Mechanical Properties Of Beam-Column Connections With Double Reduced Beam Section In Steel Frames Under The Sudden Loss Of A Central Column

Progressive structural collapse is often due to the failure of local components under accidental load,and the failure of local components leads to chain failure,which eventually leads to a wide range of structural collapse.After the failure of the column in the frame,the force transmission path of the structure will change,and the load on the upper end of the failure column will be transferred to the other members connected to it by the beam-column joint.The structural joint plays an important role in affecting the spread of the failure of the member.It has been proved in the relevant seismic studies that double reduced beam section(DRBS)connection has good deformation and energy dissipation capacity,and reasonable weakening parameters can reduce the equivalent plastic strain of the joint reduced section and delay the plastic development of the first reduced section.The performance of this kind of joint under mid-column failure condition is still scarce.Therefore,this paper studies this joint and makes a comparative analysis with the reduced beam section(RBS)connection.Firstly,the finite element analysis software ABAQUS is used to establish the fine model of the joint,and the accuracy of the models is checked by simulating experiments.Secondly,the behaviors of the RBS connection and a typical connection with DRBS under the sudden loss of a central column are made analysis and comparison to analyze the influences on the behaviors caused by the double reduced beam section,such as failure mode,bearing capacity,deformation capacity and etc.Finally,the joints with different parameters are simulated to study the influences on the mechanical behaviors,deformation capacity and the development of resistance mechanism caused by the weakening parameters and the span-to-depth ratio.The studies shows that the optimum value of parameter of DRBS connection can make the two reduced sections in an ideal stress distribution state,delay the failure of the first weakening section of the joint,and thus improve the bearing capacity and deformation capacity of the joint.On the basis of not significantly reducing the axial force and the resistance of the bending mechanism,the contribution of axial force to vertical resistance is increased by increasing the Angle of the DRBS joints,while the resistance of the catenary mechanism is greatly improved,and improve the progressive collapse resistance of steel frame structures.Weakening parameters and span-to-depth ratio influence the bearing capacity,deformation capacity and the development of the resistance mechanism.Based on analysis,the reasonable value of the parameters with different span-todepth ratio will be suggested to provide reference for the follow-up studies and application.