Experimental Study On Ultra-low Cycle Fatigue Of Transition Plate Support

With the rapid development of economy and society,spatial grid structure has been widely used in all kinds of public buildings because of its beautiful shape and good economic benefits.China is located between the two major seismic belts in the world--the ring Pacific seismic belt and the Eurasian seismic belt,often affected by earthquakes,the grid structure not only needs to meet the needs of daily activities,but also needs to be used as a shelter and relief base when the earthquake occurs.Multiple grid structure damage and related research found the collapse of grid structure under the effect of disastrous earthquake damage has obvious characteristics of ultra-low cycle fatigue.Therefore,the study of the ultra-low cycle fatigue performance of the grid structure has become an important topic in the field of disaster prevention and reduction.In the construction of grid structure,the support node is the key part connecting the grid system and the supporting system,which is the key node in the seismic design.The grid structure should assume the function of refuge after the earthquake,and is often designed as a key fortification building.It should be guaranteed that the grid structure can be normally used in the earthquake or quickly repaired after the earthquake.However,the failure of the nodes of the grid structure will hinder its safe use.The investigation results of multiple earthquake disasters in China and abroad show that the nodes of grid support are often damaged in earthquakes.Based on the National Natural Science Foundation of China “Study on Ultra-low Cycle Fatigue Performance and Evaluation Method of Bolt Ball Grid Structure under Strong Earthquakes”(51578358),The experimental research on ultra-low cycle fatigue of transition plate support nodes was carried out.The main contents and research results of this paper are as follows:(1)With the actual grid structure as the background,a full scale test model of flat support suitable for small and medium span grid is designed.Through ultra-low cycle fatigue test on nine specimens of the three types of models,the failure mechanism and failure mode of the plate support.under horizontal reciprocating load are obtained,which provides reference for the seismic design of the plate support.(2)The ultimate bearing capacity,hysteresis curve,skeleton curve,energy dissipation capacity,stiffness degradation and other ultra-low cycle fatigue properties of the bearing model were analyzed to obtain the yield displacement of the transition plate bearing joints under increased horizontal loading,which provided data reference for the constant amplitude loading of the later test.(3)The variation rules of the bearing capacity degradation,the angle of anchor and the overall angle of the support were analyzed in detail during the whole loading process of the specimen,and the rationality of the yield displacement determined by the specimen was verified.The damage accumulation degree of the joints was quantified by the degradation degree of the bearing capacity of the specimens after yielding,the angle of the anchor and the angle of the support,so as to provide a reference for the evaluation of the residual bearing capacity of the post-earthquake support.(4)The failure modes of the test models are all anchor bolt bending shear failure,which is consistent with the failure modes of support in the actual earthquake damage.The macro morphology and fracture characteristics of the bolt after fracture are analyzed to verify that the bolt failure pattern has ultra-low cycle fatigue characteristics.The plastic deformation area of the bolt is judged by combining the bolt elongation and neck shrinkage,and the ductile performance,fracture location and failure characteristics of the bolt are analyzed...