Research on Safety Performance Prediction and Warning Methods of Suspension Bridges Exposed to Oil Tanker Explosion Environments
Oil-tanker explosion fire has enormous power and poses a severe threat to the safety performance of crossing sea bridge.In order to study the structural response of suspension bridges exposed to complex extreme fire environments caused by oil-tanker explosions,and to clarify the safety of suspension bridges under complex extreme fire loads,a large-span suspension bridge was selected as the research object.The prediction process of suspension bridges safety performance(fire resistance)during oil-tanker explosion fires was provided.Firstly,the computational fluid dynamics-finite element method(CFD-FEM)coupling method was used to reconstruct the oil-tanker explosion fire environment.A three-dimensional multi-scale numerical prediction model for local girder segment and the entire bridge structure were established.The heat transfer mode of bridge segment and performance evolution of the entire bridge structure during oil-tanker explosion were revealed in depth.Subsequently,the high-temperature response and failure mode of steel box girder(stiffening girder)under oil-tanker explosion were studied,and the effects of different fire positions,distance from the fire surface to bottom plate of steel box girder,and wind speed on the fire response behavior of suspension bridge were analyzed.A fire resistance limit warning method for suspension bridges exposed to oil-tanker explosion environment was proposed.The research results indicate that the deformation of local suspension bridge segment under oil-tanker explosion continues to increase.And the fire affected bridge segment shows a failure mode of overall downward deflection followed by upward bowing in middle area,resulting in a development trend of first increasing and then decreasing for suspension cable force in the middle area.The fire position has a significant impact on the overall structural performance of the suspension bridge.As fire position approaches the mid span area,the deflection of girder segment in the middle area increases by 62％compared to the girder segment adjacent to the tower.When the distance from fire surface to steel box girder is reduced from 50 m to 20 m,the peak deflection and total bowing amplitude(the difference between peak values of deflection and bowing)of local girder segment increase by more than 19％,and the structural failure time is advanced by 10 minutes.Wind speed would change the shape of deflagration flame,significantly affecting the distribution of heating surfaces and high temperature response characteristics on both sides of box girders.When wind speed is 8 m·s-1,fire intensity of the windward side box girder is significantly reduced,and the total bowing amplitude of bottom plate is reduced by 17％compared to 2 m·s-1.The critical temperature during the bending deformation of steel box girder bottom plate is between 510 ℃-550 ℃,and limit temperature during the buckling instability of steel box girder bottom plate is between 685 ℃-715 ℃.The critical temperature and limit temperature can be used as two-stage warning temperatures for safety performance,thereby achieving two real-time warnings before steel box girder failure.The research conclusion can provide theoretical bases for the safety performance monitoring and early warning of cable supported steel bridges in complex fire environments,and further guide the safe operation and maintenance of similar bridges.
bridge engineeringoil-tanker explosion fireCFD-FEM coupling methodsafety per-formance predictionsuspension bridgewarning temperature
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