Lifetime Extension of Reinforced Concrete Slab-on-Beam Structures

Lead Research Organisation: University of Cambridge
Department Name: Engineering

Abstract

The lifetime extension of existing highway and building reinforced concrete infrastructure is a priority in terms of economic prosperity and a more sustainable future. The ability to reduce disruption, and amortise the embodied energy and the environmental impact of construction over an extended period will lead to direct, tangible and significant savings in energy and resource consumption. As construction typically accounts for up to 10% of the UK's GDP, and half of UK construction activity is associated with refurbishment and repair, it is clear that there is substantial scope to implement efficient technological innovations in the construction sector. In the UK, a major challenge is that, not only is the average age of our infrastructure increasing, but also the loading requirements are becoming more demanding. So the national pool of structures requiring intervention due to deterioration, changes of use, and/or a lack of strength is growing. For reinforced concrete (RC) structures, fibre-reinforced polymer (FRP) materials have been used as additional reinforcement to increase, or reinstate, strength capacity. These materials have a high strength-weight ratio, are durable and easy to install. To date, carbon FRP resin bonded strengthening systems have been the most common. The market share of FRP-strengthening applications has resulted in a proliferation of usage across the industry, and indeed continues to grow year on year. However, the development of our understanding has not kept pace with the growth in applications. There are significant gaps in our knowledge when typical large bridge or building structures and practical strengthening configurations are considered. The shear strengthening of RC structures is a particular challenge due to accessibility issues, the brittle nature of shear failures and the complex mechanics of the behaviour. Initial design guidance has played an important role in establishing the basis for the use of FRP systems but this guidance has necessarily drawn upon the results of specific studies which often only encompass a subset of possible parameters and interactions e.g. small-scale rectangular beams. However, there is an increasing body of evidence that suggests that a number of aspects of the fundamental shear behaviour are not captured in existing guidance. Recent studies have highlighted apparent contradictions between the predicted and observed behaviour of FRP strengthened large scale structures and structures with complex geometries. In particular, work at Cambridge University and Bath University have shown that in T-beams, which are considered representative of slab-on-beam structures, the current guidance can be unconservative yet for large scale rectangular beams, overly conservative. These contradictions pose difficulties since large-scale, slab-on-beam structures constitute a large proportion of the infrastructure that surrounds us and represents a target area for the use of FRP strengthening for lifetime extension. In the current project, a comprehensive experimental and analytical programme will be undertaken to understand the fundamental mechanics of beams strengthened in shear using bonded carbon FRP fabric systems. The effect of size will be investigated by considering strengthened T-beams with scales ranging from 'laboratory' scales to realistically sized structures found in practice. These targeted studies will lead to improved design approaches which reflect a comprehensive understanding of the failure mechanisms and the interactions that depend on the geometry and size of the structure. The deliverables will have a significant and timely impact through the provision of practical, safe and durable technological advances to enable the upgrading of existing RC structures to meet the demands of the 21st century.

Planned Impact

Construction accounts for up to 10% of the UK's GDP and about half of all activity in the UK is within the refurbishment market in order to prolong the life of our existing infrastructure. These statistics demonstrate the extraordinary economic importance in ensuring that internationally-leading research underpins major UK building-retrofit and infrastructure life-extension initiatives. Without fundamental research in this field, the UK is in danger of neglecting intellectually one of the largest single-sector contributors to our wealth. The research proposed here represents fundamental research into lifetime extension. By extending the life of our existing RC infrastructure through relying on intelligent, cost-effective and durable structural retrofit capabilities, the construction industry will not needlessly demolish structures across the UK which are presently considered structurally deficient. This therefore has significant economic and sustainability impacts. The Pathways to Economic and Societal Impacts -Enhancing the research capacity, knowledge and skills of public and private sectors: Design guidance for the strengthening of the most common of all horizontal RC construction types, namely slab-on-beam structures, will be formulated for incorporation into future editions of TR55 and inform other national and international guidelines. The attached letters of support from our collaborators testify to the importance and practicality of this project. During the research project, the steering committee members will benefit directly from the results as they are produced. As the research is published in journals, on webpages, at conferences and in design guidelines, a wider set of beneficiaries will emerge including consultants, contractors, FRP manufacturers, clients and code writers. This audience will benefit from UK expertise being seen as internationally leading with the ensuing economic benefits that flow inwards from this standpoint. -Environmental sustainability, protection and impact: This work is unique in that it addresses limitations in our understanding of the shear behaviour of all slab-on-beam structures, such as those found in buildings, bridges and car parks. The robust experimental investigation in conjunction with targeted analytical studies will lead to a fundamental understanding of the strengthened behaviour and identify the most efficient methodologies to strengthen slab-on-beam or T-beam RC structures using FRP materials. The Pathways to Academic Impacts -Training highly skilled researchers Crucially, this project will lead to the education to doctoral level of two researchers in the FRP-strengthening field, a growing area of importance from financial and sustainability standpoints. - Worldwide academic advancement The success of this project will ensure that UK academia is seen as internationally leading in this crucial field. Dissemination routes will include activity of a high-level Steering Committee (which includes all investigators and collaborators on the project), publication in world class journals and seminal conference proceedings, conference presentations, updating of a webpage throughout the project, and involvement with learned societies i.e. NGCC, ICE, IStructE and The Concrete Society. Furthermore, the insight gained will be of significant benefit to a wide constituency of academic researchers across a number of disciplines including investigators working on shear in steel-reinforced concrete, fracture and non-linear material behaviour and analyses. -Improving teaching and learning In the longer run, undergraduate students of civil engineering across the UK and worldwide will be exposed to these research findings, thereby spreading the impact of the work to ensure a lasting legacy from which society at large ultimately benefits. The applicants will also highlight developments in these fields when teaching on outreach programmes for 6th form students.
 
Description The accurate assessment of existing structures relies on a good understanding of structural behaviour. Where behaviour is not well understood, assessors will have little option but to be duly conservative to reflect this underlying uncertainty. The cost of assessing and strengthening deficient bridges structures has been estimated as being in excess of £4 billion for the UK (Middleton 2004) and $140 billion for the US (American Association of State Highway Transportation Officials 2008).

In the UK, a major challenge is that, not only is the average age of our infrastructure increasing, but also the loading requirements are becoming more demanding. So the national pool of structures requiring intervention due to deterioration, changes of use, and/or a lack of strength is growing. For reinforced concrete (RC) structures, fibre-reinforced polymer (FRP) materials have been used as additional reinforcement to increase, or reinstate, strength capacity. These materials have a high strength-weight ratio, are durable and easy to install. To date, carbon FRP resin bonded strengthening systems have been the most common.

A key objective of the research was to investigate the effectiveness of externally bonded CFRP shear strengthening as a method for extending the design life of existing concrete structures. A substantial contribution to our understanding in this area has been made. In collaboration with the University of Bath, a comprehensive series of experimental T-beam specimens were designed to reflect existing slab-on-beam structures. Unstrengthened beams and beams strengthened in shear with carbon fibre reinforced polymer (CFRP) fabric were tested to determine how the ultimate strength of the beams might vary with beam size, and the strengthening efficiency of the CFRP reinforcement.

It was found that the variability in the behaviour of some concrete T-beams can be rather large making it difficult to ascertain the true underlying strength of a reinforced concrete beam. This has ramifications when isolating any enhancement due to the investigated CFRP strengthening method. A size effect of increasing shear stress capacity with decreasing beam size was observed for the CFRP wrapped beams and for some of the unstrengthened beams. A potential model for determining a sensible upper-limit on the strengthening potential available was also proposed.

A further outcome was the development of a new modified push-off approach to elucidate the force transfer on a plane subjected to combined tension and shear. Using this new approach it was demonstrated that the contributions of the concrete, internal steel and CFRP were activated at different stages of loading and were not additive. This has significant implications for the appropriate calculation of the strengthened capacity.
Exploitation Route The findings provide direction for future research in this area and an expanded experimental database for the benchmarking of improved computational and analytical models. We have also provided proposals that may be taken forward in the development improved design guidance for practitioners.
Sectors Construction,Transport
 
Description Emerging publications are providing insight into the shear performance of carbon fibre reinforced polymer (CFRP) U-wrap strengthening systems when applied to the webs of reinforced concrete T-beams with realistic sizes. This is expanding the knowledge base for clients, designers and asset managers seeking to use CFRP strengthening to extend the life of existing slab-on-beam structures.
First Year Of Impact 2016
Sector Construction,Transport
Impact Types Societal,Economic
 
Title Research Data Supporting "Experimental investigation of reinforced concrete T-beams strengthened in shear with externally bonded CFRP sheets" 
Description Experimental results supporting associated publication 
Type Of Material Database/Collection of data 
Year Produced 2016 
Provided To Others? Yes  
Impact It is too soon to evaluate impacts, but the repository records indicate that the data has been downloaded by 14 researchers to date. 
URL https://www.repository.cam.ac.uk/handle/1810/256354
 
Title Research data supporting "Modified Push-Off Testing of an Inclined Shear Plane in Reinforced Concrete Strengthened with CFRP Fabric" 
Description Experimental research data 
Type Of Material Database/Collection of data 
Year Produced 2015 
Provided To Others? Yes  
Impact None yet known 
URL http://www.repository.cam.ac.uk/handle/1810/249023
 
Description Arup 
Organisation Arup Group
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Private 
PI Contribution Knowledge transfer, delivery of research advances and sharing of research findings
Collaborator Contribution Membership of steering committee for EPSRC funded project, Lifetime Extension of Reinforced Concrete Slab-on-Beam Structures (EP/I018972/1).
Impact Knowledge transfer, incorporation of research findings into design guidance and Industry practice
Start Year 2011
 
Description Concrete repairs 
Organisation Concrete Repairs
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Private 
PI Contribution Knowledge transfer
Collaborator Contribution Membership of steering committee for EPSRC funded project, Lifetime Extension of Reinforced Concrete Slab-on-Beam Structures (EP/I018972/1).
Impact Knowledge transfer, incorporation of research findings into design guidance and Industry practice
Start Year 2011
 
Description Fyfe 
Organisation Fyfe Co
Country United States of America 
Sector Private 
PI Contribution Knowledge transfer
Collaborator Contribution Membership of steering committee for EPSRC funded project, Lifetime Extension of Reinforced Concrete Slab-on-Beam Structures (EP/I018972/1), technical advice regarding installation of CFRP sheets
Impact Knowledge transfer, incorporation of research findings into design guidance and Industry practice
Start Year 2011
 
Description Highways Agency 
Organisation Department of Transport
Department Highways Agency
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Public 
PI Contribution Knowledge transfer, delivery of research advances and sharing of research findings
Collaborator Contribution The Highways Agency have supported a number of funded EPSRC projects including (EP/K016148, GR/S55101/01, EP/I018972/1 and EP/J002887/1). This support has included technical guidance, access to data relating to reinforced concrete infrastructure, sharing of experience in managing the strategic road network in the UK and guidance regarding the main challenges faced on the network. This has ensured the long-term relevance of our research and extensive knowledge exchange.
Impact Knowledge transfer, revision of design guidance, formulation of research proposals for funding, improved understanding of reinforced concrete infrastructure assets
Start Year 2006
 
Description Knowledge exchange between the University of Cambridge and University of Bath 
Organisation University of Bath
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution The University of Cambridge is working with the University of Bath on a joint EPSRC research project to investigate the lifetime extension of existing reinforced concrete structures (EP/I018972/1). We are collaborating on an integrated programme of research between our two Universities.
Collaborator Contribution The University of Cambridge is working with the University of Bath on a joint EPSRC research project to investigate the lifetime extension of existing reinforced concrete structures (EP/I018972/1). We are collaborating on an integrated programme of research between our two Universities.
Impact Knowledge transfer, delivery of a complementary research agenda to inform stakeholders about inherent size effects in reinforced concrete and the effectiveness of CFRP strengthening to extend the lifetime of existing structures, research collaboration, student training, research dissemination
Start Year 2011
 
Description Mouchel 
Organisation Mouchel Group PLC
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Private 
PI Contribution Knowledge transfer, delivery of research advances and sharing of research findings
Collaborator Contribution Membership of steering committee for EPSRC funded project, Lifetime Extension of Reinforced Concrete Slab-on-Beam Structures (EP/I018972/1).
Impact Knowledge transfer, incorporation of research findings into design guidance and Industry practice
Start Year 2011
 
Description Parsons Brinckerhoff 
Organisation Parsons Brinckerhoff
Country United States of America 
Sector Private 
PI Contribution Knowledge transfer, delivery of research advances and sharing of research findings
Collaborator Contribution Chairing/membership of steering committees for a number of EPSRC funded grants, technical advice and support
Impact Knowledge transfer, incorporation of research findings into design guidance and Industry practice
Start Year 2010
 
Description The Concrete Society 
Organisation Concrete Society
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Charity/Non Profit 
PI Contribution Knowledge transfer, identification of areas where Concrete Society design guidance in TR55 needs improvement
Collaborator Contribution Knowledge transfer, dissemination
Impact Knowledge transfer, dissemination to Concrete Industry, revised design guidance
Start Year 2006
 
Description Tony Gee and Partners 
Organisation Tony Gee Consultants
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Private 
PI Contribution Knowledge transfer, delivery of research advances and sharing of research findings
Collaborator Contribution TGP have been active members of the Steering Committees for EPSRC funded projects and collaborated through the provision of technical advice and guidance and case studies.
Impact Knowledge transfer, integration of outputs into technical guidance
Start Year 2006
 
Description ACIC 2015 - Presentation by Rob Foster - An Experimental Investigation into the Effect of Externally Bonded CFRP Fabrics on the Shear Behaviour of Reinforced Concrete T-beams 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Conference presentation at ACIC - 2015 Conference. Presenting implications of this research to an international audience of academics and practitioners.
Year(s) Of Engagement Activity 2015
URL http://acic-conference.com/
 
Description Advanced Composites In Construction (ACIC) 2013 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Presentation of recent experimental research at ACIC 2013. Presentation to an audience of international academics and postgraduate students.

A US based professor commented that he had considered a similar approach but had not thought that it would be technically feasible in practice. Seeing that we had been successful in carrying out our experiments, he indicated that he may encourage his lab to attempt similar work.
Year(s) Of Engagement Activity 2013
URL http://www.acic-conference.com/
 
Description Cambridge University Science Festival - Pecha Kucha Challenge 2014 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? Yes
Geographic Reach Regional
Primary Audience Public/other audiences
Results and Impact Presentation conducted several times to new audiences, stimulated a great deal of discussion and interest in the practical nature of the problems that the research addresses.

People said that it had changed their view of what researchers do - i.e. this research addresses practical, relevant and comprehensible issues.
Year(s) Of Engagement Activity 2014
 
Description Composites In Construction Engineering (CICE) Conference 2014 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Presentation at CICE 2014 Conference. Presenting some of the implications of this research to an international audience of academics and practitioners.

The ideas presented prompted an Australia based researcher doing related work, to re-evaluate some of the fundamental assumptions upon which his work was based.
Year(s) Of Engagement Activity 2014
URL http://www.cice2014.ca/
 
Description Development of a Civil Engineering session at ECCM 17 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact The 17th European Conference on Composite Materials will take place in June 2016. This is the leading conference in Europe on Composite Materials. Together with Professor Ur Meier (chair) and Guijin Xian, Dr Lees is developing a session specifically related to Civil Engineering Applications. This will promote awareness of the latest research and usage in this important field.
Year(s) Of Engagement Activity 2016
URL http://www.eccm17.org/
 
Description Hosting of ACIC 2015 at the University of Cambridge - Dr Lees was chair of the International Scientific Committee 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact The ACIC conference series is a successful forum for the presentation of industry and academic research that forges networking opportunities, discussion and debate.
Year(s) Of Engagement Activity 2015
URL http://acic-conference.com/programme/
 
Description IStructE Young Researchers' Conference 2014 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Poster presentation at annual IStructE Young Researchers' Conference

Generated a range of questions from academics and practitioners. Led a number of practitioners to question their current design assumptions for FRP strengthening.
Year(s) Of Engagement Activity 2014
URL http://www.istructe.org/events-awards/conference-and-lectures/young-researchers-conference/winners-2...
 
Description Member of ACIC 2015 Panel (Rob Foster) tasked with leading discussion of opportunities and challenges for FRP strengthening applications 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Two prestigious panel discussions were an integral part of the ACIC 2015 and were very fruitful in reflecting upon/discussing the challenges faced with the use of FRPs in construction and future developments.
Year(s) Of Engagement Activity 2015
URL http://acic-conference.com/
 
Description Network Group for Composites in Construction Research Showcase 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact The event was held at the National Composites Centre to showcase research and development at a number of UK universities. This led to increased engagement and networking amongst participants. Dr Lees presented an overview of the latest findings from the University of Cambridge.
Year(s) Of Engagement Activity 2015
URL https://compositesuk.co.uk/events/ngcc-2015-agm
 
Description Ongoing involvement with the work of COST TU1207 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Dr Lees has been actively participating it the COST TU1207 work. This has included giving presentations, submitting short research contributions and chairing sessions.
Year(s) Of Engagement Activity 2015
URL http://tu1207.eu/
 
Description Presentation at the The Hong Kong University of Science and Technology - Lifetime Extension of Reinforced Concrete Infrastructure 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact An opportunity to share research findings and explore joint interests.
Year(s) Of Engagement Activity 2015
 
Description Structures Seminar - University of Cambridge 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Presentation of project findings to date and intended future work. Presented to a mixed group of resident and visiting academics and postgraduate students at the University of Cambridge.

Prompted a discussion questioning the currently assumed debonding mode of FRP reinforcement
Year(s) Of Engagement Activity 2014