| China is located in the middle of two active seismic zones, resulting in frequent occurrence of earthquakes. The serious consequences caused by the earthquake are not only huge losses of property, but also heavy casualties. With the rapid development of economy and the continuous promotion of urbanization, Long-span rail-cum-road cable-stayed bridge has been greatly developed and widely applied. As an important part of the traffic key project and the lifeline engineering, bridges destroyed in the earthquake, which will cause property loss and bring extremely difficulties to the post-earthquake relief. Therefore, it’s of great significance to study the seismic response of this type of bridge and to take reasonable and effective seismic resistance measures to ensure the safety of the bridge in the earthquake.Based on the above background, realistic calculation model of the bridge is established combining with practical engineering example. Dynamic characteristics are calculated. Response spectrum analysis and time-history analysis are both carried out. Seismic resistance measures of the bridge are studied as well. The main works are as follows:(1) Development status and characteristics of Long-span rail-cum-road cable-stayed bridge are introduced. Summary of earthquake and earthquake damage are also presented. In addition, the existing bridge seismic theories are summarized and theoretical basis of seismic response is elaborated, which provide a better understanding of the calculation process in this thesis.(2) By use of design information of a cable-stayed rail-cum-road bridge, spatial finite element model is established by Midas Civil software, considering the cable’s geometrical non-linearity and pile-soil interaction. The dynamic characteristics of the bridge is calculated and analyzed.(3) According to the ground motion parameters provided by "safety assessment report", the response spectrum curves are determined. Then the response spectrum analysis is completed under two possible levels (El and E2) and two different seismic load combinations. The effects of levels and combinations on the seismic response of the bridge tower, key sections and key nodes are checked respectively.(4) According to acceleration process data provided by "safety assessment report", time-history analysis under uniform excitation is carried out and the seismic response of key sections and key nodes is compared with the result of response spectrum analysis. Furthermore, time-history analysis under non-uniform excitation is also carried out, considering the influence of traveling wave effect on force of key section and displacement of key nodes.(5) the basic principles of damping and seismic isolation are firstly introduced, then influence of the horizontal stiffness of movable rubber bearings have on seismic response of the bridge is studied. Viscous dampers are chosen to apply on the bridge to reduce the seismic response. Parameter optimization of the damping coefficient of viscous dampers is conducted and the influence on reduction of seismic response is also studied. |
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