Method For Continuous Collapse Analysis And Post-disaster Performance Evaluation Of Double-layer Grid Structures Under Fire

Double-layer grid structure is widely used in long-span industrial buildings such as workshops and warehouses.Fire has a great negative impact on its structural performance,and may even cause the overall collapse of the structure,resulting in huge economic losses and social hazards.Therefore,it is necessary to study the damage behavior and progressive collapse process of double-layer grid structure under fire,and to provide a basis for structural reinforcement and repair.At present,there is a lack of universal analysis method for the continuous collapse analysis of double-layer grid structures under fire.For post-disaster performance evaluation,no practical design method has been developed to guide reinforcement and repair.Combined with the above problems,this paper carried out the following research:(1)In this paper,a whole process dynamic dismantling method is proposed,which can demolish the structural members that meet the criterion of buckling under pressure in real time.It can consider the influence of the removal time of failed members on the dynamic effect in the process of continuous collapse.The influence of fire temperature on steel can also be considered.This method is used to simulate the dynamic response of a double-layer grid structure under three conditions: removing the quadric cone at the center of the grid structure,removing the support at the corner and removing the support at the side.Through the comparison with the existing finite element results,the accuracy of the whole process dynamic dismantling method is verified.(2)Using the method of the space truss structure due to bearing failure in the corner of the numerical simulation of structure dynamic response of the analysis,separately considering the fire temperature effect and the influence of duration of continuous collapse failure component removal.The key components of the doublelayer grid structure are those directly connected to the support,and the failure of these components along the support line will cause the continuous collapse of the structure.(3)This method is used to simulate the fire of the roof of a warehouse in Qinhuangdao,and the collapse behavior of the roof and the dynamic response caused by the removal of components in the process of the collapse are accurately simulated.The key components of the double-layer cylindrical latticed shell structure under fire are the transverse lower chord and the compression abutment connected with it.In the process of continuous collapse,the dynamic response of reticulated shell structure is closely related to the removal time of the failed members.The instantaneous removal method overestimates the dynamic response of the structure,accelerates the collapse of the structure,and removes the failed members within a reasonable time,so as to accurately simulate the collapse process of reticulated shell structure.(4)In order to evaluate the residual bearing capacity of double-layer reticulated shell structure after fire,a method based on uniform reliability is proposed.By compiling Fortran program,the model of double-layer reticulated shell structure with geometric defects of components can be quickly generated.Through a lot of numerical simulation,the residual bearing capacity of the structure based on uniform reliability can be obtained,and the weak parts and residual bearing capacity of the structure after fire are evaluated.