| In recent years,with the continuous improvement of people’s requirements for the use of building structures,prestressed concrete structures are increasingly used in large space and large span structures because of their excellent impermeability,anti-crack performance and cost saving and other advantages.However,many scholars at home and abroad mainly focused on the RC structure in terms of the study on the structure of the progressive collapse while the study of the PC structure is relatively few.Besides,the research based on PC structure basically remains at prestressed concrete members or plane frame test and simulation.The influence of beam-slab-column spatial collaboration work on the overall structure anti-progressive collapse performance is seldom taken into consideration and relative mechanisms of progressive collapse is not clear.Therefore,it is of great engineering significance and academic value to study the progressive collapse of PC space frame structures.Based on the current research status,this paper studies the progressive collapse of PC frame structure considering the beam-slab-column spatial collaboration.The main research contents are as follows:Based on the finite element analysis program of three-dimensional solid degradation virtual laminated element,the finite element analysis program of progressive collapse of prestressed reinforced concrete frame structures considering the synergistic effect of beam-slab-column spatial collaboration is developed with the consideration of the influence of prestress and floor slab on the anti-progressive collapse mechanism of PC frame structure under the beam-slab-column spatial collaboration.Thereby,the progressive collapse test of a two-story two-span RC space frame structure with cast-in-place slabs under failure condition and the flexural behavior test of a single bonded prestressed concrete beam are simulated and analyzed.The simulation results are basically consistent with the test results,which fully verifies the applicability of this software and the accuracy of calculation.The vertical progressive collapse simulation analysis of the four-story PC frame structure under the four failure working conditions of the long-side central column,the inner central column,the short-side central column and the corner column is carried out.The PC frame structure and RC frame structure under the limit bearing capacity of structure deformation,vertical displacement isoline,limit load under the principal stress distribution and failure column pillars load-displacement curve,stress and prestressed beam slab inside ordinary reinforced stress distribution and the development situation are compared.Those work aims to explore the effect of prestress on the progressive collapse resistance of the structure under the beam-slab-column spatial collaboration.The research shows that: under the condition of curved prestressed reinforcement,the prestress effect can effectively improve the ultimate bearing capacity and vertical deformation ability of the failure condition of the bottom long side central column and inner central column.The prestress effect has a certain contribution to the anti-progressive collapse bearing capacity of the bottom short-side central column under failure condition,but has little effect on the anti-progressive collapse performance of the bottom corner column under failure condition;the long-span transfixion beam of PC frame structure connected with the failure column when the bottom short-side central column failed,PC frame structure and RC frame structure connected with the failure column when the bottom long-side central column and the inner central column failed mainly changed from the “beam bending” mechanism in the early stage to the “arch” mechanism in the later stage.The two “overhanging beams” connected to the failure column in the bottom corner column of PC frame structure and RC frame and the span middle beam connected to the failure column in the short side middle column of RC frame structure are mainly“arch” in the whole loading process,and there is no “catenary” mechanism in the two types of structures under four working conditions.The prestress effect is helpful to enhance the effect of the pressure arch mechanism under the failure condition of long-side central column,inner central column and short-side central column at the bottom of the structure.The prestress effect improves the initial bending stiffness of the structure at the initial stage of loading,and helps to delay the failure of the far-end beam-column joints and the generation of plastic hinges of the long-span through beams connected to the failure columns,and accelerates the failure and the generation of plastic hinges of the beam-column joints around the failure columns.Under the failure condition of the bottom long side central column,inner central column and short side central column,the prestressing can make the prestressing tendon give full play to the “suspension cable” tying effect and so on.The simulation and analysis of vertical progressive collapse of a four-story PC frame structure with independent beam and ribbed beam floor at the bottom under failure condition of long-side central column and inner central column at the bottom are done.The structural deformation,principal stress distribution,vertical displacement contour line,principal stress distribution under ultimate load,stress distribution and development of ordinary reinforcement in beam and slab of four-story PC frame structure are compared and analyzed.Those efforts are completed to explore the influence of floor slab on the anti-progressive collapse performance of PC frame structure.Research showed that: under two working conditions,compared to the rib slab floor at the bottom of the PC frame structure,the PC frame structure with independent beam at the bottom only relies on the frame beam to transfer load to the surrounding frame,the weakening of the power transmission mechanism in peripheral frame beam share the less load and present at a low stress state,leading the surrounding frame beams contribute little to the overall anti-progressive ability of the structure;in the failure column area,the PC frame structure with ribbed beam floor at the bottom is divided by the part of the floor with the beam flanges in coordination with the frame beam,and the rest of the floor is operated by the “partial plate membrane” mechanism.For the frame structure with independent beam and ribbed beam floor at the bottom,the large-span transfixed beams connected with the failure columns in the process of progressive collapse all exhibit “arch” and “pressure arch” mechanisms,but never exhibit “catenary”mechanisms.Through the above study,the author hopes the paper can provide references for PC frame structure anti-progressive collapse design theory and related engineering applications. |
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