Seismic performance of reinforced concrete columns retrofitted by various methods

In this study, various retrofit methods for concrete columns with non-seismic reinforcement details were developed and investigated: steel jacketing, carbon fiber reinforced polymer (CFRP) wrapping, concrete jacketing with non-shrinkage mortar, and new concrete jacketing with amorphous metallic fiber (AMF) reinforced concrete. Eleven half-scale reinforced concrete columns including two different control specimens, which were designed to fail in shear or flexure-shear, and nine retrofitted specimens were fabricated and tested under cyclic loading, simulating earthquake loading combined with axial loading. Two different retrofit strategies were applied to the control specimens: partial retrofit in the plastic hinge zone, mainly aiming at increasing deformability, and full retrofit in the entire range of columns, aiming at increasing both shear strength and deformability. The seismic capacity of the test specimens was analyzed in terms of various factors: load-drift relationship, dissipated energy, damping ratio, effective stiffness, and ductility. The test results showed that the retrofitted specimens presented ductile failure mode and enhancement in the dissipated energy and the damping ratio, but the effect differed for each retrofit method. Furthermore, based on the test results, the variables (or conditions) used to define the modeling parameters of the nonlinear analysis specified in ASCE 41-13 were modified in order to use the parameters of nonlinear analysis after retrofitting the columns. In addition, the nonlinear load-deformation curves established based on the modified conditions were compared with the test results.