PARAMETRIC STUDY OF THE EFFECT OF CROSS-FRAMES ON THE BEHAVIOUR OF COMPOSITE STEEL-CONCRETE GIRDERS CURVED IN PLAN AND CONSTRUCTED WITH SHORING

Abstract

The use of cross frames in bridge is provided to act together with the longitudinal girders to form a system that behaves as a unit. In horizontally curved bridges, the interaction of bending and torsion causes these components to become major load-carrying elements (primary members) and not secondary members as that in straight girders. This study is concerned with parametric study of the effect of cross frames on the behaviour of composite steel-concrete girders curved in plan using finite element technique. Shoring is assumed to be used during construction and both dead and live loads according to ECP are taken into consideration in the analysis. The concrete deck slab and both steel webs and flanges are modeled using shell elements. However, both studs and cross frames are modeled using beam elements. The study includes not only the displacements but also the tangential stresses through the inner edge, middle and outer edge of the tension flange along the span of the critical outside girder. Based on the numerical results it is shown that slenderness ratio of cross frames, cross frame spacing, radius of curvature, span length and flange width have greatest effect on the warping-to-bending stress ratio. It is shown that equations which can be used for composite girders subjected to noncomposite dead loads and recommended by other authors may give inaccurate results for curved composite systems constructed with shoring. Also, they do not take the slenderness ratio of cross frames into consideration. Two equations are proposed for the preliminary design of cross frame spacing and warping-to-bending stress ratio for curved composite systems constructed with shoring. The accuracy of the results using the new equations is checked for various variables. From equations, it is recommended that the maximum slenderness ratio of cross frames should not exceed 140. Also, the distance between cross frames should be ranged from 3 to 5 m.