Axial compressive performance of square concrete-encased concrete-filled double-skin steel tube stub columns

Abstract

This paper explored the axial compressive performance of the concrete-encased concrete-filled double-skin steel tube (CECFDST) column, which comprised inner concentric steel tubes, sandwiched concrete, reinforcement cage and outer concrete. The characteristic stirrup value (λv) and nominal confinement factor (ξ) were chosen as the primary variables to investigate the confinement effects of the CECFDST. Firstly, the failure mode, ultimate strength, axial displacement, and strain responses of 10 specimens were tested and analyzed. The results showed that the combined confinement effects on the behavior of CECFDST were significant. The nominal confinement factor would impact the constraint on the sandwiched concrete and the ultimate strength of the specimens. Increasing the characteristic stirrup value could improve the ductility of the specimens. Secondly, a finite element model (FEM) was established and validated using test results. The full-ranged analysis of the typical FEM was presented, and contact stresses between the steel tube and concrete were quantified. After that, a systematic parametric analysis was conducted to explore the impacts of the primary influential factors related to the confinement effects. At the peak load, the RC component reached the corresponding ultimate strength, and the strength of the CFDST component was in the rising stage. In addition, the influence of contact stress between the RC and CFDST components on the ultimate strength was negligible. The strength reduction index of the square CECFDST stub column was proposed according to the parametric study. Finally, based on the superposition principle, a simplified design method was derived to predict the ultimate strength for the square CECFDST stub column. The simplified design formulas produced satisfactory predictions based on the test and numerical results.