Theoretic Study On The Large-span Cast-in-situ Concrete Cellular Voided Floor

The cast-in-place concrete cellular voided slab is a new form of hollow slab that the inner formworks are regularly arranged in the concrete slab. Characterized by its low self-weight and large span, this slab can be used in big column net and wide opening as a slab structure system. Up till now, however, study on this structure system is rare both at home and abroad, mechanical behavior and design method of this floor are still uncertain. In this article, mechanical behavior and deformation characteristics of the cellular voided slab subjected to vertical loads are researched. Its main contents are as follows:Based on solid element of the finite element software ANSYS, the deformation characteristics of cellular voided slab, solid slab and waffle slab under column support condition are compared and analyzed. The maximum deflection of the cellular voided slab with spandrel beam and solid plate around is bigger than the waffle slab and smaller than the solid slab. And the deformation of cellular voided slab is more likely a dish shape, which is the characteristic of two-dimensional plate fixed in four sides. Simultaneously, the deflection of the mid-span of the spandrel beam is relatively minor.The elastic thin plate theory is applied to solve internal force and deformation of the cellular voided slab and a finite element program is made for calculating the deflection and internal force of the cellular voided slab under vertical loads. Through altering the length of span and the ratio between long span and short span of the cellular voided slab with fixed four sides, the validity of the program is confirmed. In addition, the cellular voided slab is equivalented as a space lattice intersection beam system and a simplified formula for calculating the maximum deflection is put forward.The design and calculation method and the reinforcement conformation of the cellular voided slab are discussed. Based on an actual project, the relevant cellular voided slab is modeled by beam and shell element of ANSYS software. The compatibility torsion of spandrel beams is analyzed and the empirical torsion-decreasing coefficient that put forward by reference 26 is verified. A preliminary discussion is made on the influence of the spandrel beam's torsional stiffness of the cellular voided slab towards voided slab deflection and spandrel beam torsion.