Earthquake-Wind-Wave-Vehicle-Bridge Coupling Vibration Analysis Considering Foundation Scour

With the rapid economic development and increasing traffic demand,more and more long-span bridges have been built along the river and coastal areas.These long-span bridges are located in harsh environment,which not only suffers from the operating loads such as wind,wave,vehicle,corrosion and erosion,but also may face the threat of extreme loads such as earthquake,typhoon,explosion and ship collision.These long-term sustained loads and sudden extreme loads will directly affect the safety and durability of bridge structures.Due to the suddenness of the extreme action,the vehicles have no time to evacuate from the bridge when the extreme action occurs.When the extreme action occurs,the long-span bridge not only suffers from the daily loads,but also keeps the normal traffic on the bridge.Therefore,it is important to study the dynamic response of the vehicle-bridge system under multiple loads for the safety analysis of the structure and the vehicles running on the bridge.For the multi dynamic loads coupling vibration problem of the bridge structure,the dissertation mainly carried out the research work in the following aspects:(1)Based on the calculation and analysis method of the wind-vehicle-bridge coupled vibration and the programming,a numerical simulation system of earthquake-wind-vehiclebridge coupled vibration system is established by using the large mass method to simulate the earthquake action on the bridge.According to the common types of highway vehicles,the vehicle is simulated as a mass-spring-damping system with 17 independent degrees of freedom,and the bridge model is established by the finite element method.The spectrum method is used to simulate the stochastic load excitations,and these model parameters and load excitations are taken as the input parameters of the coupled vibration model.At the same time,the interaction principle among the vehicle,bridge and load excitations is elaborated.The dynamic response of the vehicle-bridge system can be obtained by means of separation and iteration to solve the coupled vibration equations of the bridge subsystem and the vehicle subsystem adopting the Newmark-? numerical integration method.(2)Taking Sutong Bridge as an example,on the basis of the established earthquake-windvehicle-bridge coupled vibration system,the coupling vibration regularity of the vehiclebridge system under the combined action of earthquake and wind is studied,and the influence of the spatial variability of seismic ground motion on the earthquake-wind-vehicle-bridge coupled vibration system is further explored.The results show that,compared with the response of the bridge in the earthquake-vehicle-bridge system,the consideration of wind load will increase the lateral vibration of the bridge mid-span,but it will restrain the vertical vibration of the bridge mid-span;compared with the response of the bridge in the earthquakevehicle-bridge system,the extreme value of lateral response at the bridge mid-span increases by about 40% under the mean wind speed of 20 m/s,which shows that the influence of daily wind load on the vibration of long-span bridge can not be ignored;compared with the vehicle response in the earthquake-vehicle-bridge system,the combined action of the earthquake and wind load does not significantly increase the acceleration response of the vehicle;when the long-span bridge structure(only under the wind and vehicle loads)in the daily operation condition is subjected to the sudden earthquake,the dynamic responses of the bridge and the driving vehicle on the bridge will increase rapidly,and the seismic ground motion controls the dynamic response of the vehicle-bridge system;the complete spatial variability of the seismic ground motion makes the vibration responses of vehicle and bridge in the coupled system change greatly,so it is necessary to consider the complete spatial variability of the seismic ground motion to ensure the safety of the derived responses of the vehicle and bridge.(3)Based on the established earthquake-wind-vehicle-bridge coupling vibration system,the nonlinear Morison formula is used to simulate the wave force on the bridge foundation considering the seismic effect,and a numerical simulation system for the earthquake-windwave-vehicle-bridge coupling vibration analysis is established.In addition,this research also introduces the safety evaluation criteria to analyze the vehicle safety.As an illustration,taking Sutong Bridge as an example,this dissertation uses the simulation system to evaluate the dynamic response of the long-span bridge and the safety of vehicles driving on the bridge under different combination of the operation loads and earthquake.The results show that under the action of vehicle,wind and wave loads,the vertical vibration of bridge girder is mainly controlled by the fluctuating wind load(fluctuating response)and the vehicle load(average response),while the lateral vibration of bridge girder is mainly controlled by the fluctuating wind load and wave load;under the combined action of earthquake and operation loads,the earthquake becomes the control factor affecting the dynamic response of the vehicle-bridge system.In addition,the existence of vehicle load increases the vertical vibration of the bridge mid-span and suppresses the lateral vibration of bridge mid-span.On the contrary,the appearance of the wind-wave load suppresses the vertical vibration of the bridge mid-span and increases the lateral vibration of the bridge mid-span.With the increase of vehicle speed,windwave load and earthquake,the dynamic response of vehicle-bridge system has gone through three stages: the control stage of wind-wave load,the control stage of both wind-wave load as well as earthquake and the control stage of earthquake;the safety of vehicles driving on the bridge decreases with the increase of vehicle speed,wind-wave load and earthquake,and the vehicles driving in the inner lane are safer than those driving in the outer lane.(4)The p-y curve reduction method is used to consider the load-displacement relationship between the pile and soil under the different scour depths.According to the scouring depth and the obtained load-displacement relationship between the pile and soil,the lateral support length and stiffness of the pile foundation are updated,and the numerical simulation system of earthquake-wind-wave-vehicle-bridge coupled vibration analysis considering the foundation scouring effect is established based on the established earthquake-wind-wavevehicle-bridge system.Based on this system,the bridge natural frequency and the dynamic response time-frequency characteristics of vehicle-bridge system are analyzed,and the influence of foundation scour on earthquake-wind-wave-vehicle-bridge coupled vibration system is revealed.Taking Jiangshun Bridge as an example,the results show that the foundation scour reduces the lateral restraint of soil on the bridge foundation,and increases the flexibility of bridge structure and reduces the natural frequency of structure;with the increase of scour depth,the lateral displacement response of bridge structure and the corresponding response spectrum amplitude increase under the action of operation load and earthquake,but the scouring effect on the vertical response of bridge structure is ignorable;foundation scour may reduce the lateral acceleration response of vehicles,but the vertical acceleration response of vehicles remain invariant with the increase of scour depth.