Performance evaluation of steel hollow box piers under bidirectional lateral cyclic loading to enhance the existing seismic verification framework

This study comprehensively evaluates the lateral performance and behaviour of stiffened steel hollow box piers under axial and lateral cyclic bidirectional loading using Finite Element (FE) analysis to develop a reliable performance-based seismic verification framework. In the first phase of the analysis, various bidirectional lateral loading patterns are examined to identify the pier's worst inelastic behaviour regarding strength, ductility, energy absorption, and failure patterns. Among these loading patterns, it was found that the circular-shaped bidirectional lateral cyclic loading (BICI) yielded the worst inelastic behaviour of the pier. Then, in phase two, an extensive comparative parametric study was conducted between the BICI and unidirectional loading pattern to evaluate the significance of important design parameters on lateral performance. Results revealed that the width-to-thickness ratio (Rf), slenderness ratio (lambda) and axial load (P) showed significant influence under both the load patterns, whereas the modified stiffener's slenderness ratio (lambda ' ), and aspect ratio (alpha) showed more s significant influence only under the BICI load pattern. Subsequently, the existing formulae proposed by authors for predicting strength and ductility under unidirectional lateral loading were reviewed and modified to incorporate the bidirectional effect. Moreover, a novel set of formulae was proposed for the BICI load pattern. Finally, an enhanced performance-based seismic verification method was developed by examining the rela-tionship between the ductility factors of steel hollow piers under both BICI and unidirectional loading patterns. This method integrates the bidirectional effect into the existing unidirectional framework, enabling a comprehensive assessment of the piers' performance and enhancing seismic resilience.