Study On Bearing Capacity Of Beam Column Joints Of Steel Frame With Variable Thickness Of Beam Flange

After the Beiling earthquake in the United States and the Hanshin earthquake in Japan,a large number of brittle failures occurred in the traditional bolt welded beam column joints,which made scholars in various countries have a new understanding of the seismic performance of the traditional beam column joints.Therefore,technical improvements were made to improve the weld quality,reduce the stress concentration in the local area,and move the plastic hinge outward.The strengthened joints corresponding to the improved technique of plastic hinge displacement are divided into ordinary strengthened joints and flange variable thickness joints.At present,compared with the traditional beam column joints,the strengthened joints have better seismic performance and ductility.However,through the study of the ordinary reinforced type test,it is found that the welding seam in the reinforced area has a negative impact on its seismic performance,and sometimes brittle fracture will occur.Although the flange variable thickness joint effectively solves this problem,it is very difficult for the production and processing of the machined variable thickness steel plate,so it can not be widely used in the beam column joint,Therefore,this paper proposes a new type of improved joint using rolled variable thickness steel plate as flange to improve the seismic performance of steel frame structure,and a new type of seismic joint for steel frame structure in the future.(1)In this paper,four specimens were designed by ABAQUS finite element method,one is S-2 with equal thickness of beam flange,three is LP-1 with variable thickness of beam flange and one is LP-2 and lp-3 with 4 ‰ change length and 6 ‰ change length,The failure mode,hysteretic behavior,bearing capacity and energy dissipation capacity of the joint are studied.The results show that the weld of LP-1 and lp-3 is broken and the ductility is not fully developed.The flange plate of S-2 and LP-2 is broken and has certain ductility.Compared with the simulation of four specimens,it is found that the seismic performance of the flange variable thickness joint is better than that of the equal thickness joint.The lp-3 specimen with the largest thickness change rate and thickness change length shows the most superior bearing capacity,deformation performance,energy consumption capacity and rotation capacity.(2)Using ABAQUS finite element software,this paper studies the influence of longitudinal thickness change rate and thickness change length of longitudinal thickness steel plate on the seismic performance of joints.A total of 24 finite element models are established,including 2%,4 ‰,6 ‰ and 8 ‰ 4 change rates and 8 change lengths of 250 mm ～ 1500 mm.According to the hysteretic curve,skeleton curve,bearing capacity and deformation of the joint,it can be concluded that the seismic performance of the joint increases with the increase of the thickness change rate and length of the longitudinal variable thickness steel plate.In order to better improve the seismic performance of the flange variable thickness joint,it is recommended to take the steel plate with the thickness change rate of6 ‰,8 ‰ and the steel plate with the thickness change length of more than 750 mm.