Esearch On Element Plastic Hinge Model Considering The Effect Of Damage And Joint Stiffness

With the development of large-span structures,spatial grid structures are widely used in social public buildings.Such structures not only meet people’s daily needs,but also act as emergency shelters under special situations.However,under the action of catastrophic earthquakes,this type of structure is subjected to large-displacement cyclic reciprocating loads,and ultra-low cycle fatigue damage cumulative damage may occur.Seismic damage analysis and related research show that the deformed shape of the damaged rods mainly appears to produce different degrees of buckling plastic deformation during the earthquake,and some even form buckling plastic hinges near the middle of the rod.Therefore,it is particularly important to study the morphological characteristics and mechanical properties of the space grid structure’s plastic hinges under catastrophic earthquakes,and to analyze its failure process and cumulative damage failure mechanism.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 Earthquake"(51578358),this article takes the round steel tube and bolt ball composite specimen model as the research object.Research the cumulative damage of material damage from the theoretical,experimental and simulation.The main work and research results are as follows:(1)Through the ultra-low cycle fatigue test of 9 sets of 88.5mm diameter and 4mm wall thickness round steel tube and bolt-ball composite specimens,the formation and development process,position,ellipse,length and elongation of plastic hinges were obtained,which provide a reference for the future setting of plastic hinges of spatial grid structures under catastrophic earthquakes.(2)Through the seismic performance of the hysteresis curve,skeleton curve,stiffness degradation and energy dissipation capacity of the specimen,the eigenvalues of the round steel tube plastic hinge model in the forcedisplacement curve are obtained,which provides a reference for future simulations.Based on the degradation of stiffness,the plastic hinge damage model formula is proposed,and the relationship between the deformation shape of the plastic hinge and the fatigue damage is obtained,which can provide a reference for the intuitive assessment of the damage state of the bolt and ball grid structural members after the earthquake.(3)Using the ABAQUS software platform,the calculation model of the actual size of the round steel tube and bolt-ball composite specimen was established.The material damage was not considered in the analysis.Taking the variable amplitude loading as an example,first,the test curve was approached in the elastic phase,and the plasticity was found the difference between the simulation curve and the test curve.Then further explore the influence of material plastic damage and other uncertain factors of the test model on the ultra-low cycle fatigue failure characteristics of the test model,so as to provide a reference for the subsequent detailed simulation analysis including the influence of the material shaping damage and other factors.