| Multi-span long continuous bridges are widely used in expressways and urban bridges because of their good mechanical properties,small deformation,less expansion joints,comfortable driving,beautiful appearance and small maintenance works.Generally,there is only one fixed pier in each longitudinal connection of continuous-beam bridges,and the rest are movable piers.Due to the existence of fixed pier under longitudinal seismic input,the distribution of inertia force between piers is seriously uneven,and the fixed pier absorbs most of the inertia force.For multi-span long continuous bridges,the inertia force of the main girder is very large.The structure of a single fixed pier usually results in serious plastic deformation or even collapse of the fixed pier.The main girder thus produces a large longitudinal displacement,which causes the collision of adjacent beams at the transition pier,further aggravating the earthquake damage.In addition,as multi-span long continuous bridges span large space in the longitudinal direction,seismic traveling wave effect can not be ignored,which may magnify the above-mentioned seismic damage of bridges.In order to reveal the influence of traveling wave effect and collision phenomena on longitudinal seismic response of multi-span long continuous bridges,and discusse the adaptive seismic strategy,First of all,a non-linear dynamic analysis model is established for a multi-span long continuous bridge across the Yellow River in Ningxia,and the influence of traveling wave effect on the longitudinal seismic response of the bridge is studied;Then,considering the collision effect and traveling wave effect at the expansion joint of the transition pier,the longitudinal seismic response characteristics of the multi-span long continuous bridge are studied;Finally,based on the seismic internal force and displacement response of bridge structure,the longitudinal seismic strategies of multi-span long continuous bridge are compared and studied,The main research work and conclusions are as follows:(1)a dynamic analysis model considering various non-linear factors is established by SAP2000 for a Yellow River continuous bridge in Ningxia.The influence of traveling wave effect on longitudinal seismic response of bridge is studied comparatively.The influence law of key factors such as apparent wave velocity is studied by parameter analysis method.The seismic vulnerability of bridge structure is studied based on capacity/demand method.Research shows: The traveling wave effect has little influence on the internal force at the bottom of the transition pier,and can reduce the internal force at the bottom of the fixed pier,movable pier,the shear force at the fixed bearing and the displacement at the beam end,and amplify the displacement of the bearings.The smaller the wave velocity is,the greater the influence of the traveling wave effect is.With the increase of the wave velocity,the influence of the traveling wave effect decreases gradually;the shear capacity of the fixed bearing is lower than the seismic critical point and it becomes the control link of the longitudinal seismic design of the bridge.(2)considering the pounding effect and traveling wave effect at the expansion joint of the transition pier,the longitudinal displacement response characteristics of the continuous-beam bridge are studied,and the effects of the parameters such as pounding gap,pounding stiffness and friction coefficient of the movable bearings on the displacement response of the upper structure and bearings of the bridge under various typical apparent wave velocities are discussed.The variation of the seismic displacement response of the continuous-beam bridge and its parameter sensitivity is revealed.Research shows: The pounding effect will increase the end displacement of the main bridge and the bearing displacement of the main bridge on the East coast,but will reduce the displacement response of the other components studied.Without considering the traveling wave effect,the impact of the pounding effect on the displacement response of the bridge will basically decrease with the increase of the initial gap,and basically increase with the increase of the pounding stiffness.The change of friction coefficient of movable bearings will have obvious influence on the displacement response of bearings,and its response value decreases gradually with the increase of friction coefficient;when considering traveling wave effect,except for a few cases,the influence of the change of parameters on the displacement response of the bridge under pounding is uniformly stimulated;the impact of traveling wave effect on the pounding phenomenon is more complex,The impact law of the traveling wave effect working on the pounding phenomena is different in different parts of the bridge and different pounding parameters.(3)Based on the characteristics of seismic internal force and displacement response of bridge structures,the longitudinal seismic strategies of multi-span long continuous bridges are studied within the framework of classical seismic design codes at home and abroad,and the effectiveness of seismic strategies such as multi-fixed piers and seismic isolation design is compared.On this basis,the reasonable aseismic strategies considering traveling wave effect and pounding effect for multi-span long continuous bridges are summarized.Research shows: Multiple fixed pier strategy has certain effects on improving the internal force response of bridge structures.The internal force response of key components is lower than that of the original working conditions,and the reduction range increases with the increase of the number of fixed piers,but the displacement response is not improved.Seismic isolation system can effectively reduce the internal force at the bottom of fixed pier and make the overall force distribution of bridge more reasonable,but it may cause the problem of insufficient limit.The seismic strategy of the isolation bearings with dampers can make up for the deficiency of the isolation strategy in the limitation problem,and its effect is ideal. |
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