Study On The Dynamic Vehicle-Roadway Interation And Tolerable Differential Settlement On The Bridge Approach

Determining the tolerable differential settlement of bridge approach is a key problem for preventing the bump at the end of the bridge, but so far on which there are little theoretical research around the world. So it was suggested as one of the five important topics for future research about the settlement of the bridge approach in the NCHRP 234. Through the Laplace transform method, the author has a systemic study on the tolerable differential settlement of the bridge approach with and without approach slabs.The author respectively gives the calculating model including the end of the bridge and the approach embankment with and without approach slabs according to the real differential settlement that occurred, and, according to the effect to the comfort and safety of the vehicle passing bridge approach, takes the tolerable differential movement of the embankment/structure interface and the tolerable differential slope of the approach slab as the tolerable differential settlement when with and without the approach slab respectively. The vehicle passing bridge approach is thought to have a forced vibration and, with three or five-degree-freedom system as the vehicle model, the vibration equations are given. According to the short lasting time of the vibration above, the Maximum Transient Vibration Value of the acceleration is selected as the comfort index, which is also the criterion to decide if the differential settlement is tolerable. To assure that the dynamic response analysis to the vehicle passing bridge approach can be done by the means of Laplace transform, the author, simplifying the vehicle as two-degree-freedom system, analyzes the dynamic response of the vehicle passing a step by means of Laplace transform and eigen equation method respectively, and the result compared is satisfactory. Then, taking into account the effect of the compression of the approach roadway and the differential slope of the bridge slab, the author analyzes the dynamic response of Man-Vehicle-Road system when the vehicle approaches and leaves the bridge by means of Laplace transform, the curve of Man's acceleration versus time, the vertical force between the vehicle and road versus time, the Man's Maximum Transient Vibration Value and the maximum force between the vehicle and road are got, and the program about the calculating progress above are edited. Based on the analysis above, the influence on the Maximum Transient Vibration Value of some parameters aboutthe vehicle and road such as the movement direction and speed and weight of the vehicle, the differential slope of the bridge slab and the length of the approach slab, are studied, and some conclusion are given. As a result of the analysis above, the procedure and method to determine the tolerable differential settlement and remaining settlement of the bridge approach are given. Finally, to consider the effect of the compression of the approach embankment to the determination of the tolerable differential settlement, this paper, considering the flexible pavement as viscoelastic multilayers and dividing the moving traffic load into Fourier series, presents the formulation and the application of a combination of transfer matrix and Laplace transform and Fourier transform approach to evaluate dynamic response of the flexible pavement subjected to a moving traffic load under modified plain-strain condition. The predictive capability of the model are verified by the laboratory model.