Lifetime Extension of Reinforced Concrete Slab-on-Beam Structures

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.

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.