Assessment of shear lag effects on cable-stayed composite bridges under ultimate and service conditions

The growing complexity and scale of modern bridges increasingly subject decks to combined axial forces and bending moments, creating critical design challenges. For steel-concrete composite cable-stayed bridges, achieving long spans requires careful consideration of these forces, particularly axial forces from cable inclination, alongside bending effects to ensure structural rigidity. Current design codes, such as Eurocode, inadequately address this interaction, omitting axial forces and associated shear lag effects while focusing exclusively on bending. This gap often forces designers to rely on computationally intensive finite element (FE) models (e.g., shell/brick elements) for accurate analysis. To address this limitation, this study proposes a novel methodology for the design and verification of twin-girder composite decks under combined axial and bending actions at both Ultimate (ULS) and Serviceability (SLS) Limit States. The paper incorporates the influence of steel-concrete connector deformability and introduces a novel non-dimensional Aspect Ratio parameter, enabling generalization across different cross-sectional geometries. The developed simplified approach is derived from a parametric FE study of generic twin-girder decks, enabling efficient stress distribution assessments by integrating results from universal beam models. The proposed procedure is more accurate than current regulations, as Eurocode provisions overestimate concrete stress under compression and combined loading compared to the reference shell model. Demonstrated through an application to an existing cable-stayed bridge, the methodology offers a practical alternative to complex linear and non-linear FE analyses and is readily adaptable to similar composite deck systems.