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Reverse-cyclic shear in reinforced concrete elements Gerin, Marc Claude

Abstract

Previously there were no simple, rational models for reinforced concrete elements subjected to seismic (reverse-cyclic) shear. Efforts to modify existing monotonic shear models resulted in complex formulations that use empirical rules to capture the complexities of the reverse-cyclic response as the fundamental mechanisms governing seismic shear in reinforced concrete were poorly understood. A primary objective of this thesis was to identify the fundamental mechanisms of seismic shear. A detailed study of experimental data from membrane elements subjected to reverse-cyclic shear identified the governing relationships between various stress and strain components. To capture these relationships in a rational model, deformations at the cracks need to be considered separately from deformations of concrete between cracks. This leads to a qualitative and quantitative understanding of the fundamental mechanisms: yielding in shear corresponds to yielding of the weak reinforcement; plastic strain in reinforcement determines the degree of pinching of the hysteresis loops; principal stress and principal strain angles deviate significantly during load reversal; apparent compression softening of concrete is a function of shear slip along cracks which increases significantly after yielding of reinforcement. In the model, shear slip along cracks is assumed to be a consequence of strain compatibility between reinforcement and concrete between cracks as they equilibrate the applied stresses. This allows the model to be formulated entirely in terms of average stresses and strains, avoiding the complexity of modelling local effects at cracks. The fundamental principles used in the proposed model provide a general framework which can be used to develop simplified models for analysis and design. As an example, a bi-linear envelope model and a reverse-cyclic model are presented. The yield point and failure point define the bi-linear envelope to the reverse-cyclic response. Together, the envelope model and the reverse-cyclic model can predict the complete cyclic shear response of reinforced concrete in a simple way.

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