Experiment Study On Contact Pressure, Deformation And Failure Pattern Of Slab-and-beam Foundation Under The Pillar

So far, slab and beam foundation has been widely used in China. In comperation with slab foundation, slab and beam foundation is more complicated in deformation, contact pressure and failure mode for its rigidity discrepancy between the slab and beam.This experiment study consists of two parts. In one part, the deformation, contact pressure and failure pattern are researched under the condation with different slab thickness and the same beam height. While in the other part, the research is done under unequal load on the column. Here is the conclusion:To the slab and beam foundation with rigid or semi-rigid beam(ratio of thickness to span is larger than 1/6) and flexible slab(ratio of thickness to span is smaller than 1/12), the beam and the slab deflects downward as a whole. The beam and the slab deflects upward locally in the inner area. The failure pattern of the slab is depended on whether the beam fails. If the rigidity of the beam is large enough to restrict the slab, the slab cracks before the beam. The first crack appears on the upper surface of the slab, extending diagonally. As the rigidity of the slab increases, the deformation of the slab is inversed from negative value to positive value. If the slab’s ratio of thickness to span is equel or larger than 1/6, the foundation behaves more like the slab foundation. The rigidity of the slab but not the beam dominates the deformation and contact pressure distribution. Then the crack appears first on the upper surface of the beam, extending to the center of the slab in parallel with the beam. At last, the crack pattern is like a cross on the upper surface of the slab.For the slab and beam foundation with the beam whose ratio of thickness to span are 1/6 and the slab whose ratio of thickness to span are 1/12, within the characteristic value of subsoil bearing capacity, contact pressure under the foundation is not uniform under equal load on the column. The average contact pressure under beam and column are almost equal, around 1.1~1.15 times of the average contact pressure. The contact pressure under the center point of the slab is around 55% of the average contact pressure. The structure cracks first at the upper surface of the slab, extending diagonally. For the corner area of slab-and beam foundation, the contact pressure under the corner column is 1.2 times of the average contact pressure, while the other area is smaller than the average. The contact pressure under the center point is the smallest, around 40% of that of the corner column. So, to the corner part of the slab and beam foundation, not only the rigidity of the beam but also the slab needs reinforcement to avoid bending failure.For the design of slab and beam foundation, on the premise of column compressive strength, the thickness of slab is determined by the worst condition among column punching failure, slab punching failure and slab shear failure calculation. The height of beam is determined by shear failure and bending failure calculation. Meanwhile, the anti-bending and anti-crack calculation of slab and the bottom of the beam. The deflection of beam should be smaller than 0.5‰, and the deflection of the slab should be smaller than 1‰.