Study On Mechanical Behavior Of The Cast-In-Situ Pre-Stressed Concrete Two-Way Hollow Slab With Two-Way Tube Fillers

The cast-in-situ pre-stressed concrete two-way hollow slab with two-way tube fillers brings a bran-new design method. This method is to allocate the tube fillers in the subarea of shear force transfer directions, and the longitudinal direction of tube fillers and shear force transfer direction are the same, so that to solves the problem of difference in stiffness and shearing strength between two-dimension caused by the tube fillers allocated by single-way.This method, however, is still lacking in the supports of experimental research and the necessary theoretical analysis. In order to study the mechanical behavior of this kind of hollow slabs, the static test and theoretical analysis were finished in this paper, and some design advices were proposed. The main research work and achievements are as followings:1. The static test of a 8m×8m slab was performed under uniformly distributed vertical loads. The test showed that the failed pattern of the cast-in-situ pre-stressed concrete two-way hollow slab with two-way tube fillers was similar to the isotropic two-way slab, and the bending cracks appeared at the bottom of the slab, expanded along the diagonals and formed plastic hinge lines finally, the slab failed in bending; the measured vertical displacements symmetry about the center line of the slab in X and Y dimensions were basically centrosymmetric, which showed the bending stiffness of two-way were basically centrosymmetric, the strain of reinforcement about the center line of the slab in X and Y dimensions were almost the same, and the difference about stress increment of pre-stressed strands in both directions was below 20%, which means the mechanical behavior in the symmetrical position of the slab was almost the same.2. The theoretical analysis and finite element calculation on the shearing strength of two-way hollow slab with two-way tube fillers were finished to study the problem of the poor shearing strength of hollow slabs with tube fillers. The analysis results showed that this kind of hollow slab with symmetrical size and symmetrical load possesses sufficient sheering strength, and the shearing strength calculation of two-dimension can be considered according to longitudinal tube fillers section. In the engineering design, it was advised that the shearing strength of this kind of hollow slabs with the similar length and width should be directly calculated using the formula of I style sections in Concrete Structure Design Regulations GB50010-2002, with the calculating width equaling to the actual rib width of the longitudinal tube fillers section. And it was advised that the formula section of concrete shear strength should be multiplied by the discount factor of 0.8, in order to ensure the safety of structure. The calculation of dinking strength of hollow slabs by applying formula of slab dinking in Concrete Structure Design Regulations GB50010-2002 and finite element method was finished. The results showed that this kind of hollow slabs, designed with the Concrete Structure Design Regulations GB50010-2002, can be ensured the dinking strength under the normal concentrated load.3. In order to study the influences of the hollow ratio, reinforcement ratio and span-depth ratio of hollow slabs with tube fillers on mechanical properties, the finite element analysis were finished. The analysis results showed that the hollow ratio should be controlled at the range of 25%-45%. And the rib width between the tube fillers should be appropriate, simultaneously, the reinforcement ratio of hollow slabs should be appropriate, so as to avoid shear failure. In practical use, it is advised that the reinforcement ratio be controlled at the range of 0.3%-0.6%, and the pre-stressed reinforcement should be arranged in order to enhance shear capacity of the large span hollow slabs. There is a non-linear relationship between the strength and the span-depth ratio of hollow slabs, and the deflection show linear relationships with the span-depth ratio of hollow slabs. It is an effective method to improve the deflection capacity of hollow slabs with two-way tube fillers by reducing the span-depth ratio of the slabs in engineering design.4. The analyses on bending, shearing, dinking strength and distortion of two-way hollow slabs with two-way tube fillers with different section parameters and marginal condition were finished, by applying the isotropic slab theory and non-linear finite element method. The analysis results showed that the deflection of the two-way tube fillers hollow slabs with the similar length and width should be calculated using the average bending stiffness and the GB50010-2002 formula. Both of the elastic theory and the plastic theory can be used to this kind of slab, depending on the design requirements. In the engineering design, the two-dimension sections of the cast-in-situ pre-stressed concrete two-way hollow slab with two-way tube fillers supported by beams and columns, can be converted into I style sections when its length and width are similar, following the principle of the equal area, equal moment of inertia, equal width and equal height, then using the relevant formula I style sections in Concrete Structure Design Regulations GB50010-2002, to calculate its bending strength.5. The analysis on the stress increment of unbonded pre-stressed strands was carried out. The analysis results showed that inner stress distribution of unbonded pre-stressed concrete hollow slab was quite similar with the solid slab. Therefore, the analysis method of solid slab can be used. The formula in China's current Unbonded Pre-stressed Concrete Structure Technology Regulations JGJ 92-2004 was a little conservative, when calculating the unbonded pre-stressed strands stress increment of cast-in-situ pre-stressed concrete two-way hollow slab. According to analysis results, this paper advises that the calculation results of this formula, when designing unbonded pre-stressed concrete hollow slabs for building floor, should mutiply 1.5.6. In this paper, the dynamic characteristics test and finite element analysis on cast-in-situ pre-stressed concrete two-way hollow slab with two-way tube fillers were carried out. The results showed that the vibration natural frequency and the ratio of peak acceleration and gravity acceleration of the hollow slabs, when conforming to the design of Concrete Structure Design Regulations GB 50010-2002, meet the allowable value of international standard association. So that, slab viberation would not arise discomforting.