Mechanical behavior of square composite columns with four interlocking spirals under compression

Abstract

The compressive capacity of square composite columns confined by four interlocking spirals and outer square stirrups are experimentally and analytically investigated. The proposed innovative transverse reinforcement configuration used for square columns can improve the non-uniform confinement of outer square stirrup and thus enhance the confinement effect for the core concrete. Eight square composite columns for axial compression and ten eccentric compression specimens were tested. The study demonstrated that the newly developed interlocking multi-spiral reinforced square composite column (IMSRSCC) with the same volumetric confinement ratio outperformed conventional single-spiral reinforced square composite columns (SSRSCC) both in terms of ultimate load, bending stiffness and ductility under eccentric compression, while in axial compression test, the proposed new square composite column obtained similar ultimate load and deformation capacity. In addition, a comprehensive parametric study is presented using finite element analysis to explore the confinement working mechanism and key design parameters of IMSRSCC. Moreover, an analytical model is developed considering the composite confinement due to outer square stirrups and interlocking spirals and the formulas for calculating the bearing capacity of IMSRSCC are proposed. The analytical results are found consistent with experimental and numerical data.