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Optimum Dimension of Post-tension Concrete Waffle Slabs

Dr. Alaa C. Galeb, Tariq E. Ibrahim

This paper aims to find the optimum dimensions of post-tension concrete (two-way ribbed) waffle slabs using standard dome size. Equivalent frame design method is used for the structural analysis and design of slab. The total cost represents the cost of concrete, strand tendons, steel, duct, grout, anchorages device and formwork for the slab. The effect of the total depth of the slab, ribs width, the spacing between ribs, the top slab thickness, the area of strand tendons and the area of steel. On the total cost of slab are discussed. The result showed that: the span to depth ratio 1/23 to 1/25 give an economic slab cost, and using 750*750 dome with 150mm rib giving minimum cost and weight. It is concluded that, the increasingin balance load, slab thickness, steel weight and total weight decrease, tendon weight increase and the 95% balance load give minimum cost.