EFFECT OF BOTTOM LATERAL BRACINGS ON THE BEHAVIOUR OF COMPOSITE STEEL-CONCRETE BRIDGES CURVED IN PLAN

Abstract

The present study is concerned with the effect of t he presence of bottom lateral bracing systems on the behaviour of horizontally curved composite bridges. A careful numerical study is car ried out by using the finite element method in the elastic range of loadi ng. Shoring is assumed to be used during construction and the system is pr ovided with cross frames. The present study includes tangential stres ses, warping-tobending stress ratio, vertical displacements and ra dial displacements through the inner edge, middle and outer edge of th e bottom flange along the span of the critical outside girder. Also, the maximum axial forces in bracing members for the most effective type are stu died. Based on the numerical results, it is shown that the presence of bottom lateral bracings in curved composite bridge results in significant r eduction of not only bending and warping stresses but also vertical and radial displacements as well as torsional angle of bottom flanges. The r eduction in stresses of curved bridges due to the presence of lateral braci ngs may exceed 25% of the stresses obtained using cross frames only and t he reduction in stresses is more pronounced for small radii of curvatures. S o, lateral bracings can be used effectively in strengthening of existing br idges or to decrease the cross sectional area of new curved composite bridge s. Also, the results show that the most effective pattern of lateral bra cings is that which consists of X-bracings in all bays. However, the pa ttern of bracing which consists of X-bracings in end panels only give the greatest stresses and displacements of all of the studied reinforcement p atterns. Furthermore, for high degree of curvature, the stresses in braci ng members should be checked since they are subjected to large stresses due to curvature in addition to those due to wind loads.