Identification Of Moving Forces On Bridge From Vibration Responses

With the development of economy and society, the quantity of transportation has increased evidently, vehicular load are getting more and more heavier, the amount and speed of vehicles also has increased. In the meanwhile, with the application of high strength material, quite a lot of bridges are very fine. As a result, information of vehicular load on a bridge deck is essential to bridge design. When the vehicle is traveling on a bridge, the moving interaction forces are time-dependenr. Identification of moving interaction forces is the second problem of inverse problem of structural mechanics, and is essential to the design of bridges.In recent years, a new method to identify moving loads using measured vibration responses has been attached more importance to, among them are the time-domain method and the frequency-time-domain method. The time-domain method is used in this article. To found the relationship between the moving forces and the vibration responses is the key of identification of moving forces by the time-domain method. If the vibration responses of the bridges has been measured, the moving forces can been identified by calculation.In this article, a bridge is modeled as a three-dimensional thin rectangular plate, of uniform thickness and isotropic material. The identification of moving forces is studied with vehicle model of time-varying force model, one degree-of-freedom model and seven degrees-of-freedom model. The effect of incomplete vehicle speed and noise are also considered.Computer simulation is used in this article. In this process, the vibration response of a bridge is computed by solving the super system of vehicle and bridge at first. Consequently, based on this vibration response, the moving loads can be identified. In contrast to the real moving loads, the effect of identification method can be proved. The following aspects are studied in this article:1. Based on the equation of motion for three-dimensional plate, the equations of moving loads identification are given.2. The vibration character of three-dimensional plate is analyzed by the method of combination of functions.3. The dynamic response of bridge under moving vehicles is analyzed in the model space.4. Computer simulation method and different vehicular models are used in the study of identification of moving loads.The present time-domain method has its own shortages, such as it only can be used in ideal model of bridges, the identification depend on the interpretive solution of modei shape functions of the plate. In addition, the amount of calculation is great. And thus this method of identification should be improved.