Structural performance of ultra-high strength concrete filled high strength steel tube stub columns under eccentric loading

This paper experimentally and numerically investigates the structural behavior and resistances of ultra-high strength concrete filled high strength steel tube (CuFShT) stub columns subjected to combined compression and bending loads. Initially, twenty CuFShT stub column specimens with a steel ratio ranging 0.14 to 0.38 were tested under various eccentric loads, constructed from steel tubes with a nominal yield stress ranging from 813 to 1153 MPa, concrete with a compressive strength of 146.7 MPa. Experimental investigation includes the examinations of failure mode, failure load and the evolution of the neutral axis for the stub column specimens under combined loading. Additionally, the development and distribution of longitudinal strains, as well as the ratio of circumferential to longitudinal strains in the steel tubes, were discussed. Following the experimental results, a numerical modeling program was implemented. Finite element models were developed and validated against test results, then used for cross-sectional stress analysis to reveal the eccentric compression mechanism of CuFShT stub columns. Finally, test data were used to assess the applicability of design rules outlined in EN 1994-1-1 (EC4), AISC 360-16, AIJ-2008, and T/CECS 987–2021 to CuFShT stub columns under combined loading. The assessment findings suggest that EN 1994-1-1 (EC4) provides accurate predictions without accounting for the second-order effect, while AIJ-2008 yields precise predictions when considering this effect. Notably, there is an enhancement in predictive accuracy observed for each simplified N-M curve, particularly notable in the case of the curve delineated by T/CECS 987–2021, following adjustments to the pure axial compressive strength and pure bending capacity. •20 circular ultra-high strength CFST stub columns were tested under combined loads.•Steel ratio and eccentricity were included as parameters and discussed.•Finite Element models were built and utilized for a detailed mechanistic analysis.•The applicability of current standards for CFST to the tested columns was assessed.•N-M curves were adjusted for application to ultra-high strength CFST columns.