Response Analysis Of Large-Span Structures Under Spatially Varying Earthquake Ground Motions

The ground motion is a complicated time-space process. There are some characters about the seismic in the process of propagation, such as incoherence effect, wave-passage effect, site-response effect and attenuation affect etc. It has been verified that the ground motions inputting at different supports of long-span structures are different, which may be modeled by phase shifts and coherency losses. The phase shifts are caused by waves propagating, while the coherency loses can be attributed to many factors such as source mechanism, path and local site effects, etc. Significant contributions on these issues have been made, and studies on response of long span structures have shown that the effects of multi-support excitations must be considered.In the paper the multi-support excitation(wave-passage excitation) is used in the analysis , the main contents of this dissertation are described as follows:1. The study of multi-support excitation analyses approach. Several analysis methods used to calculate the earthquake response of structures, such as time history method, response spectrum method, random vibration method, are introduced and discussed. The practical application of dynamic balance equations of multipoint excitation are studied and discussed in this paper.2. The responses to travelling-wave effect of earthquake about structures were analysed. Contrast of the multi-support excitation to uniform excitation, the conclusion is that the travelling-wave effect is very important for the structure. The different wave speeds produce variant effects. In general, the litter is the wave speed, the bigger effect is the internal force, but the different wave speed cause the variant effect. And between different waves,delay phenomena is occured. The time is decided by the direction of the transmiting earthquakes wave and the distance of the supports.3. A conclusion is drawn that the seismic response of the long-span structures under multi-support excitations is greatly different from that under consistent excitation. The detailed seismic analysis must be carried out in the design process of the long-span structures.