As ribbed slabs are formed by longitudinal and transverse beams rib-like; high rigidity; that link the foot of the pillars. these slabs are constructed to structures unbalanced loads. beams union of the pillars are calculated as bidirectional continuous footings. as usual; the minimum slab thickness is 20 cm. these ribbed slabs define the starts of the pillars in the meetings of the bi-directional beams.