Experimental Research And Theoretical Analysis Of Vertical Bearing Mechanism Of Untopped Precast RC Floor In OSLD

Prefabricated buildings have good social,economic and environmental protection characteristics,and meet the country’s requirements for vigorously advocating intelligent construction and building industrialization.As an important horizontal load-bearing component in the building structure,the building(roof)cover is an important part of the building structure.Therefore,the research on the untopped precast floor has important theoretical significance and application value.The composite slabs has good integrity,but its own weight is large,and there are a lot of on-site wet operations,which is not conducive to the efficient use of precast concrete and prestress technology,and is not conducive to energy saving and emission reduction.The discretely connected precast RC diaphragm(DCPCD)proposed by the research group is convenient and efficient in construction,without on-site pouring,which reduces the self-weight of the floor and reduces air pollution.Due to the existence of slab joints,the orthogonal slab laying direction(OSLD)and slab laying direction(SLD)of the slab have different stress characteristics,and the rigidity in OSLD is affected by the slab joints and connectors,which has a great impact on the overall rigidity of the slab.Therefore,in order to study the load-bearing mechanism in OSLD of the DCPCD floor slab,six DCPCD specimens and two cast-in-situ slab specimens were tested for vertical load-bearing performance and finite element simulation.Combined with the tests,the theoretical calculation method of rigidity in OSLD of DCPCD was proposed.The main work and research content of this paper are as follows:(1)The DCPCD force performance in OSLD test under vertical load is carried out.The mechanical properties such as the failure form,crack development,and flexural deformation of the slab are systematically analyzed.The results show that the DCPCD floor slab joint connectors have good mechanical performance and can effectively transmit the bending moment in OSLD;the bending rigidity is less than the cast-in-situ slab specimen,and there is no obvious plastic working stage;The flexural deformation in OSLD shows the characteristics of connecting multiple straight lines at the position of the slab joints;an increase in the number of slab joints will reduce the rigidity in OSLD of the slab,and an increase in the number of connectors will improve the rigidity in OSLD of the slab.When the position of the slab joints is located in the mid-span where the force is larger,the rigidity in OSLD of the slab will be more affected.(2)Through the establishment of a finite element analysis model of DCPCD force performance in OSLD and numerical simulation analysis,the characteristics of the force in OSLD of DCPCD slabs are further revealed.According to the finite element model of the floor,the stresses of the concrete,steel bars and connectors are analyzed,and the characteristics of the force in OSLD of the slab are revealed.Combined with the vertical force performance test of the slab,the correctness of the finite element modeling method is verified;changing the strength of the steel plate in the connector from Q235 to Q345,increased the load-bearing capacity of the DCPCD floor slab after loading.(3)Based on the principle of minimum section stiffness,broken line deformation theory and conjugate beam theory,calculation methods for the transverse slab stiffness of the DCPCD floor slab are proposed.The theoretical value was compared with the experimental value to verify the accuracy and feasibility of the theoretical calculation method;MATLAB is used to calculate the more accurate conjugate method of the bending stiffness in OSLD,and the influence of sensitive parameters such as the position of the slab joint,the thickness of the slab,the span-thickness ratio and the number of connections on the stiffness in OSLD of the slab is studied.It is found that when the number of connectors is small,the distance between the slab joints and the mid-span is beneficial to the improvement of the bearing capacity of the floor;the distance between two adjacent slab joints has a greater influence on the rigidity in OSLD of the slab,and should be within a reasonable range;the increase of slab thickness and span-thickness ratio can improve the flexural rigidity of the slab;when the slab thickness and span-thickness ratio are constant,as the number of connectors increases,the degree of improvement in the bearing capacity of the slab gradually decreases.In this paper,the force performance in OSLD test of DCPCD under vertical load was carried out,the finite element analysis model of the force performance in OSLD suitable for DCPCD was established,and the calculation methods of the stiffness in OSLD of DCPCD were proposed.It fully reveals the bearing mechanism in OSLD of DCPCD,and systematically analyzes the influence of slab joints structure and other factors on the stiffness in OSLD of the slab.It is of great significance to the research on bearing performance in OSLD of DCPCD under vertical load.Above-mentioned research findings can provide references for engineering application and further study of the discretely connected precast RC diaphragm.