Numerical modelling of CFRP-retrofitted RC exterior beam-column joints under cyclic loads

This paper presents the results of a study on the capability of nonlinear quasistatic finite element modelling in simulating the hysteretic behaviour of CFRP-retrofitted RC exterior beam-column joints under cyclic loads. In this study, several unstrengthened and CFRP-strengthened specimens tested by the first and third authors at the University of Queensland, Australia are modelled using ANSYS. Concrete in compression is defined by the modified Hognestead model and anisotropic multi-linear model is employed for modelling the stress strain relations in reinforcing bars while anisotropic plasticity is considered for the FRP composite. Both concrete and FRP are modelled using solid elements whereas space link elements are used for steel bars. Perfect bond between materials is assumed in this modelling as no considerable de-bonding occurred in the experiments. The specimens are then loaded using a step by step load increment procedure to simulate the cyclic loading regime employed in testing. In this analysis procedure, an automatically reforming stiffness matrix strategy is used in order to simulate the actual seismic performance of the RC concrete after cracking, steel yielding and concrete crashing during the push and pull loading cycles. The results show that the hysteresis simulation for both unstrengthened and FRP-strengthened specimens is satisfactory and therefore suggest that the numerical model can be used as an inexpensive tool in the design of FRP reinforcement levels to improve the hysteretic performance of RC beam-column joints under cyclic loads.