Study On Vehicle-Bridge Coupling Responses And Dynamic Characteristics Of Large-Span Deck-Type Concrete-Filled Steel Tube Arch Bridge

The main body of concrete filled steel tube bridge belongs to a flexible structural system.With the increasing span,the risks of bridge structural instability and traffic safety are increased,especially the problems of large load,high height and stability of the arch column of the super-long through concrete filled steel tube arch bridge.The structural characteristics of its super-long span also increase the risk of lateral instability of the arch bridge.With the increasing traffic flow and complex and changeable vehicle load forms,the research on its dynamic characteristics is becoming more and more urgent.In this thesis,the overall and local impact coefficient and dynamic response of the world’s first super-long deck concrete filled steel tubular arch bridge with span of 504 m are studied.The main research contents and conclusions are as follows:(1)The whole bridge model is established by MIDAS and ANSYS,and the reliability of the model is verified by comparing the natural vibration characteristics and the deflection under self-weight.By changing the stiffness of steel beam,column,arch rib and junction pier,it is found that increasing the stiffness of steel beam can effectively improve the in-plane stiffness and lateral bending and torsion performance of the bridge,but it has little effect on the out-of-plane torsion capacity.Improving the stiffness of columns and arch ribs can effectively improve the torsional,lateral bending and torsional coupling performance of bridges;increasing the stiffness of the junction pier can greatly improve the in-plane vertical bending capacity of the bridge structure,and the in-plane lateral bending capacity can also be improved to some extent.(2)Using MIDAS,the vehicle driving is simulated as a triangular load to study the influence of vehicle speed,eccentric load and column stiffness on the overall and local impact coefficient of the bridge.By comparison,it is found that the overall impact coefficient of the bridge is not enough to reflect the impact effect of vehicle load on the local components of the bridge.The three-dimensional impact effect of the end column is far greater than that of the other two columns,and the vibration response in the transverse direction is the most sensitive to the vehicle speed;with the increase of eccentricity,the deflection of bridge deck is negatively correlated with the change of its impact coefficient.Therefore,in the subsequent inspection and maintenance of the bridge,we should focus on the lateral stability of the high columns and key components and sections of the bridge.(3)A three-dimensional vehicle model with 22 degrees of freedom is established in UM,and the ANSYS bridge model is imported into UM by using interface program for joint simulation.By changing the connection mode of beam-column and the combination form of motorcade,the influence on the lateral stiffness and impact coefficient of arch bridge is studied.The results show that the rigid connection of beam-column can significantly improve the lateral stiffness at the bottom of middle column,and the bridge deck of middle column is the least sensitive to the connection mode of beam-column.When vehicles pass the bridge side by side with two cars,the dynamic impact coefficient is the largest,followed by unbalanced driving,and the front and rear driving is the smallest.Therefore,it is necessary to avoid two cars driving side by side for a long time in order to avoid excessive dynamic response to the bridge.At the same time,the impact transmitted by vehicles with different distances to the mid-span will weaken or overlap each other.Drivers should keep appropriate vehicle spacing to reduce the impact of fleet load on the arch bridge,thus prolonging the service life of the bridge.(4)The dynamic response of arch bridge under vehicle-bridge coupling is explored from seven aspects: the depth of pavement defect,vehicle speed,defect position,initial braking speed,deck irregularity,braking deceleration and braking position.It is found that the impact effect produced when the defect and braking position are located in the first half span is greater than that in the second half span and reaches the maximum at the middle span.Mid-span impact coefficient is the most sensitive to the change of pavement defect position,followed by the depth of pavement defect,and finally the speed;under the action of vehicle braking,the mid-span impact coefficient is the most sensitive to the change of bridge deck irregularity,followed by braking position and initial braking speed,and the least sensitive to braking deceleration.