Exploitation of moment redistribution in continuous FRP-strengthened concrete structures

This project addresses deficiencies in our fundamental understanding of how continuous reinforced concrete (RC) structures actually behave when they have been strengthened using fibre reinforced polymer (FRP) materials. Presently, we ignore any plasticity in such systems altogether, but this is potentially financially disastrous, overly conservative or, even worse, unsafe when considering how to best prolong the lifetime of existing RC structures. This proposal will deliver urgent structural-mechanics-based insight into how we might exploit redistribution of bending moments in FRP-strengthened continuous concrete structures such that our strengthening schemes are cost effective, safe and reliant on sound principles.

It is challenging and resource intensive to test large-scale continuous prototype structures. As a consequence, the large majority of research projects focus on small lab-scale, simply-supported structures. The problem is that almost all concrete structures are indeed continuous and it is difficult to then extrapolate the results to real-scale structures with complex geometries. We simply do not know whether our structures in reality are robust enough to deform, soften and redistribute moment. But we must know this if we are to exploit appropriately the expensive and resource-hungry materials which we use to strengthen such structures. The third edition of TR55 has just been published. The authors are uncomfortable with worldwide state-of-the-art knowledge in moment redistribution in FRP-strengthened concrete structures. Issues such as the predictable effects of FRP anchorage, the difference between redistribution into and out of strengthened zones, and limits on redistribution were all considered to represent significant gaps in our present understanding, and suitable caveats were employed. It is no exaggeration to suggest that our existing design guidelines for strengthening schemes are fundamentally flawed, worldwide, because we do not make allowances for how a structure will really behave throughout its life. We pretend in our guides that all is needed is elastic theory. This is false. Indeed research conducted by the investigators and others over the past few years has highlighted such shortcomings. This project will solve these problems by delivering a practical, mechanics-based, validated and comprehensive design tool for engineers to use with confidence. The impact that this research will have will be seen in the UK and across the world, such that further economic and carbon-saving opportunities associated with life extension of existing infrastructure may be achieved. Rational design guidelines will enable the construction industry to demonstrate quality and efficiency enhancements in the area of life-extension retrofit. Considering the size of market, such measures will lead to a more sustainable approach to construction.

Based on the direct results, design guidance for the holistic strengthening of common continuous RC structures will be formulated for incorporation into future editions of TR55, which is widely used and accepted by UK industry. As principal authors of the previous two editions of TR55, the investigators are uniquely positioned to ensure that this impact is seen through when the next edition is planned. The work will also be included in relevant Highways Agency standards i.e. BD 85/08 and inform other national and international guidelines. This can be guaranteed, as the Highways Agency are collaborators on this project.