Seismic performance of CFRP-confined circular high-strength concrete columns with high axial compression ratio

This paper presents an experimental investigation on the seismic performance of circular high-strength concrete (HSC) columns confined with carbon fiber-reinforced polymer (CFRP) composites. A total of eleven 1/2 scale columns were constructed of which nine were confined with CFRP wraps at potential plastic hinge regions. All columns were tested under combined high axial compression load and cyclic lateral displacement excursions. The primary variables of the tests were the axial compression load level, concrete strength, and the extent of the CFRP wrapping at the plastic hinge region. In order to evaluate the residual seismic capacity of CFRP-confined columns, three of the confined specimens were initially loaded to induce damage. The load was then removed after which the same columns were loaded to failure. The failure modes, hysteretic responses, energy dissipation and stiffness degradation characteristics, and the equivalent viscous damping ratios of the tested columns were then presented and interpreted. The test results showed that CFRP wraps applied at potential hinge regions resulted in significantly improved ductility and energy dissipation capacities of the columns even when tested under a high axial compression ratio. The plastic deformation capacity of the CFRP-confined columns was observed to decrease with an increase of axial compression ratio though. In addition, pre-damaged CFRP-confined columns may have insufficient residual seismic capacity due to the damage and failure in the unconfined regions under high axial compression load levels. Finally, empirical models of the degradation of effective and unloading stiffness are provided based on the test results.