Initial global imperfections of L-shaped double steel plate composite walls

Truss-stiffened double steel plate concrete composite walls (DSPCWs) are susceptible to global geometric imperfections during fabrication, transportation, and concrete casting. Existing studies often approximate these imperfections using a first-order elastic buckling mode, but this approach lacks validation against real measurement data, especially for irregular cross-sections. This study systematically investigates initial geometric imperfections in L-shaped and I-shaped DSPCWs using 3D laser scanning. Two macro-scale deformation indicators—centroidal-axis deflection and principal-axis rotation—are introduced to characterize global imperfections. By integrating finite element buckling analysis with numerical fitting, a multi-mode superposition method is proposed to represent measured imperfections more accurately. Key findings include: (1) Both L- and I-shaped walls exhibit coupled deflection–torsion deformations, with the torsional component being particularly significant—the torsion-to-deflection ratio of the I-shaped specimen reaches 2.506, underscoring the inadequacy of single-mode approximations; (2) The contribution of buckling modes to imperfections depends on limb-width ratios, with higher-order modes becoming more influential in walls with smaller ratios; (3) While multi-mode imperfections significantly influence stability strength, especially in walls with small limb-width ratios, they do not alter the global failure mode. The proposed multi-mode model offers a mechanically sound and metrologically validated approach for imperfection simulation in stability analysis of irregular DSPCWs.