Study On Impact Coefficient Of Girder Bridge On Highway Freight Corridors

Bridge is an important part of highway freight corridors. RC/PC simple supported girder bridges and continuous girder bridges have the advantages of simple structure, convenient construction, occupy a large proportion in bridges. Due to the vibrations of vehicles, pavement irregularity and other factors, when vehicles cross bridge,they will cause generate impact on bridges..The impact coefficient in General Code for Design of Highway Bridges and Culverts is only a function of the fundamental frequency, but the dynamic characteristics of bridges, the vibration characteristics of vehicles and driving condition, pavement irregularity and so have great effect on impact coefficient. The reasonable of impact coefficient and its application scope is a debatable issue.Carrying capacity and wagon flow on highway freight corridor are very large. In this paper, according to the characteristics of highway freight corridor, the midspan displacement impact coefficient of simple supported girder bridges and continuous girder bridges are calculated and analyzed.1. On the basis of domestic and foreign literature, development and research status on impact coefficient were reviewed and summarized. Compared the code value of impact coefficient of China and other countries. Impact Coefficient in different countries have large difference. Some of the results appeared in literatures and impact Coefficient in our current highway code have opposite trend.2. This article introduced the development of models about vehicle-bridge interaction, established three-axis two-dimensional vehicle model, built bridge models with the modal method, generated pavement irregularity with trigonometric series, deduced the interaction equation of vehicles and bridges, solved the equation by Newmark-β method, compled program to solve the interaction equation of vehicles and bridge with fortran language. By comparing the calculation results with the literature, this article verified correctness of this program.3.Refer to the bridges along a highway freight corridor in Inner Mongolia,this paper built simple supported girder bridge and continuous girder bridge models and simulated vehicles uniform normal driving, traffic congestion,vehicles brake on the bridges and accelerate by bridge.Considered the beam type, vehicle weight, vehicle speed, driving time interval, number of vehicles, pavement irregularity and so on. This paper generated conditions with orthogonal test and calculated the conditions using that program.It anslyzed impact coefficient trends with factors under various driving states and sensitivity of each factor. The results show that, different driving conditions, the sensitivity of impact coefficient on each factor is different and the trend of each factor is not exactly the same. Pavement irregularity is the most influential factor of impact coefficient and impact coefficient with pavement irregularity grade improvement increases greatly. Impact coefficient of vehicles uniform normal driving state is slightly larger than congestion and braking state,smaller than accelerating state.4. Considering the unfavorable factors level, this paper generated impact coefficient calculation conditions of simple supported girder bridges and continuous girder bridges by permutation and combination. According to the calculation results, this paper fitted the formula of impact coefficient containing fundmental frequency and pavement irregularity and compared the fitted formula with the current highway bridge impact coefficient code. Results show that,the code is larger under good pavement irregularity and as fundament frequency increases,the calculated values decrease.5.This paper measured the impact coefficient of a bridge with a truck and compared the measured value with the result in this paper. The formula is fitted with multi trucks and other adverse factors levels,its value is larger.