Study On Seismic Performance Of Long-span Cable-stayed Bridges Under Multi-support Excitations

In the past few years, a lot of cable-stayed bridges have been built in the world because of their special superiority in economy, structure and architecture and so on. Because bridges are lifeline engineering, it is very important to make detailed seismic analysis and design for them.Seismic ground motions can vary significantly in space. Generally, seismic response analysis of common structures is made without considering spatial variations of seismic ground motions. This is acceptable for short-span structures. But for long-span structures such as cable-stayed bridges, spatial variations of seismic ground motions can be notable and can't be neglected in the seismic response analysis. Hence, seismic response analysis of cable-stayed bridges should be carried out with considering spatial variations of seismic ground motions. The main aim of the paper is to investigate the response characteristics of cable-stayed bridges under seismic ground motions with spatial variations.The common equations of motion of the structures under uniform seismic excitations aren't applied to the structures under multi-support seismic excitations. The equations of motion of the structures under multi-support seismic excitations are detruded. The procedure is to decompose the nodal displacements into pseudo-static displacements and dynamic displacements. The pseudo-static displacements are solved with making use of static equilibrium conditions. The dynamic displacements are obtained by solving dynamic governing differential equations. Seismic response analysis of cable-stayed bridges under non-uniform seismic excitations, namely wave passage effect, is carried out with time history method. The effects of wave passage effect on the responses of cable-stayed bridges are investigated by contrasting these responses with those responses of cable-stayed bridges under uniform seismic excitations. The results indicate that the responses of cable-stayed bridges under non-uniform seismic excitations differ from those under uniform seismic excitations up to 40%. Therefore it is necessary to take wave passage effect into account in the seismic analysis of long-span cable-stayed bridges.In recent years, random vibration method has found more and more application in the field of response analysis of long-span structures under multi-support seismic excitations. Computation formula of stochastic responses of structures under multi-support seismic excitations is presented based on random vibration theory. Based on the above computation formula, the stochastic response characteristics of cable-stayed bridges under seismic ground motions with spatial variations, including wave passage effect, incoherence effect and local site effect, are investigated. The following conclusions are obtained: Wave passage effect has a more significant effect on the seismic responses of cable-stayed bridges than incoherence effect. Responses of cable-stayed bridges are considerably greater for the case of the soft soil than for the case of the firm soil under the same seismic excitations.In the end, effects of some factors on the response characteristics of cable-stayed bridges under multi-support seismic excitations are investigated. These factors involve velocity of earthquake wave, span of cable-stayed bridges, direction of seismic ground motions, connect manners between the tower and the girder, stiffness of the tower and the girder. Based on the above study, Some useful conclusions are obtained.