Study On Failure Mode Of Rubber Plate Bearing Under Horizontal Reciprocating Load

Space grid structure is widely used in public buildings such as gymnasium,station,airport and so on because of its changeable space form,beautiful and unique shape,good seismic performance and high degree of industrialization.In addition to providing daily public services,these buildings also serve as earthquake shelters and post-earthquake rescue centers.As the connection node between the upper roof structure and the lower support structure,the support node is the key part of the spatial grid structure.However,the existing earthquake damage shows that the support node is also one of the weak links of the spatial structure.Under catastrophic earthquake,the bearing joint is easy to be in complex stress state,resulting in weld cracking,anchor bolt fracture,bottom plate warping and rib plate buckling,and leading to the occurrence of ultra-low cycle failure and threatening the safety performance of the whole structure in earthquake.Therefore,it is of great significance to study the ultra-low cycle fatigue performance and failure mode of support joints for space grid structures under catastrophic earthquake.Based on the National Natural Science Foundation of China "Research on the ultra-low cycle fatigue performance and evaluation method of bolt ball grid structure under strong earthquake"(51578358),this paper carries out the ultra-low cycle fatigue test of constant vertical pressure and horizontal reciprocating variable amplitude loading for the rubber plate bearings commonly used in large and medium-span spatial grid structures,and studies its failure mode and ultra-low cycle fatigue performance,The ABAQUS finite element software is used to simulate and analyze the test process.Finally,based on the test and simulation results,the seismic design suggestions of rubber bearing under catastrophic earthquake are put forward.The main research contents and conclusions are as follows:(1)According to the requirements of relevant specifications,three groups of 6 rubber plate bearings are designed,the dimensions and specifications of each component of the bearing are determined,the material parameters are determined through the material property test,the test loading scheme and system are formulated,the corresponding test loading device and data acquisition device are designed,and the ultra-low cycle fatigue test is carried out.The test results show that under the action of cyclic load,the specimens have the phenomena of horizontal sliding,support inclination,rubber pad degumming and anchor bolt fracture failure.The root fracture of anchor bolt is the main failure mode of the specimen,and it is the weakest part in the rubber plate bearing.The 24 anchors have experienced the damage process of bump wear,necking bending,root crack initiation and development.Their fatigue life is less than 100 times,and the fracture morphology shows the typical characteristics of ultra-low cycle fatigue fracture.(2)Taking the anchor bolt diameter and vertical pressure as variables,this paper studies its influence on the ultra-low cycle fatigue performance of rubber plate bearing,such as hysteretic curve,skeleton curve,energy dissipation capacity and shear performance,and expounds the failure mechanism of bearing and the law of anchor bolt fracture evolution.The results show that the necking rate decreases slightly with the increase of anchor bolt diameter,but increases with the increase of vertical force.The fullness of the force displacement hysteretic curve of the bearing is not high,which indicates that its energy dissipation capacity and plastic deformation capacity are not high,and its resistance to catastrophic earthquake is general;When the diameter of the anchor bolt and the vertical pressure are increased,the fullness of the hysteretic loop of the hysteretic curve increases,the peak bearing capacity of the bearing increases,the average energy dissipation capacity increases,but the fatigue life decreases.When the displacement amplitude is small in the early stage of loading,increasing the diameter of anchor bolt has little effect on the shear performance of bearing,but it has a greater effect in the middle and late stage of loading with large amplitude;Increasing the vertical force has a great influence on it in the whole process of loading.(3)Using ABAQUS finite element software and considering the influence of anchor bolt damage accumulation,the simulation analysis model of rubber plate bearing is established to analyze the deformation characteristics and failure mode of anchor bolt during loading.The results show that the finite element model is basically consistent with the horizontal sliding of the test support,the rubber backing plate is pulled and degummed,compressed,and the anchor bolt is bent and broken.The finite element simulation is in good agreement with the test results;The hysteretic curve and skeleton curve of the two are in good agreement,and the error of ultimate horizontal bearing capacity is within 5%,which shows that the calculation model has the applicability of parameter analysis.The same as the test results,each anchor bolt experiences the initiation and development of plastic damage and the initiation and connection of crack,and its fatigue damage form is ductile fracture damage.(4)The existing codes mostly focus on the mechanical properties and deformation limit of rubber base plate under earthquake fortification.The anchor bolt is not used as a stressed member,but only for structural requirements.However,the earthquake damage investigation and the research results of this paper show that when encountering the horizontal displacement beyond the design capacity,the anchor bolt will play a role as the main part of the bearing to resist the horizontal force,and its failure will cause the bearing to lose the anchoring effect and induce the collapse of the structure.