Composite box girders integrating concrete webs (CWs) and corrugated steel webs (CSWs) constitute an innovative structural solution for long-span bridges. To investigate the spatial behavior of this complex system, a novel finite element (FE) model, termed the Spatial Grillage Model (SGM), was developed exclusively with beam elements. In the SGM, hybrid webs are discretized into cruciform grids to capture orthotropic stiffness, while concrete flanges are simulated as planar grillages interconnected with the web grids. Comparative validation against high-fidelity solid/shell FE models demonstrated the accuracy of the SGM, with discrepancies consistently below 5% under diverse loading conditions. Subsequently, the model was employed to analyze the structural behavior of a practical extradosed cable-stayed bridge, incorporating the construction process, live loads, and other relevant factors. The results indicate that CWs generally sustain a greater share of shear force compared with the CSWs, particularly within cable-stayed zones. When concrete creep effects are considered, shear forces redistribute among hybrid webs, leading to a substantial increase in the CSWs. Under eccentric live loads, the outer CSWs exhibit 25%-30% higher shear force than the inner ones. Concrete flanges demonstrate pronounced overall positive shear lag adjacent to the CWs, combined with localized negative shear lag at web locations. This study establishes an efficient computational framework and provides new insights into the behavior of hybrid-web girders.
