Experimental and numerical study on the buckling behavior of UHPC columns confined by stainless steel tube

Following previous work on the axial compressive behavior of stainless steel tube confined ultra-high performance concrete (SSTCUHPC) stub columns, this study focuses on the buckling behavior of SSTCUHPC intermediate columns subjected to concentric and eccentric compressive loading. An experimental program containing six specimens with varying tube thickness and load eccentricity was initiated, and the mechanical performance was evaluated in terms of the load-deformation response, load-carrying capacity, damage evolution pattern and ductility index. To explore the complex interaction between stainless steel tube and UHPC core, the biaxial strain state of steel tube and steel-concrete contact stress were analyzed through experimental measurement and finite element analysis. To extend the buckling behavior of SSTCUHPC columns from small eccentricity to large eccentricity, parametric study was conducted covering wide spectrum of member slenderness ratio, load eccentricity, tube diameter to thickness ratio and material strength. Based on the experimental and numerical results, the design formulae were proposed to construct the axial force-bending moment (N-M) interaction diagram of SSTCUHPC columns, delivering enhanced accuracy relative to the existing design codes.