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Understanding the mechanism of restraint in edge restrained reinforced concrete walls

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Concrete is the most widely used material and is essential to the global programme of infrastructure updating (global estimate ~$100Tn including UK National infrastructure plan £400Bn Excessive cracking due to restraint is a widespread problem in the concrete construction industry leading to costly remedial measures and delays. For example, a recent project in England was delayed due to excessive cracking. Subsequent changes to limit the edge restraint of early thermal and shrinkage strain produced a real cost to the client of approximately £1.75M. There are many situations when cracking due to the restraint of imposed deformations (i.e. early thermal movement and shrinkage) may be difficult to avoid. In fact, cracking from the restraint of early thermal movements (often referred to as ‘non-structural’ cracking) is the most common form of restraint induced cracking. In design, cracking is managed by the provision of reinforcement intended to distribute internal strains in such a way as to control the cracking pattern and limit crack widths. Current UK design guidance on restraint induced cracking is encapsulated in EN1992 -3:2006 and CIRIA report C660 /766. The underlying design methodology in these documents has been used for over 30 years and is flawed. This is reflected in field observations identifying cracking patterns contrary to – and crack widths in excess of – those predicted by EN1992 -3:2006 (see Fig 1). It is apparent that such ‘non-compliance’ cases result from erroneous basic assumptions; in particular; the boundary (restraint) conditions play a more significant role in determining the crack pattern.

John is the Chair of Concrete Engineering and Structures in the School of Civil Engineering at the University of Leeds and Director of the Neville Centre of Excellence in Cement and Concrete Engineering. He was awarded his first degree, a BEng (Hons) in Civil and Structural Engineering from the University of Sheffield. He received his PhD from the University of Leeds. He has seven years industry experience in the field of Structural Engineering and still regularly acts as a consultant for industry. A Chartered member of The Institution of Structural Engineers, he is on several technical committees (i.e. Eurocodes, fib, RILEM ) in the European Union. His research interests include the serviceability performance of all types of reinforced concrete composites and the dynamic performance of reinforced concrete and masonry structures.

This talk is part of the Engineering Department Structures Research Seminars series.

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