Seismic performance of reinforced concrete columns confined with two layers of stirrups

This paper presents an experimental study on seismic behavior of reinforced concrete columns confined with 2 layers of stirrups. Six specimens, namely, 3 square-section columns and 3 circular-section columns, were manufactured using 2 layers of high-strength stirrups. They were tested under cyclic lateral loading. The main parameters under investigation were the cross-section type and stirrup spacing. The seismic behavior of the test specimens was analyzed in terms of various factors: load-displacement relationship, strength and stiffness degradation, ductility, and dissipated energy. The test results indicate that in general, all tested specimens exhibited very ductile behavior and dissipated energy. They presented a flexural failure mode, and the strength and stiffness degradation of the postelastic stage was not obvious. The results also indicate that a DCS square-section column exhibited lower lateral displacement capacity than that of a companion DCC circular-section column with the same stirrup spacing. Furthermore, on the basis of principles of equilibrium and compatibility of strains as well as ACI code, we developed equations to estimate the seismic bending moment capacity, accounting for the confinement effect of 2 layers of high-strength stirrups. The calculated solutions were then compared with the test results, and the relationships were observed with reasonable accuracy for engineering applications.