Flat Grid / Waffle Slab

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FLAT GRID OR WAFFLE SYSTEMSinhagad College of ArchitectureThis Presentation is compiled by: Akshay Gawade Mihir Yadav Shanan Jaiswal

What is Flat Grid Slab / Waffle Slab System ?

Definition :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.

Appearance :The top of a waffle slab is generally smooth, like a traditional building surface, but the underside has a shape reminiscent of a waffle. Straight lines run the entire width and length of the slab, generally raised several inches from the surface. These ridges form the namesake square pockets of the entire length and width of the slab

Where this system 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 th areas which has huge spans.Waffle slab is not used in typical construction projects. They are used for specialized projects that involve clean rooms, spaces requiring seclusion from low frequency vibration or those needing low floor deflections. 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 SlabThe features of the Waffle slab are as follows :

They are used on flat sitesThey are wholly above groundNo beam excavation is requiredNo controlled or rolled fill is usedCardboard slab panel/void formers are usedSlab panels are on 1 metre grids (approximately)Trench mesh or individual bars can be usedSlab thickness is 85 - 100 mmInternal beams are 110 200 mm wideThere is minimal concrete volumeNo beam down drag from clay (above ground slab) occursShrinkage of slab is lower than stiffened rafts and footing slabsThey use 30% less concrete than a stiffened raftThey use 20% less steel than a stiffened raft.

Design & Production of the Waffle Slab

Production :Waffle slabs 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. If prefabricated products are not in the budget, consider purchasing casts for the concrete waffle slabs.The pre-casted pods are then placed directly on the site and then provided with reinforcement and filled with concrete.

Design :There are three 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.

Services Provided in Waffle Slab

Spanish architects, Alarcon & Associates, have modified the conventional waffle slab to fill it with holes so that services can be run within the depth of the slab, reducing the floor to floor height and getting some of that extra cost back. This new system they invented is called the HoledeckDue to the holes in the waffle system following services can be provided:Air-conditioningPlumbingLightingInsulation MaterialsWiring,etc.

Managing Services

Electricity and Telecomunication :

Wiring installations can flow in pipes embedded in the floor, or inside a registrable tile system .

They can also circulate through the suspended ceiling, being fully accessible by just lifting it.

Maintainance and Cleaning:

It is registrable, and performing plenum ventilation, easy cleaning of the ducts without requiring demolition or specific equipment is possible.

In addition, , immediate access to installations, enables repairs and reconfigurations withot requiring the interruption of the normal activity of the building.

Formwork Required

The formwork required for waffle slabs are as follows:Vertical support standHorizontal support beamsConnectorsDifferent Types of PodsWall connectorsClitsPodsMetal/Steel barsCube junctionsHole plates

Waffle Pods Providers (India)

The main element required to provide waffle slab is Waffle Pod.There are many Waffle pod producers all over India, and some of their names are as follows:- Supreme Fibre Glass Pvt. Ltd. (Mumbai)Envo plast (Kolkata)Teknik Kalip (Mumbai,Banglore)Utracon (Gujarat)Geo plast (Chennai)Maruti Plastics (Mumbai)

Types of slab

Index :Floor MortarWire-trayRadiant Floor ductsInsulation/Ducts SeatInstallations Tray Holedeck slabReinforcementAC Ducts

Index :AC DuctsHoledeck slabInstallation trayReinforcementInstallation drop towerAir impeller

Square Pod SystemTriangular Pod System

Reinforcements of Waffle Slab

Reinforcements Details

Reinforcement Detail at Junction of Sloping Slab and Waffle slab. Reinforcement Detail at Junction of Wall and Waffle slab. Reinforcement Detail at Junction of Beam and Waffle slab.

Example of the Slab

Reflected Ceiling View of the slabPlan of tendon placement layout3d view of the Ceiling 3d view of tendon placementLoad deflection in the provided waffle slab

Construction Technique

1.Arranging the Framework2.Fixing the Connectors3.Fixing the Framework4.Providing a horizontal connector5.Placing the Pods6.Fixing pods to the connectors7.Removing framework8.Removing connectors9.Removing pods10.Providing stacking

Construction Procedure for Floor Slab

Construction Procedure for Ceiling Slab

Advantages & Dis-advantagesAdvantages :Waffle slabs are able to carry heavier loads and span longer distances than flat slabs as these systems are light in weight.Suitable for spans of 7m 16m ; longer spans may be possible with posttensioning.It is also economical as the amount of concrete and steel is reduced as compared to flush slabs. Saving 15% concrete and 10% steel as compared to traditional T beams.These systems are light in weight and hence considerable saving is ensured in the framework as light framework is required.Coffered underside is usually left exposed for visual appearance.

Dis-advantages :Construction requires strict supervision and skilled labour.The casting forms or moulds required for pre-cast units are very costly and hence only economical when large scale production of similar units are desired.Headroom is reduced , hence increased storey height.Due to waffle ceiling , it creates problem in lighting facilities and hanging pipes or ducts.

Iconic Landmarks using Waffle Slabs

Lodytel Communication Development Centre, Spain

It was the first building to use the Holedeck pods for waffle sytem.Chattrapati Shivaji Terminal,India

It is recognized for its innovative column design which also consists waffle design.Metropol Parasol,Italy

It is the worlds largest wooden structure which is made up of waffle system.