Multi-index distortion control of steel-concrete composite tub-girders considering interior cross-frame deformation

Abstract Excessive distortion of the cross section may occur and induce significant distortional warping stresses when the steel-concrete composite trapezoidal box girders are subjected to eccentric loads. The most effective solution to control distortion is to install sufficient internal cross-frames. However, current design methods generally omit the deformation of the cross-frames. In addition, most design guidelines limit the distortion control index to a specific value, which may result in quite conservative design. Therefore, this paper aims to propose a method for distortion control of steel-concrete composite box-girders with deformable interior cross-frames considering various distortion control indices and limit values. In accordance with current studies and design specifications, three distortion control indices are selected for investigation in this research. Equations for the distortion of composite trapezoidal box girders with cantilever overhangs are first derived based on the energy-variation method. Accordingly, an efficient modeling strategy using the Beams on Elastic Foundation (BEF) analogy is developed. Subsequently, extensive parametric analyses are conducted to obtain simplified design formulas of the control indices, which well fit the numerical results. Therefore, the effective design methods for the cross-frames to control distortion are proposed, where various indices and shear deformation of inner cross-frames are considered. Analyses of bridge design examples demonstrate that the proposed method is both efficient and universally applicable to provide appropriate number and size of cross-frames to control distortion of composite tub-girders in practical design.