Axial slenderness limits for concrete-filled stainless-clad bimetallic steel square stub columns

Concrete-filled stainless-clad bimetallic steel tube (CFSCBST) members offer superior corrosion resistance and cost-effectiveness compared with conventional concrete-filled steel tubular (CFST) members, making them highly promising for engineering applications. A critical design consideration for these members is the axial slenderness limit, defined as the width-to-thickness threshold below which a plate element can fully develop its yield strength. However, no studies have addressed the determination of axial slenderness limits for this novel composite member. To fill this gap, this study conducts the first systematic investigation of the axial slenderness limits of CFSCBST square stub columns, whereas previous research focused on conventional stainless-steel or mild-steel CFST members. Building upon the authors' previous work, this research extends the application of stainless-clad bimetallic steel tubes in CFST systems through advanced finite element (FE) modelling. The columns examined in this study consist of a mild steel substrate clad with either austenitic or duplex stainless steel. For comparison, hollow columns were also investigated. A validated nonlinear FE model was employed to perform an extensive parametric study involving 920 simulations, considering key variables such as stainless steel type, cladding ratio, tube thickness, and concrete strength. The results indicated that increasing the clad ratio led to a reduction in the axial slenderness limit. The numerical results were then compared against existing design standards, revealing that current provisions are generally unconservative. The resulting numerical database enabled the development of new unified design equations for predicting the axial slenderness limits, expressed as functions of both the clad ratio and the substrate-to-cladding yield strength ratio, a framework not available in previous CFST research.