Waffle Slab

Introduction

• A waffle slab is a type of building material that has two-directional reinforcement on the outside of the material, giving it the  shape of the pockets on a waffle.
• This type of reinforcement is common on concrete, wood and metal construction. A waffle slab gives a substance significantly more structural stability without using a lot of additional material.
• This makes a waffle slab perfect for large flat areas like foundations or floors.

Where this is used??

• Waffle slab can be used as both ceiling and floor slab. They are used in the areas where less number of columns are provided, i.e. it is basically used in the areas which has huge spans.
• The concrete waffle slab is often used for industrial and commercial buildings while wood and metal waffle slabs are used in many other construction sites.
• This form of construction is used in airports, parking garages, commercial and industrial buildings, bridges, residences and other structures requiring extra stability.
• The main purpose of employing this technology is for its strong foundation characteristics of crack and sagging resistance. Waffle slab also holds a greater amount of load compared with conventional concrete slabs.

Features of the waffle slab

• They are used on flat sites.
• They are wholly above ground.
• No beam excavation is required.
• No controlled or rolled fill is used.
• Cardboard slab panel is used
• No beam down drag from clay occurs.
• Shrinkage of slab Is lower than stiffened raft.
• They use 20% less steel than a stiffened raft.

Construction of Waffle Slab

• Grids are generally limited to the interior of a slab, leaving one or two of the forms out to create a solid fill around the supports.
• The solid fills provide the strength required for shear transfer to the supports.
• The fills also reduce the compression stresses at the sofit of the floor around the supports, thus avoiding the necessity of bottom reinforcement in this region.
• Picture illustrate typical grid construction using unbounded tendons.
• A light top mesh over the grid is generally the only top reinforcement at the interior of the floor panels.

Production of Waffle Slab

• Waffle slab can be casted by placing he pods on he formwork itself or they can be available pre-casted.
• Concrete waffle slabs can be purchased and shipped to the construction site as prefabricated or precast sections, or they can be poured on-site.
• The pre-casted pods are then placed directly on the site and then provided with reinforcement and filled with concrete.

Design of Waffle Slab

• There are basic designs for concrete slabs that improve the strength-to-weight ratio. For each design, the top surface is flat while the underside is modulated with either a corrugated, ribbed or waffle design.
• Corrugated slabs are created when concrete is poured into a wavy metal form. This shape prevents the slab from sagging.
• Ribbed slabs add strength in one direction, while the concrete waffle slab design adds strength in perpendicular directions. Concrete slabs can be reinforced with rebar for additional strength.

Advantages of Waffle Slab

• Waffle slabs are used for larger span slabs or floors.
• The load carrying capacity of waffle slab is greater.
• It has good vibration control capacity.
• They provide good structural stability along with aesthetic appearance. It is constructed for airports, hospitals, temples, churches.
• Waffle slabs are lightweight and requires less amount of concrete it is economical.
• Construction of waffle slab is easy and quick with good supervision.

Disadvantages of Waffle Slab

• Construction requires strict supervision and skilled labour.
• The casting forms or moulds required for precast units are very costly and hence only economical when large scale production of similar units are desired.
• Due to waffle ceiling, it creates problem in lighting facilities and hanging pipes or ducts.