WHAT IS WAFFLE SLAB?
A waffle slab is a type of slab with holes underneath, giving an appearance of waffles. It is usually used where large spans are required (e.g auditorium) to avoid many columns interfering with space. Hence thick slabs spanning between wide beams (to avoid the beams protruding below for aesthetic reasons) are required.
Since the tensile strength of concrete is mainly satisfied by the steel bar reinforcement, only the “ribs” containing the reinforcement are kept where the remaining ‘unused’ concrete portion below the neutral axis is removed, to reduce the self-weight of the slab. This is achieved by placing clay pots or other shapes on the formwork before casting of the concrete.
PURPOSE OF WAFFLE SLAB:
Waffle slabs provide stiffer and lighter slabs than an equivalent flat slab. The speed of construction for such slab is faster compared to conventional slab. Relatively lightweight hence economical. It uses 30% less concrete and 20% less steel than a raft slab. They provide low floor deflections. It has good finishes and robustness. Fairly slim floor depth and fire resistant. Excellent vibration control.
USES AND APPLICATIONS OF WAFFLE SLAB:
It is used where vibration is an issue and where large span slabs are to be constructed i.e areas having less number of columns. For example airport, hospitals, commercial and industrial buildings etc & where low slab deflections and high stability are required.
ADVANTAGES OF WAFFLE SLAB:
1. Larger span of slab and floor with less number of columns. 2. load carrying capacity is greater than the other types of slab. 3. Savings on weight and materials. 4. Good vibration control capacity. 5. Attractive soffit appearance when exposed. 6. Lightweight. 7. Vertical penetrations between ribs are easy. 8. Economical when reusable formwork is used. 9. Fast and speedy construction.
DISADVANTAGES OF WAFFLE SLAB:
Require greater floor-to-floor height Requires special or proprietary formwork which is costly. Requires strict supervision and skilled labor. Difficulty in maintenance. Not suitable in highly windy area.