Design of hot-rolled CHS steel members by advanced inelastic analysis with CSM strain limits

Traditional steel frame design usually involves a structural analysis (i.e. first or second order elastic analysis) to determine design forces and moments. Subsequently, the members stability is assessed through individual member checks and a cross-section classification establishes the deformation capacity of the cross-sections. Beam finite element (FE) models are widely used for structural design because they are computationally efficient. However, their limitation is that they cannot capture local buckling. For this reason, an advanced inelastic analysis using beam FE models with the continuous strength method (CSM) has been developed for the design of steel structures (Fieber, Gardner & Macorini, 2020). To capture cross-section failure, the analysis requires the use of the CSM strain limits, which are applied along a characteristic length of the steel member to consider the beneficial effects from the local moment gradients. The present research carries out a second order inelastic analysis on hot-rolled circular hollow sections (CHS) steel members. The proposed design method is validated against the benchmark shell finite element models, which are deemed able to accurately capture the local buckling. Comparisons against the EN 1993-1-1(2005) design provisions are undertaken to demonstrate the advantage of using second order inelastic analysis in terms of the ultimate capacity. The proposed method has already been conducted on structural steel and stainless steel I-section and rectangular section members (Fieber, Gardner & Macorini, 2019a; Walport, Gardner & Nethercot, 2021). This research aims to fulfil the equivalent analysis on CHS members subjected to uniform bending and three-point bending. For the latter a thorough assessment is conducted to evaluate the most appropriate critical strain averaging length along the member.