Study On The Ultimate Bearing Capacity Of Precast Concrete Structure Composite Floor Slabs

The paper firstly studies the load transferring method of composite floor slabs under the vertical load and supplies reference on the vertical load calculation of shear walls and composite beams. The simulation of nine composite floor slabs in common thickness of the precast slabs, cast-in-place layer and the aspect ratio was based on ABAQUS, the finite element simulation software. Study compared with the load transferring ratio of the same thickness, size cast-in-place floor slab, and got the error rate of composite floor slabs transferring load by the cast-in-place floor slab load transferring method. The result shows that the transferring load along the direction parallel to seam is more than the theoretical one, the transferring load along the direction vertical to seam is less than the theoretical one. Transferring error between composite floor slabs and cast-in-place floor slabs is less than 3%. So the load transferring method of composite floor slabs can be equal to cast-in-place floor slabs when they are calculated in total. Study suggests that axial compression ratio limit of shear walls vertical to seam should be reduced 3% in the precast shear wall structure design.Secondly paper studies the ultimate bearing capacity of composite floor slabs under the vertical load and supplies reference on the reinforcement design. The simulation of thirty composite floor slabs in common thickness of the precast slabs, cast-in-place layer and aspect ratio 1.0?1.5 is based on ABAQUS, the finite element simulation software. There are two or three pieces of precast slabs at the composite floor slabs'bottom. The simulation got the ultimate bearing capacity of composite floor slabs that arrangement of reinforcement is according to the one-way slab reinforcement along the direction parallel to seam, constant constructional reinforcement vertical to seam and slabs are quadrilateral bearing. On the premise that the bearing capacity of slabs is invariable, according to the two-way slab calculation, the ratio of longitudinal carrying bar reduction is gotten by reducing the sectional areas of reinforcement vertical to seam. The result shows that composite floor slabs of the same size and different thickness of cast-in-place layer and the precast slabs, the more the ratio of the thickness the cast-in-place layer and precast slabs is, the more its bearing capacity is; Composite floor slabs of the same thickness of the cast-in-place layer and precast slabs and different size, the aspect ratio and the ratio of longitudinal carrying bar reduction show linear relation; Comparing with two pieces of precast slabs'composite floor slabs of the same reinforcement, the bearing capacity of three pieces of precast slabs'one is lower. Study indicates that arrangement of reinforcement of composite floor slabs is according to the one-way slab reinforcement along the direction parallel to seam, constant constructional reinforcement vertical to seam. The seam direction is the long direction. When the aspect ratio is 1:1.5, the actual ultimate bearing capacity can improve 17% comparing with the one according to the one-way slab calculation. When the aspect ratio is 1:1, the actual ultimate bearing capacity can improve 39%. When the aspect ratio is 1.5:1, the actual ultimate bearing capacity can improve 98%. When the aspect ratio is 1:1.5, the same bearing capacity, according to the two-way slab calculation, the longitudinal carrying bar in the precast slab along the direction parallel to seam can be reduced 17%, calculation can be according to the one-way slab; When the aspect ratio is 1:1.2, the longitudinal carrying bar in the precast slab along the direction parallel to seam can be reduced 30%; When the aspect ratio is 1:1, the longitudinal carrying bar in the precast slab along the direction parallel to seam can be reduced 40%; When the aspect ratio is 1.2:1, the longitudinal carrying bar in the precast slab along the direction parallel to seam can be reduced 60%; When the aspect ratio is 1.5:1, the longitudinal carrying bar in the precast slab can be removed, composite slab is equal to the one-way slab along the direction vertical to seam. The seam should avoid coinciding with composite floor slabs'central line in the arrangement of precast slabs. When the aspect ratio is greater than 1.5:1, precast slabs should arrange along the short side direction.Finally the paper studies the horizontal shear on the combined surface of composite floor, to provide the reference for truss reinforcement layout and calculation of the laminated floor, and reaches that shear strength test value on the combined surface of new and old concrete. The paper calculates reasonable arrangement spacing of truss reinforcement to meet the shear strength condition. The conclusion is that shear strength of napping treatment combined surface is 3.0MPa, and shear strength of untreated combined surface is 1.8MPa. Composite floor slabs that the span is less than 9m can't need to set the shear steel truss in practical engineering. Considering the truss reinforced setting combined surface with adhesive failure conditions, when the span is less than 3.0m and web reinforcement diameter is 4mm, spacing can be selected 600mm, and diameter is 5mm, spacing can be selected 1000mm. The span is 3.0m?4.2m, diameter is 5mm, spacing can be selected 800mm. The span is 4.2m?5.4m, diameter is 5mm, spacing can be selected 600mm. The span is 5.4m?6.0m, diameter is 6mm, spacing can be selected 800mm.