Study On Dynamic Response Of High-speed Railway Bridge Under Torrential Flood

With the continuous expansion of Chinese transportation network,the construction of high-speed railway gradually extends to the southwest mountainous areas.There are many rivers in this area,and the geological environment is extremely complex.Torrential flood caused by heavy rainfall or dammed lake break occur from time to time.In order to ensure the safe operation of existing lines,this thesis takes 32.6m high-speed railway simple supported beam with two spans of unequal pier height as the research object,and analyzes the flow field distribution and hydrodynamic pressure around the substructure of the bridge under the condition of no scouring.Considering that the foundation of high-speed railway bridge will form a certain depth of scour pit after many years of service,this thesis further reveals the influence of the change of velocity and height of torrential flood and foundation scour depth on the dynamic response of bridge and internal force of pile foundation.The main contents and conclusions are as follows:(1)Based on the introduction of computational fluid dynamics and turbulence model theory,the hydrodynamic numerical simulation model around bridge pier structure in torrential flood environment is established by using MESHING and FLUENT software,and the standard k-ε two equation turbulence model is selected to solve the flow field distribution and hydrodynamic pressure.Based on the calculation theory of foundation scouring depth,combined with the geological conditions of the bridge location,the maximum scouring depth of the foundation under the design flow is obtained.The variation of flow field and hydrodynamic pressure around the substructure in different scour depth environment is studied.(2)The basic theory of pile-soil interaction and pile group effect is expounded.On this basis,the dynamic analysis model of girder-pier-pile group structure is established by using ABAQUS.Based on the principle of fluid-solid coupling and the solution method of control equations,the third-party software Mp CCI is used to build the intermediate data exchange platform of multi physical fields,and the data of fluid calculation results are transmitted to the established structural model in real time,thus the transient dynamic analysis model of high-speed railway bridge under the action of torrential flood is established.(3)It is found that when the bridge is impacted by torrential flood with different velocities and heights,the overall law of the dynamic response of the bridge pier with time is basically the same,which is shown as follows:the lateral displacement and vibration of the substructure occur at the moment when the mountain torrent impacts the pier;When t=0.06s,the lateral vibration acceleration of pier top reaches the peak value;When t=0.16s,the lateral displacement of pier top reaches the peak.After the lateral displacement and vibration acceleration reach the peak,they both decay rapidly in the form of periodic.After t=2.0S,the lateral displacement will oscillate back and forth at a non-zero value,while the vibration acceleration will oscillate back and forth between 0m/s~2.With the increase of the velocity and height of the torrential flood,the peak value and final stable value of the lateral displacement and acceleration of the pier top increase.(4)When studying the internal force of pile group foundation under the impact of torrential flood,because the free length of pile foundation is relatively short,the bending moment of each single pile in the pile group foundation caused by the hydrodynamic pressure caused by torrential flood is small,which is far less than its own bending capacity.For the most unfavorable internal force of single pile,under the action of torrential flood with different velocity and height,the distribution law of pile bending moment along the depth direction of pile body is as follows:the maximum positive bending moment always appears at the top of pile foundation;Due to the supporting effect of soil around the pile foundation,the length of the negative bending moment zone is greater than that of the positive bending moment zone,and the maximum negative bending moment is less than the maximum positive bending moment.With the increase of velocity of torrential flood,the position of zero bending moment gradually moves up,while the position of maximum negative bending moment gradually moves down.The maximum positive and negative bending moments of pile foundation increase,but the increase of the maximum positive bending moment is larger,which leads to the difference between the maximum positive bending moment and negative bending moment increasing gradually.With the increase of foundation scouring depth,the position of the maximum negative bending moment of the pile moves down gradually;The influence of scour depth on the lower negative bending moment region is more obvious than that on the upper positive bending moment region,and the increase of maximum negative bending moment is larger,which makes the difference between maximum positive bending moment and negative bending moment decrease gradually.