| The extradosed cable-stayed bridge is a kind of competitive combined bridge type,which is evolved on the basis of two traditional bridges of continuous bridge and cable-stayed bridge.With its excellent structural performance,distinguished economic indicators,and beautiful appearance,the extradosed cable-stayed bridge has made it rapid development and gradually grown into a mainstream bridge type in the past two decades.Compared with conventional cable-stayed bridge,one of the distinctive features of the extradosed cable-stayed bridge is that the main girder has three long no-cable-zone sections.How to properly set up the lengths of no-cable-zone sections and arrange the cables along the girder,and make cable structure work in coordination with the continuous girder structure is a concern of designers.In response to this problem,the no-cable-zone lengths and patterns of a typical 3-span extradosed cable stayed bridge were demonstrated in this paper by three parameters: no-cable-zone length around the main tower,no-cable-zone length around the center of main span;and no-cable-zone length around the end of side span,These three parameters were employed to conduct the influence analysis on structural behavior.The FEM model(ANSYS)was established mainly from the structural data of an practiced long span extradosed cable-stayed bridge.Based on this referrence bridge,other FEM models were constructed for the cases that show the possible and practical changes of the designated 3 parameters.On the premise of not changing other structural parameters,the values of the research parameters were changed by increasing or decreasing the number of stay cables with the total cable areas unchanged,and multiple sets of models were constructed accordingly.The influence of parameter changes on inner forces and deflections of girder due to live vehicle loads was analyzed by computer program which was coded by ANSYS Parametric Design Language.The research work and main conclusions are as follows:(1)The bending strain energy of the structure was chosen as the objective function.And the ANSYS optimization module was used to optimize the force of the model,the optimization results were ideal.(2)The static response of the structure under the most unfavorable load conditions was obtained for each group of analysis models.Through the comparison and comprehensive analysis,the specific relationship between the research parameters and structural static behaviors was obtained.The peak value of the negative moment at the top pier is affected significantly by the length of the no-cable-zone near the tower,and the bending moment and deflection of the mid-span are significantly affected by the length of the mid-span no-cable-zone.On this basis,a reasonable range of no-cable-zone lengths to main span ratios was obtained on the conditon that the main girder is under the action of live loads.(3)Through calculation and result comparison,it was verified that the effect of structural nonlinearity on the static response of the model was less than 3%,therefore,its influence could be neglected to speed up the calculation and analysis efficiency.(4)In view of the fact that the setting method of the no-cable-zone sections makes an apparent contribution to the change of structure’s static performance,the idea of adjusting the lengths of the no-cable-zone sections to improve and optimize the overall structural responses is proposed,and the specific measures to achieve this optimization are given in this paper. |
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