What is a defining characteristic of a waffle slab?

A waffle slab is a type of reinforced concrete slab characterized by a grid-like pattern formed by the use of pans or formwork that creates a series of rounded recesses (called waffle “voids”) on both the top and bottom surfaces of the slab. This design contributes to the structural efficiency of the slab by reducing the amount of concrete and weight while still providing substantial strength and load-bearing capabilities. The use of pans to form these voids is a critical aspect, as it allows for a lighter slab that retains strength and stiffness, making it suitable for various applications, particularly in larger spans.

The other options do not accurately capture the defining traits of waffle slabs. A waffle slab is typically used in multi-span rather than single span systems, making the first choice less applicable. While they are commonly found in high-rise buildings due to their ability to handle large loads, they are not exclusively constructed for such projects, so the third option does not represent the defining characteristic. Lastly, while tension cables can be used in some structural applications, a waffle slab does not rely solely on them; rather, it incorporates reinforced concrete throughout the slab to provide its structural integrity.