Estimating Sheet

# How to use spreadsheet to design combined footing easily

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Footings transfer the vertical loads, horizontal loads, moments and other forces to the soil.

When two or more columns situated in a straight line are provided on a single spread footing, it is known as a combined footing.

The combined footing is necessary under the following conditions :-

01. When space among two columns is small and soil bearing strength of soil is inferior and their footings overlay with each other.

02. When one column is adjacent to a property line or sewer pipe, the Centre of gravity of column will not overlap with footing. Under this situation, it is essential to combine this footing with that of the adjoining internal column.

03. Dimensions of one side of footing are constrained to some lower value so as to combine column footings.

04. Area of footing = Total Load/Acceptable bearing Strength of Soil

The combined footing comes in different shapes like rectangular, trapezoidal or Tee-shaped in a plan. The purpose is to maintain consistent pressure distribution under the whole area of the footings. To make it possible, the centre of gravity of the footing area should overlap with the centre of gravity of the total loads of the two or more columns.

The following types of combined footings are generally found :-

01. Slab Type Combined Footing: Slab type combined footing provides support to two or more column containing bottom slab only.

02. Slab-Beam Type Combined Footing: Slab-beam type combined footing provides support to two or more column containing bottom slab and beam.

03. Strap-Beam Type Combined Footing: Strap-beam type combined footing is effective if one column is placed on a property line that leads to an eccentric load on a part of the footing.

To control the overturning effect, a beam should be arranged in the footing to the adjoing column footing.

Now spreadsheets are widely used to design the combined footing easily. Click on the following to download the spreadsheet. Combined footing design