Evaluation of The Optimum Pre-tensioning Forces and Construction Stage Analysis of Cable - Stayed Bridges

Abstract

This research is concerned with the study of the problems of the analysis and design of Cable-stayed bridges which are structural systems effectively composed of cables, main girders and towers. These types of bridge are highly indeterminate structures that require a highly complex degree of technology for analysis and design. Hence they demand sophisticated structural analysis and design techniques when compared with other types of conventional bridges. For cable-stayed bridges the cable forces are an important factor in the design and construction process. The cables being flexible supports require pre-tensioning. Since the response of the bridge is highly non-linear an optimization procedure is required to evaluate the pre-tensioning forces. The optimization method used to determine the cable forces is the unknown load factor method; The techniques and methods of erecting cable –stayed bridges are varied and numerous. The erection method not only affects the stresses in the structure during erection but may also have an effect on the final stresses of the complete structure. The required pretension forces in cable-stays and the corresponding structural configurations of the bridge at different erection stages have been examined and compared in detail. The objective of the construction stage simulation is to identify stresses and deformations of the concrete girder and towers, as well as the cable tension stress, to meet the design requirements. Because of the large deflections that occur in bridge during cantilever construction, construction stage analysis was performed for the cable stayed bridge. The finite element analysis program Midas Civil was used in the nonlinear analysis. In this study, TUTI BAHARI cable stayed bridge, under consideration for construction was evaluated, as a case study, determining the cable tension under the effect of Dead load (Self weight, additional loads), Initial pre- tensioning cable force, and live load (moving load) according to AASHTO 57 LRFD 2010, by considering the boundary conditions. Then, analysis of this bridge at different erection stages during construction was carried out using the backward construction process analysis. The stage by stage construction of the TUTI BAHARI cable stayed bridge was performed using Midas civil Software. The maximum cable forces were found to be within the allowable limits. Also, the stresses and displacements satisfied the requirements. The results obtained show that the method presented indeed leads to optimal structural performance for the cable stayed bridge in particular, and might be a useful reference for the design of other similar bridges.