WAFFLE SLAB.pptx

Waffle slab

1. CONSTRUCTION OF WAFFLE SLABS

2. What is Waffle Slab? A  waffle slab  or  two-way joist slab  is a concrete slab made of reinforced concrete with concrete  ribs running in two directions on its underside .  The name  waffle  comes from the grid pattern created by the reinforcing ribs. Waffle slabs are preferred for spans greater than 40 feet (12 m), as they are much stronger than flat slabs, flat slabs with drop panels, two-way slabs, one-way slabs, and one-way joist slabs. 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. Engineering and Technology Update

3. 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. Engineering and Technology Update

4. 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 the 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. Engineering and Technology Update

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6. Waffle slab characteristics are defined by the following parameters: • Total slab edge (H) • Height of the lightening formwork or lightening blocks (h) • Spacing between rib axes (e) • Basic thickness of the ribs (b), though in waffle slabs with system formwork they have a truncated pyramid-shaped core of variable thickness. • Thickness of the compression layer (c) Engineering and Technology Update

7. Design & Production of 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. Engineering and Technology Update

8. 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. Engineering and Technology Update

9. Services Provided in Waffle Slab Due to the holes in the waffle system following services can be provided: Air-conditioning Plumbing Lighting Insulation Materials Wiring, etc. Engineering and Technology Update

10. Construction Process: A waffle slab can be made in different ways but generic forms are needed to give the waffle shape to the slab. The formwork is made up of many elements:  waffle pods ,  horizontal supports ,  vertical supports ,  cube junctions ,  hole plates ,  clits  and  steel Bars . First the supports are built, then the pods are arranged in place, and finally the concrete is poured. This process may occur in three different approaches, however the basic method is the same in each: In situ:  Formwork construction and pouring of concrete occur on site, then the slab is assembled (if required). Precast:  The slabs are made somewhere else and then brought to the site and assembled. Pre- fabricated: The reinforcements are integrated into the slab while being manufactured, without needing to reinforce the assembly on site. This is the most expensive option. Engineering and Technology Update

11. Construction Technique 1. Arranging the 2. Fixing the 3. Fixing the 4.Providing Formwork connectors framework horizontal connector 5. Placing the pods 6. Fixing pods to the 7. Removing framework connector Engineering and Technology Update

12. Continued .. 8. Removing 9. Removing Pods 10. Providing Connectors Stacking Engineering and Technology Update

13. Advantages: 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 post tensioning. 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. Engineering and Technology Update

14. Disadvantages: 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. Headroom is reduced , hence increased storey height. Due to waffle ceiling , it creates problem in lighting facilities and hanging pipes or ducts . Engineering and Technology Update

15. Iconic Landmarks Metropol Parasol,Italy It is the world’s largest wooden structure which is made up of waffle system. Engineering and Technology Update

16. Lodytel Communication Development Centre, Spain It was the first building to use the Hole deck pods for waffle system. Engineering and Technology Update

17. Chattrapati Shivaji Terminal,India It is recognized for its innovative column design which also consists waffle design. Engineering and Technology Update

18. Case Study – Chattrapati Shivaji International Airport, Mumbai Long span roof of 70,000 square meters Roof supported by 30 columns, column distance of 64 meters in the N-S direction and 34 meters in E-W direction. By increasing the depth of trusses near the columns and running trusses, large spacing of cantilevers of 40 meters along the perimeter is achieved. Total truss depth = 4 meters only The columns are also designed to serve as hoist mechanism, entire roof was constructed without any tower cranes. The structure prioritizes modular construction for economy and also accelerates construction schedule. Engineering and Technology Update

19. Thank You! Engineering and Technology Update