Axial Compressive Behavior of Square CFST Columns through Direct Measurement of Load Components

Abstract

A number of experimental and analytical studies have been conducted on the axial compressive behavior of square concrete-filled steel tubular (CFST) columns, but there still exist several controversies on this issue because the loads sustained by the concrete infill and the steel tube cannot be accurately measured in a conventional axial loading test. In this study, an innovative test method was devised to directly measure the load components of square CFST columns under axial compression. Five specimens with different width-to-thickness ratios were fabricated and tested. The factors that may affect the compressive strength of concrete in square CFST columns were investigated, and it was found that the difference between the compressive strength of concrete in CFST columns and the corresponding cylinder strength was small and within the commonly accepted ranges. The measured compressive strengths of the steel tubes were compared to the available empirical formulas. It was determined that the ultimate strength of the steel tube can be reasonably estimated, but more research is needed to fully understand the post-local-buckling behavior of the steel tube and the effects of various factors. Design recommendations were proposed for the axial load capacity of square CFST columns. The existing stress-strain models for the concrete infill and the steel tube were assessed using the measured stress-strain relationships, and more credible stress-strain models were developed.