Optimum design of reinforced concrete waffle slabs

This paper deals with the problem of optimum design of reinforced concrete (two-way ribbed) waffle slabs using genetic algorithms. Two case studies are discussed; the first is a waffle slab with solid heads, and the second is a waffle slab with band beams along column centerlines. Direct design method is used for the structural analysis and design of slabs. The cost function represents the cost of concrete, steel, and formwork for the slab. The design variables are taken as the effective depth of the slab, ribs width, the spacing between ribs, the top slab thickness, the area of flexural reinforcement at the moment critical sections, the band beams width, and the area of steel reinforcement of the beams. The constraints include the constraints on dimensions of the rib, and the constraints on the top slab thickness, the constraints on the areas of steel reinforcement to satisfy the flexural and the minimum area requirements, the constraints on the slab thickness to satisfy flexural behavior, accommodate reinforcement and provide adequate concrete cover, and the constraints on the longitudinal reinforcement of band beams. A computer program is written using MATLAB to perform the structural analysis and design of waffle slabs by the direct design method. The optimization process is carried out using the built-in genetic algorithm toolbox of MATLAB.