What consists of a series of ribs, similar to small beams with a top slab, and are cast at one time with the supporting beams?

• A. Reinforced Concrete Joist Floors
• B. Flat Plate Slab
• C. Flat Slab
• D. Waffle Slab

Answer: (A)

Reinforced concrete joist floors are built as a series of shallow beams (ribs) running across the span, with a top concrete slab poured over them. The whole system is often cast in one operation so the ribs, the top slab, and the supporting beams become a single monolithic unit. This rib-and-slab arrangement is what gives the floor its characteristic line of small beams supporting a continuous top slab. Flat plate slabs and flat slabs lack that ribbed network, while waffle slabs use a grid of ribs in two directions to form a waffle pattern, not the single-direction rib system described here.