Study On Running Safety Of Trains And Windproof Measures For High-speed Railway Bridges In Strong Wind Field

Wind disaster is one of the main natural disasters that affect the operation safety of the railway. Especially in the northwest region in China, which is one of the most serious wind disaster areas of railways in China as well as in the world, the railway lines pass through some strong wind areas, where the train service is often interrupted by the wind and the train overturn accidents occasionally occur.The bridges located in the strong wind area vibrate intensively when subjected to the wind force excitation. The strong lateral wind pressure acting on the high-speed train running on the bridge greatly increases the possibility of the train derailment or overturning. Therefore, it has the significant theoretical meaning and the practical engineering value to perform comprehensive research on the dynamic responses of vehicle-bridge system under wind loads and windproof measures. This is an important issue to ensure the running safety of the train on the bridge, and to guide the design and construction of railway bridges and windbreak structures in the wind area. With the new built Lanzhou-xinjiang railway as a research background, this paper aims to establish a rational analysis framework to estimate the vibration response of the coupled vehicle-bridges system in the wind field, so as to evaluate the dynamic performance of the bridge and the high-speed train running safety. At the same time, the windbreak structures are studied to improve the running safety of the train, so that the traffic on the bridge can be interrupted as little as possible when strong wind occurs.The main research contents and results are given as follows:(1) The wind-induced train accidents at home and abroad are described to show the importance of the train safety protection in wind field. Then the current research statuses are summarized for the vehicle-bridge coupled vibration, wind-induced bridge vibration, and wind-vehicle-bridge system, running safety of the train and windbreak measures. Furthermore, the current focused problems are proposed on the dynamic analysis of wind-vehicle-bridge system and windbreak measures, and the research content and method in this paper are clarified on the basis of the previous work.(2) The wind field characteristics of bridge sites are analyzed, and the fluctuating wind speed time histories on the bridge sites are simulated by the improved numerical method. Firstly, the wind is represented as the mean wind component with the time invariant characteristic and the turbulent wind component with the time varying characteristic, and the influence of the landform and topography on the wind field is discussed. Especially, the wind environment of the bridge in the new Lanzhou-Xinjiang railway line is analyzed and the wind-sand flow characteristic in the Gobi desert area and the effect on the wind barriers are described. Then the numerical calculation formulae of the random fluctuating wind field are derived in detail, and the wind speed time histories of the bridge deck and pier on the Baiyang River Bridge are simulated.(3) The preliminary form selection for wind barriers and the effect of wind barriers on the aerodynamic performance of the vehicle-bridge system are studied. According to the correlation principle of computational fluid dynamics, the aerodynamic characteristic for the airflow through the wind barrier is analyzed by the numerical simulation method with an applicable turbulence model. The numerical simulation is performed for several different types of wind barriers on bridge. The influence rules of wind velocity are researched. The windbreak effect and the effective protection area of wind barriers are quantitatively analyzed with different heights and different porosity percentage, to determine the reasonable type of the wind barrier and the main design parameters. Any kind of wind barrier may have an impact on the wind field on bridge deck and increase the turbulence effects, which makes the wind field around the bridge structure more complex. When the train travels on the bridge with or without wind barriers, the wind load acting on the train is very different, especially in the leeward side of the train.(4) The dynamic interaction analysis model of vehicle-bridge system is established and the corresponding computation program is developed. For different types of wind barriers, considering the wind-vehicle-bridge-barrier interaction, the dynamic responses of the bridge and the running safety indices of the train are calculated under the strong wind and running train. Compared to the case without wind barrier on the bridge, the results are obvious. Taking a10-span simply-supported box girder bridge in the new built Lanzhou-xinjiang railway line for example, the dynamic responses of the train and the bridge are calculated at different train speed and wind velocity under the cases without barrier and with single-side4m barrier, single-side7m barrier and double-side7m barrier on the whole bridge.(5) The calculation formulae for wind load change acting on the car-body are derived when the train moves into or out of the wind barrier structure, and then the influence of the sudden change of wind load on the running safety is discussed. Meanwhile, the aerodynamic pulse force caused by the running train on the wind barrier is obtained, and then the time historic analysis method is used for the dynamic response of the wind barrier under the pulse force as well to external natural wind load. Taking the10-span simply-supported box girder bridge for example, the response and the running safety indices of the train are given under the cases of200m long single-side4m barrier, single-side7m barrier and double-side7m barrier of the same section on the bridge. These results are compared with those of the cases without barrier and wind barriers on the whole bridge. And the dynamic response of the key nodes of the single-side4m wind barrier is calculated under the natural wind load, or the aerodynamic pulse load as well as the combination of both.(6) An analysis program is written, based on which the dynamic responses of the vehicle and the bridge are obtained when the train passes through the common span simply-supported box girder bridge, simply-supported T-shaped girder bridge, simply-supported U-shaped girder bridge or Baiyang River continuous beam bridge. In the analysis, the cases both with the wind barrier on the whole bridge and only partial section of the bridge are considered. Then according to the evaluating method and the running safety indices, the maximum safety speeds are obtained at different wind velocities, based on which the train speed threshold curves are proposed when the train runs on the bridge with different types of wind barriers.