OPTIMIZATION OF CABLE FORCES IN ROAD AND TRAIN CABLE-STAYED BRIDGES UNDER DEAD LOADS

Based on the classical Newton-Raphson Method, an iterative process for nonlinear computation is derived to find the optimal initial cable forces for long span road and train cable-stayed bridges. Only beam-column and large displacement effects are considered in the numerical calculation, but cable sag effect is ignored. Three calculation stages, three convergence criterions and one state function are proposed in the present. In the first stage, the minimum square sum of strain energy of main components in cable-stayed bridge final dead state without any post-tensioning cable forces is the objective function. The obtained cable forces are used in the second iterative stage, in which convergence criterion is based on adjusting cable force of each cable itself. While in the third stage, the convergence. criterion is based on adjusting cable forces to other cables. The state function is that the maximum cable stress should not exceed 40 percent of the design strength of steel cable. The optimum initial cable forces are obtained by minimizing the vertical displacement of girder. The validly of the optimum procedure suggested is illustrated by numerical results.