Which best describes a two-way reinforced concrete joist floor with ribs running in both directions?

• A. Waffle Slab
• B. Flat Plate Slab
• C. Solid Slab
• D. One-Way Slab

Answer: (A)

Two-way action in a concrete floor means the load is carried in both directions, not just along a single axis. When the floor has ribs running in two perpendicular directions, those ribs form a grid that acts like many small joists, creating a waffle-like pattern. This ribbed grid is the defining feature of a waffle slab: the reinforced ribs in both directions give the floor its stiffness and strength, while the thin top slab completes the structure. Other slab types don’t have this intersecting rib grid—one-way slabs carry most loads in a single direction, flat plates have little or no ribbing, and solid slabs are uniform without a rib grid. So the description fits a waffle slab.