Experimental and numerical investigations on the behavior of a novel multilayer spirals reinforced square composite column under axial load

Abstract

Existing studies have shown that under severe ground motion the column-end damage can be significant in rectangular (including square) RC columns due to the arch effect and the consequent insufficient lateral confinement by tie reinforcement. Improving the non-uniform confinement of tie reinforcement is necessary to enhance ductility and load bearing capacity of rectangular RC column. Against this background, the author proposed a novel multilayer spirals reinforced square composite column (MLSRSCC) consisting of one layer of outer square stirrup and two layers of spirals aligned with the centroid of the specimen section. Five MLSRSCC specimens and one conventional single spiral reinforced composite column (SSRSCC) for comparison were tested. The test results showed that the ultimate load and deformation capacity of MLSRSCC were greatly enhanced even with a slightly less amount of steel compared to reference SSRSCC. Moreover, a finite-element (FE) model is established to investigate the confinement mechanisms of MLSRSCC in relation to the distributions of axial stress, confining stress and principal stress ratio. An extensive parametric study containing 1,024 FE results is carried out to explore the effects of various key design parameters on the improvement of ultimate bearing load of MLSRSCC. Furthermore, a calculation method for the ultimate bearing capacity of MLSRSCC was subsequently developed, by which higher accuracy was obtained compared with those calculated from existing design specification.