Analysis Of Progressive Collapse Resistance Of Fabricated Steel Frame Considering The Effect Of The External Walls

With the frequent occurrence of progressive collapse events all over the world,people gradually realized that once a building collapses continuously,it will cause very serious consequences.In recent years,prefabricated steel structures have been widely used in our country.However,the research on the progressive collapse performance of prefabricated steel structures was mainly focused on the substructure model tests and numerical simulation,while the theoretical research and the research on integral prefabricated steel structures were relatively less.Therefore,it is of great significance to study the progressive collapse performance of prefabricated steel structures to improve the design method of progressive collapse.In this dissertation,the progressive collapse resistance of steel frame structures with a new type of fabricated beam-column joints was studied,and the influences of the external hanging walls and the stiffness of the beam-column joints were actively explored.The main research contents and conclusions are as follows:1)Based on the systematic study of the composite structures of steel frame with external hanging RAC walls,the effects of the RAC walls and the stiffness of the beam-column connections on the mechanical performance of the structures were analyzed.The results show that:after the RAC wall was installed,the bearing capacity and lateral stiffness of the composite structure are increased by 19%and about 30%respectively,while the stiffness of the beam-column connections has less effect on these.The design parameters related to the external hanging RAC walls have less effect on the mechanical performance of the structures.2)Based on the experimental study on the mechanical behavior of a new type of fabricated beam-column joints,the effects of the directions of the beam-column connections and the lengths of the short limb of L-type connectors were analyzed.And the optimal design scheme of the beam-column joint was proposed by the finite element expansion analysis of the key design parameters.The results show that:the directions of beam-column connections have a greater influence on the bearing capacity,stiffness degradation and ductility of the joints,while the lengths of short limb of L-type connectors have less effect on the bearing capacity and stiffness degradation of the joints.In the design of the beam-column joints,the principle of approximately equal strength at the connections of each components should be followed.3)Considering the effect of the joint stiffness,the resistance requirement of the double span beam substructure(DSBS)in elastic stage was theoretically modified,and the resistance expression of the DSBS considering the effect of the joint stiffness was proposed.The results show that:the general expression obtained by fitting the relationship between the bending rigidity of the DSBSs and the joint stiffness with the exponential function can better reflect the relationship between the bending rigidity of the DSBSs and the joint stiffness,and the shape coefficients of the curves slightly increase with the increase of the section inertia moments of the steel beams.4)Based on the substructure model analysis method,the static analysis of the progressive collapse resistance of the fabricated steel frame structures considering the effect of the external walls was carried out.The influences of the positions of failure columns and the external hanging walls on the progressive collapse resistance of the damaged steel frame structures were studied.The results show that:the bearing capacity of the damaged structures of pure steel frame change from strength to weakness in the order of corner column failure,inner column failure,double column failure and side column failure.The external hanging walls can not only improve the vertical bearing capacity of the structures damaged by the failure of the steel columns around the steel frame,but also significantly reduce the bending and torsional deformation of the steel beams around the steel frame.The spans of the steel frames have a greater influence on the bearing capacity of the damaged structures in the failure of the first-story side column,and the column spacings have less influence.5)The dynamic analysis of the progressive collapse resistance of the fabricated steel frame structures considering the effect of the external walls was carried out.The influences of the positions of failure columns and the external hanging walls on the dynamic response of the damaged steel frame structures were clarified,and the influences of the key design parameters of the steel frames were further discussed.The results show that:the dynamic response of the damaged structures of pure steel frame change from small to large in the order of corner column failure,side column failure,double column failure-side column,inner column failure,double column failure-inner column.The external hanging walls increase the vertical loads of the structures,which causes the dynamic response at the failure points of the outer steel columns to increase,and at the same time increase the damping ratio of the structures,which causes the dynamic response at the failure points of the inner columns to decrease.The spans of the steel frames,the stiffness of beam-column joints and the vertical loads of structures have a greater influence on the progressive collapse resistance of the damaged structures in the failure of first-story side column,the column spacings have less influence,and the storey heights have little influence.