Effect of cold bending on the structural behavior of steel bridge girders

Abstract

Point bending is often used for cambering and curving steel girders to large radii. In this method, a fabricated straight girder is bent about its weak axis by concentrated loads applied at the third points using hydraulic jacks to form a horizontally curved girder. The new geometric curved shape (parabolic shape) is developed by permanent residual deformations induced upon removing the loads. The purpose of this report is to determine stresses and deformations induced by point loads that simulate live load incorporating residual stresses built in the curved girder from cold bending. The curved shape of the steel girder analyzed was based on a full-scale test girder for which analytical and experimental results are available. Results were used to develop a numerical finite element model based on the deformed shape of the steel girder using SAP2000 which was then loaded about its strong axis simulating typical bridge live loads. Results from the finite element model were then used to show the impact of the horizontal curvature on the steel girder structural behavior, mainly deformations, stresses and strains. Based on a quantitative comparison of the load carrying of the cold bent girder with an identical straight girder, it was found that cold bending decreases the capacity of the steel section bent about its strong axis. Recommendations for future full-scale test and more detailed finite element analyses are finally provided.