Seismic Response Analysis For Long Span Hybrid Girder Cable-Stayed Bridge

In recent years, our national economy has rapidly developed, traffic cause is prosperous, and the construction of bridges with long span has made an unprecedented progress. The cable-stayed bridge has won the favor of designers due to its advantages of rational structure and graceful configuration. The bridge with long span is usually the traffic artery, so once the bridge collapses, the traffic network will break down and the transportation will be severely affected. Earthquake is one of the most important factors which result in bridge collapse and the bridge collapse in earthquake will not only bring about serious economic loss, but also seriously affect the earthquake relief and reconstruction work. Therefore, it is of important economic and social benefits to study the laws of earthquake responses of bridge structure and to precisely design the bridge structure to assure bridge safety in earthquake.The hybrid girder cable-stayed bridge with long span is a new type and satisfactory structure, for it integrates the advantages of concrete cable-stayed bridge and steel box girder one that engineering investment decreases and the crossing ability of bridge increases. Fuzhou Changmen Bridge is a hybrid girder cable-stayed bridge being designed and its main bridge, a floating and flexible system in longitudinal direction, is composed of three spans including a steel box girder main span of 550m in length and two concrete box girder side spans.On the basis of Changmen Bridge, the cable-stayed bridge analytic model is established by using finite element software SAP2000 to study the bridge dynamic characteristics. The response spectrum analysis on the cable-stayed bridge is performed according to local site situation and suggested parameter design response spectrum offered by the document of earthquake safety evaluation. The time history analysis is performed according to natural earthquake wave. The results indicate that the lateral bridge displacement predominates with the combining action of lateral and vertical seismic ground motions; the longitudinal bridge displacement predominates with the combining action of longitudinal and vertical seismic ground motions; the bending moment of tower, the axial force and shear force at the bottom of the tower induced by the combining action of lateral and vertical loads are much larger than those induced by the combining action of longitudinal and vertical loads; the longitudinal displacements at two ends and midpoint of the main girder are virtually same; The structural dynamic responses with the combining action of many seismic waves in different directions are not definitely larger or smaller than those induced by single seismic wave; as regards the maximum magnitudes of displacement and reaction, the results obtained by response spectrum analysis are all larger than those obtained by time history analysis, but the response spectrum analysis can obtain the maximum magnitudes of bridge earthquake response and can not reflect the real response process of bridge structure during the action of whole seismic wave and the final mode of bridge structure after the action of seismic wave.