Isolated Footing Reinforcement Detailing

The objective of an isolated footing is to combat the load on a single column. It transmits the load to the broad spectrum of soil.

It is the most cost-effective type of footing that is suitable when the columns are placed at comparatively long distances.

DETAILING OF ISOLATED FOOTING:

Reinforcement Cover: The least thickness to main reinforcement in footing should not be under 50mm when footing is connected with earth surface directly, and 40mm for outside uncovered face like surface levelling PCC.

If surface levelling is unutilized, then it is essential to provide a cover of 75mm to conceal rough surface of excavation. For raft foundation, the lowest cover to reinforcement should be 75mm whether situated on PCC or directly on earth surface.

Least reinforcement and bar diameter:

The least diameter for main reinforcement should not be under 10mm.

Detailing method of Isolated Footing:

It is suggested that foundation should have been detailed in both plan and elevation in drawings.

The isolated footing normally appears as square or rectangular in plan on the basis of structural requirement and forces which operate on the column. But circular or other shapes are also applied for isolated footings.

Reinforcement Distribution in Footing:

In one-way RCC footing, the reinforcement is allocated consistently across the full width of footing.

In two-way square footings, the reinforcement that expands in both directions is allocated consistently 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 as per following calculations.

The left-over reinforcement in short direction is allocated evenly on both sides of the central band.

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