Design and Detailing of Flat Slab
The flat slab is a type of two-way reinforced concrete slab in which no girders or beams are present. The flat slabs have the ability to resist heavier loads and can also permit longer spans.
While constructing the flat slabs, a reinforced slab has been constructed monolithically along with the supporting columns. In this context, the flat slabs have been reinforced in two or more directions.
Different types and components of the flat slabs
Types
The flat slabs can be of three types, which are:
➢ Slab with drops and columns, along with the column head
➢ Slabs without drops
➢ Slabs without column heads and drops
Components
Drops
The drops have a greater thickness than the rest of the flat slabs. The drops have a length of not less than one-third of the panels in each direction.
Column heads
In some cases, the diameter of the supporting columns has been increased below the slab, which is known as the column head.
Panels
In the flat slabs, the panels are the area that has been enclosed between the centre lines, which helps to connect the adjacent columns in two directions. In addition, panels also help to connect the outline of the column heads.
The thickness of the flat slabs
According to the consideration of deflection control IS 456-2000, it has been specified that the larger span for the flat slabs should be considered.
Usefulness of constructing flat slabs
Provide flexibility in room layout
The flat slabs help to offer a wide variety of room layouts by allowing the builders to place the partitions anywhere in the building. In addition, the flat slab also allowed the builders to omit the false ceilings.
Easy reinforcement placement
The reinforcement detailing procedure of the flat slabs is easy and simple; as a result, the reinforcement placement of the flat slab is easier than the other types of slabs.
Easy installation of the framework
The big table framework has been used in the flat slabs, which are easy to install.
Reducing building heights
As no beams are used in the flat slabs, the height of the floors can be reduced; as a result, the overall height of the building structure has also decreased. In this context, around 10% of the vertical members of the building structure can be saved. The foundation load of the building structure can also be saved with the help of the flat slabs, as there are no beams in the flat slabs.
Reducing construction time
The overall construction time of the construction project has been minimised with the help of the flat slab because of the use of the big table framework.
Providing prefabricated welded mesh
The flat slab helps to provide a prefabricated welded mesh along with a standard size. This requires less installation time and also provides better quality control.
Auto sprinkler capacity
The flab slabs also make the auto sprinkler work easier.
Methods of designing flat slabs
There are two methods of designing the flat slabs, which are as follows:
Direct design method
In the case of the direct design method, there are about three continuous spans in each direction of the slab. In this context, it should be noted that the ratio of the longer span to the shorter span should not be greater than 2.0.
Equivalent frame method
In the case of the equivalent frame method, the structure has been made an equivalent frame. In this context, each of the farmers has been analysed by moment distribution methods. Any kind of variation of moments of inertia should be considered on account of provision drops.
RCC details of slabs
Determining the reinforcement spacing
It needs to be noted that the spacing of the bars within the flat slabs should not exceed two times the thickness of the slabs.
To learn more, watch the following video tutorial.
Video Source: Shefden Academy
Determining the area of reinforcement
In the case of using the drop panels within the flab slabs, the thickness of the drop panels should be less than the thickness of the drops and the thickness of the slabs. In addition, there should be a quarter distance between the drop edges and the capital edges. The minimum percentage of reinforcement is equal to 0.12% in the case of using HYSD bars and 0.15% in the case of using mild steel.
Determining the minimum length of reinforcement
The 50% of the bottom bars should be from the supports, which helps to provide support to the structure. All of the slab reinforcements have to be anchored at the discontinuous edges. In the case of the adjacent spans are not equal, the extension of the negative reinforcement beyond each face has to be done on the basis of the longer span.
