Evaluation of the Optimum Pre-Tensioning Forces for Cable Stayed Bridges

Abstract

The Cable-stayed Bridge is one of the most modern bridges. The structural system of this type of bridge is effectively composed of cables, main girders and towers. Because of their complex structural system, Cable-stayed bridges are highly indeterminate structures that require a high degree of technology for analysis and design. Hence, they demand sophisticated structural techniques for analysis and design when compared with other types of conventional bridges. In such bridges the cables, being flexible supports, require pre-tensioning. These pre-tension forces are important factors in the design and construction process. Thus, the response of the bridge is highly non-linear and an optimization procedure is required to evaluate the pre-tensioning forces. In this study, the unknown load factor optimization method is the method used to determine the cable forces. The procedure is based on using finite element analysis programs. The cable tension of a cable stayed bridge is evaluated under the effect of Dead load (Self weight, additional loads), Initial pre- tension force in the cable, and live load (moving load) according to AASHTO LRFD 2010 and using MIDAS Civil computer program. TUTI BAHARI cable stayed bridge of semi-fan type arrangement is analyzed for static load as a case study. The unknown load factor optimization method is used to determine the cable pre–tension forces to achieve a perfectly safe and stable bridge. The maximum cable forces (6670 kN), as well as the stresses (372 N/mm2) and displacements at the top of tower (0.033308m), are found to be within the allowable limits. The results obtained illustrate that the unknown load factor optimization method leads to optimal structural performance for the cable stayed bridge. Hence it might be a useful tool for the analysis and design of such bridges.