The Seismic Response Of LRB Isolation Bridge Under Bi-Direction Earthquake

Passive energy consumption equipment is the important tool which used to resist sudden dynamic loads(as: wind or earthquake) in civil engineering structures. For bridge structure the isolated bearing is usually put between the superstructure and pier or abutment, the lead rubber bearing(LRB) is widely used in bridge because of its good mechanical properties and energy dissipation capacity. On one hand , it can relief the constraining internal forces caused by temperature change; on anther, it also can dissipate the earthquake energy by increasing the structure vibration period and added damping.The Theoretical Research on isolator is rich and systemic with the development in bridge isolation. In the previous study the single freedom system is more considered, and the equivalent Stiffness and equivalent damp is got by using linearized model and spectrum analysis. However the practice indicated that there is large error if using the single freedom liner system to analysis the isolator earthquake response。One-sidedly concerns single direction isolation but not multiway isolation would lead to result distortion. There are many transverse breakage bridges in practice earthquake disaster. Therefore it is necessary that the isolated bridge earthquake response we analyse by using the Multi-degree of Freedom System and considering bearing two-way coupling effect.In this paper the selected bridges is a typical three spans continuous deck, Bouc-wen model can be used to simulate the nonlinear dynamic behavior of the force-displacement relationship for LRB, and the bearing longitudinal and transverse coupling effect is considered, Beam4 element is used to simulate the superstructure and pier and abutment. The property matrix are obtained by modal analysis using the FEM. The nonlinear motion equation which involved the contribution of LRB is built by considering the isolated effect of bearing. The Runge-Kutta iterative strategy is used to solve the nonlinear governing equation of motion, and the time history program is composite by using MATLAB. Base on the model and considering multi-parameter effect, a large quantity of calculation and analysis are carried out to obtain the laws of the bi-direction response of isolated bridge. During the analysis, different factors, such as bridge structures, stiffness of LRB, seismic site and intensity are considered.