Optimization of cable pre-tensioning force in cable-stayed bridges by simplifying the structural model with a case study of Lali bridge

Cable-stayed bridges are bridges in which the deck is connected directly to the towers by diagonal cables. These bridges are mainly known by the length of the middle span, which often falls between the span lengths of suspension bridges and bridges without cables. They are also known for their light weight, beauty, and elegance. Cable-stayed bridges are highly indeterminate and are considered significant structures, which makes their optimization a major and costly challenge for designers. The deflection and distribution of the bending moment on the deck and towers depend on the pre-tensioning force applied to the cables, making the calculation of tensile force in cables one of the most critical optimization parameters. Typically, cable pre-tensioning force is calculated through an optimization process that requires extensive analysis, which in turn requires a significant amount of time and computational power. This research aims to reduce the optimization process time by improving the analysis speed. Instead of analyzing a complete three-dimensional model of the structure, this research uses a separate two-dimensional model of the deck and tower without considering the cables. The Lali cable-stayed bridge located in Khuzestan, Iran, serves as the case study for this research. Results show that calculating tensile forces using this method induces an insignificant error compared to optimization using a complete model. The proposed model eliminates the repetitive process of updating the stiffness matrix, significantly reducing the time required to calculate cable pre-tensioning forces during the optimization process. Additionally, the proposed model produces negligible errors both in the optimization process and in the calculation of tensile forces in the cables compared to results obtained through three-dimensional modeling.