Study On Service Safety Performance Of Railway Bridge Under Foundation Scouring

With the rapid development of Chinese railway system, a large number of bridges have been built across the river.The pier in the river will reduce the cross section area of river channel, and change the surrounding flow condition. It is bound to have strong scour on pier foundation.Severe cases can lead to foundation caving, then reduce the bearing capacity of structure. When the flood hit greatly, it increases the damage probability of the bridge. Scouring reduce embeded depth of foundation and the overall stiffness of bridge.As a result, scouring can affect the dynamic performance of the bridge.lt is easy to cause resonance destruction when trains across the bridge. Therefore, the study on service safety performance of railway bridge under foundation scouring is of great significance.When analyze the pile-soil interaction, for the convenience of calculation, we often adopt linear analysis methods, such as "m" method. However, it can not consider the nonlinear feature between pile and soil.And the study on dynamic performance of the bridge under the scouring effect is too little.In this dissertation, the method of scouring calculation is summarized.Considering the nonlinear feature of soil, static analysis and dynamic analysis of bridge under the scouring effect is conducted based on "p-y" curve method.The main contents and conclusions are shown as follows:(1) Analyse the various kinds of scour mechanism. Summarize the scouring formula at home and abroad, and calculate the engineering examples based on main scouring formulas.Calculation results show that the domestic formulas have more comprehensive considerations. In the actual engineering calculation, we can give priority to choose domestic formula, and take the safety results.(2) Calculate the pile stiffness by the method of "m" and "p-y" curve. Establish the pile caps bottom equivalent stiffness (no-pile) model and pile-soil spring (whole-pile) model.Because the "p-y" curve method can consider the nonlinear characteristics of the soil, the pile-soil spring model will reflect the actual situation between piles and soil.(3) Establish the bridge finite element model based on the bridge across the Second Songhua River. Compare the key part’s change of the internal force and displacement before and after scouring. Analysis results show that although the scour can increase the internal force of pile foundation significantly, they are far less than the pile foundation bearing capacity due to their small numbers, and there is no security threat.(4) Carry out the bridge’s modal analysis considering the overall scour and uneven scour.The transverse frequency of no-pile model is much higher than that of whole-pile model under the same scouring condition.Therefore, to accurately analyze the bridge structure dynamic performance, we suggest adopt the whole-pile model.At the same time, establish the CRH2 vehicle model by ABAQUS.Solve the modal frequency of the vehicle, and compare with bridge transverse frequency of vibration.The resonance frequency range from 0.947 Hz to 1.264 Hz.When scouring from 5m to 10m, the bridge transverse frequencies decreased obviously. Under the condition of different high pier, the vast majority of the vibration frequency of the bridge go into the resonance frequency range.This can lead to resonance of the train-bridge system, then affects railway running safety.