Research On Hysteretic Behavior Of Flange Weakened With Replaceable Beam Section

The weakened steel frame flange joint is a typical joint form that realizes the outward displacement of the plastic hinge.Although it can effectively improve the stress state of the weld at the beam end,it is very difficult to repair the structure after the earthquake.Aiming at the above shortcomings,based on the seismic design concept of replaceable after earthquake,a new type of flange weakened joint with replaceable beam sections is proposed.Under the action of the earthquake,the damage of the new type of joint is mainly concentrated on the replaceable beam section,while the core area of the joint remains elastic,achieving the seismic design goal of being replaceable after the earthquake.In this paper,the finite element software ABAQUS is used to study the mechanical performance of the new node under monotonic load and the hysteretic performance under reciprocating load,and conduct variable parameter analysis.The main research contents and research results are as follows:(1)Using ABAQUS to model the flange weakening node and the end plate connection node,by comparing the results of the analysis test and the finite element calculation,the reliability of the finite element analysis and research on such problems is verified.The mechanical properties of ordinary end plate connection nodes(CPJ)and flange weakened nodes(RFJ)with replaceable beam sections under monotonic and cyclic loads are analyzed.Under the action of monotonic load,when the RFJ node fails,the plastic strain is concentrated in the weakened area of the replaceable beam section,which can be easily replaced after earthquake.Compared with the CPJ node,the yield load and peak load drop rate of the RFJ node are within 10%,which is the limit The displacement has increased by 27%.Under the action of cyclic load,the hysteresis curve shape of the RFJ node is fusiform,the area of the hysteresis loop is full,the ductility coefficient of the CPJ node is increased by 23%,and the stiffness and strength degradation curve is more stable.(2)Cyclic load is carried out on a total of 30 joint specimens in 6 series,and the weakened depth c,the weakened length b,the distance between the weakening starting point and the beam-column end plate a,the beam-column end plate thickness tb,the connecting end plate tc and the replaceable beam section length l on the hysteretic performance of joints are studied.The analysis shows the value range of each parameter test piece:recommended weakening depth c=(0.175～0.225)bf;weakening section length b=(0.7-0.9)hb;weakening starting point to beam end distance a=(0.5～0.8)bf;beam-column end plate thickness tb=(1.05～1.45)tf;connecting end plate thickness tc=(1.25～1.45)tf;replaceable beam section length l=(1.6～1.85)hb,where bf represents the beam flange width,hb Represents the height of the beam section,and tf represents the thickness of the column flange.(3)The formula for calculating the initial rotational stiffness of weakened flange joints with replaceable beam segments is derived,and the results obtained by the formula are compared with the finite element method to verify the rationality and accuracy of the formula.