Study On Anti-overturning Stability Of Large Cantilever Concrete Continuous Box Girder Bridge Under Vehicle Load

Concrete continuous box girder bridge is widely used in national transportation infrastructure because of its good mechanical performance and mature construction methods.With the continuous increase of urban traffic pressure,in order to better solve the problem of traffic pressure,the width of girder bridge is increased to relieve it,so the large cantilever bridge come into being.This bridge has the advantages of large cantilever,thin box wall,large web spacing and so on.Many large cantilever box girder bridges have been used in the construction of urban bridges at home and abroad.Although large cantilever bridges can increase the passing rate of vehicles and relieve the traffic pressure,the bridge is particularly prone to overturning when vehicles are driving on the outer side of the deck because of its long cantilever.There are two main reasons for bridge overturning.One is that the innate ability of continuous girder bridge’s transverse resistance to overturning is insufficient in the design of the bridge itself.The second is that the bridge is overloaded and unbalanced loaded during the operation,and the serious spatial deviation effect leads to the overturning of the bridge.For seriously overloaded vehicles,bridge supervision departments should pay enough attention to limit the maximum traffic load of the bridge.In order to further avoid the occurrence of bridge overturning accidents,this thesis is based on engineering examples and the summary of previous research results,applies the method of theoretical analysis and finite element calculation,according to whether there is a void in the reaction force of the bearing of the girder bridge to analyze bearing reaction trend and obtain the anti-overturning stability coefficient of the bridge,and then systematically study the influence of bearing spacing,pier bearing spacing,bridge deck width,radius of curvature,the ratio of the middle span on the anti-overturning stability of concrete continuous box girder bridge under different live load modes.Finally,according to the study of each working condition,the thesis analyzes the capacity of different types of vehicle loads on the bridge,and then makes corresponding restrictions on the driving conditions of different vehicles on the bridge,which provides the basis of the scientific management of the bridge structure in operation for the road administration department,and ultimately ensures the safe operation of the concrete continuous girder bridge,and provides practical significance for promoting the development of the traffic industry.The main conclusions of this thesis are as follows:(1)The original structure of the girder bridge remains unchanged,and under different load modes,the safety reserve of the main girder against overturning gradually decreases with the increase of the weight of the vehicles.Therefore,it is suggested to make statistical analysis according to the actual traffic situation of the existing concrete continuous box girder bridge,appropriately increase the total load weight of the checked vehicle load,and determine the tray-train action mode suitable for checking the anti-overturning stability of the concrete continuous box girder bridge.(2)Under different vehicle loads,other basic structures and variables are kept unchanged,but only one of the influencing factors is changed,such as increasing the distance between the supports of the girder bridge,increasing the distance between the middle pier supports,decreasing the width of the bridge deck,decreasing the radius of curvature,and increasing the ratio of the middle span will increase the stability of the girder bridge and the bridge is in a state of stable.On the contrary,the more unstable the girder bridge is,and the greater the probability of overturning accident is.(3)The transverse overturning damage and the strength damage caused by the seriously overloaded vehicles for the concrete continuous box girder bridge are irreversible,and it is uneconomical and unscientific to improve the design standard of the bridge blindly.Through the analysis of the capacity of the bridge under four kinds of live loads in each working condition,the paper shows that standard design load and general overload situation of vehicles can pass normally on the bridge without restriction.When the heavy vehicle fleet situation carries on to pass,they should be analyzed and restricted according to the circumstances.Vehicles such as those with severe overloading have seriously exceeded the design requirements of the bridge and should be banned.Through research and analysis,it is can be can better grasped and standardized to whether live load vehicles can drive on the bridge with specific load capacity,which can greatly reduce the occurrence of accidents.