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UBC Theses and Dissertations

Shear strength of structural concrete members using a uniform shear element approach Esfandiari, Afshin


The simplest shear problem involves a two-dimensional rectangular element with uniformly distributed reinforcement parallel to the element sides, and subjected to uniform normal stresses and shear stress. Such a uniform shear element will have uniform average stresses in reinforcement and concrete. The simplest model for elements subjected to shear force and bending moment that leads to code provisions uses one uniform shear element. Shear force is assumed to be resisted by a central portion of the cross-section acting as a uniform shear element, while bending moment is assumed to be resisted by the flexural tension reinforcement and concrete compression zone at the cross-section ends. In this thesis, the shear strength of bridge girders and squat shear walls are evaluated using a uniform shear element approach. Current code shear design provisions for beams are necessarily simplified procedures that are generally conservative. While the extra costs are small for new design, it may lead to unnecessary load restrictions on bridges or unnecessary retrofitting when used for shear strength evaluation. A new shear strength evaluation procedure for structural concrete girders is proposed. The procedure accounts for the influence of more parameters and provides more insight into the failure mode than code design methods. To verify the procedure, predicted trends are compared with Modified Compression Field theory (MCFT) for uniform shear elements, and Response-2000 for beam elements subjected to combined shear and bending moment. Shear strength predictions are also compared with results from strength tests on reinforced and prestressed concrete beams, together with predictions from current code shear design provisions. The current Canadian building code CSA A23.3 2004 contains new provisions for the seismic design of squat walls that were developed using a uniform shear element approach. These new code provisions are rigorously evaluated for the first time in this study. A new method to account for the flexure-shear interaction at the base of squat shear walls is proposed as well as refinements to the 2004 CSA A23.3 shear strength provisions for squat shear walls. These are verified by comparing the predicted trends with the predictions of MCFT-based nonlinear finite element program VecTor 2.

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