Analysis On Slip Damage Of Laminated Rubber Bearing Under Strong Earthquake And Its Influence On Seismic Performance Of Bridge

At present,small and medium span girder bridges are still the main form of bridges in China,and laminated rubber bearing is widely used in small and medium span highway bridges.The post-earthquake investigation report of Wenchuan earthquake shown that the damages of girder bridges in the seismic area were mainly the slip of the laminated rubber bearings,damage of blocks,displacement of girders and falling girders.The damage rate of piers was very low,which resulted from the frictional sliding of the support reduced the inertia force of the upper structure that transmits to the pier.It is beneficial to the overall seismic resistance of bridges.And the scholars have studied the the bearing works normally in detail,but the research on damages of the bearing under earthquake is still developing.This paper will analyze the performance and damage after the bearing slip,and explore its influence on the bridge seismic resistance,which mainly includes the following points:(1)The laminated rubber bearing is placed between the upper steel plate and the concrete pad for compression-shear quasi-static destructive test.The test phenomena such as curling and void after friction sliding of the laminated rubber bearing is observed.The horizontal shear force,equivalent stiffness and hysteretic energy consumption of the bearing are analyzed through the hysteretic curve,and the variation law of parameters in the sliding process of the bearing is summarized.The skeleton curve is made and adjusted to the constitutive model which belongs to the bearing slip,and this is used in the following seismic analysis.(2)A refined finite element model of the laminated rubber bearing is established,and the accuracy of the model is verified by the test data.The whole process of the bearing from working normally to frictional slip is analyzed.The damage is expressed by steel plate stress,total rubber strain and stiffness.The results show that the steel plate will yield partially,but the rubber is not damaged.The bearing size and friction conditions are changed to explore the influence on the bearing damages.We can see the bearing size change and the increase of the friction coefficient after sliding have a great impact on the deformation and internal damage,while the friction coefficient has little impact on the damage when the bearing is not sliding.(3)Based on the finite element model and machine learning,the bearing damage degree is classified.According to the magnitude of pressure and shear deformation,the bearing damages are divided into four levels,combined with the description of appearance damages.And then the bearing damage degrees under earthquake action are expressed accordingly.(4)A finite element analysis model of a three-span prestressed concrete simply supported box girder bridge is established.The bearing deformation increases from linear elasticity to slip by inputting seismic wave excitation with different amplitude.The above bearing rating mechanism is used to reflect the damage degrees of each bearing,and the influence of the corresponding bearing on the block,pier and girder collision is explored.At the same time,the influence of bearing sliding and block failure on the overall seismic performance of the bridge is considered.The results show that the bearing sliding will increase the girder displacement and further damage the block,but it will also reduce the pier response,and the bearing sliding and block failure will have greater energy dissipation capacity.