Dynamic Response Analysis Of High-speed Railway Concrete Simply Supported Girder Bridge With Damage Under Vehicle-bridge Coupled Vibrations

With the existence of damages,the static and dynamic performances of high-speed railway concrete simply-supported girder bridges will be changed.Previous studies have paid more attention on the influence of concrete diseases on the static performance of simply supported girder bridges,but there are less attentions paid to the effect of damage on the dynamic characteristics of bridges under dynamic loads,especially under coupled vibration of vehicle-bridge system loads.In views of the fact that there are few studies on the effects of various damage conditions on the dynamic response of existing damaged bridges under dynamic loads,this dissertation chooses a certain type of high-speed railway train and a three-span high-speed railway concrete simple-supported beam bridge with standard span of 32 m,and establishes a coupled vibration model of high-speed train-bridge based on multibody dynamics and finite element simulation method.The track irregularity spectrum is input into the vehicle-bridge system as an external excitation by a self-compiled MATLAB program,and the finite element method is used to simulate the bridge structure under different damage conditions at the same time.The dynamic responses of the concrete bridge under train-bridge coupling vibration load under different damage conditions,such as concrete surface damage and cracks at the bottom of the beam,is deeply studied.Based on the response changes of the bridge,the feasibility of using the dynamic load test to detect the damage of bridge structures is discussed.The main contents and conclusions of this dissertation are as follows:(1)On the basis of summarizing the diseases of high-speed railway bridges,this dissertation pointed out that concrete bridges will change the response of structures under external loads when they are damaged.Therefore,it is becoming more and more important to study the dynamic response changes of existing damaged bridges compared with healthy bridges.At the same time,in view of the current structural diseases,it is necessary to develop more efficient bridge disease detection methods.(2)On the basis of systematically discussing the basic theory,this dissertation establishes the space vehicle model of four-axle train and deduces formula of the vibration equation of the train running on the flat straight trails using Lagrange equation.Based on modal superposition method the dynamic equations of simply supported beam bridge of high-speed railway which has a standardized span of 32 m is established.By the using of substructure analysis,the separate train models and bridge models can be coupled through FEMBS interface of SIMPACK.(3)The multi-body dynamics software SIMPACK is used to simulate the calculation model of high-speed train,and the method of vehicle-bridge coupling analysis with FEMBS interface is elaborated in detail.The diseases of high-speed railway concrete bridges are classified,and the finite element models of damage and crack damage in different parts of concrete are established,as well as the corresponding vehicle-bridge coupling vibration analysis model is established.(4)This dissertation analyzes the dynamic response of various damage models under vehicle-bridge coupling vibration.The results show that the damage of concrete surface and the crack of concrete bottom plate have obvious influence on the dynamic response of simply supported concrete beam bridge under vehicle-bridge coupling vibration load.The damage of bottom plate position has greater influence on the vertical displacement response than that of web position,and the damage response of mid-span position is obviously greater than that of 1/4 span position;while the impact of web position damage on peak acceleration is greater than that of bottom plate.The damage condition will increase when the web position is damaged in general,and the stiffness of the cracked section will be weakened by the cracks in the mid-span of the structure,which will affect the vertical displacement and acceleration peak value of the bridge structure.(5)The finite element method is used to simulate the actual experimental process referring to the detection method of dynamic load test of structure,and the acceleration response is processed mathematically.The time history curve of vertical acceleration is processed by wavelet decomposition technology,and the damaged part of bridge structure is judged based on the acceleration information already obtained.It provides a reference for bridge structure damage detection method by means of dynamic load test.