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Innovation in concrete frame construction 1995–2015 Dr Éanna Nolan BRE Centre for Concrete Construction
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Innovation in concrete frame construction 1995–2015
BRE is committed to providing impartial and authoritative information on all aspects of the built environment for clients, designers, contractors, engineers, manufacturers and owners. We make every effort to ensure the accuracy and quality of information and guidance when it is published. However, we can take no responsibility for the subsequent use of this information, nor for any errors or omissions it may contain. BRE is the UK’s leading centre of expertise on the built environment, construction, sustainability, energy, fire and many associated issues. Contact BRE for information about its services, or for technical advice: BRE, Garston, Watford WD25 9XX Tel: 01923 664000
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BR 483 © Copyright BRE 2005 First published 2005 ISBN 1 86081 762 9
Innovation in concrete frame construction 1995–2015
Contents
Summary ................................................................................................................................page 5 1 1.1 1.2
CARDINGTON AIMS AND ACHIEVEMENTS ................................................................... 7 The aims of the European Concrete Building Project 7 The achievements of the European Concrete Building Project 8 1.2.1 Flat slab reinforcement rationalisation 1.2.2 Use of proprietary main reinforcement 1.2.3 Use of proprietary shear reinforcement 1.2.4 Electronic reinforcement information 1.2.5 Early striking and reduced back-propping 1.2.6 Strength assessment using the LOK test 1.2.7 Advanced deflection prediction techniques 1.2.8 Special concretes – self-compacting and high strength concretes 1.2.9 National Structural Concrete Specification
2 2.1
OTHER INNOVATION 1995–2005.....................................................................................18 Innovation in concrete 18 2.1.1 Self-compacting concrete 2.1.2 Pumpable concrete 2.1.3 High strength, high performance concrete 2.1.4 Ultra high strength concrete 2.1.5 Lightweight aggregate concrete 2.1.6 Recycled aggregate concrete 2.1.7 Fibre reinforced concrete Construction practice and techniques 22 2.2.1 Formwork systems 2.2.1 Core wall construction Construction techniques 25 2.3.1 Post-tensioned concrete 2.3.2 Hybrid construction Other techniques 26 2.4.1 Kickerless construction 2.4.2 Continuity strips Reinforcement technology 26 2.5.1 Contractor detailing
2.2
2.3
2.4
2.5
3 3.1 3.2 3.3
IMPLEMENTATION OF INNOVATION..............................................................................27 The impact of Cardington Research 27 Current industry perspectives on innovation 28 What do clients want from concrete frames? 31
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4
4 4.1 4.2
4.3
4.4
Innovation in concrete frame construction 1995–2015
FUTURE TRENDS IN CONCRETE FRAME INNOVATION.............................................32 Identifying trends 32 Green / environmental issues 32 4.2.1 General perceptions 4.2.2 Recycling and increasing the value of recycled concrete 4.2.3 Use of primary aggregates 4.2.4 Reducing waste on-site 4.2.5 Energy use in the production of cement and steel 4.2.6 Use of waste materials from other industries 4.2.7 Design for long life and adaptability versus demolition and replacement 4.2.8 The influence of thermal design on structural solutions 4.2.9 Local manufacture/reduction of transport Efficiency 35 4.3.1 Speed of construction 4.3.2 Cost 4.3.3 Quality Labour issues 38 4.4.1 Training and education versus less requirement for skill 4.4.2 Scarcity of labour 4.4.3 Language and communication 4.4.4 Health and safety
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CONCLUDING COMMENTS..............................................................................................40
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REFERENCES AND FURTHER READING ......................................................................41
APPENDIXES ................................................................................................................................43
Innovation in concrete frame construction 1995–2015
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Summary
This report examines innovation in concrete frame construction over the past 10 years and looks into the future to predict likely drivers for future innovation. The report draws on the proceedings of a workshop held at BRE and detailed interviews with industry practitioners. It finds that the research from the European Concrete Building Project at Cardington has had a positive impact on the concrete frame construction industry and that many of the innovations trialled there have become used and are regarded as important by industry. A study of other innovations that have changed the way in which concrete frames are designed and constructed identified lightweight formwork systems and computer-based software tools as having had the greatest impact. The major trends and issues likely to be the focus of innovation in the concrete frame construction industry over the coming decade were identified as being green issues, efficiency of production and aspects of labour and training.
Project Steering Group Members • • • • • • • • • • • • •
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Pal Chana, British Cement Association Markus Blake, GMVL (formerly St George) Bob Gordon, Mace Tony Jones, Arup Bendt Arup, CRC Technology Bernard Watston, WSP Group Peter Goring, John Doyle Bill Hewlett, Laing O’Rourke Bjorn Watson, SKM Anthony Hunt Associates Chris Payle, WSP Group Hamid Attisha, Babtie Mario Soutsos, University of Liverpool Mike King, Mitchellson Paul Byrne, Dewhurst Macfarlane and Partners
Acknowledgements BRE acknowledges the funding from the Department of Trade and Industry under the Partners in Innovation Scheme. The participation of all members of the organisations (listed in Appendixes A and B) who took part in the industry interviews and the workshop held at BRE is gratefully recognised. The contribution of the project steering group is also acknowledged.
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Innovation in concrete frame construction 1995–2015
Innovation in concrete frame construction 1995–2015
1.
Cardington aims and achievements
1.1
The aims of the European Concrete Building Project
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1
The European Concrete Building Project , commonly known as the Cardington Project, was a large-scale collaboration between government, industry, research organisations and academia which sought to analyse and improve the production of concrete framed structures in the UK. It included the design and construction of a seven-storey reinforced concrete frame building in the BRE Large Building Test facility at Cardington, near Bedford, shown in Figure 1.
Figure 1: Cardington test structure during construction. The basic aims of the project were stated as: ! re-engineer the design and construction process ! reduce costs and improve speed, quality and safety ! increase client value. The project looked at both process engineering and performance testing aspects of concrete frame construction. After the construction of the demonstration structure, subsequent DTI2-5 funded research was aimed at dissemination of the most relevant information to industry 2 gathered during the project. Nine individual ‘innovations’ were identified . These innovations are examined in the next section. A brief comment on what the innovation constituted is given, followed by industry comment on whether they were used in practice and what were the major barriers to adoption.
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Evidence for the industry’s attitudes comes from the proceedings of a one-day workshop held at BRE in April 2005 and from industry interviews, which were held in the two months preceding the workshop. A list of all contributors is given in Appendixes A and B. Further evidence of industry attitudes and drivers was collected in the execution of three DTI-funded case studies 2, 4 . which examined the innovations being applied to commercial projects in the UK
1.2
The achievements of the European Concrete Building Project
1.2.1
Flat slab reinforcement rationalisation
Reinforcement rationalisation can be described as the reduction of the number of different reinforcing bar (rebar) types and shape codes to simplify ordering and fixing operations on-site, and hence to minimise overall costs. The objective is to balance finance, labour and reinforcement material costs to achieve the overall minimum cost. The Cardington research also suggested that there was a relationship between the method of analysis employed in design and how conducive the solution was for reinforcement rationalisation. 6
Figure 2 shows the effect of steel price increases in recent years on the level of rationalisation giving the minimum cost. The figure illustrates clearly how fluctuations in the labour / materials / finance balance can change the decision on the level of rationalisation to adopt. When questioned about flat slab reinforcement industry responded as shown in Figure 3. The workshop discussion group broadly agreed with these results, which adds confidence in their relevance. Speed Construction speed Slow Minimum overall cost now?
High
Cost
Fast Previous minimum overall cost
Finance
Changed cost curves after recent steel price increases (circa 2004)
Low
Labour, plant & preliminaries
Material Highly detailed
Usual
Rationalised
Highly rationalised
Level of rationalisation of reinforcement 6
Figure 2: Rebar rationalisation schematic♦ (after Goodchild )
♦ It is acknowledged that the reinforcement rationalisation categories used are subjective. A more complete explanation is beyond the scope of this document. The diagram is schematic and is not to scale.
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How useful is∇ flat slab reinforcement rationalisation? 70% 11% Cost
Time
22%
opportunity
Design team dependant
67%
23% Occasionally Yes
46%
No
31%
Do you use flat slab rationalisation?
What are the barriers to increased use of flat slab rationalisation?
Figure 3: Interview results – flat slab reinforcement rationalisation What can be seen is that the innovation is seen as being useful and that it had been used by over three-quarters of the interviewees in real construction projects. The main barrier to using rationalisation on every project was identified as being that it was dependent on the design team adopting rationalisation. Other barriers were cost (where the case for rationalisation was unproven) and time opportunity. A point made in the workshop was that clients or their representatives can sometimes demand that rationalisation is not used. The argument that is made is that the designer favours it as it means less work for him while the client pays for the extra material cost. While, as explained above, this is an incomplete analysis of the effect of rationalisation (labour costs and time are not included), it does identify a potential requirement for targeted education. 1.2.2
Use of proprietary main reinforcement
The use of proprietary main reinforcement such as ‘roll-out’ mats and welded fabric mats are also considered to provide advantages to productivity and safety. Both types of product tend to lend themselves to schemes in which the reinforcement has been rationalised. They are generally used in schemes that have large slab areas with few columns, walls or changes of plan shape. Figure 4 shows the usefulness, use and barriers to use that emerged from the interviews. 4
In the process of carrying out the smaller scale case studies with industry it was suggested that proprietary main reinforcement was found to be best used in projects where an investment has been made in a formwork system that maximises the speed of construction. It also indicated that many people had used these systems previously and that they chose to use them when most appropriate. This finding was backed up by the interview results, which show that just over half of the people had used proprietary reinforcement but most of them were choosing to use it on an individual project basis.
How useful is proprietary main reinforcement? 80% ∇
Interviewees were asked to rate the usefulness of the innovation out of 5. In some cases this was assessed from their response. The average of the scores recorded was then converted into a percentage.
Innovation in concrete frame construction 1995–2015
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Occasionally No
46%
Requires repetition
Contractor reluctance
54%
31%
Cost
15%
Do you use proprietary main reinforcement?
What are the barriers to increased use of proprietary main reinforcement?
Figure 4: Interview results – proprietary main reinforcement The main barrier to using proprietary reinforcement more often was that its application was found to require repetition and large slab areas. The findings indicate that the industry is choosing the type of project where it is viable to use proprietary main reinforcement. It also highlights that future best practice advice might include advice on where the innovation is most applicable. 1.2.3
Use of proprietary shear reinforcement
Proprietary shear reinforcement comes in a variety of forms, shear ladders, shear studs and rails, and including the American Concrete Institute (ACI) system of shear stirrups (which is not currently approved for use in the UK and is not strictly a proprietary system). These products are used to replace individual reinforcement links, which are often found to be time consuming to fix on-site. While these products carry a cost premium over traditional solutions, the time and labour savings in fixing often make their use economic. It can be seen from Figure 5 that a large percentage of interviewees had used proprietary reinforcement at least occasionally. Generally reports on their effectiveness were very positive, with many larger frame contractors reporting that they actively sought their use on most projects. This is backed up by the very high usefulness rating of 84% given by industry respondents. How useful is proprietary shear reinforcement? 84% 54%
31%
Do you use proprietary shear reinforcement?
What are the barriers to increased use of proprietary shear reinforcement?
Figure 5: Interview results – proprietary shear reinforcement The barriers to more widespread use of proprietary shear reinforcement are mostly related to contracts and contractual arrangements for specific projects. The ‘contractor and designer
Innovation in concrete frame construction 1995–2015
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dependent’ replies shown in Figure 5 indicate that interviewees thought that they were not empowered or motivated by the contractual relationship they were working under to propose or adopt their use. It is interesting that the use of proprietary shear reinforcement solutions do appear to require the request for their use by the frame contractor and that a redesign is required in many instances. Avoiding the need for redesign every time might be made the focus for any further development of this innovation. Some designers reported that smaller contractors were not always happy to use proprietary systems.
Figure 6: One proprietary shear option (shear rails) One way to get around this problem may be to allow designers on smaller projects to make some of these decisions based on technical guidance and discussion with the client. When this type of solution was proposed in the workshop it was not universally accepted. 1.2.4
Electronic reinforcement information
The transfer of reinforcement information from the detailer to site and from site to the reinforcement supplier is currently available commercially. The original Cardington project identified this innovation as being potentially significant to the UK frame industry as a whole. The industry interview response supported this conclusion as it rated electronic reinforcement information as being potentially very useful (Figure 7).
How useful is electronic reinforcement information? 86%
Innovation in concrete frame construction 1995–2015
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8%
Yes
38%
Occasionally No 54%
Do you use electronic rebar information?
What are the barriers to increased use of electronic rebar information?
Figure 7: Interview results – electronic reinforcement information The information from the interviews also indicated that only about half the people questioned had used the system and that a very large percentage of people had bad experiences in trying 2 to use the system. In support of this finding one BRE case study had difficulties in trying to make the system work practically. The workshop discussions gave further endorsement to this view. This is a potentially very useful innovation, which seems not to be used on small to medium sized projects generally due to a range of complex factors including: • IT compatibility problems. • The requirement for three separate organisations to have compatible information management software. 4 • Compatible detailing/design software and price (although in the Newbury Park case study this was subsidised by the steel producer). There are reports of this system working extremely well on large projects where the time, effort and expense of setting up a system is worthwhile. The lack of a widely used and widely compatible standard system of receiving electronic rebar data in the UK means that currently this potentially very useful system is not achieving the impact which it promises. Clearly, there needs to be a broad agreement in the industry to address the barriers identified in this study. Recommendations include: • Making a widely compatible system which is available as general issue. • Perhaps adopting a data transfer method which is based on a widely used current software program such as MS Excel or similar spreadsheets. • Focus on providing simple and flexible IT solutions especially for site use. • Government assistance to set up. • Giving ownership of the system to a respected industry body such as CARES. • Widespread industry advertisement and dissemination. 1.2.5
Early striking and reduced back-propping
This study in Cardington sought to minimise the cycle time for formwork and to examine the 3, 5 was developed for estimating peak conrequirements of back-propping. Best practice advice struction loads, strength requirements for stripping and early age loading. Advice on achieved back-prop preloading and the interaction between temporary works and permanent works designers was also produced as part of this strand of research.
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As can be seen from the interview response in Figure 8, industry judged these items to be very useful (84%), with practically all those questioned having addressed these issues on projects, at least occasionally. One point which did come from looking at barriers to increased use was the frequency with which the industry said that reducing cycle times was not always a prime concern. Segments of opinion indicated that others controlled this initiative (see Figure 8 – dependent on contractor and dependent on designer were identified by different interviewees). This is perhaps symptomatic of contractual arrangements that do not allow for timely interaction between designer and constructors and do not give parties an incentive to innovate. How useful is early striking and reduced back-propping? 84% 20% Yes Occasionally
70%
No
10%
Do you use early striking and reduced back-propping?
What are the barriers to increased use of early striking and reduced back-propping?
Figure 8: Interview results – early striking and reduced back-propping 1.2.6
Strength assessment using the LOK test
The early age strength assessment using the LOK test was not viewed as important by the interviewees or in general comments made by the workshop. As well as a low usefulness score, no interviewee had used the method and the barriers to more widespread use were not easily addressed. The scatter of results and the idea that there was little benefit over the use of site cured cubes (in terms of cost and time) are significant barriers which account for over half of the replies in Figure 9. The remaining interviewees were predominantly unaware of the existence of the LOK test. These issues were explored in more depth at the workshop where the question was asked of designers present, ‘Can the LOK or similar types of test replace identity cube testing?’ The general answer was no, with no dissenting views given. While this should not stop research in this area it does point out that industry in general is unlikely to turn away from cube or cylinder identity testing without significant technical justification and widespread effective education. A more fruitful line of research may well be the use of embedded maturity measurement devices, which are currently being developed. 4
The opinions raised in the case studies were repeated in the interview results with lack of awareness (one interviewee had tried and failed to find out where to buy the apparatus); a scepticism that the LOK test could replace standard identity testing, and a feeling that when used with identity testing it was too expensive.
Innovation in concrete frame construction 1995–2015
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How useful is the LOK test? 40% 8%
Little
34%
demand
25%
No better than cubes
Not aware
Results scatter
33%
No
100%
Do you use early LOK test?
What are the barriers to increased use of the LOK test? Figure 9: Interview results – LOK test
It should be remembered that LOK testing was discussed only in the context of concrete frame structures and that the apparatus is believed to be successfully used in a range of other applications. 1.2.7
Advanced deflection prediction techniques
An advanced deflection prediction technique was developed for accurate manual and spreadsheet calculation of deflection in two-way spanning slabs. Advanced deflection prediction techniques do not rate highly in perceived usefulness by interviewees (Figure 10). Designers were the target for this innovation and so much of the negative reaction recorded was due to lack of direct interest on the part of other disciplines.
How useful is the advanced deflection prediction technique? 38% 20%
18% Yes
No
82%
Do you use the advanced deflection prediction technique?
What are the barriers to increased use of the deflection prediction technique?
Figure 10: Interview results – Deflection technique
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3, 4
The main output of Vollum’s research was a simplified method for taking account of the effect of early age striking and peak construction loading in deflection calculations. Whatever method is used for deflection prediction, it is essential to account for cracking in addition to creep. Elastic finite element analyses can significantly underestimate deflections unless the elastic modulus is reduced to account for the effects of cracking, creep and shrinkage. 4
The opinions raised in the case studies were repeated in the interview results with lack of awareness (one interviewee had tried and failed to find out where to buy the apparatus); a scepticism that the LOK test could replace standard identity testing, and a feeling that when used with identity testing it was too expensive. 1.2.8
Special concretes – self-compacting and high strength concretes
Both self-compacting concretes (SCC) and high strength concretes (HSC) were assessed by industry interviews as being reasonably useful in concrete frame construction. From the workshop discussion, self-compacting concrete was seen to be a very important prospect for the future, whereas high strength concrete was seen as being less important. Interviewees indicated that many did not use SCC or HSC although all respondents were aware of them as available products. The major barrier to more widespread use was that they were currently viewed as being economic for specific applications alone. For SCC these applications included congested reinforcement, restricted placement access and a requirement for a high quality surface finish. HSC was viewed as being normally used only for lower vertical elements in tall frame structures over 10–20 floors. The technical requirements of producing SCC often mean that currently its strength is often higher than normal strength concrete. Again, a significant proportion of those interviewed (both designers and constructors) did not feel empowered to use SCC more often. The special concretes category also included ultra high strength concretes (UHSC) (circa C150). This was omitted from the questionnaire, as it was known that it was not widely used in industry. UHSC is explained briefly in Section 2 of this report ‘Other innovation 1995–2005’, although it was trialled in the Cardington research.
How useful are ‘special’ concretes? 70% dependant Engineer dependant
For specific applications
46%
%
Cost
18%
25%
Occasionally
No 75%
Do you use special concretes?
What are the barriers to increased use of special concretes?
Figure 11: Interview results – special concretes
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Innovation in concrete frame construction 1995–2015
Figure 12: Self-compacting concrete being poured on-site 1.2.9
National Structural Concrete Specification
Of all Cardington innovations the National Structural Concrete Specification (NSCS) had the highest rating in terms of how useful it was perceived to be, with an average score of 90% (Figure 13). This is a strong endorsement for the idea of a standard specification, which was echoed by the workshop group. How useful is the National Structural Concrete Specification? 90% 17% 33%
Yes Occasionally No
50%
Do you use the NSCS?
What are the barriers to increased use of the NSCS?
Figure 13: Interview results – National Structural Concrete Specification
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From the interview data it is clear that the NSCS is not used widely, as yet. The respondents indicated that the most appropriate champion for the NSCS would be the Engineer and some designers indicated that they currently use regularly updated systems such as the National Building Specification as company policy and find it difficult to change. That 30% of interviewees were not aware of the NSCS is surprising. It indicates that more promotional activities targeted at designers should be considered. Neither in the workshop, case studies or interviews was there an informed argument put forward as to why the NSCS was not desirable or practical to use for concrete frame structures. The barriers to increased use identified are straightforward and can be overcome. In particular it is recommended that advertising of the advantages to engineers should be continued and that the inclusion of the NSCS in systems such as the National Building Specification should be pursued.
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2.
Innovation in concrete frame construction 1995–2015
Other innovation 1995–2005
This review is not intended to be a comprehensive review of all academic papers on the individual subject, rather it is meant to be an overview of changes and trends perceived.
2.1
Innovation in concrete
It should be pointed out from the outset that the commercial supply of concrete in the UK is set up to deliver concrete in a financially efficient way. Common measures such as owner drivers, batching plant operators being paid production bonuses etc. all mean that this industry is very focused on cost and productivity. In addition the ready-mixed concrete industry has a huge range of ‘products’ (concretes), intrinsically variable supplies of natural aggregates and a range of standards to comply with. Over the past 10 years the industry has seen the introduction of British Standard European Normative (BS EN) standards, which have replaced most of the traditional British Standards used in the concrete industry. This process has engaged the technical personnel in the sector to a varying extent and may perhaps have impacted in some way on the amount of other innovation or change we have seen in the past few years. 2.1.1
Self-compacting concrete
Self-compacting concrete (SCC) can be defined as ‘concrete that is able to flow under its own weight and completely fill the formwork, even in the presence of congested reinforcement, 7 without the need of any vibration, whilst maintaining homogeneity’ . Self-compacting concrete in the UK is now used on a few projects today, whereas 10 years ago it 8 was primarily a research topic. It is reported that 6% of all concrete produced in the UK by one ready-mixed concrete provider was SCC in 2004, although this may be an overestimate. The promoted benefits are that there is a reduced labour requirement on-site, may be an enhanced 9 surface finish, and a reduction of health and safety risks on-site . Currently SCC is often used only to overcome a specific technical risk in construction. Innovation on the part of the concrete producers has led to the development of a range of SCC concretes, which are now sold as proprietary mixes by many of the major ready-mixed concrete producers. Reference 7 gives a range of examples and case studies from UK industry showing applications as diverse as a suspended concrete slab with congested reinforcement to use in columns of unusual shape which had to be poured avoiding construction joints. A study of the Swedish 10 market indicated that SCC was used most commonly in applications that gave better value at less cost. This is despite the cost premium over the supply of conventionally compacted concrete and increased requirement for pre-construction testing and site acceptance control. While SCC is becoming more widely used in the UK, it currently could be termed a class of concretes that are used only for special applications. From anecdotal evidence it appears to complement the use of tunnel form construction well.
Innovation in concrete frame construction 1995–2015
2.1.2
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Pumpable concrete
The use of pump mixes has increased in the past 10 years. While pumped concrete was 11 available, and used 10 years ago (guidance was available 20 years ago ) it was mainly used in civil engineering applications or for specific applications that required pump use. Over the past 10 years its use has become much more widespread with its use on concrete frame construction sites being common. As evidence, the industry has seen fit to produce a recent guide for the use of pumps on sites that is targeted at small contractors who now routinely hire concrete 12 pumps . Pumpable concrete is commonly not specified, but is often selected by the contractor or frame subcontractor as part of construction planning, either to reduce cranage or labour or to eliminate health and safety risks associated with using concrete skips. 2.1.3
High strength, high performance concrete
Ten years ago high strength concrete was available and was used only in specialised applications. In many respects this still holds although higher strength concretes (circa 100 MPa) are available from major ready mix concrete suppliers in the form of proprietary mixes. There has 13 been detailed UK design guidance on high strength concrete available since 1998 . 1, 14
The European Concrete Building Project at Cardington in columns and some of the base foundations.
used high strength concrete (C85 MPa)
High strength concrete has achieved a relatively small niche position in the UK concrete industry, where its use is considered mainly in the lower vertical elements of high-rise structures. There is little current indication that its use will increase dramatically in the near future. It is currently a relatively well understood material and remains available for incorporation into innovative solutions. 2.1.4
Ultra high strength concrete
Ultra high strength concrete (UHSC) has only recently appeared on the UK market as a commercial product. Reference 15 suggests that given the inter-relationship between material and structural form, UHSC has sufficiently different properties to warrant its own special designs and that it has yet to ‘establish its own empire of applications’. The term ultra high strength is ill defined generally. It is used in this document to describe concretes of compressive strength greater than roughly 130–140MPa. Practical examples of this material are limited, especially in the UK. Its use in bridges and in forming shell roof structures is outlined in reference 15. A product which is currently commercially 16 available in the UK marketed by CRC has been used for applications such as replacing cast iron drain covers, the manufacture of precast balcony sections, precast ultra thin stairs, jointing of precast units together on-site to make slabs and frames (Figure 14). From the review of literature, this type of product has not made a significant impact on the UK concrete frame business, although it does have the potential to revolutionise the way in which 17,18 . precast concrete could be used to make concrete frames as well as other applications
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Innovation in concrete frame construction 1995–2015
Figure 14: Ultra high strength concrete used for jointing precast units♠ 2.1.5
Lightweight aggregate concrete
Lightweight aggregate concrete (LWAC) was a special application concrete 10 years ago and in practically all respects it still is. Over the past 10 years it has been used mostly in composite slabs as a part of steel frame construction. Lightweight concrete is not used commonly for concrete frame construction in the UK. Eurolightcon, a pan European BRITE Eu-Ram research programme undertook to develop a 19 reliable and cost effective design and construction methodology for structural concrete . The project achieved a measure of success in sharing and advancing technical knowledge and common practice between participant countries. There is a relative dearth of non-academic technical information available on lightweight aggregate concrete use, which underlines its marginal place in UK construction, despite use on 20 some high profile projects such as 25 Canada Square, Canary Wharf . In the BCA publication 21 Concrete practice LWAC merits only a passing mention, indicating its peripheral status in 13 practice and Concrete Society Technical Report 49 refers to the use of high strength lightweight concrete only where data is available.
Four precast slab panels jointed to each other and to a precast column. Bar laps at joints of 10 diameters. This prototype arrangement was load tested to destruction as part of a BRE project ‘innovative assembly of structural components’ funded by DTI. Failure occurred at 1.6 times ultimate design load.
♠
Innovation in concrete frame construction 1995–2015
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LWA concrete retains the potential to increase its market share due to a current industry driver – 22 namely the reuse of waste products. CIRIA Publication C608 gives one example of lightweight aggregate made from waste products, although from its recommendations it is clear that the use of this type of material in concrete has yet to prove itself economically or indeed practically. 2.1.6
Recycled aggregate concrete
Much research has taken place over the past 10 years on the use of replacement and recycled aggregates (RA) in concrete. The Environmental Building at BRE was also used to showcase 23 the use of RA concrete , where 90% of in-situ concrete used on site employed recycled aggregates. Despite this research, the use of RA in the construction industry is mainly confined to road construction, and unbound fill applications and is not used commonly in concrete frame construction or indeed in ready-mixed concrete generally. It is currently viewed as being uneconomic and impractical to produce. Internationally there is interest in this area of research. One of the more advanced practical reports being given in reference 25, which gives a Japanese account of a field application of reuse of concrete demolition waste in concrete. Recycled aggregates in concrete normally require additional production checks and controls as RAs suffer from variability in supply that currently make their widespread use economically unattractive. 25
BRE Digest 433 gives accessible technical information to the designer and specifier for the use of recycled aggregates in concrete and road construction. Research into recycled aggregate concrete has yet to meaningfully impact on concrete frame construction in the UK. However if the current drivers for more sustainable construction remain, 26 then the use of recycled aggregates are likely to become more commonplace in the future . Any development will necessarily start with its adoption either in non-structural concrete or as part replacement for primary aggregates. 2.1.7
Fibre reinforced concrete
Fibre reinforced concrete 10 years ago was used in special applications only, whereas today its use is more widespread. Three main types of fibres – steel, polypropylene and synthetic fibres for structural applications (synthetic structural fibres) – are used for different circumstances. Steel fibres have been shown to provide enhanced flexural strength and alter the failure mechanism of concrete from a brittle to a ductile failure type. Polypropylene fibres are often 27 used to provide added fire resistance to a concrete or control plastic cracking and possibly 28,29 . Anecdotally, the use of (there is some debate on this point) increase freeze thaw resistance both of these types of fibre has increased over the last 10 years. A newer form of fibre – 30 synthetic structural fibres – have become available in the past few years which purport to carry out a similar role to steel fibres in concrete. The use of these fibres is currently being investigated and debated by industry. Fibres have become more widely used in commercial concrete frame construction in recent years – especially in applications such as ground bearing slabs and also composite slabs in 31 steel frame construction, eliminating the use of steel bar reinforcement . The use of fibres in concrete is still not routine currently although the trend for their use is accelerating.
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2.2
Innovation in concrete frame construction 1995–2015
Construction practice and techniques
Identified as having an influence on concrete frame construction over the past 10 years, the following construction practices have been found to contribute to innovation in concrete frame construction. 2.2.1
Formwork systems
Lightweight aluminium formwork systems In frame construction 10 years ago it was very common to find wooden forms being constructed on-site prior to casting all elements. Currently the market is dominated by lightweight formwork systems, which are often aluminium, based, and are considered functional and designed to be erected and dismantled quickly by unskilled or semi-skilled operatives. Systems have various efficiency-based features, such as the ability to strike soffits while retaining the supports as props to the new slabs. They are generally modular systems. The emphasis has been on improving ease of use, speed and the reduction of dependence on skills, which are in short supply. This has meant that their adoption by UK industry has been rapid. This innovation has possibly had the greatest impact on UK frame construction over the past 10 years in that it has increased the speed of erection substantially and reduced labour skill requirement. That the development of many of these systems has been abroad has meant that there has been comparatively little written in the UK technical press, either on their development or on their impact on construction.
Figure 15: Lightweight formwork system during erection
Innovation in concrete frame construction 1995–2015
23
Flying forms 2
Flying forms can be described as large prefabricated formwork panels (up to 100 m , often forming a complete bay of a suspended floor slab), which can be rolled out from underneath a newly formed slab. They are then taken by a crane and placed at the next position, ready to repeat the process. The system requires enough space around the new construction to fly the panel beyond the extent of the building line on every use. The system also allows smaller teams of operatives to handle each section of formwork. Flying forms are used quite routinely for larger 32 projects such as Greenwich Millennium Village phase 1, St. George Wharf , the Norfolk and 33 34 Norwich Hospital and the Chicago Beach Project in Dubai . Tunnel form Tunnel form construction is a factory made steel formwork system that allows walls and slabs to be cast monolithically to speed up construction. The system is best used where there are a large number of repeat rooms (hotels, prisons and apartment blocks). The structure is generally resolved into one-way spans of not greater than 7.5 m and storey heights of up to 3.5 m. The formwork is often expensive and a large number of repeat uses is normally required to justify its 35 use. The system is credited with major reductions in construction time for buildings and 36 reductions in labour required (one-third the workforce required) . The system is also often used in conjunction with self-compacting concrete, to ensure high quality finishes to walls, which can eliminate the requirement for plastering in some instances. The use of tunnel form reduces the requirement for operatives and skilled trades on-site. Adjustable column forms The use of metal column forms has become much more prevalent in the UK over the past 10 years. One innovation, which is currently marketed in the USA, is the use of adjustable, reusable column forms. As shown in Figure 16 these forms can be clamped together to form a range of different sizes of column. These forms are not widely used in the UK currently, although they reportedly have 37 been used on the Broadgate Development in London with reported productivity benefits (two men took 30 minutes to strip a 7 m high column and reposition it). Cardboard/paper column forms The use of cardboard-based formwork to form circular concrete columns has been used occasionally in the UK on projects such as the Doncaster Earth Centre. The different products available claim to provide a low skill, cost-effective method of providing formwork which is lightweight and reported to be environmentally friendly. They can also be manhandled without the requirement for a crane, cut to size on-site and stripped relatively easily. Inserts can be used to form square or rectangular columns – see Figure 17). These forms often have a prepared inner face which needs no further application of mould release oil but the forms generally have to be protected from rain prior to use. The column forms are normally tied down during concreting to avoid lifting. When stripped after one use the form is discarded although in theory, at least, it can be recycled.
24
Innovation in concrete frame construction 1995–2015
Figure 16: Adjustable column form
Figure 17: Disposable cardboard formwork
Innovation in concrete frame construction 1995–2015
2.2.2
25
Core wall construction
Slipform construction. While slipforming is not a new method, its use in concrete frame construction is relatively new. It is essentially a method of vertically extruding a reinforced concrete section and can be used for the construction of cores. Rising at rate of roughly 300 mm per hour, the form requires 24-hour concrete and rebar supply until it finishes its operation. Traditionally slipforming was used mainly in civil engineering projects. More recently its use in tall framed buildings has become more commonplace. This form of construction requires extensive preplanning, special detailing and has little flexibility for change once construction has begun. The main advantages of this form of core construction are speed on-site, reported efficiency and the fact that the formation of the core in advance of the rest of the structure takes it off the critical path. Slipformed cores are best suited to tall structures with repetitive details. Jumpform construction. Another method of constructing cores is by using formwork that is fixed to climbing brackets. This allows the formwork and working platforms to be struck from the concrete on one lift, and be raised by crane to the next position, quickly. Normally this operation takes place ahead of the rest of the frame and the method is claimed to reduce crane time and give safe access for working at height. Self-climbing jumpform construction. The main benefit of this type of technique is that it cuts down the requirement and dependence for crane time on site considerably. As crane time can be a limiting resource on site this independence is especially valuable. Reference 39 indicates that self-climbing forms were used during periods where cranes were not able to operate due to high wind speeds, thus decreasing dependence on the weather. While the formwork is not widely used at present, it is commercially available and has been used in the UK. It is expected that the market share obtained by this innovation will grow significantly, especially on congested urban sites where crane time is at a premium.
2.3
Construction techniques
2.3.1
Post-tensioned concrete
Post-tensioned solutions are commonly used to reduce both the quantity of reinforcement required in structures and the depth of floor slabs required. Post-tensioning has in the past been mainly restricted to structures such as bridges, offshore structures and other heavy civil engineering applications. However, in recent years has become much more used for slabs in framed structures, particularly where spans exceed 7.5 m. Questions have been raised about whether the user/owners of such structures are competent to manage structures of this type. Irrespective of this education need, post-tensioned structures look like becoming far more common in future years, as they use substantially less reinforce40 ment than comparable traditional reinforced concrete structures and/or allow thinner slabs . 2.3.2
Hybrid construction
Hybrid construction is generally held to involve the use together of precast and in-situ concrete construction to arrive at a solution that can have significant benefits over conventional frame construction. A few examples of this type of construction have been carried out in the UK, with
26
Innovation in concrete frame construction 1995–2015
41, 42
reported benefits in terms of cost savings . Other reported benefits are quoted in terms of an increase in the speed of construction, a reduction in labour required on-site and improved quality of finish from the precast sections used. To date, bespoke solutions have been generally used in the UK although perhaps the greatest advantages of this type of construction could probably be realised from standardised or modular systems.
2.4
Other techniques
2.4.1
Kickerless construction
While not a formwork system, the kickerless construction technique is sometimes used to speed up site operation and ideally should be included in the reinforcement detailing of a structure. Instead of using a traditional kicker to form walls and columns it is possible to use shot-fired wooden battens or using adjustable metal T-spacers. This is not a particularly popular technique, currently. 2.4.2
Continuity strips
Continuity strips are used to form joints in reinforced concrete slabs or walls. While bending back reinforcement has its potential problems (in terms of brittleness induced by bending), most systems promise a joint that is properly formed. Speed of construction and reduction of operative skill are the main reasons that continuity strips are used. The use of continuity strips in frame construction is currently limited.
2.5
Reinforcement technology
Three reinforcement-based innovations are described in Section 1 of this report. 2.5.1
Contractor detailing
The main change in design and detailing of reinforcement over the past 10 years has been the introduction of contractor detailing to the UK industry. While not by any means widespread yet, the idea that detailing is carried out by those who understand best the impact detailing can have on construction and site efficiencies can be seen to have advantages. Reference 43 reports that the practice is widespread in both the USA and continental Europe. The issue of design liability which arises from this split in what traditionally was the responsibility of the designer can be resolved by using independent checking through a third party. There is a balance between rationalising reinforcement and providing robust details. Whoever carries out the detailing must be mindful of both economy and robustness of the structure should circumstances arise that it is put into a distressed state (such as overloading). There has been no widely quoted analysis or measurement of the benefits that this innovation brings to the industry, although it has a growing number of proponents, and is becoming more commonly considered on ordinary contracts. A list of benefits of contractor detailing are given in Reference 44 which include ‘decisions made in the light of planned construction methods, likely pour sizes, the overall programme and a knowledge of factors such as the availability of cranes on site.’
Innovation in concrete frame construction 1995–2015
3.
Implementation of innovation
3.1
The impact of Cardington Research
27
Assessing the impact of Cardington research on industry is quite difficult, in that it is impossible to separate developments trialled at Cardington from those developed outside that research programme. It is also impossible to accurately measure what spin-off innovations the research promoted in industry more widely. The proceedings of the industry workshop and the comments of interviewees on changes in the industry can be used to give a non-scientific indication of the impact of aspects of the Cardington research. The interviewees were asked what were the most significant changes that they recognised in the concrete frame industry over the past five to 10 years. The results are listed and ranked in Table 1 in order of number of occurrences. Table 1: Largest (or most significant) changes in the concrete frame industry What are the largest changes in the concrete frame industry over the past 5 to 10 years? Rank 1. 1. 1. 4. 4. 6. 6. 6. 6. 6.
Topic More professional behaviour/approach (all parties). Speed improved. Health and safety is now a priority. The use of flat slab solutions much more prevalent. Efficiency improved. Quality of concrete supply better. Supply of reinforcement quicker. Buildability improved. Using more reinforced concrete. A work force whose first language is not English.
Note: topics in bold relate to the stated aims of the Cardington Research.
Interviewees were also asked to name the innovation that had the largest impact on their day-today operations. Two answers predominated, namely computer technology and software, and the use of lightweight aluminium forms. Notably, the value of lightweight forms was demonstrated by 2 the St. George Wharf case study of Cardington innovation. The items highlighted in bold (Table 1) indicate answers which are in keeping with the Cardington project’s stated aim to: • re-engineer the design and construction process • reduce costs and improve speed, quality and safety • increase client value. Interviewees were not told the aims and objectives of the Cardington work, so this could be considered a blind evaluation. As can be seen the Cardington aims are picked out as having been largely achieved or partially achieved.
Innovation in concrete frame construction 1995–2015
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This is not to suggest that the work at Cardington was responsible for all of this perceived development, although the workshop when questioned indicated that the Cardington research disseminated to industry had: • acted as a catalyst • provided an example • provided reassurance to industry professionals. While these findings, along with those presented in the analysis of Cardington innovations, cannot be claimed to be a scientific evaluation, they indicate that the Cardington research was worthwhile, well targeted and a flagship for change in the concrete frame industry at the time.
3.2
Current industry perspectives on innovation
When asked about how their company gathered information and ideas for innovation, respondents to the interview gave answers as shown in Figure 18. It showed that word of mouth, trade press and research organisations largely informed the industry on new developments which they could adopt. At the workshop one delegate commented on the lack of presence of professional bodies in these answers.
30% Trade press Word of mouth
8% 25% 4%
Research organisations Internet Suppliers
8%
Projects 25% Figure 18: Interview results ‘Where do you learn about innovation?’ Note: Suppliers category is not taken to include trade bodies or organisations.
When asked the reasons that they felt unable to innovate on every project (Figure 19), interviewees suggested that late involvement, constrained attitudes/motivations within the project team and cost/risk considerations were the main barriers. When asked who, in their own experience, generally carries the risk (financial) of innovation on a concrete frame construction project (Figure 20), respondents indicated that the concrete frame contractor was most likely to carry the risk. This could also be said to be true for innovations that carry smaller risks – such as reinforcement detailing. However, when dealing with larger innovations that could impact on the design philosophy or design intent, it must be acknowledged that the designer does carry risk. The failure of the interview results to reflect this is perhaps due to the fact that the Cardington innovations are now viewed as best practice rather than as carrying substantial technical risk.
Innovation in concrete frame construction 1995–2015
29
13%
Figure 19: Interview results ‘What stops you innovating on every project?’
23%
Frame contractor The person who innovates Main contractor Client
54%
15% 8%
Figure 20: Interview results ‘Who carries the risk of innovation?’ When asked to identify who benefited from innovation (Figure 21), most interviewees indicated that the benefits were generally spread among everyone from subcontractor to client and end user. Taken together, Figures 20 and 21 indicate that it is being left to one party to innovate, but that everyone is likely to benefit. While it is acknowledged that this is a simplistic analysis it points to a current prevailing barrier to innovation. Frame contractors seem to be forced to innovate alone, as many projects make no provision for managing innovation. In order to promote a more benign climate for innovation in concrete frame construction it may well be necessary for projects to manage innovation risk based on shared endeavour as well as on a shared pain and gain. A combination of the NEC℘, Engineering and Construction Contract (ECC) and a part45 nering approach together has been reported to provide both savings and promote continuous improvement on a recent larger scale development.
℘
New Engineering Contract. www.newengineeringcontract.com
Innovation in concrete frame construction 1995–2015
30
23%
Everyone Main contractor
8%
Client
69% Figure 21: Interview results ‘Who benefits from innovation?’ Figure 22 describes the results of a question aimed at discovering why some frame contractors seem to be more innovative than others. The judgement as to what constituted a more innovative frame contractor lay with the interviewee. It is acknowledged that the question was leading in that it strongly suggested that there was such a thing as more and less innovative frame contractors. 11%
Figure 22: Interview results ‘What makes an innovative frame contractor?’
It was felt that the size of the organisation was the most important factor, with larger frame 4 contractors being more innovative. This raises an issue that was identified previously namely; smaller projects were found to have complicating issues such as: • Contractual agreements adopted meant that construction time was often not so important to the frame contractor. • Very limited lead times – an early start on-site was often important. • Little or no opportunity for contractor input into design. • A lack of engineering resource on-site restricted the opportunity for innovation. The category ‘does not use direct labour’ refers to the idea that organisations with direct labour on-site tended to try to maximise the use of their labour resources on-site rather than targeting efficiency-based innovation.
Innovation in concrete frame construction 1995–2015
3.3
31
What do clients want from concrete frames?
The interviewees were asked to prioritise their perception of clients’ real requirements. As indicated in Figure 23, over 50% of the responses put quicker erection times first, with cheaper being the next and quality being deemed the least important requirement.
Figure 23: Interview results ‘What do clients want? Better/Quicker/Cheaper’ Note: Interviewees were asked to prioritise, from their experience, client’s true requirements from the drivers listed. Choices such as health and safety were recorded but are not used in this analysis.
One interviewee stated that he felt that clients did not think about quality because a concrete frame is generally hidden. While not a major study of attitudes, Figure 23 gives an indication of the required focus of future innovation in concrete frame construction.
Innovation in concrete frame construction 1995–2015
32
4.
Future trends in concrete frame innovation
4.1
Identifying trends
Both the interview results and the workshop independently identified three major areas where there was a requirement to change the concrete frame industry over the next 10 years.
11% Energy /effort
31% 21%
Waste/recycle Design life Use of resources Health and safety Labour/skills
5% 16% 5%
Cost/efficieny
11%
Figure 24: Interview results ‘What trends will force concrete frame construction to change in the next 10 years?’ From above the response to the interview question can be summarised as: 1. Green / environmental issues 2. Efficiency improvements 3. Labour issues (Listed in perceived priority order, as given by interviewees) Of the major trends that were identified, only the green/environmental issues are relatively new to concrete frame construction. Both efficiency and labour issues can be recognised as having played a part in innovation in the past. In the sections below these main trends in future innovation are examined in more detail to identify strategies, technologies and issues which may well play an important part in the competitiveness of concrete frame solutions in the medium term. This section of the report draws heavily on the proceedings of the one-day workshop held at BRE. Many of the points that came out were generic to construction and not always specific to concrete frame construction.
4.2
Green / environmental issues
4.2.1
General perceptions
Currently, reinforced concrete, as well as steel solutions, is generally viewed in a less than favourable light with regard to green and environmental issues. Neither material can claim very
Innovation in concrete frame construction 1995–2015
33
low embodied energy values and both will have to maximise their potential for environmental and sustainability savings over the coming years, in response to the demands of society. There is also a perceived trend that taxes with green intentions would make construction products comparatively more expensive (both concrete and steel). Some of these taxes are already in place – such as landfill tax. Other taxes such as carbon dioxide emission based taxes look likely over the next 10 years. 4.2.2
Recycling and increasing the value of recycled concrete
It is expected that in 10 years’ time innovation will be more focused on reducing dependence of structural concrete on primary aggregates. In many ways the technical aspects of using crushed concrete as aggregate are reasonably well understood. The practicalities of dealing with recycled aggregates’ provenance, moisture content and inherent variability all need to be established before recycled aggregate can be used generally within the ready-mixed concrete market. Currently these practical issues ensure that the use of recycled aggregate concrete is rarely economic. Currently concrete is crushed and re-used particularly in unbound applications such as roadway sub-base. It is expected that in the future the requirement to increase the value of recycled products will mean that ready-mixed concrete will use a larger percentage of recycled aggregates in new concrete. 4.2.3
Use of primary aggregates
It is expected that the use of primary aggregates will continue to attract an increased premium and that the concrete industry will innovate to reduce its dependence on primary aggregates. As stated above, recycled aggregates are an obvious choice, although there are other options available. The use of aggregates manufactured from industrial byproducts and wastes is another avenue that it is expected to produce solutions that enhance concrete’s environmental credentials. Again, transport issues and local waste products are likely to create a patchwork of different solutions based on geographical location. 4.2.4
Reducing waste on-site
The reduction of waste on-site is also likely to become an increasingly strong driver for innovation. The increasing price of disposal of mixed building waste from site is already forcing contractors to address this issue. It is likely that in 10 years’ time the driver will be much more pressing and will become an essential and important component in a viable concrete frame construction business. Strategies for reducing waste generated on site include: • Use of precast elements • Ready-mixed concrete that is ordered but is extra to that found to be required, to be put to a productive use of similar value on the project. • The development of a service which delivers just the right quantity of concrete to a project and takes away the excess for re-use elsewhere (with no loss of quality). • The continued shift towards the use of more proprietary forms of reinforcement and an elimination of cutting and bending on-site. • The further development of multi-use formwork systems.
34
4.2.5
Innovation in concrete frame construction 1995–2015
Energy use in the production of cement and steel
Both cement and steel both use comparatively large amounts of energy in their production, by the nature of the high temperature processes involved in manufacture. There are obvious attractions in reducing the energy required for both of these materials and it could be expected that this will remain a primary target for manufacturers of both materials for the foreseeable future. The development of innovative cements with low carbon dioxide profiles and lower kiln firing temperatures (which sometimes use a variety of different constituent feed materials) are currently at the research stage. The drive to develop these research ideas into full commercial products is likely to be increased over the next 10 years, although due to the nature of the leap in technology the introduction of new materials is likely to take 5–10 years to bring to market. 4.2.6
Use of waste materials from other industries
Concrete has a long history of incorporating waste from other industries to change and enhance the properties of the hardened concrete. Materials such as fly ash (pfa), ground granulated blastfurnace slag, microsilica originate as byproducts from other industrial processes and are now routinely used in concrete production to such an extent that their disposal has become much less of an issue for the UK. The driver to incorporate other suitable and available waste byproducts into concretes will undoubtedly increase as disposal becomes more of a pressing issue for all industries. 4.2.7
Design for long life and adaptability versus demolition and replacement
A particular failing which could be levelled at some current structural design processes is that the solutions adopted may become functionally obsolete long before they have reached their intended design life. This waste of resource is unlikely to be allowed to continue in the medium term. There was a difference of opinion in both the workshop and interview results which provided two different views on how framed structures in the future might be designed. One view was that buildings would be designed to be flexible in use and would be designed to last for long periods of time. The counter view was that buildings would be designed to last shorter periods of time and that they would be demolished and rebuilt over shorter periods than the current normal 60 year design life. There is currently no clear indication as to which of the two approaches will be deemed the more sustainable in time. At first glance it might be suggested that the long-life solution is more sustainable as it does not require the effort to deconstruct and construct periodically. There will undoubtedly be an increased investment required for extra or enhanced material/design required to give the extra service life and flexibility of use required for long-life structures. The balance of basic material cost versus cost of redevelopment (assuming that sustainability drivers will be more fully included in cost than is currently the case) is likely to be fine and variable therefore concrete as a material may possibly require to develop both strategies. Outside influences such as EU or UK government policies are likely to move industry in one direction or the other over the coming 10 years and their decisions will be led by cultural and general attitudes from wider society. 4.2.8
The influence of thermal design on structural solutions
Currently, thermal mass is generally recognised as being desirable to produce internal environments which are comfortable and energy efficient, when the building has good air-
Innovation in concrete frame construction 1995–2015
35
tightness. However, there is currently little direct guidance or quantifiable benefits readily available to designers. It is expected that over the next 10 years guidance to industry on thermal mass will become more explicit allowing designers and clients to choose thermal mass based solutions over more lightweight solutions for better defined technical reasons. This development may well have an influence on the shape of structural solutions adopted for concrete frames, with mass being located to suit both the structural and thermal design of the structure. This movement towards a design based on thermal considerations might be expected to be more attractive if designs for long-life are adopted. 4.2.9
Local manufacture/reduction of transport
It could be expected that over the coming 10 years transport will become more expensive and that the concrete industry may change as a result. While concrete is generally made with local materials (aggregates, water), the production of cement (the one component of concrete (12–15% by mass) which often has to be transported significant distances) may face a trend towards smaller more regional plants and away from importation of cements to the UK. Concrete as a material would be expected to benefit relatively from a trend in increased transport costs as it is largely a local product which is used locally.
4.3
Efficiency
4.3.1
Speed of construction
From our interviews and workshop there seemed little doubt that speed of construction was viewed as the most important driver for clients. As a result, it is likely that this drive will continue to challenge the concrete frame industry to reduce the time taken to construct concrete buildings in the future. This analysis of clients’ requirements is supported by the fact that steel frames have taken and retained a large market share of frame construction over the past 10 to 20 years. The recent large increases in steel prices have not had any immediate impact on this market share. Steel solutions, while having a longer lead time, are generally recognised as having quick erection periods. From this it can be predicted that speed of erection will continue to be a major driver for innovation in concrete frame construction over the coming 10 years. The major avenues for innovation and improvement are assessed as being the following. Hybrid solutions The use of precast members in standard concrete solutions. Hybrid solutions offer the potential to give a step change in speed of construction, especially on buildings where the formation of vertical elements is assessed as being a limiting factor on speed of erection. These systems, again developed primarily outside the UK, offer the potential to alter the speed of concrete construction in a similar way in which formwork developments over the past 10 years have done. Formwork innovation The use of self-climbing forms, and yet quicker erection and striking solutions from the formwork manufacturers are expected to bring further improvements in speed of erection. Early age strength determination of in-situ concrete in the near future is likely to be dominated by maturity measurement solutions from embedded sacrificial probes.
Innovation in concrete frame construction 1995–2015
36
4.3.2
Cost
Cost is defined here primarily as the initial capital cost of the structure, although the whole life costs are expected to become increasingly important to more and more clients over the coming 10-year period. Reduction of waste The Japanese term ‘muda’, meaning waste or futility, is often used in manufacturing industry to identify wasted time and effort spent in production. In practice, on construction sites (of all types) there are large levels of wasteful practices such as: • Subcontractor re-design (two designs for the one structure), • Late value engineering (why not have VE before design, not after?) • Unnecessary contractual matters which absorb effort and good will between partners • Double handling • Repair of substandard elements of the work. The concrete frame industry has the opportunity to reduce or eliminate the production of waste materials from site practices, to reduce futile work from concrete specific elements of construction. Over-specification/design Gross over-specification of concrete properties or grossly conservative reinforcement design is also an area where concrete structures could reduce cost. Appropriate design and appropriate specification could be expected to come not from actual innovation but perhaps from research and guidance to industry on the subject. This should not be confused as a desire to limit a designer’s scope in managing risk or uncertainly, it is rather a desire to reduce over-specification and design arising from a lack of management of risk or uncertainty. Use of post-tensioned slab solutions In recent years, post-tensioned concrete solutions have become more widely used in slabs in concrete frames as they have been found to provide some particularly cost effective solutions. It is expected that this innovation will continue into the future and become more commonplace over the coming few years. Post-tensioned structures are not generally held to be as adaptable as equivalent reinforced concrete structures. As there is expected to be more post-tensioning on concrete frame sites, innovation may well offer the possibility of making the currently specialised process into a more routine operation. Adding value to the frame There is a possibility that reinforced concrete solutions could offer a project more than just a frame. The relatively large mass of some elements could be used as a housing for other services. Services such as wireless data transmission barriers, information storage, improved thermal storage are but some of the opportunities that are expected to be investigated in the future. A major innovation in this area perhaps offers the most promise in delivering a step change in the perceived cost of concrete frame solutions. Contractual relationships A comment on all construction is that the most appropriate forms of contract between the parties are not always adopted compatible with the respective needs of the different parties.
Innovation in concrete frame construction 1995–2015
37
The impact of this on concrete frame construction is perhaps disproportionate as there are generally several individual organisations involved in the design and construction of any concrete frame – client, architect, designer, main contractor, frame contractor and various specialised subcontractors such as reinforcement fixing and suppliers. All parties require appropriate motivation and reward for skill and risk from their contracts in order to pull together to achieve the finished frame. Innovation in contractual relationships, their basis and their operation, would offer a very significant opportunity for reducing cost and perhaps most importantly, improving effectiveness. Computers and communication The ability of geographically diverse groups to work together collaboratively using state-of-theart communication and portable computing must be recognised as a large opportunity to improve efficiency. Widely available mobile conferencing facilities, as well as handheld computing facilities may well mean that managers and engineers can spend more time on-site and less time in an office or site office. As an example of this type of innovation, radio frequency identification (RFID) tags are currently being examined for use in some precast concrete applications unconnected with concrete frames. Given the impact computers have made to productivity in the past 10 years it can only be predicted that they will continue to provide benefits to sectors that can make use of their future possibilities. 4.3.3
Quality
There is an increasing move in many areas of industry and commerce for items and activities to become commodities, driven only by price because performance is implied or assumed. Against this background it is clear that reinforced concrete needs to continue to target quality and customer perceptions over the medium term. The reliability of achieving good quality concrete structures first time offers an opportunity for improved reliability of product achieved – i.e. right first time, more of the time. While reinforced concrete is a forgiving material that allows extensive and effective repair, attitudes in the medium term will probably view repair as wasteful in terms of natural resource, image loss and a financial burden. Self-compacting concrete At least one member of the workshop articulated what is understood to be a more widely held view, namely that self-compacting concrete (SCC) will become more prevalent in UK construction in 10 years time, than high flow concretes. There are several drivers for this, one of which is certainty of quality achieved. SCC has the potential to dramatically increase the certainty of product delivered, as well as offering an opportunity to have all or any concrete surfaces finished to a high fair-faced standard (dependent on formwork). Precast concrete The increased use of precast concrete elements in concrete frame construction offers the possibility of giving a step change in quality of finish and certainty of product. The idea that quality control can be better managed in a factory environment is widely held and currently promoted by precast manufacturers. To become a significant part of frame construction precast manufacturers are probably going to have to produce more modular commodity-based solutions, rather than relying on bespoke designs.
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Innovation in concrete frame construction 1995–2015
4.4
Labour issues
4.4.1
Training and education versus less requirement for skill
Training in the construction industry in general has reduced significantly over the past 10 to 20 years. This is due in no small measure to the emphasis given by successive governments to academic training of graduates at the expense of trade and vocational training. The loss of skills built up by apprenticeships has changed the face of the UK construction industry. It must be predicted that there will be no substantial change in the current trend in the near future, although the Learning and Skills Council are attempting to introduce modern apprenticeships to the construction industry. The lack of training and skills means that in general the business of construction needs to aim to be made less reliant on skill. To an extent concrete frame construction has taken steps in this direction over the past 10 years (formwork systems, proprietary reinforcement solutions, selfcompacting concrete etc.) If the strategy of using less trained labour is to continue then the focus on making concrete frames easier to build must be retained. The strategy of developing specialised squads of operatives to carry out specific more complex pieces of work, or even specific types of project, was also proposed at the workshop. This strategy might offer some of the advantages of both approaches to the lack of trained industry personnel. The Inland Revenue’s recent restrictions on the use of the self-employed, leading to the very recent trend for companies to take labour back in-house may also, in time, mean a change in the way in which development of skills is treated by the construction industry generally. This approach makes the UK out of step with approaches in the EU where skills and training are reported to be more valued. It also means that in the EU there are generally fewer personnel on-site, who are better trained and who are more productive due to better organisation and planning. 4.4.2
Scarcity of labour
There is a perceived lack of labour (skilled and unskilled) in the construction industry generally. The background for this is a shifting source of labour to the general industry. While currently an issue, there has been no suggestion that it has become a chronic problem. Recent RICS 46 studies indicate that labour need is currently being mostly met by migration from Eastern Europe. While migration is an old solution to the problem of labour shortages, the use of foreign workers brings its own challenges, as is described in the section on language and communication below. The lack of site labour is certain to remain a strategic challenge over the coming years and may well become a powerful driver for innovation and change. The flow of graduates into the design offices of engineering consultants is reported to be at a low ebb currently. There was an uneasy feeling at the workshop that modern graduate engineers were being trained to operate computer software rather than getting a good appreciation of structures in general. A comment from one delegate to the workshop indicated that there had, in his experience, been a few notable cases of excessive deflections arising from ill-defined finite element analysis predictions recently – a trend he viewed as worrying. The incorporation of rule of thumb checks into the design process seems the most straightforward method of addressing the risks identified. It was felt that the trend was not helped by the way in which design engineers are expected to fee bid for work.
Innovation in concrete frame construction 1995–2015
4.4.3
39
Language and communication
The strategy of using less skilled labour on-site also leads to the problem of communication with site operatives whose first language is not English. This issue is especially critical in terms of general health and safety, but also important in getting work done effectively and in the right way. Use of foreign labour on construction sites is not a new phenomenon in the UK, although language barriers have not generally been a major problem until recently. The whole issue of communication means that UK construction will be forced to adopt simpler solutions and will have to invest in English language tuition for their workforce. Any trend that outsources design or detailing to other parts of the EU or indeed the world has inherent risks and challenges. While not common, currently isolated cases which have taken place are reported to have resulted in solutions which were not optimal for UK conditions. For example, in one quoted case, detailing carried out in South Africa produced a solution that was not rationalised appropriately for the UK. This was because in South Africa the balance between labour, material and financing costs is very different to the UK and the detailers were necessarily using their own experience to produce solutions. 4.4.4
Health and safety
As mentioned above, health and safety (H&S) on-site will undoubtedly drive innovation in concrete frame innovation in the future. The requirement for safer systems of work is currently tending to focus on edge protection issues. Over the longer term H&S may well influence material choice such as the increased use of self-compacting concrete. The focus on H&S may well drive off-site manufacture and hybrid systems as well as any solution that minimises working at height. Precast elements with balanced lifting points and integral formwork for ultra high strength jointing compounds also offer the possibility of reduced work on-site. Formwork innovation, which has been focused reasonably directly on providing solutions that were quicker and easier to use over the past 10 years, could be expected to produce systems that promote even safer working practices.
40
5.
Innovation in concrete frame construction 1995–2015
Concluding comments
The Cardington Project must be judged a success in helping the concrete sector to adopt new innovations. There has been real progress in meeting the original aims of the project and in general it has helped to make flat slab construction a widely used frame solution. The best 5 practice advice which has come from the project continues to be read and used by the industry. If one particular challenge to the future of concrete frame construction could be isolated from the overall findings, it is perhaps the role of contracts. This comment is equally applicable to practically the whole construction industry. That all participants in a project are not empowered and motivated to meet and exceed the clients’ needs is a major hurdle to innovation. Currently used contract forms provide no effective or equitable means for management of innovation risk. Mechanisms for sharing benefits of innovation on the basis of factors such as risk, skill and endeavour are required to give motivation to improve or change. While the idea of partnering has been around for many years, it seems to have made little impact on the way in which the concrete frame industry operates. This report shows that despite the barriers identified in this report, the concrete frame industry has changed quite considerably over the past 10 years. After examining its expected challenges the industry will need to increase the rate of change achieved over the coming 10 years. It could be expected that the construction industry as a whole will face growing pressures to change radically as pressure for ever more sustainable construction starts to impact on the economics of construction and existing balances which underlie the current status quo. If one particular opportunity for a step change in performance was to be isolated from this study then it would probably be the potential that precast and hybrid systems possess to revolutionise the concrete frame business in the future. It can be seen that concrete frame construction has the potential and the ability to improve upon its current performance in the future. Even now, there are a number of technical ideas and initiatives for every challenge that the sector will face in the future. The future direction of research and development in the concrete frame sector must take cognisance of the importance of understanding the clients’ requirements. There also needs to be a strategy for developments and innovations to be effectively communicated to everyone in the sector so that all parties are clear as to the direction concrete frame construction is expected to take in the future.
Innovation in concrete frame construction 1995–2015
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References and further reading
1.
The European Concrete Building Project, The Structural Engineer, Vol.78, No.2, 18 January 2000.
2.
Moss R, Best practice in concrete frame construction: practical application at St George Wharf, BRE Bookshop, Garston, Watford, 2003. BRE Report 462, 20 pp
3.
Vollum R, Backprop forces and deflections in flat slabs: construction at St George Wharf. BRE Bookshop, Garston, Watford, 2003. BRE Report 463, 31pp.
4.
Nolan E, Best practice in concrete frame construction: case studies. BRE Bookshop, Garston, Watford, 2005. BRE Report 479, 16 pp.
5.
Best Practice Guides for In-situ Concrete Frame Buildings: • Concreting for improved speed and efficiency • Early age construction loading • Early age strength assessment of concrete on site • Early striking and improved backpropping for efficient flat slab construction • Flat slabs for efficient concrete construction • Improving concrete frame construction • Improving rebar information and supply • Prefabricated punching shear reinforcement for reinforced concrete flat slabs • Rationalisation of flat slab reinforcement • Reinforcement rationalisation and supply • Slab deflections • Special concretes • St George Wharf Project Overview Best practice guides can be downloaded free from: http://projects.bre.co.uk/ConDiv/concrete%20frame
6.
Goodchild C, Optimising the use of steel reinforcement in design, Which way forward for concrete reinforcement? BPCF Conference, Loughborough, 8 December 2004.
7.
The Concrete Society. Self-compacting concrete – a review. Camberley, 2005. Technical Report 62. 96pp.
8.
Lafarge’s top secret centre creates modern classics, Construction News, 18 November 2004. pp 28–29.
9.
Bartos J.M. and Cechura J. Improvement of working environment in concrete construction by the use of self-compacting concrete. Structural Concrete, Vol.2, No.3, September 2001, pp 127–132.
10. Skarendahl A. Market acceptance of self-compacting concrete, the Swedish experience. Ozawa K and Ouchi M (eds), Proceedings of the Second International Conference on Self-Compacting Concrete, Tokyo, COMS Engineering Corporation, Japan, 23–25 October 2001, pp 13–24. 11. The Concrete Society. Pumping concrete, Camberley, Digest No 1, 8pp. New edition 2005. 12. Gaved A. Pump hirers' guide to shake up lax sites, Construction News, 13 May 2004. p20. www.cnplus.co.uk/archive 13. The Concrete Society. Design guidance for high strength concrete. Camberley, 1998. Technical Report 49, 180 pp. 14. Concrete frame undergoes crash trial. Concrete Quarterly, Issue 198, Spring 2001. 4 pp. www.concretequarterly.com 15. Maeder U, Lallemant-Gamboa I, Chaignon J and Lombard JP. Ceracem, a new high performance concrete: characterisations and applications, Proceedings of International Symposium on ultra high performance concrete, Schmidt M, Fehling E and Geisenhansluke C (eds),Kassel, Germany, 13–15 September 2004. Kassel University Press, pp59–68. 16. Arup B, The next generation: UHPC, BPCF Conference ‘Which way forward for concrete reinforcement?’ Loughborough. 8 December 2004.
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17. Man-Chung T, High performance concrete – past, present and future. Proceedings of International Symposium on ultra high performance concrete, Schmidt M, Fehling E and Geisenhansluke C (eds), Kassel, Germany, 13–15 September 2004. Kassel University Press, pp 3–9. 18. Moss R. High strength jointing methods, Concrete, Vol. 36, No. 2, February 2002. pp52–53. 19. Lightweight aggregate concrete – state of the art. European BRITE Euram report R2. December 1998. Available free from www.sintef.no/static/BM/projects/EuroLightCon/Rapportoversikt.htm 20. 25 Canada Square, Canary Wharf, Concrete, Vol. 36, N. 9, October 2002. pp32–34. 21. Blackledge G. and Binns A. Concrete practice. British Cement Association, Camberley. 3rd ed. 2002. 74pp. 22. CIRIA. Use of sewage sludge products in construction. London, 2004. Publication C608. 166pp. 23. The BRE Environmental Building – a model for the 21st century. http://projects.bre.co.uk/envbuild/envirbui.pdf 24. Yoda K, Harada M and Sakuramoto F. Field application and advantage of in-situ concrete recycling systems. Proceedings of Conference Recycling and reuse of waste materials, Dundee, Thomas Telford, 2003. pp 437–446. 25. BRE Digest 433. Recycled aggregates, CRC, Watford, 1998. 6pp. 26. Smith RA, Kersey JR and Griffiths PJ. The construction industry mass balance: resource use, wastes and emissions, Viridis Report VR4. 2002, revised 2003. 104pp. ISSN 1478-0143. 27. Clayton N and Lennon T. BRE Report 395, Effect of polypropylene fibres on performance in fire of high grade concrete. CRC, Watford, 2000. 32pp. 28. BBA Agrement Certificate No. 00/3735, Fibrin Fibreflex, British Board of Agrement, Watford. 2000. 29. Harrison TA, Dewar JD and Brown BV. Freeze-thaw resisting concrete: its achievement in the UK. CIRIA, London, 2001. CIRIA Report C559. 80pp. 30. Perry B. Strux 90/40 synthetic structural fibres. BPCF Conference, Which way forward for concrete reinforcement? Loughborough. 8 December 2004. 31. Fibre concrete speeds up composite floors, New Civil Engineer, 16 September 2004, p10. 32. Parker D. New ideas put to the test, New Civil Engineer, 29 March 2001, pp 4–6. 33. SGB on form, Construction News, 2 September 1999, pp 16–17. 34. Atkins on the crest of a wave, Construction News, 6 March 1997, pp 20–21. 35. Newman K, High speed construction, Construction News, 4 May 1989. Concrete Supplement, pp12. 36. Crates E, Taking the hard work out of hotels – Innovative ideas to speed up construction, Construction News, Concrete special feature, 26 July 2001. 37. Bennett D, Innovations in concrete, Thomas Telford, London, 2002. 362 pp. 38. www.slipform-int.com, Slipform International, PC Harrington. 39. Cutting edge – Doka lifts formwork speeds, Construction News, 28 April 2005, p23. 40. The Concrete Society, Post-tensioned concrete floors – design handbook, Camberley, 2nd edition, 2005, Technical Report 43, 110pp. 41. Goodchild C and Glass J. Best practice guidance for hybrid concrete construction, The Concrete Centre, Camberley, 2004. Available from www.concretecentre.com/main.asp?page=438 42. Parker D. Decent exposure Hybrid structural frames using a mixture of in-situ and precast concrete have been heavily promoted lately, New Civil Engineer, 28 May 1998. 43. Reading University, A study of reinforcement procurement, The Concrete Society, Camberley, 2000, Project Report 1, CS121. 44. The Concrete Society, Towards rationalising reinforcement for concrete structures, Camberley, 1999. Technical Report 53. 42pp. 45. NEC cuts residential building costs, NEC User Newsletter, January 2005, www.newengineeringcontract.com/newsletter/article.asp?NEWS_ID=527 46. Skills shortage in industry drop to 29 month low, Building, 1 April 2005, p19.
Innovation in concrete frame construction 1995–2015
Appendix A – Workshop delegates • • • • • • • • • • • • • • • • • • •
Stuart Holdsworth, NRM Consultants David Fung, Waterman Partnership Darron Haylock, Foster and Partners David Rathbone, Alan Baxter & Associates Wayne Davies, Taylor Woodrow Construction Bob Gordon, Mace Christer Isgren, Byrne Bros Bill Gains, Scanmoor Antatol Himowicz, Stephensons John Hannah, The Concrete Centre Peter Kelly, Bison Bob Viles, Fosroc Jack Sindhu, London Concrete Charles Allan, Hanson Premix Robin Holdsworth, CONSTRUCT Paul Gregory, The Concrete Centre Éanna Nolan, BRE Stuart Matthews, BRE Flavie Moulinier, BRE
Workshop held on 15 April 2005 at BRE, Garston.
Appendix B – Industry interviews • • • • • • • • • • • • • •
Prof. George Somerville, CARES David Rathbone, Alan Baxter & Associates Christer Isgren, Byrne Bros Alan Hammond, Wates Jerry Taylor, M J Gleeson Group plc Peter Milburn, McDermott Bros Mathews Hockly, Donald Halstead Assocates Rod Webster, Concrete Innovation and Design Jonathon Gee, Taylor Woodrow Construction Patrick Fischer NRM Consultants Brian White NRM Consultants Simon Buck, Taylor Woodrow Construction Pat Masterson, Mitchellsons Mike O’Neil, Getjar
All interviews were carried out by telephone between February and April 2005.
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