Study On The Analysis Methods Of Hollow Floor And Punching Issues Of Slab-column Connection

The hollow floor structure is a new kind of floor system with top slab, bottom slab and inner hollow by embedding void filler into the traditional solid floor; due to the high prefabrication ratio, building material economization and light self-weight, the hollow floor structure has prominent advantages in aspects of energy conservation, consumption reduction and mechanical behavior. Therefore the hollow floor structure has been promoted by the Ministry of Housing and Urban-Rural Development of P.R.China and is widely used. Although researchers showed great passion on the development of void filler, the researches on the mechanical behavior and analytical methods of the hollow floor were limited. The analytical methods of current technical specifications are basically inherited from flat-plate floor system. Meanwhile, the research on the punching strength and deformation behavior of slab-column connection are also immature, thus restricting the application of the hollow floor structure as well as the flat-plate floor system. This paper focuses on the structural analysis methods of box-filler hollow floor and the punching behaviors of slab-column connection. The main contents are as follows:Firstly, three polymethyl methacrylate(PMMA) single box beams and one PMMA multi-cells unilateral rib slab were tested and calculation precision verification of the FEM was accomplished.To study the direct design method, 224 specimens of cast-in-situ box-filler hollow floor and solid floor supported by columns were computed respectively by ABAQUS. Both a hollow floor and the corresponding solid floor were analyzed and the section moments were obtained. Then parametric analysis of the hollow floor was carried out. The column size ratio, hollow ratio, span ratio, beam relative flexural stiffness and beam relative torsional stiffness were all considered as analysis parameters. The first-round and second-round moment distribution coefficients in both interior panel and edge panel were achieved. The results show that: for both the hollow floor and solid floor, the moment distribution in interior computational strip and edge computational strip are similar, the difference in moment distribution is mainly the positive moment; While the span ratio≤1.0 and the column size ratio≤0.2, the affection by support size can be ignored; There is still a relatively large gap between calculated values and codes for the moment distribution coefficients in some parts of the critical sections, the coefficients should be adjusted. According to the analysis results, the first-round and second-round moment distribution coefficient tables were presented.To study the analogue slab method, the effect of shear deformation on box girder element was analyzed. In accordance with the theory of elastic thin plate, equivalence principle and computational accuracy of three different analogical methods were analyzed under several boundary conditions. The theoretical modified shear modulus and practical deflection modification method of the equivalent solid floor were proposed. The deflections of the structurally isotropic hollow floor, structurally orthotropic hollow floor and PMMA beam calculated by the proposed method were compared with real values. The results show that: the Code analogue method which based on the equivalent flexural rigidity cannot calculate the shear deformation exactly; the proposed theoretical modified shear modulus and practical deflection modification method which based on “equivalent shear rigidity” are suitable for both the structurally isotropic hollow floor and the structurally orthotropic hollow floor, and can predict the deflection more precisely.To study the analogue cross beam method, the effect of torsional rigidity on section force distribution of grillage-beams was analyzed. In accordance with the multi-cells torsion theory, the equation for the torsional moment of inertia was deduced, and the practical analogue methods of the equivalent grillage-beams were proposed. The hollow floor section moments calculated by the proposed method were compared with the real values under rigid edge supported condition, flexible supported condition and column supported condition, respectively. The results show that: the influence of torsional rigidities of the equivalent grillage-beams is prominent. The analogue method proposed by the Code which based on the equivalent flexural rigidity cannot predict the torsional rigidity exactly. The proposed equation for the torsional moment of inertia and practical analogue methods are suitable for various hollow floors, and can yield more precise section forces.To study the punching behaviors of slab-column connection, based on the experimental phenomena, a relatively comprehensive bending-shearing critical crack model(BSCCM) which can be used to calculate the punching load and deformation simultaneously was established.The BSCCM includes the the bending-shearing crack mechanism, the layer model in shear-compression zone and the determination method of the critical surface. The size effect and dowel action were also taken into account by the BSCCM. The accuracy of BSCCM was verified by 45 test results. The equivalent conversion method of the non-standard case was deduced by the yield line theory. The applicability and accuracy of BSCCM to the non-standard case were checked by 98 test results. By numerous theory calculation and parameter analysis, the factors that effect the punching load and deformation were studied, and the simple formulas were deduced to calculate the punching load and deformation, which include the concrete strength, yield strength of the steel, reinforcement ratio, geometric dimension of the slab and column. Finally, the rationality and accuracy of the formulas were verified by 432 test results.