| At present,the research on the resistance to continuous collapse of PC frame structure is more focused on the planar frame,while the research on the resistance to continuous collapse of PC space frame structure considering the spatial synergistic effect is less,and the research considering the influence of the construction process is rarely involved,which has affected the further improvement of the theory of PC frame structure resistance to continuous collapse.In this paper,the three-dimensional nonlinear finite element analysis program of continuous collapse of PC frame structure considering the construction process is used to carry out the simulation study of continuous collapse of PC frame structure considering spatial synergy,that is,considering the local layer factors(spatial coordination of beams,plates and columns)and vertical factors(superstructure),so as to explore the influence on the continuous collapse of PC frame structure.The main research contents are as follows:VFEAP,a nonlinear finite element analysis software based on the theory of three-dimensional solid degradation virtual laminated elements,realizes the continuous collapse simulation analysis of PC frame structure considering the construction process by adding tension and column removal sub-programs in the PC structure nonlinear finite element analysis program,and verifies the applicability and reliability of the program by comparing the test results and simulation results.After designing a two-layer 2×1 span PC frame structure,establishing a finite element model of PC and RC space frame structure considering the construction process and not considering the construction process,and simulating and analyzing the continuous collapse,the following main conclusions are obtained:(1)The PC space frame structure should consider the influence of the construction process,which is less important than the construction process,and the bearing capacity is increased by 16.8% and the displacement is increased by 13.6%;For RC space frame structure,the influence of its construction process can be ignored.(2)Due to the spatial synergy effect of beams,plates and columns,compared with the PC plane frame structure,the influence of the construction process on the bearing capacity of the PC space frame structure is reduced,from 20% to 16.8%.(3)Compared with the RC space frame structure,the prestressing effect of PC space frame structure helps to improve the bearing capacity and deformation capacity of the structure.YJK was used to design a three-layer 4×3 span PC frame structure,and 12 finite element models were established using the PC frame structure continuous collapse three-dimensional nonlinear finite element analysis program considering the construction process,and the continuous collapse simulation study was carried out under different initial tensile control stress,prestressed rib arrangement,bottom non-prestressed rib reinforcement ratio,and top non-prestressed rib reinforcement ratio,and the influence of the above different factors on the ultimate bearing capacity,ultimate displacement and collapse mechanism of the structure was analyzed.It was compared with the results of the PC planar frame study.Then,four models were selected to compare and study the anti-continuous collapse mechanism of PC space frame structure when different columns of the underlying layer failed,by analyzing the rebar stress curve and the side column displacement curve of the cross-section.The following main conclusions are drawn:(1)All of the above models have undergone the transition from beam mechanism to arch mechanism,but none of them have a catenary mechanism.(2)For PC space frame structure,a reasonable increase in the initial tension control stress can promote the structure to tend from the arch pressing mechanism to the catenary mechanism;Changing the arrangement of prestressed ribs and the reinforcement ratio of non-prestressed ribs at the bottom have a certain impact on the arching effect of the structure.The reinforcement ratio of the top non-prestressed ribs has little effect on the arching effect of the structure.(3)The influence of the initial tension control stress and prestressed rib arrangement on the bearing capacity of the press arch of the PC space frame structure is significantly different from that of the PC plane frame structure.The effect of non-prestressed rib reinforcement ratio is even smaller.(4)Under the different failure conditions of the bottom layer,the compression arch effect of the PC space frame structure exerts from strong to weak: inner center column> long side middle column> short side middle column > corner column.The finite element model of two single-layer 4×3 span PC frame structures and two two-layer 4×3 span PC frame structures with the failure of the bottom single column and double column respectively were established,and the influence of the superstructure on the continuous collapse resistance of the PC frame structure after the failure of the bottom single column and double column was studied,that is,by analyzing the changes of the axial force and collapse mechanism of the upper coaxial frame column of the failed column of the two columns,the following main conclusions were drawn:(1)The superstructure can improve the bearing capacity of the PC frame structure after the failure of the bottom column,but reduce its ductility.(2)The influence of the superstructure against continuous collapse is closely related to the stiffness of the superstructure,the rigidity of the superstructure is strong,the vertical displacement of the bottom layer and the upper layer of the structure is not synchronized,and the "beam plate pulling column" mechanism tends to appear.The rigidity of the superstructure is weak,and the vertical displacement of the bottom and upper layers of the structure tends to be synchronized,and the "box structure" mechanism is more inclined.As the number of floors increases,the rigidity of the superstructure increases,and whether it is a single column failure or a double column failure,the superstructure will eventually tend to appear the "beam plate pulling column" mechanism.(3)Considering the influence of the superstructure,the influence of the prestress effect against continuous collapse is reduced compared with the single-layer structure,and the prestressed ribs do not fully function.(4)The stiffness of the superstructure has an important influence on the emergence or exertion of the catenary mechanism.The catenary mechanism appears in the single-layer structure,but for the multi-layer structure,considering the influence of the superstructure,the "beam plate pulling column" mechanism or the "box structure" mechanism will appear,so that the catenary mechanism is difficult to fully play or not appear.As the number of floors increases,the stiffness of the superstructure increases,and whether it is a single column failure or a double column failure,the catenary mechanism will eventually not appear.Through the above research,the conclusions reached can provide reference for the further improvement and development of the continuous collapse research of multi-layer PC frame structure considering the construction process. |
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