Research On Coupling Motion Of Long-span Cable-Stayed Bridges And Their Approach Bridges

Past earthquakes show that when subjected to seismic loadings, vibrations oflong-span cable-stayed bridges and their approach bridges (usually are simplesupported bridges or multi-span continuous bridges) are coupled. Also the seismicresponse affects each other. Longitudinal coupling motion may cause pounding orfalling down of main girders. On the other hand transversal coupling motion maychange respective vibration characteristics and seismic response.Based on reading and understanding of related literatures on pounding theoryand method of bridge structures, the many kinds of methods are summarized. Andthen under the background of a typical two tower cable-stayed bridge, a dynamicmodel including contact elements is set. The pounding effects between adjacentgirders and the effects because of transversal vibration are obtained using nonlineartime-history analysis under longitudinal earthquake.When considering the aspect of longitudinal coupling motion, at first detailedanalysis on the pounding effects at the movement joints of main bridge and theapproach bridge is made, and the influence of pounding is also discussed. Also therigidity and damping coefficients of spatial contract elements used in the model areconsidered and compared. Then in order to mitigate the pounding effects to thestructure, dampers are used and its effect is researched. At last the effects of someparameters such as adjacent bridge segments period ratio, natural periods ratio, initialgap at expansion joints are investigated. Some conclusions are obtained.When considering the aspect of transversal coupling motion, first three modelsare set-only main bridge, only approach bridges, the whole bridge. And theninfluences on vibration characteristics of the three models are analyzed. Based onthose results, influences on seismic response of transitional pier, fixed pier, maintower are all researched. In the end proper bearings, isolation devices, and otherreasonable structural connectors which can reduce the coupling response of bridgesare discussed.