DESIGN OF WAFFLE SLAB FLOOR SYSTEMS USING MATLAB

Abstract

The structural function of any floor system is to collect all the gravity loads and transfer it to the vertical structural system comprising columns and the interconnecting lateral elements (slab/beams). The floor system receives the gravity load acting normal to its plane and hence it transfers the load through bending and shearing actions. Bending moment induces both tensile as well as compressive stresses within the same small thickness of the floor. Materials such as concrete not being good in resisting tensile stresses have to depend upon the embedded steel bars. This situation makes one think about the suitability of concrete in the tension zone wherein it gives all the self-weight but no moment resisting capacity. It would, therefore, be prudent to remove the concrete from the tension zone as much as possible. Removal of concrete from the appropriate locations would result-in substantial reduction in the dead load moment, making the floor behave as interconnected uniformly distributed small T-beams. It is a structural floor having the top portion of its depth in uniform compression and tension in steel bars at small regular intervals. This is an ingenious way of providing an RC slab floor system for comparatively large spans. This, however, throws up some problems in terms of fixing suitable sizes of form-work which can be adopted for frequent use in floors of various shapes and sizes (spans) and providing adequate shear resistance. Formwork of suitable shape and sizes may be induced at regular spacing along both the orthogonal directions to achieve the reduction in dead load of the otherwise solid slab. Such a slab (open-ended at the bottom) is commonly referred to as waffle slab. . The primary aim of the present dissertation is to minimize the self-weight of the slab, and thereby minimizing the dead load moment, by inducing sufficient number of waffles of appropriate size in both the orthogonal directions. The slab should be safe enough both in moment as well as shear capacities without affecting the stiffness of the slab system. To accomplish this task, the analysis of waffle slab is carried out using Equivalent Frame Method with different waffle sizes to find out the optimum dimension suitable for certain range of floor size and percent reduction in dead load due to waffles. The design is done as per IS 456:2000 and ACI 318:2008. As the numerous iterations are involved in this process, a program has been developed in "MATLAB" environment, which is known for its capability of handling the mathematical expressions effectively.