Behaviors of Square Thin-Walled Steel Tubed RC Columns under Direct Axial Compression on RC Core

Abstract

This paper presents an experimental study on the behaviors and modes of failure of square thin-walled steel tubed RC columns subjected to concentrically axial load applied directly to the RC core. The main variables were the compressive strengths of the concrete, the wall thicknesses of the steel tube and the tie spacing. The dimensions of the column specimens were 150mm wide and 750mm long. A total of 36 specimens, including 24 tubed RC specimens and 12 RC specimens, were tested. It was found that the tubed RC columns have a linear elastic behavior up to approximately 60-70% of their axial compressive capacity. Then, the behavior of the columns is gradually nonlinear and can be classified into 3 types: strain hardening, elastic-perfectly plastic and strain-softening. The mode of failure of the columns is in progressive mode with very large axial deformability. The wall thickness of the steel tube and the compressive strength of concrete are the major factors, influencing the behaviors, axial compressive capacity and modes of failure of the columns. No full interaction and confinement between the RC core and the steel tube were observed and the EC4 design equations for the composite column significantly overestimate the axial compressive capacity of the tubed RC column.