Coupled bending-shear-torsion behaviors of U-shaped composite girders with corrugated steel webs

U-shaped composite girders with corrugated steel webs (U-CSW) exhibit considerable promise for widespread implementation in urban rail transit viaducts, owing to their superior prestressing efficiency, excellent shear resistance and effective mitigation of cracking. During service, eccentric loading subjects U-CSW members to coupled bending–shear–torsion interactions, yet the underlying interaction mechanisms remain insufficiently understood. This study systematically investigates the mechanical behavior and failure mechanisms of U-CSW under combined bending–shear–torsion loading, and proposes a predictive approach for determining the ultimate bearing capacity associated with distinct failure modes. Finite element models of U-CSW are developed and validated against available experimental data, followed by comprehensive parametric analyses incorporating key parameters such as the bending-to-torsion ratio, web thickness-to-height ratio, span-to-height ratio, width-to-height ratio, and boundary conditions. The findings indicate that the dominant failure mode of U-CSW shifts from flexural failure to bottom slab shear failure as the bending-to-torsion ratio decreases. Simply supported U-CSW with shorter spans are particularly susceptible to bottom slab shear failure, whereas smaller web thickness-to-height ratios (e.g., 1:250, 1:167, 1:147) promote shear buckling failure in the corrugated steel plates. Through theoretical derivation and numerical simulations, interaction relationships among bending, shear, and torsion are established. These research outcomes offer valuable theoretical support and practical design guidance for the application of U-CSW under eccentric loading scenarios.