Shear Design and Evaluation of Concrete Structures

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The objectives of this long term research program are to understand how cracked reinforced concrete transmits shear and to use this understanding to develop simple, general, rational and accurate procedures for the shear design of new reinforced concrete structures and for the evaluation of existing structures. Shear failures can cause concrete structures to collapse without warning and hence, are of critical concern for public safety. In the last five years, major progress has been made in improving the quality of shear design provisions which will greatly reduce the chance of catastrophic shear failures for new concrete structures. However, we also now know that many existing concrete structures are deficient in shear capacity. Such structures are particular prone to collapse during earthquakes. The major objective of the next five years is to develop the tools to decide which structures must be repaired and to provide practical procedures to do so. This will be done by conducting experiments on intensively instrumented elements of reinforced concrete subjected to loadings which simulate the actual conditions encountered in practice. Recently developed techniques will be improved to enable the formation, opening, propagation and sliding of critical cracks to be recorded so that the characteristic crack patterns of impending shear collapse can be accurately defined. The influence of cycles of load on crack propagation and bond deterioration for members containing reinforcement details representative of those in existing structures will be studied and the effects of restraint of shrinkage and thermal movements, which occur in actual structures, will be simulated. The experimental studies will be supplemented with extensive non-linear 3D finite element analyses. Finally simple analytical models suitable for use by practicing engineers to evaluate existing structures for shear safety will be developed. The research will be conducted by graduate students who will develop a deep understanding of the shear behaviour of reinforced concrete structures under extreme loadings. After such research they will be equipped to contribute to the safety assessment of Canada's critical infrastructure.