Study On Seismic Performance Of The Bolt-weld Steel Frame With Abnormal Joint With Different Column Sections

The bolt-welding abnormal joints with different column sections of steel structure is a joint with different cross-section of the upper and lower column.The main characteristic of such joints is that the shape of the cross section of the core area is changedthen forming the abnormal joints domain,and its mechanical properties is different from the normal joints.Based on the previous studies,This dissertation mainly focus on the seismic performance of Steel frame variable section column abnormal joints were systematically.The main research contents and conclusions are as follows.The prototype of the study is based on one high-rise steel residential building.Six models scaled in 1:2 were manufactured and low-cyclic reversed loading test has been implemented.The failure process and pattern were observed under low cyclic reversed loading.The strain distribution of core zone,hysteretic loops and skeleton curves were obtained.Mechanical behaviors such as bearing and deformation capacity,degradation of rigidity,energy dissipation capacity were analyzed.Test results show that deformation of abnormal joints with different column section occurs mainly in the core area during loading.The final typical failure mode is the tensile cracking of weld at the junction of the upper flange of the beam and the core area of the joint.The nonlinear finite element simulation analysis had been implementated for the aforesaid experimental models with the software of ABAQUS.The analysis results also compare with experimental results.On the basis of validating the reasonable parameters of finite element modeling,the numerical simulation model of abnormal joints were established,the influence of column axial compression ratio and thickness of core zone of mechanical behavior of abnormal joints with different column section were analyzed.According to the test result and finite element simulation result,the mechanism of core zone was studied,a simplified mechanical model and the calculation formulas of shear bearing capacity were proposed.The calculated results which established in this paper was agree well with experimental results,which show that the calculation formula is reliable.In order to systematically study the seismic performance of the bolt-weld steel frame with abnormal joint with different column section.One steel frame model with a scale of 1/2 is designed.The seismic response under different seismic wave function was studied by pseudo dynamic test then the failure pattern,the framework of the load-displacement hysteresis curves,skeleton curves,yield mechanism,ductility and other mechanical properties were studied by the pseudo static test.The static elastoplastic analysis was carried out on the bolt-weld steel frame with abnormal joint with different column section by the finite element software ABAQUS,then the deformation capacity,weak position,mechanism and mechanism of failure were studied.Results show that the up and down the bolt-weld steel frame with abnormal joint with different column section has good ductility and seismic performance.Because of the different node up and down the column section,the change of stiffness is larger,leading to the interlayer displacement distribution is different from the conventional steel frame that without stiffness or quality mutation regularity;The result also show that the "weak node" phenomenon and stress concentration occur in the abnormal node,then it is easy to produce local deformation concentration and even brittle fracture.