WHAT IS WAFFLE SLAB – PURPOSE & USES ?

Waffle slab is a structural component which is plain on its top and contains grid like system on its bottom surface. In other word , waffle slab is a type of slab with walls underneath, giving an appearance of waffles . It is known as Ribbed slab .

The top of ribbed slab is normally thin and the bottom grid lines are generally ribs which are laid perpendicular to each other with equal depth.

WHY WE PROVIDE IT

• 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.

• Waffle slabs are generally suitable for flat areas.
• Volume of concrete used is very less compared to others.
• The reinforcement in the waffle slab is provided in the form of mesh or individual bars.
• The bottom surface of slab is looks like waffle which is obtained by using cardboard panels or pods etc. he width of beams or ribs provided in waffle slab are generally 110 to 200 mm.

• Spacing of ribs recommended is 600 to 1500 mm.
• Reinforced waffle slabs can be constructed for the span up to 16 m while beyond that length prefabricated waffle slab is preferable.
• Waffle slab is good against shrinkage and it is lower than stiffened rafts and footing slabs.
• Waffle slab requires only 70% of concrete and 80 % of steel from the concrete and steel used for stiffened raft.

• The thickness of waffle slab recommended is 85 to 100 mm while the overall depth of slab is limited to 300 to 600 mm.
• 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.

Advantages

• Concrete and steel volume required is small, hence, light framework is enough for waffle slab

• Lightweight.
• Vertical penetrations between ribs are easy.
• The load carrying capacity of waffle slab is greater than the other types of slabs

•  Larger span of slab and floor with less number of columns.
• Economical when reusable form-work is used.
• Fast and speedy construction.
• They provide good structural stability along with aesthetic appearance. Hence, it is constructed for airports, hospitals, temples, churches etc.

Disadvantages

• Skilled workers are required during its construction.
• Form-work tools required are very costly
• The floor height should be more hence number of floors are reduced.
• The services provided in the waffle arrangement without proper maintenance may causes damages to the slab.
• They are not suitable for sloped areas. If there is slope area, the area must be leveled with filling or by excavating. For soil filling, good soil should be used.
• They are not suitable against high winds or cyclonic areas because of their light weight.