Cyclic behavior of reinforced concrete columns confined with two layers of stirrups

Abstract

Reinforced concrete (RC) columns confined with two layers of stirrups (TS) are a novel type of RC column, which consist of two layers of stirrups and longitudinal reinforcement. In this paper, the seismic behavior of TS‐RC columns is investigated through a series of experiments, in which six one‐half‐scale column specimens were subjected to axial forces and lateral cyclic loading. For comparison, an additional six specimens are included in Li et al. The design and details of all specimens correspond to the same, except for the axial compressive load ratio. The test variables include the axial compressive load ratio applied to the columns, the cross‐section type, and the spacing of transverse reinforcement. All specimens failed in a flexural mode, showing stable hysteresis loops. Because of the confinement of the two layers of stirrups, the TS‐RC column specimens exhibit excellent ductility and dissipated energy even at the axial load ratio of 0.4. The lateral force–drift relationships, backbone curves, energy dissipation, displacement ductility, stiffness degradation, final damage observed, and damage index are presented and discussed.