The Dynamic Characteristic Research Of Isolated Girder Bridge System Under Earthquake Action

With the development of the society and economic, there are more and more bridges appeared in the world. As one of Life line project, bridge structures are in the throat of highway and railway whether in peacetime or in emergency situations, therefore the bridge's safety is very critical to us. In recent years, in our country, earthquake disasters occurred frequently, and the earthquakes had strong destructive power. So how to ensure that the bridges can resist the damage of the earthquake effectively, reduce the occurrence of secondary disasters, and can play an important role in the following rescue action, is an important problem that the engineers have to face and solve. The traditional seismic though is trying to strengthen bridge's strength to achieve the purpose of seismic, but the effect of "hard against hard" is not very good. Isolated technique is proved valid to avoid the bridge being destroyed, so more and more bridges adopt isolated technique. And the purpose of isolated technique is to separate the structure with the earth motion, so the structure can be protected well.Seismic analysis methods are the basic and precondition of bridge seismic design. So in this paper the response spectrum method, the time history method and the random vibration method are introduced. Especially Precise Integration Method (PIM) which has high stability and high accuracy is emphatically introduced, then a method called Pseudo Excitation Method (PEM) is introduced in detail, Precise Integration Method has broken the random vibration approach's efficiency-bottleneck, and appears to be very effective in dealing with such multiple excitation random analyses. In our country, a lot of isolated bridges'isolated devices are Lead Rubber Bearing (LRB), but different bridges with different parameters LRBs, isolated effects are different. So the isolation effect is discussed when parameters of LRB and bridge are changed, some valuable conclusions are drawn.Spatial effects of the ground motion on responses are quite significant to the long span continuous girder bridge and must be considered. Pseudo Excitation Method is an efficient and accurate method of random vibration, in can analyze linear bridge accurately and rapidly, it has applied in linear bridge which considered spatial effects successfully, but this method has applied in isolated bridge rarely. In this paper, LRB is simulated as equivalent linearization model, Pseudo Excitation Method is used to investigate the relationship of spatial effects including wave passage effect, incoherence effect and site response effect with isolated bridge's isolated effect, and the result could be a beneficial consult to the engineers.