Experimental and Theoretical Studies of Hexagonal UHPC-Filled Double-Skin Steel Tubular Columns under Combined Compression and Bending

Abstract

In this study, the authors conducted five low-cycle reciprocating loading tests on hexagonal ultrahigh-performance concrete (UHPC)-filled steel tubular (UHPCFST) and UHPC-filled double-skin steel tubular (UHPCFDST) columns. The main parameters investigated in this research program are the hollow ratio, axial load ratio, and column type. Based on the experimental results, the failure modes, lateral load-story drift ratio curves, lateral load-strain curves, ultimate lateral load and corresponding base moment, and ultimate story drift ratios are obtained and discussed. The results show that hexagonal UHPCFST and UHPCFDST satisfy the requirements of ductility in GB 50936-2014. Moreover, the authors developed a fiber beam model (FBM) to predict the hysteretic behavior and strength under combined compression and bending. Subsequently, a parametric study was conducted, based on the validated FBM, to investigate the effect of material strength, outer steel tube thickness, and hollow ratio on the strength of hexagonal columns under combined loadings. Comparisons of the predictions from T/CESS 7, AISC 360, and EC4 and numerical results suggest the necessity of a design method with higher accuracy. Finally, the authors proposed a calculation formula for hexagonal UHPCFST and UHPCFDST columns, which effectively predicts the strength of these two types of columns under combined compression and bending.