Design of Rectangular Footing to Support RCC Column

Given Data:
Load carrying capacity of Column = 800 KN
Size of Column = 600mm x 400mm
Safe Bearing Capacity of Soil = 200 KN/m²
Concrete Grade = M15
Steel Grade = Fe250

Design Steps:

1. Determination of Size of Footing:
To design a rectangular footing, the size of the footing is determined based on the load-carrying capacity of the column and safe bearing capacity of the soil. Assuming the weight of the footing and soil pressure, the minimum size of the footing is calculated as follows:

Let, qsafe = Safe Bearing Capacity of Soil = 200KN/m²
Load on Column = P = 800 KN
Assuming the weight of Footing = 10% of the total Load = 0.1 x 800 = 80 KN
Total Load on Footing = Ptotal = 800 + 80 = 880 KN
Size of Footing = B x L

Let, B = Breadth of Footing
L = Length of Footing

From the formula of safe bearing capacity of soil,

q safe = Ptotal / (B x L)

Substituting the values, we get

200 = 880 / (B x L)

Therefore, B x L = 4.4 m² (Minimum size of Footing)

Assuming the breadth of footing as 1.5 times the breadth of Column and length of footing as 2 times the breadth of Column, we get:

B = 1.5 x 0.6m = 0.9m
L = 2 x 0.4m = 0.8m

Therefore, the size of footing is taken as 0.9m x 0.8m.

2. Determination of Depth of Footing:
The depth of the footing is calculated based on the moment of resistance required for the footing. Assuming the depth of footing, the moment of resistance is calculated to check whether it satisfies the given condition. If not, the depth is adjusted and the process is repeated until the required moment of resistance is obtained.

Let, d = Depth of Footing
B = 0.9m
L = 0.8m
Ptotal = 880 KN
Weight of Footing = 80 KN
Weight of Column = 0.6 x 0.4 x 2.5 x 25 = 60 KN (Assuming the Density of Concrete as 2.5g/cm³ and 25mm as the thickness of Steel Reinforcement)

Total Load on Footing = Ptotal = 880 KN

Assuming the depth of footing as 0.15m, the moment of resistance is calculated as follows:

M = Ptotal x e x (d/2) + (Weight of Column + Weight of Footing) x (d/2)

Where, e = Eccentricity = (L/2) - (B/2) = (0.8/2) - (0.9/2) = -0.05m (Negative sign indicates that the load is eccentric to the footing)

Substituting the values, we get

M = 880 x (-0.05) x (0.15/2) + (60 + 80) x (0.15/2)
M =