Analytical Study on the Buckling Behavior of Steel U-Shaped Girders

Before the concrete deck cures, torsional stiffness of the steel U-shaped girders is small and the top flanges are in compression. Because of it, the top flanges are susceptible to lateral torsional buckling. Therefore, several bracing is necessary to avoid buckling. But, after the composition, the deck provides continuous lateral bracing for the top flanges and also closes the cross section, the compressive stress of the top flanges is small and the concrete deck is in most compression. Thus, the lateral and torsional bracing placed in the U-shaped girders for construction loadings is no longer required after the concrete has hardened. So that, it is necessary to minimize. In this study, an analytical research was performed to study the buckling behavior of U-shaped girders under uniform moment conditions. Based on torsional bracing theory, a simplified U-shaped girder finite element model was first developed to isolate factors affecting buckling behavior. A more complete U-shaped girder finite element model was then created to verify the simple model and study the differences between rectangular and trapezoidal cross-sectional shapes. Finally, the analytical results were compared with design equations for I-shaped beams with continuous torsional bracing.