Kinematics-Based Modelling of Short Coupling Beams Retrofitted with FRP Wraps

Abstract

Reinforced concrete short coupling beams are placed between shear walls to create a coupled-wall system. It provides very effective lateral bracing for buildings subjected to earthquakes or wind loading. This type of beams have commonly aspect ratios a/h smaller than 2.5 approximately. As a result, they are susceptible to brittle shear failures that need to be suppressed with dense transverse and diagonal reinforcement. To improve the shear behavior and suppress such failures in deficient existing coupling beams, it is now common to use fiber-reinforced polymers (FRP) which are wrapped around the section. The aim of this thesis is to propose an extension of an existing Two-Parameter Kinematic Theory (2KPT) developed by Mihaylov et al. (2015), which predicts the shear behaviour and deformations patterns of conventional reinforced concrete short coupling beams, to account for the effect of FRP wraps. To assist in the development of the model, data from tests of coupling beams strengthened with FRP wraps has been collected from the literature. The 2KPT for conventional RC coupling beams uses two degrees of freedom and is based on first principles: kinematics, equilibrium and constitutive relationships for the s of shear resistance. The model considers five components of shear resistance across the critical shear cracks: diagonal compression in the critical loading zones, aggregate interlock, tension in the stirrups, and dowel action of the longitudinal reinforcement. The kinematic model predictions (implemented in a Matlab code) are compared to 4 tests from the literature. It is shown that the model captures properly the shear behaviour for diagonal tension failure. Finally, to account for the shear contribution of FRP wraps, another component of shear resistance must be implemented in the kinematic model. Two approaches are studied depending on the failure mode of FRP wraps described in the literature review: rupture or debonding. To validate the extended kinematic model, a comparison with test results is performed. It is shown that the predicted shear strengths agree well with values found in the experimental studies.