Two or more column footings connected by a concrete beam is
known as combined footing . This type of beam is called a strap
beam. It is used to help distribute the weight of either heavily or
eccentrically loaded column footings to adjacent footings.
The function of a footing or a foundation is to transmit the load form
the structure to the underlying soil. The choice of suitable type of
footing depends on the depth at which the bearing strata lies, the soil
condition and the type of superstructure.
Whenever two or more columns in a straight line are carried on a
single spread footing, it is called a combined footing. Isolated
footings for each column are generally the economical.
Combined footings are provided only when it is absolutely necessary,
as
1. When two columns are close together, causing overlap of
adjacent isolated footings
2. Where soil bearing capacity is low, causing overlap of adjacent
isolated footings
3. Proximity of building line or existing building or sewer, adjacent
to a building column.
Types of Combined Footing
- The combined footing may be rectangular, trapezoidal or Teeshaped in plan.
- The geometric proportions and shape are so 缫xed that the centeroid of the footing area coincides with the resultant of the column loads. Click Here Download
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