Study On Risk Assessment Of Laozhang River Long-span Bridge Under The Condition Of The Flood

The bridge and aqueduct are not only the important building for crossing the rivers and valleys,but also the key of the lifeline engineering.The safety and uninterrupted work of them is the important link in the smooth traffic.Due to the frequent flood disaster,often occur traffic breaking.It is important to carry out flood risk analysis in order to ensure for the safety and smooth of road and eliminate flood threat.The risk analysis of flood control not only can reasonably control the risk of bridge during the life cycle,but also is helpful for design optimization,making scientific maintenance management plan and reducing the loss cost.In this paper,scouring risk,impact risk and bearing capacity risk of pile foundation are researched.Basing on Laozhang River long-span bridge of Xingheng expressway.The content studied includes the following several respect mainly:(1) Analyses and review of risk analysis of flood control under the action of flood.(2) Scour damage classification of bridge foundation is determined and membership function of the three levels damage is constructed.Furthermore,limit state equation of bridge scour is established by applying the theory of fuzzy-random reliability.By programming with MATLAB,JC method is introduced to calculate the scour reliability of the bridge.Take Laozhang River long-span bridge as an exemple, from the data we can see that flood frequency and scouring depth increase with flow rate and the pile long can optimize.(3) For the impact force of floating objects under the action of the flood,this research mainly calculate impact force of different angles by considering the objects such as floating wood and oil drums and so on.(4) Considering the small failure probability of bridge and the problem of the monte carlo simulation needing a great lot of calculations,Marko Chain Monte Carlo method basing on the subset theory is put forward.This method not only can simulate random variables with any distribution,but also can greatly decrease the number of times of simulation on the premise of the same simulation precision.Through establishing the limit state equation on bridge foundation,this method is applied to calculate bearing capacity risk of pile foundation in normal operation and flood state,then calculating risk probability of bearing capacity of single pile through the programming in MATLAB. Take Laozhang River long-span bridge as an exemple,bearing capacity of pile foundation meet the safety requirements in normal and flood conditions.(5) Summarizing the research work in this paper and the research emphasis in the future is expected.