Design Procedure of Column Footings Foundation Design

Design Procedure of Column Footings  Foundation Design

Here is a step-by-step guide to Column Footing Design:
Column Footing Plan and Section | Foundation Design
Column Footing Plan and Section | Foundation Design

Step 1

Area required for footing
Square = B = (w+w1)/P0
Where, Po = safe bearing capacity of soil
w1 = self weight of footing
w = self weight of footing
For Rectangle = b/d = B/D
A = b x d
Net upward pressure on the footing
q/p = W/A

Step 2

Bending Moment
Critical section for maximum bending moment is taken at the face of the column
For a square footing,
Mxx = q x B/8 (L – a)2
Mxx = q x L/8 (B – b)2
Myy = q x B/8 (L – a)2

Step 3

To fix the depth of the footing shall be greater of the following:
Depth from bending moment consideration
d =square root(M/Qb)
where, Q = moment of required factor
Depth from shear consideration
Check for one way shear
Check for two way shear or punching shear
Critical shear for one way shear is considered at a distance ‘d’ from face of the column.
Shear force, V = qB [ ½(B – b) d]
Nominal shear stress, Tv = k . Tc
Tc = 0.16square rootfck

Step 4

Check for two way shear
Critical section for two way shear is considered at a distance at a distance d/2 from all the faces of the column.
SF, V = q [ B2 – (b + d)2]
SF, V = q [L x B – (a + d)(b + d)]
Nominal shear stress, Tv = V/2((a+d)(b+d)d) ——- {for a rectangle
Tv = V/4((b+d)d) ——- {for a square
Tv = k . Tc
k = 0.5 + Beta > 1 ; [Beta = ratio of sides of the column
Tc = 0.16square rootfck
Area of steel, Ast = M/((sigma)stjd)

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