Research On Dynamic Characteristics For67-type Railway Pontoon Bridge

Compared with the conventional bridges, floating bridges are less costly with a short execution term, so they have been more and more widely used gradually. In the meantime, many scholars at home and abroad are both making the different theoretical exploration and experimental research of mechanical characteristics for floating bridges. However, the fluid were often assumed to be static in most of these methods, in which the floating bridges are only bear the buoyancy, but the effects for floating bridge under different conditions of flow(such as water depth, flow direction,wave height and frequency, etc.) have been not taken into account. Based on the survey of the present research situation, from a new point of view the paper will find out a more reasonable method which can be used for the analysis of hydrodynamic effect for the floating bridges.Firstly, by using potential theory and related mathematical methods, the expressions of total velocity potential and the boundary conditions for the flow field for a simply floating model are obtained in present paper. Secondly, based on the third Green function and the 3-D source distribution method, the velocity potential can be obtained. Then, with the help of finite element knowledge, according to the coupling effects of those static and dynamic loads on the different parts of floating bridge, the dynamical equations for the floating bridge can be deduced in both time domain and frequency domain. By solving these equations, the changes of the force,displacement, acceleration, bridge deflection, rotation and other mechanical parameters under the force of wave, trains and other loads can be given. As a result, a new idea for the research of mechanical characteristics for 67-typy floating bridge is proposed.In order to validate the reliability of the present method, a floating bridge example is carried out as the calculation model. By compared with the result by using this method and other results in the reference, two kinds of results are very much in agreement, it can be known that the present method is valid. The method also has thegeneral applicability, which can be used to analyze the hydrodynamic characteristics for various floating bridges.Then, by the present method, the influence of the wave height, frequency and other parameters on the dynamical characteristics for a 67-type emergency railway pontoon bridge on the Ji canal in Beijing-Shanhaiguan line are investigated.Finally, the combined effects of the hydrodynamic of wave and train loads on the floating bridges are studied, and the carrying capability of the pontoon bridge under the different axle load and speeds are discussed.