Structural Performance Analysis And Optimization Design On Cable-stayed Bridge Subjected To Earthquake,Wave And Current

With good dynamic characteristics,the cable-stayed bridges are widely used in sea-crossing bridges which have been built and being planned.Once the cable-stayed bridge has been in use,it will withstand complex environmental loads,including earthquakes,waves and ocean currents.Therefore,when subjected to complex environmental loads,it has important theoretical and practical significance for seismic design and revising seismic code to study the optimization design of the whole life seismic performance of the cable-stayed bridge and analyze dynamic model test of cable-stayed bridge withstanding earthquake,wave and ocean current under single and combined action.This paper is devoted to the dynamic performance under complex environmental loads and the whole life seismic optimal design of the cable-stayed bridge.Based on the linear diffraction wave theory and the linear radiation wave theory,it is proposed that the wave force and hydrodynamic coefficient of the pile cap can be calculated by using the projection area of the pile group in the transverse direction of the pile cap.Then,the dynamic model test of the tower of the cable-stayed bridge under single/combined action of earthquake,wave and ocean current is carried out.Finally,According to the seismic design principle of cost-benefit criterion theory,a new method based on multi-objective genetic algorithm and integrated life cycle seismic optimum design of seismic structures by combining seismic design with seismic risk is proposed.The main work of this paper is as follows:(1)Based on the linear diffraction wave theory,the interference effect of the lower group pile structure on the diffraction wave force on the platform structure is considered.the analytical solution of the diffraction wave force on the platform was given based on the cross-sectional area of the platform in the horizontal direction with the interpolation method.Through the example,the change rule of diffraction wave force on the platform is analyzed by the different wave numbers,the radius of the platform,the water depth,the water depth of the platform.The results show that when the different wave numbers is small,the radius of the platform is small,and depth is larger,the diffraction force of the platform with MacCamy method and Williams method will lead to large errors.Therefore,we propose to use the method of solving the diffraction wave force on the platform proposed in this paper.(2)Based on the theory of linear radiation wave,the interference effect of the lower group pile structure on the radiant wave force on the platform structure is considered.the analytical solution of hydrodynamic coefficient of cap was given based on the cross-sectional area of the platform in the horizontal direction with the interpolation method.Through the example,the hydrodynamic coefficients of the platform are analyzed by the radiation wave frequency,the radius of the platform,the water depth,the water depth of the platform and the effect of ignoring the surface wave.The results show that when the water depth is large,the frequency of the platform is low,and the in water depth is small,the additional mass coefficient and the additional damping coefficient on the cap with MacCamy method and Williams method will lead to large errors.Therefore,we propose to use the method of solving the hydrodynamic coefficient of cap-cap proposed in this paper.On this basis,the dynamic response analysis method of deepwater bridge under seismic wave and incident wave alone or in combination is established.(3)Dynamic model test and numerical simulation study of the pylon and pile group foundation structure of cable-stayed bridge under single/combined action of earthquake,wave and ocean current show that when encountering the random load,the acceleration response is mainly located at the pile cap,the strain of the upper part of the pile group and the lower part of the pylon becomes larger and the ground motion has the greatest contribution to the hydrodynamic pressure,followed by the wave,and the flow has the least influence.The amplitude of dynamic response at the top of pylon of cable-staved bridge is related to the input ground motion characteristics.Besides,when the seismic load is combined with the sine wave of high sea state,the earthquake contributes much to the acceleration at the top of the tower and even the contribution of the wave is small,it cannot be ignored.Through this experiment,a test program of the dynamic model under the combined effect of waves,ocean currents and earthquakes is given,which can provide reference value for other similar structural tests.Meanwhile,the results of this test are also available for the reference of similar structural design and theory validaty.(4)Based on the principle of "investment-benefit",the basic idea of seismic performance design is taken as the theoretical support,the requirements of social,economic,environmental,technological and structural functions are all considered to seek a reasonable,satisfactory and sufficiently safe design scheme that can be accepted by society and involved by the owners,a multi-objective optimization design of circular single column reinforced concrete piers considering initial cost,earthquake damage expectation,remnant value and environmental pollution during dismantling is given,and proposes a new method of integrated life-span seismic design optimization based on multi-objective genetic algorithm,ductile seismic design and seismic risk.The proposed method of full-life seismic design optimization of bridge can provide the best life-span cost and the best seismic performance design.