Flat slab

FLAT SLABSK.TARUN KUMAR

What is mean by Flat Slab?

• A reinforced concrete slab supported directly by concrete columns without the use of beams.

• Flat slabs are highly versatile elements widely used in construction, providing minimum depth, fast construction and allowing flexible column grids.

Construction:The benefits of choosing flat slabs include a minimum depth solution, speed of construction, flexibility in the plan layout (both in terms of the shape and column layout).

Types:1. Typical flat slab2. Slab without drop and column with column head.3. Slab with drop and column without column head4. Slab with drop and column with column head.

Uses of column head:•Increase shear strength of slab .•Reduce the moment in the slab by reducing the clear or effective span.

Uses of drop panels : •Increase shear strength of slab •Increase negative moment capacity of slab.

1. Typical flat slab:-

• This may be called as beam-slab construction. Hence in warehouses, offices and public halls some times beams are avoided and slabs are directly supported by columns.

• This types of construction is aesthetically appealing also. These slabs which are directly supported by columns are called Flat Slabs.

2.Slab without drop and column with column head:

• The column head is some times widened so as to reduce the punching shear in the slab.

• The widened portions are called column heads. The column heads may be provided with any angle from the consideration of architecture but for the design, concrete in the portion at 45º on either side of vertical only is considered as effective for the design.

3.Slab with drop and column without column head:

• Moments in the slabs are more near the column. Hence the slab is thickened near the columns by

providing the drops.• Sometimes the drops are called as capital of the

column.

4.Slab with drop and column with column head:

Flat slab system:

• 1.One way system:• One way slab is supported on two opposite side

only thus structural action is only at one direction. Total load is carried in the direction perpendicular to the supporting beam.

• If a slab is supported on all the four sides but the ratio of longer span to shorten span  is greater than, then the slab will be considered as one way slab.

2. Two way slab:

• Two way slabs are the slabs that are supported on four sides and the ratio of longer span to shorter span is less than.

• In two way slabs, load will be carried in both the directions. So, main reinforcement is provided in both direction for two way slabs.

Advantages:• Simple formwork• No beams—simplifying under-floor services outside

the drops• Minimum structural depth.

Disadvantages:• Drop panels may interfere with larger mechanical

ducting.• Vertical penetrations need to avoid area around

columns.