Lifetime Extension of Reinforced Concrete Slab-on-Beam Structures

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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.