Structural behaviour and strength design of stainless-clad bimetallic steel CHS gapped K-joints

This study presents a numerical investigation into the structural behaviour and strength prediction equations of stainless-clad (SC) bimetallic steel circular hollow section (CHS) gapped K-joints subjected to brace axial loading. A refined finite-element (FE) model was developed and validated against experimental results in terms of failure modes, load-deformation responses, and joint strengths. The model explicitly represented the stainless steel cladding and carbon steel substrate using a dual-layer configuration and incorporated both the cladding-substrate interfacial behaviour and the fracture of the constituent metals. Based on the validated FE model, a parametric study comprising 75 FE models was conducted to quantify the effects of geometric parameters, material properties, and interfacial characteristics on joint behaviour. The results showed that the cladding-substrate interface in the chord at the tension brace intersection maintained effective stress transfer, with no evidence of premature debonding prior to the attainment of the ultimate brace tensile resistance. The chord diameter-to-thickness ratio 2 γ , brace-to-chord diameter ratio β , gap-to-chord thickness ratio g / t 0 , and the corresponding cladding ratio β sc significantly influenced the joint strength. By contrast, the brace-to-chord thickness ratio τ and interfacial properties satisfying the minimum standard interface strength had negligible influences. Existing design provisions in ANSI/AISC 360–22 and EN 1993–1–8 generally underestimated the resistance of SCCHS gapped K-joints. Based on the FE database, new mean strength equations were proposed for the SCCHS gapped K-joints governed by chord plastification under brace compression. The proposed equations provided accurate predictions, with a mean predicted-to-FE strength ratio of 1.01 and a coefficient of variation of 0.04.