Axial compression behaviour of circular and square UHPC-filled stainless steel tube columns

To improve the durability and mechanical behaviour, an ultra-high performance concrete (UHPC)-filled duplex stainless steel tube stub column is proposed in this study. To explore the axial compression performance of UHPC-filled duplex stainless steel tube (UFSST) stub columns, a total of 12 UFSST, 6 confined concrete-filled duplex stainless steel tube (CFSST) and 6 hollow duplex stainless steel tube (HSST) stub columns were sub-jected to axial compression. The experimental parameters included the section type, the tube thickness and the core concrete strength. For the UFSST stub columns, when the constraining index (& xi;) exceeds 0.82 and 1.52 for circular and square stub columns, respectively, the failure mode changes from shear-type failure to waist-drum failure. The concrete contribution rate (CCR) is positively correlated with the concrete strength and negatively correlated with the tube thickness, whereas the variation law for the strength index (SI) is the opposite. The circular UFSST stub columns have a higher CCR than the square columns. A test database, including UFSST and UHPC-filled steel tube (UFST) stub columns, was established to evaluate the applicability of existing design codes. Furthermore, a modified ultimate load prediction formula with higher accuracy is proposed and verified.