Cyclic Load Test and Shear Strength Degradation Model for Columns with Limited Ductility Tie Details

For existing buildings in low and moderate seismic zones, various nonseismic ties not conforming to special seismic requirements have been used in columns for convenience in reinforcing bar placement. This study investigates the failure mode and deformation capacity of such columns. First, cyclic loading tests of 12 columns with different section geometries, tie details, and axial load ratios are performed. The test results show that postyield shear failure occurs in the columns with nonseismic ties as the inelastic deformation increases, and the ductility of the columns is affected by the spacings and anchorage details of ties. Then, to estimate the deformation capacity of the columns, a postyield shear strength degradation model depending on displacement ductility and tie details is proposed. The proposed method is applied to 80 existing column specimens with a wide range of design parameters. The postyield strength degradation and deformation capacity predicted by the proposed method agree well with the test results.