Seismic Respones Analysis For Long-Span Bridges Under Multi-Support Excitations

Bridges are vital elements of the economic functioning of modern societies. As one of the most devastating natural disaster, earthquakes always cause tremendous losses of life and property. In the event of an earthquake, failure or even damage of a bridge can pose a significant life hazard, and cause difficulties in the emergency response to the earthquake as well as in subsequent recovery activities.Seismic ground motions can vary significantly over distances which are of the same order of magnitude as the dimensions of some extended structures, such as bridges. Three phenomena are responsible for these variations: the difference in the arrival times of seismic waves at different stations;the loss of coherency of the motions due to reflections and refractions of the waves in the heterogeneous medium of the ground, as well as due to the difference in the manner of superposition of waves arriving from an extended source at various stations;and the difference in the local soil condition at each station and the manner in which they influence the amplitude and frequency content of the bedrock motion. Recent analyses with array recording have shed light on the nature of these effects and their relative importance. It is important to develop reliable methods for predicting the performance of new bridge designs and for evaluating the existing structures.It is known that, under realistic conditions, the variations in the support motions can significantly influence the internal forces generated in the structure. While in most cases the magnitudes of these forces are reduced, there are situations where the variations in the support motions may result in larger internal forces. It is important for a better understanding of this phenomenon, and for the development of practical analysis methods that can accurately account for its effects.The main contents of this dissertation are described as follows:1. The simulation of multipoint earthquake wave. The suitable earthquake wave is very important for the analyses of structure. In this paper, the method to simulate multipoint earthquake wave is systematically studied.2. The study of multipoint excitation analyses approach. Several analysis methods used to calculate the earthquake response of bridges, such as the time-domain approach, the frequency-domain approach, the approximation approach and the mixed approach, are introduced and discussed. The practical application of dynamic balance equations of multipoint excitation are studied and discussed in this paper.3. The analyses of the effect of multipoint excitation.4. The contrast of multipoint excitation to uniform excitation. The conclusion is that the travelling-wave effect is very important for the design of Long Span concrete filled steel tube arch bridge.