Seismic Performance of FRP-Confined Circular RC Columns

To investigate the seismic performance of FRP-confined circular RC columns with high axial compression ratio, six third-scaled 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. The maximum axial compression ratio (P/f'(c)A(g)) was 0.65 and the shear span ratio was 3.5. Test results demonstrated marked improvement in the ductility and energy dissipation of the columns due to CFRP wrapping at plastic hinge region. The study also found that the contribution of hoops to confining effect should not be ignored under the condition of high axial compression ratio. To accurately simulate the seismic performance and obtain the hysteretic shear-deformation curves of FRP-confined columns, a nonlinear analytical procedure was developed using fiber model based on OpenSees (Open System for Earthquake Engineering Simulation). A stress-strain model which considers the confining effects of both the internal hoops and external CFRP jacketing was used. The analytical results indicated that inclusion of the both confining effects results in better simulation of the test results from this and other studies. But, if the axial compression ratio is less than 0.3, the analytical results are not affected even considering the contributions of hoops. The lateral loading capacity of columns begins to decrease when the axial compression ratio exceeds 0.6 and when the length of wrapped CFRP at the plastic hinge region exceeds 1.2D (D is the diameter of columns), the seismic performance could be improved to a level equivalent to fully wrapped columns.