MISCELLANEOUS SLAB

1 ROOM CHAJJA OR LOFT :

This kind of chajja (Slab)  is provided in drawing rooms and kitchen for storing House material. The usual difference between low roof slab and Room chajja is Low roof slab hides house material and whereas Room Chajja or Loft doesnt hides house material they are open and provided above the door side. This is a one of the types of concrete slabs.

2 KITCHEN SLAB :

The slab is provided in kitchen for its platform. For placing stove and other kitchen material is called Kitchen Slab. It has a breadth of 0.5m and length of wall and thickness is 2″.

3 LINTELS:

Lintels are provided Inside building  above the doors and windows to re direct the top load. There are two types of lintels
Pre cast Lintels: Lintels which are manufactured in factories is called Pre cast Lintels
Cast in situ: Lintels are casted at site itself is called Cast in situ lintels.
The length of lintel is more than door length and has a width of wall, thickness of lintel is 0.1m

4 SUN SHADE SLAB:

Sun Shade is provided outside building above the Doors and windows are called Sun shade slab. The slab stops rain to come inside the building    and direct sunglight. This is a one of the types of concrete slabs.

Slab which is provided below the washrooms to hide the sewage pipes or sewerage pipes is called Sunken slab. Since the pipes that carry water are concealed below the floor, care has to be taken to avoid leakage problems.  After casting sewage pipes in the slab the slab is filled with coal or broken pieces of bricks. There are two types of sunken slab.

1. The slab which is provided below the normal floor level at a depth of 200mm to 300 mm and filled with broken pieces of bricks is called Sunken slab

2. The Slab which is provided above the normal floor level at a height of 200mm to 300mm and filled with coal or broken pieces of bricks called sunken slab.

The slab which is casted on surface of the wearth is called a Ground slab. This type opf slab is used in Basement floor.

There are two types of Grade slabs:

Usually after casting Plinth beams. Sand is filled at an height of 0.15m and then Sand level is rammed. Then PCC is poured on sand upto a height of Plinth beams. Its an economic way of constructing ground slab which use majorly in India.

In high rise buildings after constructing Plinth beam the termite control is done in between the beams and then polythene sheet is laid to avoid termites inside the slab and then steel mesh is provided and concrete is filled. This costs more when compared with the previous one and requires more concrete than first one.

The slab which has one side fixed and the other side is free is called as Projected Slab. These type of slabs are generally constructed in hotels, Universities, function halls, etc. to use that area for dropping or picking up zone and for loading and unloading area. This is a one of the types of concrete slabs.

The slab which provided above the door for storage purpose is called. Low roof slab. Slab is closed at all ends and open at one end. This slab lies below the actual slab and above the door sill level. These types of concrete slabs are used in houses.

If the span of the slab is very long, then we go for cable suspension slab which is supported on cable such as London bridge, Howrah bridge etc. Generally in construction of houses for every 4m we provide a column wheras in cable suspension slab for every 500m we provide a column. This kind of slab is provided where length of span is more and difficulty in building columns. The slabs are tied with cables and these cables are joined to columns.

The slab which is tensioned before placing the slab is called Pre tension slab. The slab has same features of Post tensioning.

The slab which is tensioned after constructing slab is called Post tension slab. Reinforcement is provided to resist the compression. In Post tension slab the reinforcement is replaced with cables/ steel tendons.

Post-tensioning provides a means to overcome the natural weakness of concrete in tension and to make better use of its strength in compression. The principle is easily observed when holding together several books by pressing them laterally. Linder such pressure the whole row gains enough stiffness and strength to ensure its integrity. In concrete structures, this is achieved by placing high-tensile steel tendons/cables in the element before  casting When the concrete reaches the desired strength  the tendons are pulled by special hydraulic jacks and held  in tension using specially designed anchorages fixed at each end of the tendon  This provides compression at the edge of the structural member that increases the strength of the concrete for resisting tension stresses. If tendons are appropriately curved to a certain profile, they will exert, in addition to compression at the perimeter, a beneficial upward set of forces (load balancing forces) that will counteract applied loads, relieving the structure from a portion of gravity effects. This is a one of the types of concrete slabs.
In this type of slab cables are tied instead of reinforcement. In Steel reinforcement the spacing between bars is 4inch to 6inch where as in Post tension slab the spacing is more than 2m.  This is a one of the types of concrete slabs.

Advantages:

It allows slabs and other structural members to be thinner
It allows us to build slabs on expansive or soft soils
Cracks that do form are held tightly together
Post tension slabs are excellent ways to construct stronger structures at an affordable price.
It reduces or eliminates shrinkage cracking-therefore no joints, or fewer joints, are needed
It lets us design longer spans in elevated members, like floors or beams
Disadvantages:

The post tension slab can be made only by skillful professionals.
The main problem with using post tension slab is that if care is not taken while making it, it can lead to future mishaps. Many a times, ignorant workers do not fill the gaps of the tendons and wiring completely. These gaps cause corrosion of the wires which may break untimely, leading to some failures unexpectedly.

This is a type of slabs which is generally adopted in construction of bridges. Bridges are subjected to  two loads moving load from the vehicles and Wind load. These slabs are adopted at a place where there is a need of redirecting wind load and if there is a long curve in direction of slab these slabs are adopted.  It resists the fall of bridge due to heavy wind load.

They were originally built of stone or brick but these days are built of reinforced concrete or steel. The introduction of these new materials allow arch bridges to be longer with lower spans. This is a one of the types of concrete slabs.

Pitch roof is an inclined slab , generally constructed on resorts for a natural look. Compared to traditional roofing materials Tile-sheets used in pitch roof slab  are extreamely lightweight. This weight saving reduces the timber or steel structural requirements resulting in significant cost savings.Tile-sheets are tailor made for each project offering labour cost savings and reduced site wastage. And the thickness of slab is depends on the tiles we using it may be 2″-8″. This is a one of the types of concrete slabs.

Advantages:

1. It sheds off rain water better.
2. It gives you internal storage or room space.
3. It is less likely to leak.
4. Roof coverings are cheaper.
5. If it is a standard pitch, building materials are more cost-effective

Disadvantages:

This type of slabs are not suggested for long spans.
Repairs in slabs ike plumbing repair or electric wiring on slabs is difficult.

These kind of slab is generally constructed in temples, Mosques, palaces etc. And Dome slab is built on conventional slab. Thickness of Dome slab is 0.15m. Domes are in semi circle and shuttering is done on conventional slab in dome shape and concrete is filled in shuttering forming dome shapes. This is a one of the types of concrete slabs.

Waffle slab is a reinforced concrete roof or floor containing square grids with deep sides. This kind of slab is majorly used at entrance of hotels, Malls, Restaurants for good pictorial view and to install artificial lighting. This a  type of slab where we find 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 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?

A waffle slab is a type of slab with 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 the 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.

Types of Waffle slabs:

Based on the shape of Pods (PVC Trays) They are classified into different types some of them are:

Triangular pod system
Square

Advantages:

Waffle slabs are able to carry heavier loads and span longer distances than flat slabs as these systems are light in weight
Waffle slab can be used as both ceiling and floor slab.
Suitable for spans of 7m – 16m ; longer spans may be possible with posttensioning.
These systems are light in weight and hence considerable saving is ensured in the framework as light framework is required
Disadvantages:

Waffle slab is not used in typical construction projects.
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.
Construction requires strict supervision and skilled labour.

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

The dimensions of Hardy brick is 40cm x 20cm x 20cm

The process of execution is as follows:

Step 1   : Formwork is arranged and then shutters are fixed on the formwork.
Step 2  : Hardy blocks are placed on the shutter with one brick gap on the entire shutter.
Step 3  : The gaps between the bricks are called as rib. Reinforcement is provided in a form of beam within the gap.
Step 4  : After placing the rib, the plane steel mesh is placed on entire slab area resting on ribs.
Step 5  : Now pouring of concrete is done on slab.

Where to use?

Hardy slab is used where temperatures are very high. To resist the temperature from top the slab thickness is increased. Heat coming from walls are resisted by using special bricks which has thermacol in it. Thermacol is a best insualtor of sunlight.

Advantages:

Reducing slab weight by reducing amount of concrete below neutral axis.
Ease of construction, especially when all beams are hidden beams.
Economic for spans > 5m with moderate live load: hospitals, office and residential buildings.
Improved insulation for sound and heat.
Disadvantages:

If not properly handled, the hollow core ribbed brick units may be damaged during transport.
Not economic for small spans.
Difficult to repair and strengthen
Hardy slabs are further classified into two types:

One way Hardy Slab
Two way Hardy slab

Hollowcore 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, maximising structural efficiency. The cores also have a benefit in sustainability terms in reducing the volume of material 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. This kind of slab is used where the construction has to be done fast. These kind of slabs are Pre cast slabs which are readymade.  The hollowcore 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 a one of the types of concrete slabs.

By using tower cranes Hollow slabs are inserted between the beams. The gaps between the slab is filled with screed.

Screed is a concrete material generally we use 20mm aggrgegate in concrete whereas in screed we use baby chips(small broken stones) as aggregates.

Hollow core ribbed slabs have excellent span capabilities, achieving a capacity of 2.5 kN/m2 over a 16m span. The long-span capability is ideal for offices, retail or car park developments. Units are installed with or without a structural screed, depending on requirements. Slabs arrive on-site with a smooth pre-finished soffit. In car parks and other open structures, pre-finished soffits offer a maintenance free solution.

Advantages:

Using hollow core ribbed slab not only reduces building costs it also reduce the overall weight of the structure.
Excellent fire resistance and sound insulation is the another attributes of hollow core slab due to its thickness.
It eliminates the need to drill in slabs for electrical and plumbing units.
Easy to install and requires less labor.
Fast in construction
No additional formwork or any special construction machinery is required for reinforcing the hollow block masonry.
Disadvantages:

If not properly handled, the hollow core ribbed slab units may be damaged during transport.
It becomes difficult to produce satisfactory connections between the precast members.
It is necessary to arrange for special equipment for lifting and moving of the precast units.
Not economic for small spans.
Difficult to repair and strengthen

The slab which is supported with Beams and columns is called conventional slab. In this kind of slab the thickness of slab is small whereas depth of beam is large and load is transferred to beams and from beams to columns. It requires more formwork when compared with the flat slab. and there is no need of providing column caps in conventional slab.  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. Normally it is 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. hese types of slabs are used in constructing floors of multi storeyed building.

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

One-Way Slab
Two-Way Slab
1. ONE WAY SLAB:

One way slab is a slab which 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 because this 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 dhrinkage stresses.

In general length of slab is 4m. But in one way slab one side length is 4m and other side length is more than 4m. So it satisfies the above equation. In one way slab 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 an practical example of one way slab.

. TWO WAY SLAB:

Two way slab is a slab 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 the two spans in this load is transferred in 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 slab is more than 4m. So distribution bars are provided at both the ends in two way slab. To resist the formation of stresses.

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

Flat slab is a reinforced concrete slab supported directly by concrete columns or caps. Flat slab dont have beams. 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 architectural point of view. The plain ceiling diffuses the light better and is considered less vulnerable in the case of fire than the usual beam slab construction.The flat slab is easier to construct and requires less formwork. The thickness of Flat slab is minimum 8″ or 0.2m. This is a one of the types of concrete slabs.

It can be used where :

To provide plain ceiling surface giving better diffusion of light
Easy constructability with economy in the formwork
Larger head room or shorter storey height & pleasing appearance.
This kind of slabs are provided in parking
Flat slabs are generally used in parking decks, commercial buildings, hotels or places where beam projections are not desired.
Advantages:

It minimizes floor-to-floor heights when there is no requirement for a deep false ceiling. Building height can be reduced
Auto sprinkler is easier.
Less construction time.
It increase shear strength of slab
Reduce the moment in the slab by reducing the clear or effective span
Disadvantages:

In flat plate system, it is not possible to have large span.
Not suitable for supporting brittle (masonry) partitions.
Higher slab thickness.
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THERE ARE FOUR DIFFERENT  TYPES OF CONCRETE SLABS (FLAT SLABS):-

Slab without drop and column without column head(capital).
Slab with drop and column without column head.
Slab without drop and column with column head.
Slab with drop and column with column head.