**DESIGN OF FOOTINGS – IS-456 RECOMMENDATIONS:**

**GENERAL**1. In sloped or stepped footings, the effective cross – section in compression shall be limited by the area above the neutral plane, and the angle of slope or depth and location of steps shall be such that the design requirements are satisfied at every section. Sloped and stepped footings that are designed as a unit shall be constructed to assure action as a unit. 2. Thickness at the edge of footing: In reinforced and plain concrete footings, the thickness at edge shall be not less than 150 mm for footings on soils nor less than 300mm above the tops of files for footing on piles. 3. In the case of plain concrete pedestals, the angle

Fig.1

**MOMENTS AND FORCES**1. In the case of footings on piles, computation for moments and shears may be based on assumption that the reaction from any pile is concentrated at the centre of the pile. 2. For the purpose of computing stress in footings which support a round or octagonal concrete column or pedestal, the face of the column or pedestal shall be taken as the side of a square inscribed within the perimeter of the round or octagonal column or pedestal.

**3.**

**Bending Moment:**i. The bending moment at any section shall be determined by passing through the section a vertical plane which extends completely across the footing and computing the moment of the forces acting over the entire area of the footing on one side of the said plane. ii. The greatest bending moment to be used in design of an isolated concrete footing which supports a column, pedestal or wall, shall be the moment computed in the manner prescribed in (i) at section located as follows: a. At the face of the column, pedestal or wall, for footings supporting a concrete column, pedestal or wall. b. Half way between the center line and the edge of the wall, for footings under masonry walls, and c. Half way between the face of the column or pedestal and the edge of the gusseted base, for footing under gusseted bases. 4. Shear and Bond i. The shear strength of footings is governed by the more severe of the following two conditions: a. The footings acting essentially as a wide beam, with a potential diagonal crack extending in a plane across the entire width, the critical section for this condition shall be assumed as a vertical section located from the face of the column, pedestal or wall at a distance equal to the effective depth of the footing in case of footings on soils and a distance equal to half the effective depth of footing for footing on piles. b. Two way action of the footing, with potential diagonal cracking along the surface of truncated cone or pyramid around the concentrated load: in this case, the footing shall be designed for shear in accordance with appropriate provisions discussed below. (Fig.2)

Fig.2 – Critical Section for Shear

ii. In computing the external shear on any section through a footing supported on piles, the entire reaction from any pile of diameter**TENSILE REINFORCEMENT**The total tensile reinforcement at any section shall provide a moment of resistance at least equal to the bending moment on the section calculated in accordance with B(3). Total tensile reinforcement shall be distributed across the corresponding resisting section as given below: i. In one way reinforced footing, the reinforcement shall be distributed uniformly across the full width of the footing. ii. In two way reinforced square footing, the reinforcement extending in each direction shall be distributed uniformly across the full width of the footing. iii. In two way reinforced rectangular footing, the reinforcement in long direction shall be distributed uniformly across the full width of the footing. For reinforcement in short direction, a central band equal to the width of the footing shall be marked along the length of the footing and portion of the reinforcement determined in accordance with the equation given below shall be uniformly distributed across the central band.

**TRANSFER OF LOAD AT THE BASE OF COLUMN**The compressive stress in concrete at the base of the column or pedestal shall be considered as being transferred by bearing to the top of the supporting pedestal or footing. The bearing pressure (

**NOMINAL COVER**For footings, minimum nominal cover shall be 50mm.

**NOMINAL REINFORCEMENT**The nominal reinforcement for concrete sections of thickness greater than 1m shall be 360