Free Download of Design Isolated Footing Spreadsheet
Footings are structural elements that transfer column or wall loads to the underlying soil underneath the structure. Footings are designed to transmit these loads to the soil without surpassing its safe bearing capacity, to avoid unnecessary settlement of the structure to an acceptable limit, to diminish differential settlement, and to get rid of sliding and overturning.
The settlement counts on the intensity of the load, type of soil, and foundation level. Where possibility of differential settlement takes place, the different footings should be designed in such away to settle independently of each other.
Foundation design involves a soil study to establish the most appropriate type of foundation and a structural design to determine footing dimensions and required amount of reinforcement. Because compressive strength of the soil is generally much weaker than that of the concrete, the contact area between the soil and the footing is much larger than that of the columns and walls.
Definition of Isolated Footing: An isolated footing is used to support the load on a single column. It is usually either square or rectangular in plan. It represents the simplest, most economical type and most widely used footing. Whenever possible, square footings are provided so as to lessen the bending moments and shearing forces at their critical sections.
Isolated footings are used in case of light column loads, when columns are not closely spaced, and in case of good homogeneous soil. Under the effect of upward soil pressure, the footing bends in a dish shaped figure. An isolated footing must, for that reason, be provided by two sets of reinforcement bars situated on top of the other near the bottom of the footing. In case of property line restrictions, footings may be designed for eccentric loading or combined footing is used as a substitute to isolated footing.
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