Incorporation of shear-extension coupling in softened membrane model

Abstract

The Modified Compression Field Theory (MCFT) and the Softened Membrane Model (SMM) can be used to predict the non-linear behaviour of a wall-type Reinforced Concrete (RC) structural member under increasing in-plane shear stress due to lateral loads generated during an earthquake. The present study is based on the SMM. This model considers an orthotropic formulation of the in-plane strains to incorporate the Poisson’s effect in a membrane element. The formulation assumes that the reinforcement grid is symmetrical with respect to the principal axes of applied stresses. In the present study, a two-dimensional anisotropic formulation is used to extend the applicability of SMM to an element where the symmetry of reinforcement is not maintained. This formulation is a mechanics based approach to consider the shear strain generated due to the principal stresses in addition to the normal strains, which is referred to as the effect of shear-extension coupling. A model is proposed for the estimation of this shear strain based on test results from the literature. Next, the solution algorithm of SMM is generalised to incorporate the proposed model. The modified algorithm is corroborated based on the predictions of the behaviour of a series of RC panels tested under increasing in-plane shear stress.