Influence Of Column Axial Force To Weld Internal Force At Beam-to-column Joint In All-welded Steel Frame

In the existing design, the bending moment, shear, existed axial force which are carried on beam and used in the calculation of the internal force of welds in the all-welded beam-to-column joints. Meanwhile, it does not include the influence of the axial force. Actually, due to the rigid beam-to-column connection, the corresponding compressive deformation of column will be produced under axial stress, which can drive the same directional deformation and internal force on the rigid end-beam welds. Once this force adds to the beam-to-column joints, it will be too high for the carrying internal force of welds in beam-to-column joints. So it is possible to the actual internal force greater than the design internal force in the beam-to-column joints welds. During the big earthquake, because of the great swing of the structure, the column axial force in many high-rise buildings are increased, and it can drive this phenomenon more obvious and become the main factor of the damage in the beam-to-column joints. The influence of column axial force to weld internal force at beam-to-column joint will be analyzed in this paper.The work that has been done as following:1) Simplified model for analysis was established and the finite element analysis was used in the simplified model. 30 ANSYS finite element models were selected for simulation in the paper. The stress and deformation of the model were analyzed on the axial force of column and the comparative analysis of various parameters on internal force of weld joints by using stress ratio and equivalent plastic strain.2) The impact of the actual stress state in welds on the axial force of column was determined by comparing three types of operating conditions: only imposing the axial force of column, only imposing the force in the beam, imposing the force on column and beam at the same time. According to the current specification design formula, a proposed correction method was presented. Conclusions could be drawn:In the analysis of models imposed with the axial force of column only, the change of the column flange and web thickness is obvious to the internal force of the welds in beam-to-column joints; the effect on the change of the beam flange and web is small; Decreasing the size of the beam scallop helps to reduce the stress concentration; the column stiffener settings can effectively maintain the stability of the column web and the transference to the beam-to-column joints welds. Comparison of three types of loading conditions, the applied axial force of column can make the flexural and shear capacity near the column flange become more significantly, but less in the 2/3 and one side welding angle size; The bending phenomenon on the web weld area is not significant, but the shearing is apparent under the applied axial force of column. The shear stress in the middle of web weld is almost zero instead of the traditional theory of parabolic distribution.