Shear behavior of square ultra-high performance concrete-filled high-strength steel tube members

High-strength steel and ultra-high-performance concrete (UHPC) can increase structural resistance and reduce material consumption efficiently. However, current design specifications do not permit the use of them in concrete-filled steel tube members due to the lack of research. To address it, this paper experimentally investigates the shear behavior of square ultra-high performance concrete-filled high-strength steel tube (referred to as CuFTh hereafter) members. A total of 20 CuFTh specimens were tested, considering the effects of the span-todepth ratio, width-to-thickness ratio of the steel tube, yield stress of steel, and fiber volume content of UHPC. The test results showed that: (i) the failure mode was governed by the shear span-to-depth ratio (a/H), including shear failure (a/H = 0.2 or 0.5) and combined shear-flexural failure (a/H = 0.8 or 1.0); (ii) the shear strength increased with decreasing shear span-to-depth ratio and the width-to-thickness ratio of the steel tube; (iii) increasing the yield stress of steel and fiber volume content of UHPC improved the shear strength. The applicability of current specifications for estimating the shear strength of square CuFTh members was evaluated. It was shown that CECS 28 (CECS 2012) had the most reasonable estimation.