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Estimating Sheet

Isolated Footing Design & Reinforcement Details

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Several types of foundation are available depending on no. of a factor. The isolated footing is commonly used foundation all through the globe.

Isolated footings are mostly used for Reinforced cement concrete column since it is simple and very inexpensive. The purpose of an isolated footing is to support a single column. Isolated footings belong to independent footings which are arranged for a single column.

This type of footing is utilized in the following conditions :-

1. Columns are not placed narrowly.
2. Fewer loads are delivered to footings.
3. The Safe bearing strength of the soil is normally greater.

The Isolated footings basically comprises of a bottom slab. The following types of bottom slabs are generally found :-

1. Pad footing (having identical thickness)
2. Stepped footing (having inconsistent thickness)
3. Sloped footing (trapezoidal section)

Reinforcement detailing of isolated footing

1. Concrete cover of Reinforcements: With adherence to IS 456-200, the minimum thickness to main reinforcement in footing should not remain lower than 50 mm when footing gets in touch with earth surface directly, and 40 mm for external exposed face like surface leveling PCC. When surface leveling is unused, then it is necessary to provide a cover of 75 mm to cover irregular surface of excavation.

Also Read: Process for isolated footing design for foundation

2. Minimum reinforcement and bar diameter: Minimum reinforcement should not be lower than 0.12 percent of the total cross sectional area. The minimum diameter for main reinforcement should not be lower than 10 mm.

3. Reinforcement Distribution in Footing: In one-way RCC footing, the reinforcement is equally allocated across the full width of footing. In two-way square footings, the reinforcement that expands in both directions, is allocated equally across the full width of the footing. But for two-way rectangular footings, reinforcement is allocated across the full width of footing in long direction.

However for short direction, the reinforcement is allocated in the central band according to calculations given below. The rest reinforcement in short direction is allocated evenly on both sides of the central band.

Reinforcement in central band/Total reinforcement in short direction= 2/(x/y)+1

Here y denotes the long side and x denotes the short side of the footing.

4. Dowel reinforcement: The objective of dowel reinforcement is to bind the isolated footing to the above column. As per dowel reinforcement development length, the development length of dowel bars into the column and the isolated footing should be arranged and clearly demonstrated in the design drawings.

5. Lap splice: Splice length of dowel and column reinforcement should be evidently demonstrated. Anchorage of both flexural and dowel reinforcement lengths should be properly examined to resist bond failure of the dowels in the footing as well as resist failure of the lap splices among the dowels and the column bars.

Isolated Footing Design & Reinforcement Details