Seismic performance and post-peak behaviour of reinforced concrete beam-column joints

Reinforced concrete beam-column joints are known as the most critical regions in frame structures since the joints are subjected to both vertical and horizontal shear stresses with magnitude many times higher than those in the adjacent members. The structural behaviour of beam-column joints is very complex due to the interactions between shear, bonding and confining actions. Without proper design considerations, premature failure of beam-column joints may happen, resulting in collapse of the whole structure. The traditional seismic resistant design philosophy states that the joints should remain elastic throughout the loading history; however, joint inelasticity is usually unavoidable under seismic excitation.;In this thesis, an investigation of seismic behaviour and post-peak performance of reinforced concrete exterior beam-column joints is presented. Extensive computational simulations are carried out to study the structural performance of beam-column joints with various design parameters under both reversed cyclic loading and seismic excitations. The parameters of interest include the joint shear reinforcement, column axial load level, beam-to-column depth ratio, column arrangement and beam width. The influences of each parameter to the overall behaviour of specimens and the shear strength of joint are identified clearly based on the simulation results. Furthermore, it can be assumed that the shear resisting mechanism of exterior beam-column joints is composed of three concrete struts resulting from three different actions: the arching action due to the compression forces in beam and columns, bond interaction resulted from the longitudinal bars and confining action provided by the joint horizontal stirrups.;The post-peak behaviour and shear strength degradation of beam-column joints are studied in detail. The trends of shear strength degradation with inter-storey drift ratio and the influences of each parameter are discussed. The post-peak performance of reinforced concrete beam-column joints is evaluated using the shear ductility index which is proposed for quantifying the post-peak behaviour of shear-dominant members.;A theoretical model is developed to model the reinforced concrete elements with bond interactions. This composite model is derived based on the theory of micromechanics to determine the homogenised properties and mechanical responses of the composite element at macroscopic level. The Mori-Tanaka homogenisation scheme is adopted to determine the averaging properties of reinforced concrete composite material. Concrete is modelled by anisotropic damage plasticity model. Steel reinforcement and bond-slippage are modelled by introducing an additional internal variable, which represents the slip strain of reinforcing bars, in the classical plasticity model. The composite model is used to model the exterior beam-column joints. The simulation results show reasonable agreement between the proposed composite model and conventional component-based finite element model.