Determination of optimum post-tensioning cable forces of cable-stayed bridges

Modern cable-stayed bridges can be economically designed by applying optimum post-tensioning cable forces to achieve a minimum deflection and a uniform bending moment distribution in the bridge deck under the effect of dead loads. The determination of the optimum distribution of post-tensioning cable forces is an important task that affects the overall design of the bridge. In this study, a novel approach, combining finite element analysis, B-spline curves, and an optimization technique is presented to determine the optimum post-tensioning cable forces under dead load corresponding to the final configuration of the bridge. The new approach is based on using the B-spline curves to model the post-tensioning functions along the bridge. The Genetic Algorithm (GA), as a global search technique, is utilized to optimize shapes of post-tensioning functions to achieve minimum vertical deflections along the bridge deck. Optimizing shapes of post-tensioning functions instead of the cable forces decreases the number of the design variables. This reduction improves the convergence speed, the accuracy of final solutions, and the performance of the optimization technique. Another advantage of the proposed method is that it minimizes the vertical defection of the deck and the horizontal deflection of the pylon, simultaneously. The validity of this proposed method is checked by applying it to a bridge with geometry similar to an existing cable-stayed bridge.