Study On The Dynamic Characteristics Of Combined Steel-truss Bridge And Vehicle Under Seismic Action

Bridges account for a larger proportion of high-speed railway due to varied landform and complex geological condition of China.With the constant development of Chinese high-speed railway,more and more railways are in seismically active zones,and the probability of running into earthquake is growing when operating.Researches about railway bridge vibration under train load and seismic action have obtained tremendous achievements domestically and abroad.However,researches about combined bridge vibration under seismic are less,researches about the influence of car load on bridge structure are even lesser.Hence,in order to secure the structure of bridges and the operation of vehicles,it is necessary to study the coupled vibration of vehicle and combined bridge under the seismic action.This paper,taking a certain combined bridge as the object,carries out the following researches.(1)Design and complete bridge scale-model test.Use dynamic acquisition instrument DH-5923 N to measure the vibration mode and damping of the scale-model.In order to study the structure dynamic laws,the time history datum about the displacement and acceleration of the scale-model under moving vehicle load were measured.The simulation model was established in ABAQUS,and the simulation characteristics were compared with the scale-model test datum and the bridge design documentation to ensure the reliability of the scale-model test and the simulation model.(2)Refined vehicle-rail-bridge model was established in ABAQUS.The Cartesian element was applied to simulate the bridge rail connection and the wheel-rail contact force.Train model was 27 degrees of freedom model,and the subroutine dload in ABAQUS was written by Fortran to establish the car model.Variable vehicle speeds were defined to obtain the dynamic responses of bridge model.Study shows the relationship between impact factor at bridge mid-span and load speed are not linear exactly with the increasing vehicle speed,and the abnormal impact factor will appear around certain vehicle speed.Influence on bridge caused by train load are much greater than the car load for medium and small span bridge.(3)Seismic waves were applied on the bridge supports with the method of relative movement method,and the vehicle-bridge coupled vibration under seismic action was studied.Researches show that influences on lateral mid-span displacement and acceleration caused by seismic action are greater than vertical ones.The maximum increase of the peak values at vertical mid-span displacement are 37%,while the lateral ones are more than 10 times.According to the codes,lateral displacement are over-limit seriously endangering the bridge and vehicle operating.Seismic action was normalized to study the vehicle bridge vibration.When the seismic intensity reaches 0.20 g,lateral displacements of bridge mid-span will be over-limit.When the seismic intensity reaches 0.20 g and 0.15 g,vertical and lateral acceleration will both be over-limit,and the passenger comfort will get worse.When the seismic intensity reaches 0.10 g and 0.15 g,the derailment coefficient and rate of wheel load reduction of the train will be over-limit.