Study On Vehicle-bridge Coupling Vibration Characteristics Of Long-span Rail Cable-stayed Bridge With Unequal Tower

With the breakthrough of key technologies in bridge construction,the long-span track bridge has been developed rapidly in recent years.When the traditional cable-stayed bridge with equal altitude tower can not meet the requirements,the high-low tower cable-stayed bridge with appropriate span combination can adapt to the terrain and be more economical.However,the asymmetrical statically indeterminate structure of high-low tower cable-stayed bridge will cause the bridge to have greater stiffness nonuniformity along the line direction,and cause the additional track irregularity.When the subway train passes,the additional irregularity caused by the change of bridge stiffness will aggravate the vibration of the vehicle body and threaten the running performance.Therefore,it is urgent to build a set of bridge-vehicle coupling vibration theory suitable for high-low tower cable-stayed bridge of track,and to study the dynamic characteristics of long-span high-low tower track cable-stayed bridge,in order to provide some reference for the research on coupling vibration of the same type of bridge,and provide some theoretical basis and suggestions for later operation and maintenance.Based on the world’s largest span track cable-stayed bridge,Chongqing nanjimen Yangtze River special railway bridge,and based on the linear elastic theory,this paper establishes the precise spatial mechanical model of the long-span cable-stayed bridge with high-low towers,and carries out nonlinear optimization design of the bridge model based on the optimization algorithm,so as to make the key vibration mode and frequency closer to the actual engineering structure.Then,based on the theory of vehicle bridge dynamic interaction,ANSYS is redeveloped to establish a three-dimensional refined dynamic interaction model of metro train high and low tower track cable-stayed bridge,and on this basis,research the dynamic characteristics of bridge-vehicle system of long-span high-low tower track cable-stayed bridge.The research results are as follows:(1)Through the optimization algorithm,the nonlinear optimization design of the bridge model is carried out.After 35 times of iterative optimization analysis,the key vibration modes and frequencies of the bridge are closer to the actual engineering structure,which can more accurately reflect the vibration characteristics of the vehicle bridge system.It is suggested that the follow-up research should carry out nonlinear correction on the numerical model of the long-span bridge,so as to provide a more accurate bridge sub model for the vehicle bridge analysis.(2)Based on the dynamic interaction model of train high and low tower track cable-stayed bridge,the dynamic response of train bridge system under different speed conditions,different train formation forms and different bridge crossing directions is simulated and analyzed,and the dynamic characteristics of train bridge system under different train operation modes are explored.(3)Aiming at the asymmetric stiffness characteristics of high and low pylon cable-stayed bridge,the dynamic response difference between high and low pylon bridge structures under multiple speed conditions,and the influence mechanism of train speed change on the dynamic response difference between high and low pylon bridge structures are analyzed,and the variation law of dynamic response difference between high and low pylon bridge structures under different bridge crossing directions is analyzed.The results show that: the dynamic response data of the low tower side girder structure is significantly larger,and with the increase of train speed,the response gap between the two sides of the bridge is also increasing;it shows that the influence of the asymmetric structure of high and low towers on the dynamic characteristics of the vehicle bridge system is very significant and can not be ignored,so special attention should be paid in the design and construction!(4)The dynamic response law and trend of the vehicle bridge coupling system are studied when the vertical stiffness of the main girder,the vertical stiffness of the tower and the second stage load of the bridge change.The results show that: the bridge structural parameters studied in this paper have a slight impact on the train response,and the bridge dynamic response has a high sensitivity to the above key parameters of the bridge structure.