Optimization Of Cable-stayed Bridges Based On Strain Energy Criterion

The bridge designers attach importance to design of long span bridge as the traffic project develops rapidly. Cable-stayed bridge is a classical form of the long span bridge. Because the girder of cable-stayed bridge is one of the key load-carrying members and its elevation and cross-section form directly influence the distribution of stress, traveling condition and economic performance of the whole system, so design and security of cable-stayed bridge are very important. But the cable-stayed bridge is a kind of statically indeterminate structure with high indeterminacy and the distribution of girder stress are complex, so it is very difficult to design the girder. The Convention design generates the size of the structure according to experience, then get the structure form which meet to the restrictive condition by multiple pilot calculations. It can only produce a feasible result. So, it is very important to do some research on optimum design of cable-stayed bridges.In this dissertation the transverse topology, longitudinal shape and size optimization of the cable-stayed bridge girder are researched by ANSYS which is a large finite element program and the program APDL. The examples for Junshan Yangtse Rive Bridge are calculated. The main contents are as follows:(1) A strain energy criterion is proposed in this dissertation to construct bi-directional evolutionary structural optimization method. The method of dynamic delete ratio is used in order to avoid the irregularity in calculation. The procedure of structural optimization developed by the program APDL which provided by ANSYS. The samples show that the procedure proposed in this dissertation converges rapidly to the optimum topology and is easy to program.(2) Using the Bi-directional Evolutionary Structural Optimization method based on strain energy criterion, the transverse topology optimization of the cable-stayed bridge girder proves that box girder is the best cross-section for steel large-span cable-stayed bridges. This also shows that the method is practical and feasible. This method can delete more material and clearer topology can be gained. At the same time, the accuracy of the method does not depend on the finite element mesh.(3) The longitudinal shape and size optimization of the cable-stayed bridge girder is studied and the structural model consists of shell, beam and cable cells. The results of the study show that the intervals between longitudinal ribbed slabs and their positions greatly effect the distributions of stresses and displacements of the top and the below plates of the girder. If the space betweens were too large, the thicknesses of the top or below plate would also be large in order to meet the stresses, displacements and other challenges.(4) The optimum distributions of cable tensions for completion state of the cable-stayed bridge is studied because it is necessary to calculate the girder stresses and displacements when the structural model is spatial. The results of the study show that it can reduce the maximums of cable tensions. And the optimization of cable tension makes them more uniform.