Waffle Slab

Waffle Slab

Waffle slab is a reinforced concrete roof or floor containing square grids with deep sides and it is also called as grid slabs. This kind of slab is majorly used at the entrance of hotels, Malls, Restaurants for good pictorial view and to install artificial lighting. This a  type of slab where we find a hollow hole in the slab when the formwork is removed.  Firstly PVC trays (pods) are placed on shuttering then reinforcement is provided between the pods and steel mesh is provided at top of the pods and then concrete is filled. After concrete sets, the formwork is removed and PVC pods are not removed. This forms a hollow hole in it in which hole is closed at one end. 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 is a one of the types of concrete slabs.

Where to use Waffle Slab & Waffle slab details:

A waffle slab has a holes underneath, giving an appearance of waffles. It is usually used where large spans are required (e.g auditorium, cinema halls) 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. 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.

Advantages of Waffle slabs:

uWaffle slabs are able to carry heavier loads and span longer distances than flat slabs as these systems are light in weight.

uWaffle slab can be used as both ceiling and floor slab.

uSuitable for spans of 7m – 16m ; longer spans may be possible with posttensioning.

uThese systems are light in weight and hence considerable saving is ensured in the framework as the light framework is required.

Disadvantages of Waffle slabs:

uWaffle slab is not used in typical construction projects.

uThe 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.

uConstruction requires strict supervision and skilled labour.

Hardy Slab

Hardy Slab

Hardy slabs are generally seen in Dubai and China. Hardy slab is constructed by hardy Bricks. Hardy bricks are hollow bricks and made up of concrete Hollow blocks. These blocks are used to fill portions of the slab. Hardy slabs saves the amount of concrete and hence the own weight of the slab is reduced. This kind of slab has a more thickness 0.27m when compared with the conventional one.

Where to use Hardy Slab?

uHardy slab is used where temperatures are very high. To resist the temperature from top of the slab thickness is increased. The heat coming from walls are resisted by using special bricks which has thermal in it. Thermal is the best insulator of sunlight.

Advantages of Hardy Slab:

uReducing slab weight by reducing the amount of concrete below neutral axis.

uEase of construction, especially when all beams are hidden beams.

uEconomic for spans > 5m with moderate live load: hospitals, office and residential buildings.

uImproved insulation for sound and heat.

Disadvantages of Hardy Slab:

uIf not properly handled, the hollow core ribbed brick units may be damaged during transport.

uNot economic for small spans.

uDifficult to repair and strengthen.

Hollow core ribbed Slab or Hollow core slab

Hollow core ribbed Slab or Hollow core slab

Hollow core ribbed slabs derive their name from the voids or cores which run through the units. The cores can function as service ducts and significantly reduce the self-weight of the slabs, maximizing structural efficiency. The cores also have a benefit in sustainability terms in reducing the volume of concrete used. Units are generally available in standard 1200 mm widths and in depths from 110mm to 400 mm. There is total freedom in length of units. These type of slabs are Pre casted and it is used where the construction has to be done fast.

The hollow core ribbed slabs have between four and six longitudinal cores running through them, the primary purpose of the cores being to decrease the weight, and material within the floor, yet maintain maximal strength. To further increase the strength, the slabs are reinforced with 12mm diameter steel strand, running longitudinally. This is one of the types of concrete slabs.

Hollow core slab Advantages :

uHollow core ribbed slab not only reduces building costs it also reduce the overall weight of the structure.

uExcellent fire resistance and sound insulation are another attributes of hollow core slab due to its thickness.

uIt eliminates the need to drill in slabs for electrical and plumbing units.

uEasy to install and requires less labor.

uFast in construction.

uNo additional formwork or any special construction machinery is required for reinforcing the hollow block masonry.

Hollow core slab Disadvantages:

uIf not properly handled, the hollow core ribbed slab units may be damaged during transport.

uIt becomes difficult to produce satisfactory connections between the precast members.

uIt is necessary to arrange for special equipment for lifting and moving of the precast units.

uNot economic for small spans.

uDifficult to repair and strengthen.

Conventional Slab (solid Slab)

Conventional Slab (solid Slab)

 

The slab which is supported on Beams and columns is called conventional slab. In this kind, the thickness of slab is small whereas depth of the beam is large and load is transferred to beams and then to columns. It requires more formwork when compared with the flat slab. In conventional type of slab there is no need of providing column caps.  The thickness of conventional slab is 4″ or 10cm. 5″ to 6″ inches is recommended if the concrete will receive occasional heavy loads, such as motor homes or garbage trucks.

Conventional concrete slabs are square in shape and has a length of 4m. Reinforcement is provided in conventional slab and the bars which are set in horizontal are called Main Reinforcement Bars and bars which are set in vertical are called Distribution bars.

Based on length and breadth of Conventional Slab is classified into two types:

u1.One-Way Slab.

u2.Two-Way Slab.

     1. One Way Slab:

One way slab is  supported by beams on the two opposite sides to carry the load along one direction. The ratio of longer span (l) to shorter span (b) is equal or greater than 2, considered as One-way slab. In this type slab will bend in one direction i.e. in the direction along its shorter span. However minimum reinforcement known as distribution steel is provided along the longer span above the main reinforcement to distribute the load uniformly and to resist temperature and shrinkage stresses.

In general length of the slab is 4m. But in one way slab one side length is 4m and another side length is more than 4m. So it satisfies the above equation. Main reinforcement is provided in shorter span and distribution reinforcement is provided in longer span. Distribution bars are cranked to resist the formation of stresses.

Example: Generally all the Cantilever slabs are one Way slab. Chajjas and verandahs are a practical example of one way slab.

2. Two Way Slab:

Two way slab is supported by beams on all the four sides and the loads are carried by the supports along both directions, it is known as two way slab. In two way slab, the ratio of longer span (l) to shorter span (b) is less than 2. The slabs are  likely to bend along both the directions to the four supporting edges and hence distribution reinforcement is provided in both the directions.

In this kind of slab, the length and breadth of the slab are more than 4m. To resist the formation of stresses distribution bars are provided at both the ends in two way slab.

These types of slabs are used in constructing floors of multi-story building.

ADVANTAGES

uHigh span time due to relatively deep beams.

uResisting lateral loads due to the beams.

uSlab is light due to the relatively less thickness.

uPunching shear failure is not crucial.

DISADVANTAGES

uFloor to floor height is high which increases the building height.

uBeans disturb the air circulation and light in the building.

uFormwork is complex.

uReinforcement is complex.

uConstruction time is high. 

FLAT SLAB

Flat Slab

uThe flat slab is a reinforced concrete slab supported directly by concrete columns or caps. Flat slab doesn’t have beams so it is also called as beam-less slab. They are supported on columns itself. Loads are directly transferred to columns. In this type of construction, a plain ceiling is obtained thus giving attractive appearance from an architectural point of view. The plain ceiling diffuses the light better and is considered less vulnerable in the case of fire than the traditional beam slab construction. The flat slab is easier to construct and requires less formwork. This is one of the types of concrete slabs.

uThe thickness of the Flat slab is minimum 8″ or 0.2m. 

Flat Slabs are used at:

uTo provide plain ceiling surface giving better diffusion of light.

uEasy constructability with the economy in the formwork.

uLarger headroom or shorter story height & pleasing appearance.

uThis kind of slabs are provided in parking.

uFlat slabs are generally used in parking decks, commercial buildings, hotels or places where beam projections are not desired.

Advantages of Flat Slab:

uIt minimizes floor-to-floor heights when there is no requirement for a deep false ceiling Building height can be reduced.

uAuto sprinkler is easier.

uLess construction time.

uIt increases the shear strength of the slab.

uReduce the moment in the slab by reducing the clear or effective span.

Disadvantages of Flat slab:

uIn flat plate system, it is not possible to have large span.

uNot suitable for supporting brittle (masonry) partitions.

uHigher slab thickness.

There are four different  types of concrete Flat Slabs:

uSlab without drop and column without column head(capital).

uSlab with drop and column without column head.

uSlab without drop and column with column head.

uSlab with drop and column with column head.

 

TYPES OF SLABS

TYPES OF SLABS

• Slab

Slabs are constructed to provide flat surfaces, usually horizontal in building floors, roofs, bridges, and other types of structures. The slab may be supported by walls or by reinforced concrete beams usually cast monolithically with the slab or by structural steel beams or by columns, or by the ground. Slabs are classified into 16 types.

• Different Types of concrete slabs in construction

There are different types of Slabs in Construction. Some of them are outdated and many of them are frequently used everywhere. In this article, ill give a detailed explanation of each slab where to use particular slab. Below are the types of concrete slabs.

Since this is a lengthy article, we have created a table of contents below for easy navigation.

1. Flat Slab

 https://slabsat.blogspot.com/2020/02/flat-slab.html

2. Conventional Slab (solid Slab) 

https://slabsat.blogspot.com/2020/02/conventional-slab-solid-slab-slab.html

3. Hollow core ribbed Slab or Hollow core slab

https://slabsat.blogspot.com/2020/02/hollow-core-ribbedslab-or-hollow-core.html

4. Hardy Slab

https://slabsat.blogspot.com/2020/02/hardy-slab.html

5. Waffle Slab