Behavior and design of concrete-filled narrow rectangular steel tubular (CFNRST) stub columns under axial compression

Abstract

In recent years, the concrete-filled narrow rectangular steel tube (CFNRST) has drawn much attention for practical engineering applications. Compared with the commonly used concrete-filled rectangular steel tube (CFRST), the cross-sectional aspect ratio (the ratio between widths of wider and narrower sides of the steel tube) of CFNRST is larger and exceeds 2.0, which is considered as the upper limit of aspect ratios for ordinary CFRSTs reported in the literature. In this paper, experimental results are presented involving 24 specimens of CFNRST stub columns subjected to axial compression. The axial resistant behavior of CFNRST columns is investigated concerning the effects of key parameters including: (a) cross-sectional aspect ratio, (b) confining factor, and (c) width-to-thickness ratio of wider side of steel tube. By analyzing the observed and measured test results, the failure modes, ductility performance, strength enhancement effect and residual resistance of the specimens are discussed in detail. Moreover, 173 test results of CFRST stub columns under axial compression reported in the literature are collected and compared with the test results of this study; hence, the effect of extremely large cross-sectional aspect ratio on the behavior of CFRST columns is presented. Finally, typical equations specified in design codes are examined to reveal their validity in predicting the ultimate axial resistance of both CFNRSTs and ordinary CFRSTs. This study can provide valuable information for practical designs of CFNRST stub columns under axial compression.