FLAT SLAB Flat slab are also known as beamless slab, is a type of slab in which the flooring slab is directly supported on columns without the agency of beam or girders. For span from 5 to 9m thin flat slabs are the preferred solution for the construction of in- situ concrete frame building, where a square or near square grid is used. They are provided in theatres, factories, and mills, shopping complex and other buildings.

A flat slab, generally spanning 6m to 13m,provides minimum construction depth and allows rapid construction. Flat roofs are a distinguishing feature of many modern buildings. They off the possibility of both minimizing the enclosed volume and maximize the planning envelope in volume terms. Flat slab can be classified as one way slabs.One way slabs,as the name suggests,can be used for narrow rooms with a maximum width of 10’ to 12’ and have steel reinforcement designed to be spanned one way only making them more economical.

Two way slab can be spanned both ways Two way slab can be spanned both ways. The steel usage is more but large column free rooms (16’x20’, 18’x20’ etc.) are possible. The spatial feel inside room can be well articulated by the height of the roof plane,its shape and its slope.Flat roof slab provide that feeling.

The thickness of floor is 13cm and above depending upon the span and supported on R.C.C column arranged in such a manner that they form square of nearly square panels. The size of panel should not exceed 9mx9m. There must be three rows in two directions at right angles. The ratio of length to breadth of any two adjacent panels should not differ by more than 10% of the greater length.

Some times instead of providing uniform thickness of slab a portion of slab is thickened symmetrically around the column . The thickened portion is called drop. The flat slab may be designed either with or without drop panels. At their head 4cm below the drop, the columns are enlarged so as to form diameter equal to 0.21 to 0.25 of the span. This flared portion of column head is called capital.

The extra thickness around the column is there to strengthen the column floor connection and resist the negative moments. The floor itself can be thinner with less dead weight. Flat slab exhibits several advantages such as providing architectural flexibility more clear space, lower building ht. Easier formwork,and consequently shorter construction time.

Cheaper shuttering Flat underside of slab Simplicity of formwork and resulting in speed of construction low floor to floor ht. Reduce the total building height thus reducing the lateral loads, cost of building cladding, cost of vertical mechanical and electrical lines,and air conditioning cost

Cost effective in case of large span, High quality construction Flat soffit Just paint,no painting is required 300 m2 of slab erected in one day Improve and enhance property

Adaptable to meet engineers and architects requirement. Saving in labour and time make these system always worthwhile. Windows can go as high as the ceiling because there are no beams.

Limitation : Holes in flat slabs near columns need special attention as they reduce to both bending and punching shear.very small isolated holes can be ignored. The provision of additional localized reinforcement can permit larger holes with a dimension up to about 1/20of span. Holes larger than this will require specific consideration in both analysis and design.

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