Study On Resistance Progressive Collapse Of Weak Axis Connection In Box-shaped Pannel Zone Under Middle Column Loss

The steel structure is widely used in the field of industry and civil construction because of its good mechanical properties.However,the continuous collapse of the structure caused by accidents such as explosions,fires,and collisions has caused huge economic losses and adverse effects on the society,and the impact of steel frame structure nodes(connections)on the overall performance of the structure is very large.Therefore,it is of great practical significance to study the resistance of steel structures to continuous collapse.Taking the general three-column and two-span planar steel frame frame frame frame as the research object,ABAQUS applied finite element software to simulate the continuous collapse process of different types of box nodes under the failure of the middle column.The characteristics of bearing capacity and vertical displacement curve of failure column and the developing process of beam cross section stress are analyzed.The effects of different weakening or strengthening parameters and floor plate on the failure resistance of substructures were studied.The main conclusions are as follows:(1)The bearing capacity of the failure column-vertical displacement curve has gone through four stages: the beam mechanism stage,the plastic development stage,the mixing mechanism stage,and the catenary mechanism stage.(2)In addition to the standard connection of the cantilever section and the standard connection,the cantilever mechanism of the other weak axes has been fully utilized,showing good anti-continuous collapse performance.(3)The impact of the floor on the continuous collapse performance of the sub-structure framework is relatively obvious.Compared with the pure steel nodes without floor,the initial stiffness and plastic bearing capacity of the composite joints have been greatly improved.The drawing effect of longitudinal reinforcement in the plate can extend the length of the joint catenary phase and make the catenary mechanism more fully play.Improve the tensile strength of the node.At the same time,the existence of the floor plate causes the Liangzhonghe axis to move upwards,increasing the risk of pull-off damage at the lower edge of the beam.(4)RBS weakens the rigid joint and the top bottom steel semi-rigid node have a large rotational capacity,and the catenary effect can be fully exerted,but their bearing capacity is small.(5)The thickness of the end plate has a greater impact on the collapse resistance of the long-end plate connection node.When the end plate thickness is too large,the stiffness of the node is relatively large,and the bearing capacity of the node depends on the tensile strength of the bolt.The plastic deformation ability of the high-strength bolt is poor.Therefore,it will limit the play of the node catenary mechanism;When the thickness of the end plate is small,local damage will occur in advance at the end plate,resulting in the failure of the catenary mechanism.Recommended end plate thickness and skin plate thickness.(6)The failure of the reinforced joint of the top corner steel begins with the failure of the inner corner of the corner steel or the failure of the bolt.The plastic strain ability of the top bottom corner steel and bolt has a great influence on the rotation ability of the node.