Experiment and finite element analysis of the seismic behavior of CFRP-confined RC circular columns with high axial compression ratio

To investigate the seismic behavior of FRP-confined circular RC columns with high axial compression ratio, six columns confined with Carbon Fiber-Reinforced Polymer (CFRP) at plastic hinge region and two control columns were tested under constant axial load and cyclic lateral force. Test results demonstrated marked improvement in the ductility and energy dissipation of the columns due to CFRP wrapping in the plastic hinge region and the contribution of hoops to the confining effect should not be ignored under the condition of high axial compression ratio. A nonlinear analytical procedure was developed using fiber model method based on OpenSees (Open System for Earthquake Engineering Simulation). The simulation results agree well with the experimental results for axial compression ratios less than 0.45. Inclusion of the confining effects of both the hoops and CFRP results in better simulation of the test results if the axial compression ratio exceeds 0.45. Finally, influences of axial compression ratio and length of CFRP in the plastic hinge region on the seismic performance of FRP-confined columns were analyzed. The results indicate that the lateral loading capacity of columns begins to decrease when axial compression ratio exceeds 0.6. If the length of wrapped CFRP in the plastic hinge region exceeds 1.2 times the column diameter, the performance could be equivalent to that with fully wrapped columns.