| The investigation of seismic damage after strong earthquake shows that the failure of spatial grid structure with bolted spherical joints often has the characteristics of ultra-low cycle fatigue failure.In this paper,according to the failure characteristics of spatial grid structure with bolted spherical joints in earthquake damage,the plastic hinge calculation model of bar element is studied.In this paper,a large number of ultra-low cycle fatigue tests are carried out on the composite specimens of circular steel tube and bolt ball joints(hereinafter referred to as the tube ball composite specimens).Based on the simulation analysis technology,the experimental simulation and the analysis of the influence factors of the plastic hinge calculation model are carried out,and the plastic hinge model of the bar element considering the joint stiffness and plastic cumulative damage is obtained,It provides the research basis and reference for the elastic-plastic calculation and analysis of this kind of structure system under strong earthquake.Based on the project of National Natural Science Foundation of China(51578358),this paper studies the plastic hinge calculation model of bar element considering the influence of joint stiffness and plastic cumulative damage by using the analysis method of combining experiment and numerical simulation.The main contents and conclusions are as follows:(1)Ultra low cycle fatigue tests were carried out on 81 tube ball composite specimens under three loading regimes.The deformation process,failure mode,force and displacement of the specimens were recorded.The test results show that the deformation and failure modes of the test model are basically consistent with those of the bar element in the bolt ball joint grid structure in the earthquake damage investigation.Through the detailed arrangement and analysis of the test data,it can be seen that the hysteretic curve of the test model is basically Z-shaped and not full,the tension and tension of the curve is asymmetric,and the joint stiffness has a great impact on its stiffness degradation and energy dissipation capacity.Therefore,the influence of joint stiffness should be considered in the elasto-plastic dynamic analysis of bolted spherical joint grid structure.(2)The finite element model of tube ball composite specimen for test was established by ABAQUS software.The thread engagement between bolt ball and bolt and the contact relationship between sleeve,bolt ball and sealing plate were simulated by setting face-to-face contact.Meanwhile,the influence factors such as steel damage and initial defects of tube ball composite specimen were considered,and the finite element model was used to simulate the test results the simulation analysis is carried out.The simulation analysis of the test process shows that the refined finite element analysis can better simulate the test process.The influence factors of the bar element plastic hinge model are analyzed by using the simulation analysis model of the test process,and the influence law of the joint stiffness on the bar element plastic hinge model is obtained.(3)Based on the finite element model of experimental simulation analysis,the influencing factors of the bar element plastic hinge model of bolt ball joint grid structure are analyzed parametrically,and the experimental data are supplemented.Based on the results of parametric analysis of influencing factors of plastic hinge of bar element,an improved calculation method of tensile yield bearing capacity and compressive stability bearing capacity of bar element is proposed.Coefficient and coefficient are introduced into the calculation formula to consider the influence of joint stiffness of bar end.At the same time,considering the influence of joint stiffness,the mathematical expression between stiffness degradation and ductility coefficient of bar element is established.(4)The hysteretic curve of the tube ball composite specimen is simplified by using the simple coefficient.In this paper,a plastic hinge model of bar element for tube ball composite specimens is proposed.The effects of joint stiffness and plastic cumulative damage are considered by introducing ? etc.a new plastic hinge model of bar element is obtained by modifying the plastic hinge model of SAP2000 bar element.The results of the modified plastic hinge model are compared with those of SAP2000 plastic hinge model.The results show that the hysteretic curve calculated by the modified plastic hinge model is better than that calculated by SAP2000 plastic hinge model.(5)Based on the proposed plastic hinge model,the SAP2000 bar element plastic hinge model is modified.The SAP2000 bar element plastic hinge model and the modified bar element plastic hinge model are used to analyze the elasto-plastic dynamic time history of the case.The results show that the failure modes of the structure are the same after the dynamic time history analysis with the two plastic hinge models,and they are concave.However,the number of plastic hinges and the degree of plastic development of the two models are different.Because the modified plastic hinge model considers the influence of joint stiffness,when the peak seismic acceleration is the same,the internal force of the member is higher,the number of plastic hinges is 16.9% ? 28.01% less than that of the grid structure with SAP2000 plastic hinge model,and the peak acceleration of failure limit is 17.0% lower than that with SAP2000 plastic hinge model 17.23%?47.05%.It can be seen that the failure limit acceleration peak value of spatial grid structure with bolted spherical joints under strong earthquake will be overestimated if the influence of joint stiffness is not considered in the dynamic elastic-plastic analysis,so the influence of joint stiffness should be considered in the dynamic elastic-plastic analysis. |
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