Dynamic Optimization Design Of Extradosed Cable-stayed Bridge Under Earthquake Excitation

In nature,bridge structures not only bear static load,but also dynamic load.Many bridges inevitably suffer from vibration,impact and interference of external environment during their service,such as earthquake,wind-surges,sea wave,ship collision,etc.,resulting in structural damage.In order to improve the static and dynamic characteristics of the structure and ensure they can work safely and reliably under the dynamic environment,the most effective way is to carry out the structural optimization design of the structure.In this thesis,an Extradosed Cable-stayed Bridge,Dalian Changshan Bridge,is used as the engineering background,on the basis of learning and summarizing the theory of bridge static and dynamic characteristics optimization,the dynamic optimization of Changshan Bridge under earthquake excitation is studied.Firstly,the spatial finite element beam-pole model of Changshan Bridge is established in ANSYS.Then the response surface method is employed to optimize the bridge vibration frequency,and the optimum design of structural dynamic characteristics is carried out for initial finite element model.What's more,the optimization method of the experimental design is chose to optimize the dynamic response of the structure under seismic vibration,and the optimal design of structural dynamic response is carried out.The main research contents and conclusions are as follows:(1)According to the construction design drawings of Changshan Bridge,by compiling APDL parameterized command and assisting with the powerful geometric modeling ability of AutoCAD,the spatial finite element beam-pole model of the whole bridge is established in ANSYS.Changshan Bridge is a high-order statically indeterminate system with a complex stressing state.In the modeling process,effective strategies are developed to simplify the processing of some components,which greatly improves the modeling efficiency.(2)In order to obtain an accurate finite element model consistent with the static and dynamic characteristics of the real bridge,the initial finite element model is modified.The dynamic and static characteristics of the Changshan Bridge model are corrected successively by response surface method and iterative optimization method.The dynamic characteristic correction is based on the vibration frequency,the bridge material parameters are used as design variables,and the response surface method is utilized.The static characteristic correction is based on the bridge static cable force,and the cable pretension is used as the design variable,and the iterative optimization method is used.After the correction,the vibration frequency is consistent with the frequency of the actual bridge audit report,and the difference rate of cable tension is significantly reduced.(3)The structural dynamic optimization is different from the structural static optimization.Before the dynamic optimization,the dynamic response analysis of the structure is required to carry out.According to the analysis of the geological environment of the Changshan Bridge,there are some seismic conditions for the occurrence of moderate-strong earthquakes in the near-field area.According to the regulations,under the action of the El(normal)earthquake and the E2(rare)earthquake,three sets of internationally common seismic waves are used.EI-Centro wave,Taft wave,San Fernando wave,12 earthquake excitation forms are designed to study the dynamic response of the bridge.Seismic time-history response analysis of Changshan Bridge is calculated by transient dynamics analysis in ANSYS.The results show that under the El earthquake,the whole bridge remains in the elastic working range.However,under the E2 earthquake,local repairable damage occurred in the structure in a certain extent.And different seismic wave input methods have different effects on unidirectional seismic response.(4)Based on the seismic dynamic response analysis,the main design parameters of Changshan Bridge are optimized by the optimization method of experimental design.By comparing the structural responses of Changshan Bridge before and after optimization under seismic load,the results show that the optimized design of the structural dynamic response is optimized by the experimental design optimization method,under the premise of ensuring the integrity of the bridge structure,the potential of the structure can be fully utilized to reduce the seismic dynamic response of the bridge.