Study On The Vertical Progressive Collapse Mechanism And Dynamic Effect Of Base-isolated Structure

Because the superstructure horizontal stiffness of the base-isolated structure is more than ten times or several times that of the isolation layer,the isolation layer produces large deformation to dissipate energy,the superstructure is safe under the earthquakes.The isolation technology is widely used in hospitals,bridges,other lifeline and crowded projects.But many scholars gradually pay attention to the isolated structure safe that under occasional load,such as terrorist attacks(hit,explosion,etc.),human error(fire)and man-made damage.The study on the progressive collapse under the accidental load of different structures was reviewed,such as steel structure,concrete frame structure and large span structure,and the lessons from the foreign design code of resisting progressive collapse was drew,then a reasonable analysis method was selected to research the ability of resisting progressive collapse about the base-isolated structure.The research work and achievements are as follows:(1)The static non-linear analysis method based on the alternative load path is used to study the vertical progressive collapse mechanism of base-isolated structure,and several isolated structures were established by Sesimo Struct soft to analyze the influence factors of progressive collapse mechanism.The factors include floor types,seismic design and bearing stiffness.The result show that the existence of slab and the increase of fortification intensity can improve the bearing capacity of the isolated structure under the beam mechanism.The increase of the horizontal stiffness of the isolation layer has little effect on the vertical bearing capacity of the structure.Compared with the traditional structure,because of the weakening of the isolation layer restraint,the failure of the plastic hinge at the beam end of isolated structure can be delayed.(2)The dynamic analysis method is used to analyze the influence of the height of the story the number of stories,the reinforcement area of the frame beam and the stiffness of the isolation layer on the progressive collapse of the isolated structure.Taking a 7-story frame structure as an example,the dynamic effect and the dynamic effect area are analyzed.The result shows that the increase of the beam reinforcement area and the decrease of the story height can improve the ability to resist progressive collapse of the structure.After the failure of the component,the internal force of structure is redistributed and the force of component near failure member is changed greatly.(3)An analysis method that through substructure was put forward to assess the ability of isolated structure to resist progressive collapse.The sub-structure was selected based on the progressive collapse of the dynamic effect region,and connection element was used as the constraints boundary to set model.And the accuracy of the method is verified by the comparative analysis of the whole model and the substructure model.By the substructure model can open a door for new possibility to better analysis the structure precise and to provide a help for structural testing.