Numerical Investigation of Local Geometric Imperfections on the Seismic Behaviour of Thin-Walled Steel Hollow Piers

Steel hollow box piers are widely utilized in modern infrastructure owing to their high strength-to-mass ratio, torsional rigidity, and superior seismic resistance. However, despite these advantages, thin-walled steel sections are susceptible to local buckling under seismic excitation, resulting in notable reductions in strength and ductility when subjected to lateral cyclic loading. Initial geometric imperfections introduced during fabrication, welding, transportation, or assembly significantly affect this behaviour. This study presents a detailed numerical investigation on the influence of Local Geometric Imperfections on the lateral stability, deformation characteristics, and cyclic load-carrying capacity of steel hollow piers. Finite element analyses were conducted using ABAQUS, incorporating an elasto-plastic bilinear stress–strain model with combined hardening. LGI profiles derived from buckling mode shapes through eigen value analysis were introduced into the finite element model, which was subsequently subjected to cyclic lateral loading after the application of an initial axial load (𝑃/𝑃_𝑦). The results reveal that local geometric imperfections have a substantial impact on the seismic performance of steel hollow piers, particularly when located within the lower one-third of the pier height, where local buckling typically initiates. The reductions in maximum strength (𝐻_𝑚ax /𝐻_𝑦) and ductility (𝛿_𝑚ax/𝛿_𝑦) intensified with increasing slenderness ratio (𝜆) and axial load ratio (𝑃/𝑃_𝑦), reaching up to 17% in critical conditions. Moreover, limiting the local imperfection amplitude in the bottom one-third region to about 1% of the pier width was found to maintain strength reduction below 10%, ensuring acceptable seismic performance. These findings emphasize the necessity of explicitly accounting for local geometric imperfections in the seismic design and performance evaluation of steel hollow piers.