Seismicbehavioranalysis Of Steel Frame Joints Considering Crack Growth

With the extensive construction of high-rise and super-high-rise buildings in China,steel frame structures have been widely used because of their advantages of light weight,good seismic performance and convenient construction.A large number of earthquake damage investigations show that the weld or heat-affected zone of steel frame joint of steel frame structure under strong earthquake is most prone to fracture and damage due to crack propagation,which eventually leads to the collapse or damage of the structure.However,there are few researches on the damage of steel frame joints considering crack propagation in the engineering field,which will overestimate the deformation of the structure and the ability of the structure to resist collapse.In this paper,by means of the expansion finite element method and the experimental study of joints with initial cracks,the seismic and fracture behaviors of joints with crack propagation are studied.The crack propagation and cumulative damage development law of joints under reciprocating cyclic load are studied.The main work of this paper includes the following five aspects:(1)Based on the theory of fracture mechanics and damage mechanics,the extended finite element simulation of weld zone of joint is carried out by using ABAQUS,and the mechanical mechanism of weld fracture of joint of steel frame is analyzed.The 3-D finite element method considering crack propagation and cumulative damage is further perfected.Combined with the joint test of steel frame with initial crack,it is proved that the extended finite element method can accurately simulate the cumulative damage degradation characteristics and macro-and micro-damage morphology of joint of steel frame.It provides a powerful tool for further parameter analysis of influencing factors.(2)The cyclic loading tests of four joints with initial cracks were carried out under different loading systems,and the effects of different loading history,peak value size and sequence on the damage process of the joints were studied.The loading tests of three joints of different structural types with initial cracks under reciprocating cyclic loads were carried out.The effects of different structural types on the seismic and damage processes of the joints were studied,and the hysteretic performance and macroscopic failure patterns of the joints were analyzed.The ductility and damage degradation characteristics are analyzed,and the accuracy of the extended finite element method(XFEM)is verified.(3)Based on the above research results,the parameters of the control factors affecting the seismic and fracture performance of joints are analyzed,and the different energy input histories are studied.The effects of different structural types and different initial crack lengths on the seismic behavior and cumulative damage of joints considering crack growth are analyzed.The influence of various control factors on the seismic performance,damage degradation and the development of crack growth are analyzed.(4)Considering the effect of welding residual stress on the damage and degradation of steel frame joint,the transient welding process of steel frame steel frame joint was simulatedby the finite element software ABAQUS,and the welding temperature field was obtained.Distribution and development of residual stress and strain.(5)In order to reflect the initial defects of steel frame joint more truly,the influence of welding residual stress and initial crack on joint damage and degradation is proposed.The development law of crack propagation and the degree of influence on the seismic behavior and fracture performance of joints under the coupling of residual stress and initial crack are obtained.