| This study deeply investigated the effects of cast-in-place slab on the performance of RC frame structures and RC slab-column structures against progressive collapse.The accuracy of the finite element model established by degenerated 3D solid virtual lamination element in this paper was verified through the simulation analysis of static collapse experiments of a two-story frame and a single-story slab-column structure.Then,the progressive collapse failure processes of single-storey frame structure and slab-column structures(with or without drop panels)considering the overall action of floor slab,with three different columns disabled,was analyzed by alternate path method.Combined with the ultimate deformation,displacement and stress contour distribution,load-displacement curve and reinforcement stress changes among key positions: it was concluded that the frame structure under corner-column failure could play a notable “compressive membrane action” and inducing partially“tensile membrane mechanism” depending on the torsional rigidity of two discontinuous beams,structural capacity under this condition is highest;for the situation of the penultimate-internal column failing,the “tensile membrane action”within slabs is weak because of the plastic hinge at the adjacent column end occurring,structural capacity under this condition is second and ductility is poor;when the penultimate-external column fails,the membrane action is limited due to adjacent corner column yield under bending and the structural capacity is the lowest.The slab-column structure without drop panels under different column-failure situations presents same bending-shear failure,membrane action is limited.The slab-column structure with drop panels under different column-failure situations presents same bending failure,the joint form of “strong slab-weak column” appears because the excessive bending moment at the column end caused by the existence of drop panels.By comparing the development of “yield line” and “tensile membrane action”within slabs among three structure systems,it is concluded that the "compression ring" which provides the development of tensile membrane in the boundary range is generated by the interaction of the independent parts divided by the plastic hinge line,and the tensile membrane action of the slab is strictly controlled by the exertion of the“compression ring”.At the same time,the strength of the “compression ring” is positively correlated with the bending constraint and the bearing capacity of the slab.Furthermore,by changing the number of stories,the collapse processes of RC structures with three stories and five stories under initial failure of penultimate-internal column is demonstrated.Combined with the ultimate deformation,displacement and stress contour distribution,the load-displacement curve and the column axial force redistribution,multi-story structures can effectively evenly distribute load within failure zone and avoid the premature occurrence of local damage compared with one-story structures,each column axial force peak decreases with the increase of the story number.However,there is no obvious performance difference between three-story structures and five-story structures.Moreover,for the multi-story slab-column structures without drop panels,the even load redistribution in each floor would significantly expand the range of progressive collapse.Through the above research,it can provide a reference for the further improvement and development of the design for RC frame structures and RC slab-column structures design against progressive collapse considering the participation of floor slab. |
