Study On Performance Of Gusset Plates Based On Micromechanical Fracture Mechanism

Gusset plate is the key part of steel gusset plate joints,whose mechanical property affect the safety of the whole structure.Ductile fracture of gusset plates may occur under monotonic loading and seismic load action.So,the research on ductile fracture of gusset plate has great theoretical significance and engineering practical value.In this paper,micromechanical fracture models and the finite element analysis were combined in the prediction of the ductile fracture of gusset plates.Finite element models were setup for steel tubular gusset plates to predict the fracture position and the ultimate load bearing capacity of the joints.The generation and propagation of fracture were simulated by finite element analysis.The rule of damage accumulation of steel tubular gusset plates under cyclic loading was investigated.The energy dissipation capacity of gusset plates of the brace was studied for multi-story steel structures and the reasonable size of gusset plates was advised.The ultra-low cycle fatigue life of gusset plates under cyclic loading were predicted by micromechanical fracture models.The influence of different parameters on the fatigue life of gusset plate was discussed.The results showed that:(1)Micromechanical fracture models,VGM and SMCS,can give accurate prediction of the ductile fracture of the steel tubular gusset plates under bending.The fracture position and ultimate load bearing capacity of the joints predicted by micromechanical fracture models agreed well with test results.(2)The generation and propagation of fracture were simulated by finite element analysis with the use of VUSDFLD subroutine of ABAQUS and VGM.Mesh size were suggested for the finite element analysis,which can ensure the accuracy of the calculation and save computation time.(3)Increasing the thickness of gusset plates can improve the ultra-low cycle fatigue and hysteretic performance of the joints under cyclic loading.The cumulative damage increased nonlinearly under constant amplitude cyclic loading.The ultra-low cycle fatigue life of joints can be predicted accurately by the rule of damage accumulation based on constant amplitude cyclic loading.(4)Considering buckling of the gusset plate of the brace under compression can take full advantage of the post-buckling strength and improve the hysteretic performance of gusset plates in multi-story steel structures.The initial imperfection had little influence on post-buckling strength of gusset plates.Thickness of gusset plates had great influence on fracture position and ultra-low cycle fatigue life of the joints.(5)Wrap-around weld and free edge stiffeners can extend the ultra-low cycle fatigue life of gusset plates of the brace.The size of the free edge stiffeners was suggested to improve the mechanical property of gusset plates and save steel consumption.