Experimental And Numerical Study Of Concrete Composite Hollow Core Slab With Precast Prestressed Concrete Ribbed Panel

Based on the advantages of the precast ribbed slab concrete composite floor system and the cast-in-place hollow floor slab, that was proposed a new composite hollow core slab could be formed with internal tube filler stuffed into precast ribbed floor in a regular way. Relevant experimental researches and necessary theoretical analyses haven’t yet been carried out on this floor, so it hasn’t yet been applied to any practical project at present. This dissertation performed a systematic experimental study and finite element analysis on the shear performance of the combined interface, the mechanical performance of the simply supported slab in the prestressed direction, the loading features of the simply supported slab in the piecing direction, and the two-way loaded effects of the composite hollow two-way slab in four-edge simply supported concrete of this composite hollow core slab. In addition, a relevant elasticity calculation theory and plastic calculation method were proposed.(1) A push-off test and finite element analysis were conducted on 20 composite specimens and composite hollow core specimens, which confirmed the effectiveness of the “chain keying effect” provided by the holes in precast ribbed floor after composition. The test indicated that the layout of internal tube filler didn’t produce obvious impact on the combined interface’s shear performance, and that the inter-hole ribs’ shear performance would become a main controlling factor for specimen failure when the combined interface had a high shear performance. A finite element contact mechanical parameter suited to the simulation of interfacial behavior in composite floor’s lamination was determined based on the test results, and an analysis helped figure out the proportion of the various components of the shearing resistance in the composite floor’s composite interface, providing reliable theoretical foundations for the finite element numerical analysis of concrete composite hollow core slab with precast ribbed panel.(2) A bending and shear test, as well as a finite element analysis, was carried out on the simply supported slab of 10 composite hollow floors with different floor types and sectional dimensions in the prestressed direction. The result indicated that composite hollow core slab and cast-in-place hollow core slab showed the same loading features and deformable features, and the composite slab’s flexural performance index and shear performance index calculated according to the I-shaped section at the thinnest flange of the tube coincided well with the measured value. Within the slab thickness range, the change in the tube filler’s diameter size and layout mode didn’t cause crack and slide in the composite interface, but the test pieces’ tension stiffening effect was weakened to varying degrees, so it’s suggested that the short-term stiffness of composite hollow core slab should be equal to the post-cracking stiffness of control section. A stress analysis of composite interface helped compare the calculation threshold of perpendicular slab’s vertical tube width, as well as the upper and lower flange thickness, with floor slab’s actual structure size, showing that the composite interface’s shear strength could meet the requirements of safety use in practical projects.(3) A detailed experimental and theoretical analysis was conducted on the tested slab’s fracture conformation, ultimate capacity and short-term stiffness based upon a test over concrete composite floor with precast ribbed slab in the direction of piecing. The analysis result suggested that the stress excess of stressed steel bar in crack was the major cause for the change of slab’s mechanical property and failure mode. An analysis was carried out on the analysis of the reinforcement stress, equivalent tension method and finite element parameter on this basis, in accordance with the test result, and based on the cracks, educing a computational formula suited to the crack development, ultimate bearing capacity and short-term stiffness of the simply supported slab in the direction of piecing. The result of both formula computation and test suggested that the placement of anti-crack reinforcement in crack could help control crack width and give full play to the bearing capacity of the slabs in the direction of piecing, but there was a limited impact on the test pieces’ stiffness after cracking.(4) A static test and finite element analysis was successfully conducted on a four-edge simply supported composite hollow core floor with a span of 4m×4m. The test indicated that composite hollow core floor and cast-in-place floor showed a similar deformation behavior and failure mode, cracking phenomenon wasn’t observed on the combined interface, a diagonally unfolded plastic hinge line was formed at the bottom, and it was observed through a load-deformation relationship that stiffness’ orthotropic character wasn’t obvious. An analysis on the strain development law of the bar and concrete in the orthogonal direction in the symmetric position showed that the load-bearing bar in the direction of piecing had an excess stress in the early and middle period of loading, and it tended to be uniform with prestressing steel in the later period of loading; there was pre going strain of concrete in the direction of piecing, obviously greater than the strain of concrete in the prestressed direction around the 1/4 loading zone, suggesting that the floor crack in the direction of piecing first unfolded in the prestressed direction. Attention should be paid to the control over the crack width in this direction. Finite element analysis shows that composite hollow core floor is still an orthotropic slab, and floor should be calculated and designed according to the orthotropic plate theory.(5) A differential equation was deducted for composite hollow core slab with orthotropic elastic thin plate theory as a basis. A calculation formula for section bending stiffness and warping rigidity in which composite hollow core slab’s construction features are taken into consideration was proposed, and that the deflection and bending moment figured out according to the formula coincided well with the test result; it was proposed in accordance with the ultimate balance theory that composite flooring’s bearing capacity could be calculated based on the use of post-cracking stiffness ratio to determine a torque ratio in the principal axis direction, which could help project planners master the real internal force and carrying capacity state of the new floor slab superposed by multiple orthotropic effects, to improve the reliability of design.