Soil Seismic Responses And Its Effect On The Behavior Of Suspension Under Earthquake Excitation

Bridges, especially the large span bridges, play an important part in transportation. Once they are destroyed in the earthquake, it is very difficult or even impossible for people to repair in a short time, which will be a huge obstacle for people to rescue and rebuild after the earthquake. The cost and social influence of long-span suspension bridges are much greater than other general bridges, so it is very necessary to study of response and possible destroy of the suspension bridges under earthquake loads.The difference among the mechanism of ground motion, the transmission characteristics of seismic waves, the topography and geological structure makes sesmic waves change in time and space. Especially for the suspension bridges, the multi-support excitation problem prominent in the earthquake is well worth of attention. So the research of response under multi-support excitation is particularly important. The following are the main work and some conclusion:1. Several seismic analysis methods for large span structures is summarized, then the advantages and disadvantages is also compared.2. Three dimensional finite element model of a suspension bridge is established using general finite element software ANSYS. Dynamic characteristics of the suspension bridge is calculated, a conclusion is drawn that the pile-soil interaction make the structure system more flexible while the frequency decreases.3. A computer program for equivalent-linear earthquake site response analyses of layered soil deposits (EERA) is used to analyze the site soil of the bridge, and the result is that the surface seismic reaction is larger than the bedrock because the foundation is covered with soft soil.4. The influence of pile-soil interaction, traveling wave and the propagate direction of seismic wave on the suspension bridge is considered and the large mass method is used to analyze the time history response of the bridge in earthquake. Calculation results are put forward and the conclusions is bellow:①Pile-soil interaction decreases the longitudinal internal forces response of the bridge tower, but increase the longitudinal displacement;②Traveling wave effect increases the displacement reaction of the suspension bridge, but decreases the longitudinal internal forces reaction of the tower’s bottom and crossbeams,which is especially favorable for the more rigid tower;③Due to excitation of non-conformance, traveling wave effect have a great impact on the internal force and displacement reaction of stiffening girder;④When seismic wave transmit along two longitudinal direction, the longitudinal bending moment of tower bottom is different.5.For suspension bridge with a floating system, longitudinal damper is set at the end of the beam.①It makes the longitudinal displacement of main girder decrease.This effect is more obvious under the uniform excitation, and less obvious under traveling wave excitation;②Makes the longitudinal displacement of the top of tower decrease,but have few effect on vertical displacement of the middle of the main span;③Makes the longitudinal moment response of the tower bottom increase under uniform excitation, but decreases it under traveling wave excitation.