Seismic Performance of Shear-Controlled CFRP-Strengthened High-Strength Concrete Square Columns under Simulated Seismic Load

Abstract

Ten high-strength shear-controlled square columns are constructed and seven of them are strengthened with carbon fiber–reinforced polymer (CFRP) straps. These columns are then tested under simulated seismic load at the standard axial compression ratio range from .119 to .714. The main variables in this study include the value of axial compression ratio, CFRP layout, number of CFRP sheets, and predamaged condition. The failure modes, lateral load-displacement curves, and several important seismic parameters are analyzed. The test results show that the seismic behavior of the columns is obviously increased by wrapping CFRP sheets around the columns even at an ultrahigh axial compression ratio, which confirms the validity of loosening the allowable axial compression ratio for strengthened columns. Based on the study of ductility and ultimate lateral capacity, it is suggested that the CFRP straps are more suitable to strengthen the columns than is the fully wrapped CFRP layout at the same volumetric ratio of CFRP and confined concrete. Finally, an effective stiffness degradation model and an ultimate shear capacity model are proposed. It is evident that satisfactory accuracy and good agreement between the theoretical predictions and the test data from this research and other relevant literature are achieved for the two proposed models.