation into O&M manuals copy of revised software to be maintained.
E3.5 Documentation • The commission for design of the gantry should include responsibility for the preparation of O&M Manuals. They should describe, in clear English, all operational, emergency, inspection and maintenance procedures, including service intervals and requirements for training and recording all gantry operations, inspections, tests and usage. The O&M Manual should include directly or by reference the Design Manual which sets out the design basis, lists and provides all relevant design/construction drawings, designers’ risk assessments and analyses, and specifications, design certificates and check certificates according to standards or as otherwise specified. These manuals shall also include the related documents from all the specialist supplier/designers who shall be bound by contract to supply information to similar standards to the Lead Designer. All the documents should be prepared carefully and with a view to providing information to the various users in a clear and easily accessible fashion. Attention should be paid to the format, contents structure and indexing. Diagrams should be used as appropriate to illustrate and make clear key points for attention. • New proprietary equipment should be CE marked. • It is not possible to specify a comprehensive standard to which a gantry should be designed however it is considered that the following documents offer guidance: – structural and mechanical design to BS EN 1300143 – BS 540032 Parts 2 and 3 can be used in conjunction with BS EN 180839 for runway beams, including wind loading (including
– – –
nominal vertical wind if appropriate) and temperature requirements any structural parts subject to fatigue to BS 760845 software to BS EN 6150846, need to establish the Safety Integrity Level (SIL) BS EN 180839 and BS 6037-137.
E4 Checklist of some design issues relating to operation and maintenance of bridge access gantries The following points have been covered elsewhere in this guidance document. They may be usefully considered when compiling a checklist for operation and maintenance of gantries: • have suitable equipment selection procedures been used, e.g. are temporary gantries the most appropriate work equipment? • have thorough risk assessments been carried out with respect to the design and operation of the gantry, and prior to the production of method statements and work procedures? • have high consequence/low probability events been considered in the risk assessments? Have measures been taken to mitigate high consequence events whatever the probability of occurrence? • do the risk assessments follow the hierarchy of risk prevention and control, and in particular give preference to engineering control measures rather than management systems and systems of work, and to control measures which protect everyone affected rather than individual protective measures? • are safety critical features of the gantry system designed to fail to safety where possible? Has preference been given to secondary or back-up safety systems to provide a suitable degree of redundancy rather than relying solely on ‘overengineering’ of components? • are adequate and reliable end-stops in place at all times at the open ends of all runway beams or tracks, and at locations where there is a possibility of collision with other plant or equipment? • is the positioning and movement of the gantry under positive control at all times? • could failure, disconnection or removal of a single component result in catastrophic failure of the gantry, or overload of other structural components? • has the current capability of the bridge
IStructE The operation and maintenance of bridge access gantries and runways
Appendix E
61
•
•
•
•
62
superstructure and its component parts to safely carry the gantry loads been adequately assessed by a competent person for all stages of the gantry operations? could human error, by means of an action or inaction, lead to a catastrophic failure of the gantry, or overload of other structural components? are there sufficient competent trained personnel to safely operate, supervise and manage gantry operations? Are they supported by adequate information and instructions? are there suitable management systems in place to monitor and audit the implementation of the method statements and work procedures? have responsibilities for gantry design, checking,
Appendix E
•
•
•
inspection, operation and maintenance been clearly assigned? are the climatic limitations on the use of the gantries, e.g. wind speeds and directions, fog, ice formation etc. clearly set out. Are these limitations properly understood and adequately monitored? are there suitable and periodic gantry inspection and maintenance regimes in place? Are safetycritical items checked frequently enough, e.g. before each use? are modifications to and/or reconfigurations of the gantry permitted and if so, are procedures for assessing their significance and authorising them adequate to ensure safety?
IStructE The operation and maintenance of bridge access gantries and runways
Appendix F Gantry and runway inspections and maintenance more detailed guidance
This Appendix provides some detailed guidance on inspections, preventative maintenance and reactive maintenance. It should be read together with the relevant sections of Chapter 5.
F1
• •
gantry supervisor or supervising engineer record general findings in the bridge database and complete gantry logbook secure gantry access and return keys to control room.
Inspections
Table 5.1 summarises a typical schedule of inspections. More details for each category of inspection are given below. F1.1 Pre-use inspection A pre-use inspection is a visual inspection to check the general condition and operation of all moving components and the mechanical and electrical systems. It can be compared to the checks made before a vehicle is driven and can be carried out by a driver if competent to do so. Typical items that may be included in a Pre-use inspection are considered in Appendix C. F1.2 Weekly inspection Typical content of a weekly inspection might include: • check the access ladder and platform is in good order • check the flooring is in good order and secure • check the side mesh and railings are in good order • check the gantry ladders and hatches are in good order and operate correctly • check that the structural members (where commonly visible) are in good order • check that the trolley wheels/rollers/pins/ connections are in good order • check that the connections between trolleys and gantry structure are in good order • check all handles, levers and latches are fitted and in good order • check hydraulic system and pipework for signs of leaks or damage • check electrical sockets and emergency stops for damage or defects • check that the storm rigging is fitted correctly and in good order • check that the rated load signage is clearly visible • check that the general housekeeping is in good order • report any findings requiring urgent action to the
F1.3 Special inspection Special inspections may be required at any time. They should be carried out after a severe incident such as an exceptional gale or collision, after a report of a serious anomaly in operation, or after a substantial repair or alteration. They should consist of an inspection of the particular area with due consideration to possible damage to other components or defects causing concern. Following an operational anomaly, all similar gantries should be inspected. F1.4 Intermediate inspection The intermediate inspection of the mechanical and electrical systems of the gantry should encompass a visual examination, tests and checking lubrication in accordance with the manufacturer’s instructions. F1.5 Six-monthly inspection The six-monthly inspections involve the structural, mechanical, and electrical systems. They may generally be carried out most conveniently at the beginning of the painting season. Care should be taken to make sure that the inspection covers all components, especially critical elements such as axles and pinned joints which will need attention to their mechanical function as well as their structural aspects. For the structures the inspection will involve a visual examination of all components of the gantry, its runways and their connections to the bridge. For mechanical components it will be a visual inspection and test in accordance with an agreed schedule. For electrical components it will be a full inspection and test in accordance with BS 767112 taking advantage of the sampling allowances mentioned in Guidance Note 313 where previous records are available. If an insurance certificate is required for continued use of the gantry, then an annual inspection should be carried out in conjunction with the insurer’s representative.
IStructE The operation and maintenance of bridge access gantries and runways
Appendix F
63
A full six-monthly inspection would consist of travelling the gantry loaded for the work in hand the full length of its runways and making all changes of configuration at least once. The inspection would also include operation of all gantry-mounted moveable platforms, i.e. scissor lifts, telescopic arms and cradles over their full range. During the inspection all accessible parts of the gantry should be observed for signs of distress, distortion or loose connections. Particular attention should be given to the gantry structure and those components which form the direct load paths between the bridge and the gantry. The six-monthly inspections of runways will provide an opportunity to check all components of the runways which affect their integrity as a support structure for the gantry. Their inspection should include: • wear – thickness checks on tracks and runway beam flanges and webs • deterioration – corrosion, including bolts, fractured welds, including use of NDT where appropriate especially at support points • connections – fracture and tightness checks on bolts • distortion – untoward distortion or movement, especially at splice joints of beams • alignment – tendencies of wheels to depart from the required alignments on the runway beams/ tracks. The runway inspection allows the condition of the gantry support structure to be assessed and its compliance with the design specification determined. If it complies then no further action is required. If it does not comply then either the design should be reassessed based on the inspection findings and the operation of the gantry restricted accordingly or the defective/deteriorated components should be replaced/refurbished to restore the structure to design specification. F1.6 Six-yearly inspection A principal structural inspection of gantries and runways should be carried out every six years. This inspection should include a close up/hands-on visual inspection of all gantry components including the underside of the gantry structure to observe any signs of corrosion, wear, distress or distortion. Inspection of tension connections, including bolts in tension, e.g. bolts supporting the upper flange of runway beams, should be given particular attention. For some gantries it may not be possible, without unacceptable costs,
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to gain access whilst the gantry is on the bridge, to all parts requiring visual inspection. In such cases, it may be more convenient and cost-effective to take the gantry off the bridge for inspection. Prior to this inspection, a load path analysis should be undertaken to assist in identifying critical areas and components. After a risk assessment, a complete or partial dismantling, as necessary, should be undertaken to expose internal components, such as shafts, pins, bolts and welds for visual inspection. In addition small portable equipment, such as paint meters and cover meters, etc. should be used to augment visual inspections. Inspection of tension connections should be given particular attention. Where parts vital for the safety of the gantry cannot be visually inspected, NDT techniques to establish their condition should be used or, if such techniques are not available replacement of these parts should be scheduled on a regular basis. Criteria for component replacement should be based on condition or period in use. Replacement periods should be set depending on gantry use, conditions of exposure, extent of redundancy, and the degree of protection of the parts against corrosion and other damage. A similar approach should be applied to the tension connections of runway beams to the bridge structure. Mechanical components should be inspected, replaced and retested where appropriate. Electrical systems should be subject to the full annual inspection and test in accordance with BS 767112. F1.7 Structural inspection A structural inspection forms part of the sixmonthly and six-yearly inspection routine. It should be factual and based on a common standard such that inspectors are not asked to make a judgement regarding serviceability for which they may not be qualified. To this end defects should be assessed according to extent, (e.g. area affected, length, measured clearance), and severity (e.g. over 10% loss of section, over 0.25mm wear). Both aspects are essential to maintenance and safety decisions. The use of a defect classification is therefore recommended, such as is given in Table F.1, together with a priority and recommended action. Such avoids confusion between a single but severe defect and extensive but superficial deterioration.
IStructE The operation and maintenance of bridge access gantries and runways
Table F.1 Defect classification Extent
Severity
A No significant defect
1 Insignificant
B Slight, not more than 5% affected (of area, length, etc.)
2 Minor defects of a non-urgent nature
C Moderate, 5% to 20% affected
3 Heavy defects of an unacceptable nature which should be included for attention within 12 months
D Extensive, over 20% affected
4 Severe defects where action is required before the gantry or runway can be used
Recommended action
Priority
I
R Review (at next Principal Inspection)
Inspect
M Monitor
L Low (within 2 years)
R Repair
M Medium (within 12 months)
P Paint
H High (within 6 months)
C Replace
I
Immediate
The Inspector has some degree of freedom when classifying defects in accordance with Table F.1. Inspectors should classify defects with care and any defects which fall outside the standard should be reported immediately to the bridge operator. Assessment of priority should take account of the consequences arising from a defect. Immediate action should be taken if safety is in jeopardy. Structural inspection should seek to identify not only structural defects but also any untoward or unrecognised changes in operating conditions that might affect the safety of the gantry. For example, the loading of the gantry and its runways should be considered. The self-weight of the gantry should be known, preferably by weighing in-situ. Protective enclosures may have come into use and it will be important to check that the structure is capable of safely carrying them and any associated additional wind load. Stronger storm anchors may then be needed. Reporting should be carried out on a report proforma relevant to each gantry and runway installation. The inspector should complete all parts of forms and justify any omissions where these occur. Where the condition of an element is less than Al, the inspector should describe the defects in written narrative on a continuation sheet. Modern gantries may have sufficiently few components and detailed drawings and manuals to allow individual items to be listed and measured against drawings. In these cases it will be possible to produce gantry-specific report forms.
Photographs are of great value in gaining an overall appreciation of structural condition. All reports should contain at least a general photograph and a photograph of each item scoring less than Al. All structural and suspension components of permanently installed gantries should be inspected and maintained according to their routine schedules. The only exceptions to this rule are temporary or removable gantries or access systems which are removed to a covered storage area where the equipment is fully dismantled and inspected prior to being put back into service.
F1.8 Mechanical inspection The mechanical systems of gantries should be inspected concurrently with the carrying out of scheduled preventative maintenance operations. Particular attention should be given to the gantry suspension and its articulation. The supervision and frequency limits for maintenance should be carried out as set out in Chapter 5, Table 5.2 which takes account of whether the equipment has been in or out of use. A report of each inspection should be written by the Inspector and submitted to the bridge operator who will determine whether any actions are necessary and arrange for them to be carried out. A copy of the Inspection Report should be retained in the lifetime records of the gantry. The bridge operator is responsible for ensuring that the inspections are carried out correctly and at the required intervals and that records are maintained.
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Appendix F
65
F1.9 Electrical inspection Electrical reports should be presented in the form specified in BS767112 using the documents specified in Guidance Note 313. BS 7671 places great emphasis on providing a thorough visual inspection of the electrical installation, with as little dismantling as possible, supplemented by testing, to verify the safety of the installation. Whatever electrical maintenance takes place, the opportunity should be taken to inspect and test all affected circuits and components. Although inspection and testing is combined in the standard, they are considered separately in this Guide for the sake of clarity. A visual inspection of all electrical equipment should be carried out every time before use, to ascertain the general condition of the various component parts of the gantry electrical installation. Particular attention should be paid to signs of corrosion and physical damage, before any attempt is made to gain access to electrical enclosures. Any obvious signs of deterioration should be reported immediately. Photographic records provide a valuable means of recording condition. Once access has been gained to component terminations, an assessment is required of the likelihood of terminals becoming loose due to vibration and any requirement for suitable locking arrangements. Cables should be visually checked for signs of damage to the cores and insulation and the enclosure inspected for signs of water or dust ingress. Any damaged seals or gaskets, should be replaced at the same time. A report on the condition of cables, terminations and the overall security of the enclosure should be given to the person in charge of maintenance standards. If the inspection procedures recommended in BS 767112 are implemented, most defects will be exposed. It is also likely that all legal requirements regarding electrical safety will be met. In addition to the visual inspection, the effectiveness of operation of moving safety devices should be checked by actual operation of the components themselves. An assessment of their suitability for use in the environment should be made. This should be included in the final report. A schedule of test results in the form prescribed in Section 17 of Guidance Note No. 313, should accompany the report on the formal inspections and testing. The requirement for periodic inspection and testing, together with recommended maximum times between them, should be assessed and included in the report.
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It is recommended that a Defect Classification System be adopted as advocated for the structural inspection (Section F1.7).
F2 Preventative maintenance Section 5.5 introduces the principles of preventative maintenance. Some details are given below. F2.1 Structural preventative maintenance Preventative maintenance of the structures of gantries and their runways will be limited to cyclic repainting, washdowns to remove dirt, etc., the replacement of limited-life materials and the clearance of drainage systems. Components vital to the safety of the structure which cannot be inspected in service, (e.g. bolts in tension connections of runway beams to the bridge), should be the subject of special attention and the bridge operator should be satisfied that they are capable of carrying the loads that can be imposed upon them (e.g. it may be necessary to consider some form of pull-out testing or remotely operated load test). Where dissimilar metals are present, e.g. steel and aluminium, the possibility of deterioration because of galvanic action should be borne in mind and prevented if possible. Repainting and the choice of paint maintenance systems will depend on the initial surface treatment and the location of the gantry installation. Initial frequencies will necessarily be determined from experience and laboratory test but the results of the annual and sixyearly inspections will give a more exact programme. There is a limit to the amount of repainting any structure can accept. When this limit is reached all paint has to be removed. All mechanical and electrical parts should be thoroughly protected if grit-blasting is to be employed for paint removal. Washdowns are used on most large bridges to remove salt deposits and bird droppings, etc. thus extending the life of the paint systems. Although they may be equally applicable for gantries and runways, especially for the removal of bird droppings, great care will be required that sensitive electrical and mechanical equipment is fully protected from any damage during the process. Replacement of limited-life materials is an operation that can only be undertaken with the knowledge and experience gained with time. The need to replace certain short-life materials such as timber will be obvious but other items will only be discovered from detailed examination of inspection reports and assessments.
IStructE The operation and maintenance of bridge access gantries and runways
F2.2 Mechanical preventative maintenance and testing The bridge operator should prepare, in association with the gantry manufacturer and equipment suppliers, a schedule of preventative maintenance and testing operations which should be carried out typically at the following intervals: • intermediate (every three months but may be extended to six months for infrequent gantry use) • every twelve months • every six years. The schedules and programming of inspection and maintenance should take account of any statutory regulations for examination, inspection or testing of equipment used in the gantry. The schedules should also take into account the requirements of the insurance and mechanical plant inspection company. The bridge operator should prepare, in association with the manufacturer, a list of spare parts and consumables which should be retained for the immediate replacement of parts having a high risk of becoming defective or which may not be readily available from suppliers. F2.3 Electrical preventative maintenance and testing A visual inspection, looking for signs of damage to equipment and conductors, should be carried out on each occasion before use is made of the electrical installation. Moving parts should be examined and, where necessary, tested for conformity to their product specification and lubricated. This should be carried out to the instructions given in the Operation and Maintenance and/or Gantry Manual. In the absence of more detailed information, all moveable electrical equipment should be subjected to a full inspection and test on a three-monthly basis, for a gantry in regular use, or longer as appropriate. For gantry-mounted fixed electrical equipment, a full inspection and test in accordance with BS 767112 should be undertaken on an annual basis. Where the electricity supply for the gantry is taken from bridge mounted electrical outlets, installed in accordance with the requirements of BS 767112, it may be allowable to increase the time between tests to a maximum of six years. This would assume that the electrical installation is deemed to be permanent and that conformity to Section 611 of BS 7671, could be claimed.
Whatever the type of electrical installation, where equipment and enclosures are subject to severe weather conditions, an annual inspection and test is recommended. A programme of electrical preventative maintenance and testing should be undertaken as follows: Pre-use where appropriate • Check the physical operation of all mechanicallyactuated electrical safety devices and lubricate if necessary. • Check the operation of optical sensors. • Where plug and socket or in-line removable connections are used, check that the plugs are correctly inserted and circuits are operating correctly. • Check for the correct operation of warning sirens/ klaxons and, if the gantry is being used at night, all luminaires. • If easily accessible, check circuit breakers for freedom of movement and fuses for signs of overheating. • As soon as power is available, check any residual current devices (RCDs) for effective operation by pressing the test button. • Check cables used for distributing electricity around the gantry and, where appropriate, those used to supply the gantry with electricity, to ensure that they are fixed and/or supported in positions such that they will not be subjected to abrasion, undue strain or other forms of mechanical damage. Intermediate (three-monthly or longer depending on gantry usage) • Check all items listed previously and, in addition, carry out a visual inspection of the installation as described in BS 767112 chapter 73. • Check limit switches to ensure that they are correctly positioned and orientated. • Lubricate all moving parts as necessary. • Report any anomalies to the bridge operator. Annually • Carry out the full inspection and testing specified in BS 767112 Chapter 73. Pay particular attention to equipotential bonding and provisions for Direct and Indirect Contact Protection. • Lubricate moving parts as necessary. • Check the contacts of all contactors in the electrical panel, for signs of arcing or other
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Appendix F
67
physical damage or replace as necessary. Provide a full Periodic Inspection Report and Schedule Test Results, based on the examples in Guidance Note 313.
An assessment will remain effective as long as the loading and condition do not alter. A prime purpose of subsequent inspections is to monitor changes in condition.
The internal combustion engines of portable or fixed generators should be subject to appropriate maintenance procedures to prevent premature failure. The use of test equipment to verify the conclusions of each inspection is advocated. Unseen electrical defects can be located by the proper use of correctly maintained test instruments. Any changes to control software should be made by suitably qualified personnel and in a manner consistent with the method described in Appendix E.
F3.2 Mechanical reactive maintenance Defects in the operation of the mechanical components should be reported immediately to the bridge operator who should have absolute discretion whether the gantry should continue to be used. If there is any doubt, the gantry should not be used. Significant defects which prevent the gantry from being used in a safe manner should be reported immediately to the bridge operator who should decide what remedial action should be taken and arrange for it to be carried out. The gantry should not be used operationally but may be returned to its parking position if safe to do so. Non-significant defects should be entered on the gantry logbook and the attention of the gantry supervisor drawn to them at the start of each period of use. If practicable, non-significant defects should be rectified as quickly as possible. Repair work should only be undertaken when the gantry is out of service, except for emergency repairs to facilitate recovery of the gantry to permit evacuation of personnel. Details of any repair work carried out should be recorded in the lifetime records of the gantry. All spare parts taken from stock should be reordered and replaced.
•
F3 Reactive maintenance Section 5.6 introduces the principles of reactive maintenance. Some details are given below. F3.1 Structural reactive maintenance Structural reactive maintenance concerns: • paint or protective systems • replacement of corroded members • retightening or replacement of bolts which have become loose or fallen out • replacement of fractured or corroded bolts/rivets • repair of defective welds • replacement of broken or distorted members. Replacement of corroded members is an operation calling for like-for-like replacement and appears superficially straightforward. However, the actual works may be very complex, requiring extensive temporary works or the removal of the gantry from the bridge. They should be supervised by a Chartered Engineer. A distorted or broken member, weld or bolt should be replaced if it has been subject to loads for which it was not designed, if it was under-designed or not up to specification in the first place, or if it was abused during construction, e.g. over tightening of a bolt. A structural assessment of the installation should be carried out to determine the reasons for failure and the replacement item sized and detailed to prevent any recurrence of the failure. A structural assessment of the gantry and runways should be carried out if: • the gantry or runway has been structurally modified • there has been significant structural deterioration • the loading specification has been increased.
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F3.3 Electrical reactive maintenance Some safety systems have built-in redundancy, i.e. more than one device has to fail before an unsafe situation can occur. Fail-safe systems should always be used, no matter how many redundancies are builtin. This does not mean, however, that complacency can be allowed. Any failure should be rectified as soon as practicalities allow, otherwise catastrophic failure may follow. Where redundancy is not built into the system, an immediate response to signs of defective equipment is essential. Any means possible should be used to find the faults. It is best to train operatives who regularly use the equipment to look for and report any visual signs, unusual behaviour or unusual noises during operation of the gantry. A pre-use check list of items likely to cause danger in the case of failure should be consulted and checked before each use of the gantry is permitted.
IStructE The operation and maintenance of bridge access gantries and runways
Appendix G Gantry operation and maintenance manuals – contents
The gantry Operation and Maintenance Manuals should contain all the necessary detailed procedures and instructions for the bridge operator’s staff, or service contractors, to operate the gantry safely and to maintain it in commission throughout its operational life. The Manuals should be supported by referenced drawings, data and information provided by the gantry designers and manufacturers.
G1 Typical contents for a combined Operation and Maintenance Manual (dependent on the nature, scale and complexity of the gantry system) G1.1 General • Introduction. • Scope. • Description of gantry and its function. • Management of care and use of gantry. • Procedure for updating, revising, and issuing manuals. • Health and Safety measures. G1.2 Management of gantry operation • Access to gantries. • Pre-use inspections. • Operational procedures. • Operational faults and breakdowns. • Emergency procedures. • Gantry driver’s log book and records. • Induction for gantry visitors. G1.3 Gantry maintenance • Routine servicing. • Maintenance of drive systems, bogies, hydraulic, electrical and control systems. • Dismantling, adjusting and reassembling bogies and mechanisms. • Handling of equipment onto, on, and from gantry. • Removal of gantry from bridge and reinstallation. • Maintenance of runways. • Inspection and test requirements. • Principal test and inspection. • Test track.
G1.4 Appendices • Drawing register. • General arrangement drawings. • Detail drawings of bogies, mechanisms and components. • Circuit diagrams for electrics, hydraulics and controls. • Equipment suppliers listing. • Recommended oils and lubricants. • Spare parts list. • Check lists: – pre-use check – weekly inspection – six-monthly inspection – principal test and inspection – routine maintenance. • Gantry driver’s log book sheet. • Bridge operator’s risk assessments for gantry operation and gantry maintenance. • General safety induction for gantry visitors (a handout).
G2 Work instructions for gantry operation The work instructions in the Operation Manual for supervisors, gantry drivers and other personnel to access and operate a fully serviced gantry in commission safely should cover as appropriate. G2.1 Gantry crew • The gantry driver should always be accompanied by another trained gantry driver as solo working is unacceptable; and to cover incapacity and act as spotter where the gantry requires two people to monitor travel. • Movement of some gantries or some routine operations may require a larger crew to work under the direction of the gantry driver: the size and training of the crew must be defined. G2.2 Authority to access or operate • Authorisation process. • Control of keys. • Permit to work.
IStructE The operation and maintenance of bridge access gantries and runways
Appendix G
69
G2.3 Access to gantries • Access routes for personnel to and from gantry. • Access routes for delivery and removal of equipment, material and services. • Access for removal of waste. • Methods of reaching the access points safely from the maintenance yard. • Traffic management arrangements to enable safe access, escape and rescue. • Egress from place of work. G2.4 Communication system and equipment • Between gantry driver and spotter. • Between gantry driver and supervisor or manager. • With emergency services. G2.5 Safety equipment • Requirements. • Provision on gantry. • Issue and wearing of PPE. G2.6 Actions to meet third party requirements • Liaison. • Possessions. • Protective measures. • Communication. G2.7 Gantry actions • Driving instructions for starting, travelling and parking in span. • Securing for tasks on gantry. • Storm anchorage. • Negotiating piers or towers. • Reconfiguring and secondary motions. • Disconnection and lowering off. • Reinstallation. G2.8 Pre-use check by supervisor Immediately prior to use, for each working shift, check: • designated gantry driver and trained crew available and ready • communications system operational • arrangements for delivery of personnel, equipment and material to and from gantry in place • other gantry personnel trained or inducted • safe systems of work for task authorised • agreed measures with third parties in place • gantry team briefed (toolbox talks)
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Appendix G
• • •
weather state and forecast acceptable required safety equipment ready and in good order as required, issue of permit to work.
G2.9 Pre-use check by gantry driver Immediately prior to use and before start of movement for each shift, check: • preparedness of gantry for operation • all personnel briefed and wearing PPE correctly • communications system operational • required safety equipment on the gantry • loading of gantry within working limits. (During gantry travel the gantry driver and spotter should look out for any obstructions to the passage of the gantry and personnel, or to free travel on the runway beams.) G2.10 Post-operation action At the end of each working shift the gantry driver should: • check gantry is correctly parked and secure • check all waste and used equipment has been removed • complete gantry driver’s log book • undertake actions, as appropriate, for – shutdown – storm anchoring – weather protection – immobilisation – removal of machinery – removal of gantry. G2.11 Environmental measures • Protection of work or workers from wind. • Prevention of falling material or waste. • Measures to deal with dust, fumes or overspray. • Measures to deal with dirty water. G2.12 Mechanical mishaps Instructions within the gantry driver’s competence and capability to deal with mishaps and malfunction of gantry mechanisms, for example: • power or drive failure • crabbing • loss of traction (wheel slip). G2.13 Emergencies Procedures must be specified for all recognised emergency situations, and should include: • raising the alarm
IStructE The operation and maintenance of bridge access gantries and runways
• • • • •
actions of personnel on the gantry first aid arrangements actions of supervisor on being alerted emergency escape contacting the emergency services.
G2.14 Records Gantry driver’s log book. • Supervisor’s reports and close-out reports.
G3 Maintenance of the Operation and Maintenance Manual The bridge operator will need to update and revise the Manuals from time to time. It is essential that the Manuals are maintained as controlled documents within the bridge operator’s quality management system, so that: • Manual revision is undertaken by competent personnel and properly authorised • only the current edition is used • users are aware of the status of Manuals in their possession.
IStructE The operation and maintenance of bridge access gantries and runways
Appendix G
71
