| At present,many scholars have found that cast-in-place slab usually acts as bidirectional tension membrane mechanism and beam acts as arch mechanism to catenary mechanism on progressive collapse process of structures when they take part in the resistance.Therefore,it is necessary to accurately consider the factors of the span-depth ratio of the beam and cast-in-place slab,which affect the performance and mechanism of the progressive collapse of the structure.The nonlinear finite element analysis method of degenerated 3-D solid virtual laminated element is a finite element analysis method based on entity degradation unit,which introduces virtual node and virtual area to form entity degradation virtual laminated element.This method can simulate the geometric and material nonlinearity and realized the synergistic effect of slab-beam-column interactions.Spatial positioning of longitudinal reinforcement or transverse reinforcement(stirrups)in beams,slabs,columns or complex joints can also be carried out,and real simulation of reinforcement is realized.In this paper,two progressive collapse tests are simulated respectively.The simulation analysis shows that the destruction process and destructive form of the structural collapse are highly consistent with the experimental description,which fully verifies the precise applicability of the finite element program in the simulation analysis.In this paper,the whole process of vertical anti-progressive collapse of the four story RC frame structure without slab on the ground floor under the condition of demolishing the inner column and the side column is analyzed and studied.The collapse process and destructive form of bottom independent girder(no floor participation)and second floor(including floor participation)in the process of structural collapse,the stress distribution law under ultimate load and the reinforcement stress in beam and slab are compared and analyzed to explore the influence of cast-in-place slab participation in the the synergistic effect of slab-beam-column interactions.It shows that the beam formed by independent beam grid has obvious "pressure arch" and "catenary" mechanism under the synergistic effect of slab-beam-column interactions,and there is no "pressure arch" and"catenary" mechanism formed by the cross through beam formed by the second floor.The grillage range of the failure column area of the slab floor except for the floor near the beam rib area is in the form of flange joint with the frame beam,and almost all floors are in eccentric tension state.Through the simulation analysis and research on the whole process of vertical continuous collapse resistance of four story RC frame structure with different floor thickness under the condition of demolishing the bottom inner column,the collapse process and destructive form of the four story RC frame structure with different floor thickness,the stress distribution rule under ultimate load and the variation law of reinforcement stress in beam and slab are compared to explore the influence of floor thickness participation in the synergistic slab-beam-column interactions.It shows that the floor tension area of bottom near the failure column increases with the increase of floor thickness.The wider the tensile area of the bottom plate and the greater the tensile stress,the smaller the plate top compression area and the smaller the pressure stress.The whole process of vertical progressive collapse resistance of RC frame structures with different span-depth ratio is studied.The collapse process and destructive form,the stress distribution law under the ultimate load,the redistribution of the axial force at the top of the failure column and the reinforcement stress in beam and slab and column are compared and analyzed to explore the influence of floor thickness participation in the synergistic slab-beam-column interactions in the process of the collapse of the RC frame structure with different span-depth ratio.It shows that strengthening the structural integrity and increasing the redundant load transfer path to resist the progressive collapse of structures.Through the above research,it can provide a reference for the further improvement and development of the anti-progressive collapse design theory of the RC frame structure considering the synergistic effect of slab-beam-column interactions. |
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