Implications of the embedded through-section technique for improving the resilience and sustainability of existing reinforced concrete infrastructure

Lead Research Organisation: University of Birmingham
Department Name: Civil Engineering

Abstract

The strength enhancement of structurally deficient concrete infrastructure is an application of considerable economic and strategic importance, particularly in the case of bridges. In the United Kingdom alone, it has been estimated that there are approximately 10,000 bridges on the strategic road network and 150,000 bridges on local roads, of which a considerable number need strengthening or replacement. The estimated cost of assessing and strengthening such structures is in excess of £4 billion. Other countries, e.g. the United States, are faced with the same challenge, so emphasising the global significance of the issue.

During the past two decades, fibre reinforced polymer (FRP) reinforcement has gained acceptance as strengthening systems for existing reinforced concrete (RC) structures. The use of FRP strengthening systems is advantageous due to their excellent mechanical and durability properties. Extensive research has resulted in approved FRP flexural strengthening methods for RC structures. In contrast, FRP shear strengthening of RC structures is not yet fully understood.

To date, FRP shear strengthening systems for existing RC structures have primarily been applied as externally bonded (EB) or near-surface mounted (NSM) reinforcement. In order to utilise these systems, both sides of individual beam webs must be accessible. However, it is difficult to provide such an access in several practical situations. Moreover, laborious and time-consuming surface or groove preparation is required to ensure adequate bond between the concrete and the EB or NSM systems respectively. Furthermore, unless proper anchorage is provided, both the EB and NSM systems debond from the concrete at a stress level of 20% to 30% of the ultimate strength of the FRP reinforcement.

The embedded through-section (ETS) technique is a recently developed shear strengthening method for existing RC structures. In this method, vertical holes are drilled upwards from the soffit in the shear spns of existing RC beams. High viscosity epoxy resin is then injected into the drilled holes and FRP bars are embedded into place. The ETS technique provides higher strengthening effectiveness than that provided by the EB or NSM systems. Other advantages of the ETS technique include higher protection against fire and vandalism, less epoxy consumption, and no need for access to the top slab or time-consuming surface preparation.

Research investigating the shear behaviour of RC beams strengthened with ETS FRP bars has been limited. All beams tested to date had effective depths of less than 400 mm. This is unrepresentative of several practical situations where RC bridge beams have significantly higher effective depths. Moreover, the effect of other parameters that influence the structural behaviour of the strengthened beams, such as the shear span to effective depth (a/d) ratio and FRP bar type, has not been sufficiently investigated. A proper understanding of the effect of the above-mentioned parameters on the strengthened behaviour is vital for the best utilisation of the ETS technique.

This project will investigate, experimentally and numerically, the effect of a/d and FRP bar type on the behaviour of realistically sized RC beams strengthened in shear with ETS FRP bars. The combination of experiments and numerical techniques will ensure an integrated modelling approach that will inevitably lead to a better understanding of the strengthened behaviour. The experimental results will be used to check the accuracy of current design standards and improve their predictions where needed. The insight gained from this project will enable the utilisation of FRP reinforcement for improving the sustainability and resilience of existing RC infrastructure. The concepts encompassed in this work will underpin our understanding of the behaviour of FRP-strengthened concrete structures and thus have parallel implications in a variety of other areas of concrete construction.

Planned Impact

The primary output of this research will be a better understanding of the behaviour of concrete structures strengthened in shear with embedded through-section (ETS) fibre reinforced polymer (FRP) reinforcement. This will enable the utilisation of such a promising technique for improving the sustainability and resilience of existing concrete infrastructure.

The proposal, through the steering group, brings together stakeholders from a broad range of disciplines (The Highways Agency, academia, and industry). The proposal's deliverables will aid policy makers, planners and other high-level decision makers in ensuring more resilient and sustainable concrete infrastructure exist; and ultimately benefit the societies that they serve, the UK economy, and international research agendas. The beneficiaries of the project include:

1. The strengthening and repair sector of the UK Civil Engineering industry: this project will provide consultants, designers, and contractors with new knowledge and methods that will give them a market advantage in international terms.

2. The international academic community, which will benefit from both the experimental and numerical outputs of this research as they will provide insight into the behaviour of concrete structures strengthened with ETS FRP reinforcement.

3. FRP manufacturers who have already developed interest in the ETS technique (see for example the statement of support from Fyfe Europe) as it is generally more practical than other shear strengthening methods.

4. The Post-doctoral Research Associate and their future employer, who will gain invaluable experience from research in this growing field.

5. Infrastructure owners and/or managers, who will be able to make direct use of the research findings to deliver more resilient and sustainable infrastructure, not to mention the long-term environmental benefits resulting from reducing the carbon emissions associated with building new concrete infrastructure.

Finally, this research will also benefit a sector of the public not traditionally targeted by University research, i.e., school children. This will be achieved through four visits to both primary and secondary schools within the West Midlands and through a poster campaign which will be developed from a competition involving such schools. It is envisaged that working closely with such schools will encourage pupils to consider pursing scientific careers and take an interest in challenges facing the UK transport infrastructure. In addition to the school visits and competition, invited lectures and public seminars will be organised to highlight the research innovation, and to present the findings of the project.

Publications

10 25 50
 
Description The experimental programme critically examined the shear behaviour of full-scale unstrengthened as well as deep embedment (DE) shear strengthened reinforced concrete (RC) T-beams. A three-dimensional nonlinear finite element (FE) model for concrete members strengthened in shear with DE fibre-reinforced polymer (FRP) bars was developed and validated. The FE model was used to carry out a wide-ranging parametric study investigating the influence of DE FRP bar orientation, concrete compressive strength, shear span to effective depth ratio, effective beam depth, and interaction between DE FRP bars and internal steel shear reinforcement on the predicted behaviour of RC beams strengthened in shear using DE FRP bars. The accuracy of the Concrete Society TR55 design model for DE shear strengthened concrete members was evaluated using both experimental and numerical results. The main findings of this research are summarised below.

* The DE FRP bars enhanced the shear force capacity of deep and slender RC beams by up to 38% and 96%, respectively.

* The DE FRP bars did not affect beam stiffness up to the formation of inclined cracks. Subsequently, the strengthened beams had a slightly stiffer response as the DE FRP bars resisted inclined crack opening and consequently controlled deflection.

* The comparison of FE and TR55 predictions with experimental results demonstrates that the FE model is a significant improvement over TR55 design model. The FE model had a mean predicted/experimental shear strength enhancement ratio of 1.08 (standard deviation of 0.25) whereas TR55 overestimated the shear strength enhancement with a mean predicted/experimental ratio of 1.57 (standard deviation of 0.54).

* The use of 45° inclined DE FRP bars, compared with vertical DE FRP bars, enhanced the predicted shear force capacity for beams with and without steel stirrups.

* The predicted shear strength enhancement was positively influenced by the increase in concrete compressive strength but decreased with increasing the a/d ratio and steel stirrup to-DE FRP bar ratio.

* The increase in effective beam depth did not have a substantial influence on the percentage shear strength enhancement offered by the DE FRP bars.

* Compared to the FE results, TR55 design model overestimated the influence of effective beam depth on the shear strength enhancement, especially for the case of strengthened beams with shear links. TR55 does not consider the effect of DE FRP bar orientation, concrete compressive strength, shear span to effective depth ratio and interaction between steel stirrups and DE FRP bars.

The results confirm the effectiveness of the DE technique and show that it overcomes many of the shortcomings of other strengthening techniques.
Exploitation Route The findings will be useful in understanding and predicting the structural behaviour of strengthened members. The FE model may be used for carrying out further parametric studies. This will be of significant interest to both researchers and practicing engineers.

It is crucial to provide the future generation of engineers with the appropriate knowledge to improve the sustainability and resilience of existing concrete infrastructure. To this end, the research findings can be incorporated into appropriate Civil/Structural Engineering undergraduate and/or postgraduate programmes. This will be of significant interest to academics in the UK and elsewhere.
Sectors Construction,Education

 
Description The findings are being regularly communicated to Highways England. It is envisaged that the research findings will help Highways England as well as the strengthening and repair sector of the UK Civil Engineering industry utilise a more efficient shear strengthening technique for existing concrete infrastructure. This project has benefited school children, a sector of the public not traditionally targeted by university research. Visits have been organised for primary schools within the West Midlands. The aim was to generate interest among school pupils in civil engineering. Many activities including a presentation on bridges, Q&A session and a bridge building exercise were carried out. It is envisaged that such activities will encourage pupils to consider pursing scientific careers and take an interest in challenges facing the UK transport infrastructure. The Research Fellow (RF) has been appointed as a Lecturer at Liverpool John Moores University. The expertise they gained in the area of concrete shear strengthening will prove invaluable for their future research.
First Year Of Impact 2015
Sector Construction,Education
Impact Types Societal,Economic

 
Description UGC - UKIERI Call for Research Proposals 2017-18
Amount £50,000 (GBP)
Funding ID UGC -UKIERI -2017/18-017 
Organisation UK-India Education and Research Initiative (UKIERI) 
Sector Academic/University
Country United Kingdom
Start 04/2018 
End 03/2020
 
Title Finite element model 
Description A three-dimensional non-linear finite element (FE) model for reinforced concrete (RC) beams strengthened in shear with embedded fibre-reinforced polymer (FRP) bars was developed. Representative constitutive models were used for the concrete, steel reinforcement, FRP reinforcement and FRP-to-concrete interface. To validate the results, the FE model was benchmarked against experimental results from the published literature for three series of tested RC beams. The validated FE model was used to investigate the effect of the following parameters on the performance of FRP-strengthened RC beams: concrete strength, shear span to effective depth ratio, beam depth, FRP bar inclination and interaction between steel shear reinforcement and embedded FRP bars. The details of the FE model and the results of the parametric study were disseminated via a journal article (http://dx.doi.org/10.1016/j.compstruct.2016.04.017). 
Type Of Material Computer model/algorithm 
Year Produced 2016 
Provided To Others? Yes  
Impact It is envisaged that the FE model will have notable impact in a number of areas. In particular, the utilisation of non-corrosive FRP reinforcement for improving the sustainability and resilience of existing RC infrastructure will result in social and economic benefits. To this end, the model has helped with elucidating the effect of several parameters (concrete strength, shear span to effective depth ratio, beam depth, FRP bar inclination and interaction between steel shear reinforcement and embedded FRP bars) on the behaviour of FRP-strengthened beams. Moreover, the FE model helped minimise the high costs associated with the production of large-scale specimens which often restricts the conduct of parametric studies. 
 
Title Research data supporting "Finite element parametric study of reinforced concrete beams shear-strengthened with embedded FRP bars" 
Description This dataset presents results of finite element (FE) parametric studies carried out on reinforced concrete beams strengthened in shear with deep embedment (DE) fibre reinforced polymer (FRP) bars. Full details can be found at https://doi.org/10.1016/j.compstruct.2016.04.017. The parametric studies showed that the FE-predicted shear strength enhancement was positively influenced by the use of inclined DE FRP bars and the increase in concrete compressive strength but decreased with the increase in shear span-to-effective depth ratio and internal steel stirrup-to-DE FRP bar ratio. The predicted percentage of shear strength enhancement was not significantly influenced by size effect. 
Type Of Material Database/Collection of data 
Year Produced 2016 
Provided To Others? Yes  
Impact This research has resulted in further funding (UGC -UKIERI -2017/18-017). Moreover, it is envisaged that the database will be of significant interest to the international community involved in strengthening and repair of concrete infrastructure, in a number of universities around the world, and in the research and development divisions of leading national and/or international engineering consultancy firms. 
URL https://doi.org/10.25500/eData.bham.00000158
 
Title Slender beam database 
Description This high quality dataset provides new insight into the utilisation of advanced composite materials for improving the sustainability and resilience of existing reinforced concrete infrastructure. The dataset includes detailed information on the load carrying capacity, deflection behaviour and strain in the reinforcement of both unstrengthened and shear-strengthened full scale reinforced concrete beams. 
Type Of Material Database/Collection of data 
Year Produced 2015 
Provided To Others? Yes  
Impact It is envisaged that the database will be of significant interest to the international community involved in strengthening and repair of concrete infrastructure, in a number of universities around the world, and in the research and development divisions of leading national and/or international engineering consultancy firms. 
URL https://doi.org/10.25500/edata.bham.00000305
 
Description Collaboration with Professor Amar Nayak 
Organisation Veer Surendra Sai University of Technology
PI Contribution I worked together with colleagues at Veer Surendra Sai University of Technology to develop a bid for the 2017 round of UKIERI research grants. My contributions involved co-authoring the research proposal (both technical and non-technical parts) and reviewing a presentation delivered for a panel of judges.
Collaborator Contribution My partners contributions included co-authoring the research proposal as well as preparing and delivering a presentation for a panel of judges.
Impact The research work is yet to be carried out. There are no current outputs or outcomes.
Start Year 2017
 
Description Conference (Nanjing, China) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact The research findings were presented at the 12th International Symposium on Fiber Reinforced Polymers for Reinforced Concrete Structures (FRPRCS-12) and the 5th Asia-Pacific Conference on Fiber Reinforced Polymers in Structures (APFIS-2015) Joint Conference which took place in December 2015 in Nanjing, China. The research findings generated interest among members of the international research community including Professor Yu Zheng (Dongguan University of Technology, China). Research collaboration is being established with Professor Zheng who visited the University of Birmingham on 9 March 2016 to give a presentation and discuss future plans.
Year(s) Of Engagement Activity 2015
 
Description Conference (Sheffield, UK) 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other audiences
Results and Impact The research findings were presented at the 8th Advanced Composites in Construction (ACIC 2017) Conference which took place in September 2017 in Sheffield, UK. The research findings generated interest among members of the international research community.
Year(s) Of Engagement Activity 2017
URL https://acic-conference.com/
 
Description Presentations (HA, peers, researchers and the general public) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Other audiences
Results and Impact This activity involved presenting the research findings to a representative of the Highways Agency, other project collaborators, academics and postgraduate researchers at Birmingham University and the general public. The attendees were in the range of 11 to 15 persons. The questions and discussions following the presentation reflected the attendees' interest and engagement.

The engagement activity took place very recently hence it is difficult to measure its full impact at this stage.
Year(s) Of Engagement Activity 2014
 
Description Research Visit to Shanghai Jiao Tong University (China) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact This activity involved engaging MSc and PhD students as well as staff at Shanghai Jiao Tong University (SJTU) with the findings of the research. Research collaboration is being established with colleagues at SJTU as a result of this visit. It has been agreed that such collaboration will include, where appropriate, joint funding applications, staff and student exchanges and access to facilities.
Year(s) Of Engagement Activity 2015
 
Description School Visit (Ark Tindal Primary School) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact Pupils from Ark Tindal Primary School (Tindal Street, Birmingham, B12 9QS) attended the University of Birmingham for a school visit. A presentation was given on bridge types and the pupils were given the opportunity to witness construction of a scaled bridge. The aim was to raise the pupils' interest in civil engineering. The pupils were very interested in bridges and much liked the bridge construction exercise.
Year(s) Of Engagement Activity 2016
 
Description School Visit (SS John and Monica's Catholic Primary School) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact A visit was made in December 2015 to SS John and Monica's Catholic Primary School (Chantry Road, Moseley, B13 8DW). The aim of the visit was to generate interest among school pupils in civil engineering. A presentation on bridge types was delivered followed by a quiz. Amazon vouchers (£5 each - 10 in total) were given as prizes to those students who answered the quiz questions correctly. The received feedback indicates that the pupils enjoyed the presentation.
Year(s) Of Engagement Activity 2015