Evaluating the Shear Resistance of Deep Beams Loaded or Supported by Wide Elements

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/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 nonlinear finite element models (FEM). It is shown that, with appropriate simple modifications to account for the loading/support conditions and the dowel action of the longitudinal web reinforcement, the 2PKT captures well the shear strength of 10 tests specimens from the literature. In addition to similarly adequate shear strength predictions, the more complex FEM also captures the strain concentrations measured in the tests. It is recognized that FEM analyses and detailed experimental measurements need to be used to ultimately develop a rational approach for evaluating the stress concentrations for the needs of both kinematic and strut-and-tie modelling.