Vertical Seismic Effects On High-speed Railway Prestressed Concrete Continuous Girder Bridges

With the observations of bridge damages which can not be explained by the traditional views, it is found the effect of vertical earthquake is underestimated. So there are more attentions for possible structural failure due to vertical earthquake. Considering the vibration characteristics of bridge structure, the vertical seismic can’t be ignored, it is necessary to do research on this issue.In this paper, the critical seimic response studies of vertical earthquake on prestressed contuious girder bridges are summarized firstly; we take the 5-span high-speed railway prestressed contiuous girder bridge in Tianjin-qinhuangdao passenger dedicated line as the research object. The finite element model of the bridge is established by the finite element program SAP2000. The seismic response of five span prestressed concrete continuous girder bridge is obtained by nonlinear time history analysis under vertical earthquake.Main research contents and conclusions are as follows:1. The response of the moment at the middle of the girder,vertical displace ment,vertical force of bearings,axial force of piers under vertical earthquake are researched.2. The response of the longitudinal prestressing reinforcement under vertical earthquake are researched.3. The nonlinear time history analysis of long span prestressed concrete continuous girder bridge under vertical earthquake is carried out, and the seismic response of the bridge is obtained. Under 8、9 degrees frequent vertical seismic, the bending moment at the middle of the girder and at the support increase to a certain extent than under the action of dead load;the vertical displacement at the middle of the girder increases, the vertical pressure of the bearings increases,the axial force of the piers has a certain increase; but it has a small influence to the bridge. Under 8、9 degrees of rare earthquake, the bending moment at the middle of the girder and at the support increase significantly;the vertical displacement of mid-span exceeds the specification limits; the vertical pressure of bearings are too large, may exceed the vertical bearing capacity, resulting in damage to the bearing "crushing"; the axial force of piers also have a significant increase, May caused axial compression ratio changes, the ductility of the pier increase; the influence can not be ignored. When do the seismic design, we should pay more attentions to the middle span of the girder, bearings and the ductility of piers.4. Under the action of vertical earthquake, through the analysis of longitudinal prestressed steel,The prestressed steel in the top plate, bottom plate and web plate shows similar varation:in the length direction, showing the trend of first increasing and then decreasing.8 degree and 9 degree frequent vertical seismic, the internal force of the longitudinal prestressed reinforcement is smaller, the stress of the prestressed reinforcement has little effect.8 degrees and 9 degrees rare vertical seismic, the longitudinal prestressed steel is larger than under the constant load. Among them, the largest increase is the prestressed reinforcement at the bottom of the girder, the second is the prestressed reinforcement at the deck of the girder, the prestressed steel at the web increase the smallest, which has a certain influence on the stress of the prestressed reinforcement.