Kinematics-Based Modelling of Shear Critical Coupling Beams with and without FRP Strengthening

Short coupling beams with conventional orthogonal reinforcement are susceptible to shear failure along inclined cracks. Typically, the failure occurs along wide diagonal cracks and can limit the displacement capacity of the member, which in turn limits the seismic performance of the entire coupled-wall system. A strengthening solution to suppress diagonal tension failure in conventional coupling beams is represented by fibre-reinforced polymer (FRP) sheets that act as external stirrups. However, despite that FRP materials possess high tensile strength, the FRP sheets exhibit debonding and brittle rupture. Therefore, their contribution to the shear resistance cannot be evaluated accurately without an explicit consideration of the compatibility of deformations with the existing beam, while existing residual crack width poses an additional challenge when designing such a retrofitting solution. To address this research gap, this paper presents a kinematics-based model able to predict the complete shear response of orthogonally reinforced short coupling beams with and without FRP strengthening. The kinematic model is validated with tests from the literature and is used to study the effect of FRP sheets, including the effects of debonding and rupture of the strengthening sheets.