Evaluating the shear resistance of deep beams loaded or supported by wide elements

Abstract

Abstract It is common in concrete structures to encounter deep beams that are loaded or supported by wide elements such as shear walls in buildings and large piers in bridges. This type of boundary condition results in stress concentrations at the edges of the loading or supporting elements, and this in turn results in steep diagonal cracks and concentrated diagonal struts. In this study the shear strength of deep beams affected by stress concentrations is studied in detail with two methods: a two-parameter kinematic theory (2PKT) and a nonlinear finite element model (FEM) VecTor2, which is based on the Disturbed Stress Field Model and the Modified Compression Field Theory. It is shown that, with appropriate simple modifications to account for the loading or support conditions, as well as the dowel action of the longitudinal web reinforcement, the 2PKT captures well the shear strength of 10 test specimens from the literature. The average test-to-predicted ratio for the peak strength, as determined from the 2PKT, was 1.09 with a coefficient of variation of 8.69%. The average test-to-predicted ratio for the peak strength, as determined from the VecTor2 models, was 0.99 with a coefficient-of-variation of 5.27%. The VecTor2 models are also able to accurately capture the strain concentrations measured in the experiments. These FEM analyses and detailed experimental measurements assist in ultimately developing rational approaches, including kinematic and strut-and-tie methods, for evaluating deep beams with stress concentrations, as occurs in members with large loading or supporting elements.