Dynamic And Static Analysis Of Urban Bridge Under The Effect Of Vehicle Jam

By the end of August2011, the motor vehicles reached219million in our country.Among them, car ownership for the first time exceeded100million. Accounting for45.88%of the total are motor vehicles. With the rapid growth of China’s motor vehicle ownership, thetraffic congestion in the major cities occurred frequently, the congestion roads are unceasinglyincreasing, the traffic congestion degree is intensifying,which bridging a lot of influence tourban economic development, urban trips and the safety of the urban bridges.Through analyzing the composition of the urban vehicles and the distribution of car flowin urban bridges, and by investigation the type of vehicle, the length of vehicle, axle load,wheelbase, distance of adjacent vehicle and so on, the vehicle loading models are established.Two typical urban bridges are selected to study, by calculating the static load effect of thesetwo bridges under the traffic jams, and the dynamic effects of the engine in idle frequency,reveal the static and dynamic force characteristics of urban bridges in the state of traffic jams.The study finds that the car and bus congestion static loads will not cause direct harm tothe urban bridges. When the urban bridges congestion are caused by wagon congestion, theeffect of the loads have basically been above or very close to the standard value of the bridgeload effects. Considering the overloading of wagon, which even may cause direct damage tothe urban bridges.When traffic congestion occurs, the engine is at idle engine speed, and the enginerotation speed is from600to800r/min (frequency10.0~13.3Hz),this frequency is in thefundamental frequency of most of the bridges. Considering the engine idling vibration, thedisplacement and stress level of the bridges have a significant increase to the displacementand stress level under the static loads. In this paper, example one produces obvious resonancephenomenon under the engine idling at600r/min, but by changing the bridge stiffness canavoid resonance occur.Considering the engine idle vibration, the dynamic coefficients of the urban bridges aregreater than the impact coefficient of the standard, and the dynamic coefficients caused by carcongestion is the largest, the displacement of the dynamic coefficients far exceeds the impactcoefficient several times. Car congestion is happened Almost all the time in major cities, thehappened frequency is high. At present, our bridge standards do not consider this situation,only consider the impact factor. The frequency when the vehicle on is much larger than thepreliminary limited rank frequencies of the bridges, the probability of the resonance is lower.When designing the urban bridges, only consider the dynamic effects brought about bythe impact coefficient regardless of the resonance caused by the idle speed of the vehicle bridge congestion is not enough, in the future should pay attention to the research of thisaspect.