Study Of Risk Assessment Method About Steel-concrete Continuous Girder Bridge On Ground Fissure During Service Period

Building roads through mountains,constructing bridges encounter rivers,this is the original statement about bridges’ function.Transport is the lifeblood of the economy,bridges are the throat of traffic.As the country’s investment in infrastructure increases,80.53 million bridges have built in China by the end of the 2017.While the bridge plays an important role in the national economy,the risk accident of bridge is increasing.At present,although both domestic and abroad scholars mainly focus on the construction period risk assessment,there are few the researches on risk assessment of bridge during service period.Therefore,it is an urgent problem to improve the risk assessment mechanism during bridge service period and draw up effective risk control measures.In this paper,on the basis of summarizing and analyzing the existing research results at domestic and abroad,treated the scientific research project of Shaanxi Provincial Department of transport in 2016 as the background,this paper takes XI’an Yanta Road interchange as example,the service period risk assessment method of the steel-concrete continuous girder bridge which cross the F12 ground fissure was studied and researched.The main research contents are as follows:1、By summing up the risk accidents data,the bridge project risk accidents that occurred in the service period in recent years were analyzed,the database of the risk accidents were set up,then the primary cause of the accidents and frequencies were analyzed based on the database;2、The basic concepts and operation steps of risk sources identification were introduced.and the characteristics of the risk sources are summarized.Furthermore,the advantages and disadvantages of the three common methods of risk sources identification were studied.Considering the shortcomings of the qualitative methods with lacking persuasion and the weakness of quantitative methods with huge nunber of calculations,a new method which is the brainstorming + analytic hierarchy process(BS+AHP)for identifying the risk sources was put forward based on the common methods of identifying the risk sources;3、The basic theory of reliability,risk probability,risk loss and neural networks are expounded.Then,Combined with the disadvantages of the mean walue first order second moment method(MVFOSM)solves the reliability index is nonuniqueness and the Monte Carlo method(MCM)solves the reliability index have huge work,the advantages of the B-P neural network method can solve the approximation problem of the nonlinear objective function well,an original method which is based on time-varying reliability + B-P neural networks for calculating the risk probability was put forward,and the feasibility of the method is verified by examples.4、Firstly,the bridge engineering risk loss during service period were devided into four categories They are respectively structural damage,traffic delay,social environment impact and casualties.Then,in order to simplify the risk loss assessment process,the risk loss was classified as economic loss and casualty loss and the risk loss assessment grade was given in the end.5、Combined with engineering examples,the service period risk of the steel-concrete continuous girder bridge that across the F12 ground fissure was assessed,furthermore,specific research on one of the important risk sources ground fissure disaster was made,and it concluded that the risk probability grade is 1 level,the risk loss grade is level 3,the overall risk assessment grade is Ⅱ level under the ground fissure disaster.Finally,according to the characteristics of the bridge during service period,the corresponding risk response measures were put forward.