Multi-parameters Optimization-Design Research Of Extradosed Bridges

During the design of Extradosed Bridge, depth of girders, cross-sectional areas of cables, prestressing forces in cables and prestressing tendons arrangement were key parameters. As those parameters were interactional and intercoupling to each other in the highly indeterminate structure, designers had to design and do structure analysis repeatedly to meet the stress and deformation requirement of the structure, which was a cumbersome and time-consuming work. Still, using this single parameter analysis method, a reasonable mixed-configuration of cross-sectional size of girders and pylons, cable stays and prestressing tendons couldn’t be approached, making the final design a feasible one, but not a best optimized one.Presently, many optimization design researches have got some achievements on cable prestressing forces optimization, but few of them referred to the hybrid optimization included girder and pylon cross-sectional size, cable areas and prestessing tendon configuration, which limited the optimization effectiveness,Some researches were did in this thesis, aiming at solving problems existing in the design and optimization of Extradosed Bridges, which were as followed:1. A mixed-paraments optimization design method was proposed in this thesis, of which the total cost of concrete, cable tendons and prestressing tendons were set for target, and cross-section sizes of girder and pylon, cross-sectional areas and corresponding fixed-end prestressing stresses of cables and cross-sectional areas prestressing tendons were set for optimization variables, and various kinds of stress and deflection control were set for constraint conditions.2. The optimization algorithm NLPQLP, a fortran implementation of a sequential quadratic programming algorithm with Distributed and Non-Monotone Line Search, adopted in this thesis was introduced and corroborated. A structure analysis program code was reprogramed, adding an interface adapting to the optimization calculation program and, at the same time, providing a structure analysis function for it. 3. An extradosed bridge with one single pylon arranged single cable plane is taken for example. After optimization, the maximum bending moment decreased58.5%in the initial design, and bending moment is evenly distributed in the girder. The maximum compression stress in the girder and the pylon is17.7MPa, and the maximum tension stress in the girder and the pylon is0.3MPa, and the maximum vertical displacement of the girder is4.14cm, which are all satisfy the code requirements. After optimization, the total cost of conceret, cables and prestressing tendons was decreased12.5percent in the original design. The computational process costs about50minutes. The optimization solution is not only steady, but also computationally cheap. The optimization result demonstrates that the optimization method proposed in this thesis can efficiently get a fan configuration cross-sectional size of girders and pylons, cable stays and prestressing tendons and can minimizes the total cost of concrete, cable tendons and prestressing tendons. With this optimization method, a best optimized design can be achieved.