Study On The Effect Of Heavy Traffic On Fatigue Of Expressway Bridge

With the development of transportation, the vehicle load type on the expressway bridges has changed greatly and the trend of overweight load is obvious. When overloaded vehicles passing through the bridge frequently, it will cause serious damage to the bridge, and may even lead to crack of beam. Although the cracks will be temporarily closed when unloading after the bridge cracking, this kind of damage will cause bridge’s carrying capacity decline, and even can’t for normal use. For most old bridges, they have cracks already, because of overloading vehicles frequently passing through the old bridges, which leads to the cracks rupture violently, eventually may even causes bridges collapse. Thus, in order to ensure the safety of the bridge, and provide technical references to the construction units and bridge operation management department, this paper do many traffic investigations about multiple expressways in Hebei Province and fatigue test researches, the main researches are as follows:1. Through actual investigations and data collections about the volume of traffic, traffic composition, axle load, wheel base, vehicle speed and vehicle spacing in Hebei multiple expressways, the proportion of different models and different load level of vehicles were analyzed, the discipline of probability distribution was determined. According to the fatigue damage equivalent principle, the actual vehicle load spectrum was obtained. Compared with the standard grade expressway-Ⅰvehicle load effect, auto load increase coefficient under heavy traffic load was put forward.2. By the method of four stages, the traffic forecast about the future of Beijing Hong Kong and Macao expressway was carried out, and the main influence factors about the changes of the future traffic volume were analyzed. Overloaded vehicles division lane rule was concluded through the actual site survey about four and six lanes in expressway, respectively. Grey GM(1, 1) prediction model, BP neural network forecasting model and grey-BP neural network combination forecast model were used to predict overloading traffic driving rule about six lanes(eight lanes) expressway, the predict results indicate that the grey-BP neural network combination forecast model prediction is excellent, and the prediction has highest accuracy.3. Based on the 16 meters standard span prestressed concrete beam in Beijing Hong Kong and Macao expressway(Beijing-Shijiazhuang section) reconstruction project, the fatigue properties of prestressed concrete beam under the effect of long-term overloaded were investigated through reasonable reduced scale model and constant amplitude fatigue test researches, such as change rules of concrete strain, non-prestressed and prestressed reinforcement, development rules of deflection and crack, stiffness degradation and allowable fatigue life under the effect of overloading.4. The research on the failure pattern and failure characteristics of prestressed concrete beam under two levels of variable amplitude fatigue load was carried out by variable amplitude fatigue test, the effect of loading sequence and load level on fatigue life of prestressed concrete beam was obtained. Miner criterion and modified Miner’s guidelines were used to estimate the variable amplitude fatigue life. The calculation results show that the Miner criterion to estimate the allowable fatigue life prediction of variable amplitude fatigue test is dangerous, on the contrary, the revised standards of Miner is more accurate, and more conservative. At last, allowable fatigue cumulative damage threshold DCR is 0.8 by two levels of variable amplitude fatigue test.5. A entity model about 16 meters span prestressed concrete beam was set up by finite element analysis software. According to the statistics analysis of the traffic survey data, combined its related distribution, the Monte Carlo(Monte Carlo) method and random traffic simulation program compiled by Matlab software were used, the typical vehicle model and the stochastic vehicle model were loaded on the bridge with the finite element model to simulate of the actual operating cars across the bridge, the transient dynamic analysis was carried out by finite element software. Fatigue damage of the typical vehicle under different vehicle spacing, different speed conditions, intensive operating condition, and the general operating state is calculated by applying theory of fatigue cumulative damage.