Local buckling behavior of stainless-clad bimetallic steel circular hollow section stub columns

Stainless-clad (SC) bimetallic steel, as an advanced high-performance structural material, has seen growing adoption in bridge engineering and architectural applications. Current research efforts, however, have predominantly centered on characterizing its fundamental material properties rather than evaluating structural member performance. Particularly for welded circular hollow section (CHS) structural members under axial compression, those with elevated diameter-to-thickness ratios present critical stability challenges where localized buckling phenomena may significantly compromise load-bearing efficiency. This necessitates comprehensive investigation into their local stability mechanisms and subsequent development of optimized design methodologies. To this end, this paper investigates the local buckling behavior and design of CHS stub columns made of SC bimetallic steel through experimental and numerical studies. A total of eight stub column specimens were fabricated from hot-rolled bonded SC bimetallic steel plates with various thicknesses. The dimensions and geometrical imperfections of the specimens were precisely measured using a non-contact 3D laser scanner. Two measurement methods were employed to process the scanned data, providing a more accurate analysis of imperfections. Finite-element (FE) models incorporating geometric imperfections derived from the 3D-scanned data were developed and validated against both the test results presented herein and independent results from other researchers. Comprehensive parametric studies were conducted using the verified FE models, considering various clad ratios, diameter-to-thickness ratios and steel grades. The applicability of current codified design methods to the SC bimetallic steel CHS stub columns was evaluated by comparing the standards with the numerical results. Based on the parametric studies and evaluation of existing design methods, a diameter-to-thickness ratio limit and effective cross-section formulae were proposed. The design methods presented in this paper offer improved efficiency and consistency, making them suitable for future applications of SC bimetallic steel structures.