Design of Shallow Foundation (Isolated Footings)

Design a square footing for a column size of 400x400. The compression axial load for the load combination of (1.5 DL + 1.5 LL) is 2000 KN. The safe soil bearing capacity is 150 KN/m2 at a depth of 2 metres below E.G.L. Participants are free to go for either a tapered or stepped footing. Besides the total axial load, also account for the self-weight of the footing and soil above it. Assume M25 concrete grade. Do the following checks:

• If the gross bearing pressure under the footing is within safe bearing capacity
• Provide sufficient depth and longitudinal steel for resisting bending and shear
• Sufficient anchorage for column steel into the footing
• If the bearing pressure at column-footing joint is within 0.45 times the maximum concrete compressive strength

Provide a simple sketch showing the size of the footing, maximum and minimum depth of the section, flexural reinforcement in both directions and anchorage of column steel.

ANS :

AIM : To design a square footing for a column size of 400 x 400 and to provide a sketch showing the size of the footing, maximum and minimum depth of the section, flexural reinforcement in both directions and anchorage of column steel

PROCEDURE :

Given data :

Column size = 400 x 400 mm

Soil bearing capacity = 150 KN/mmsq

Compression axial load = 2000 KN

Compressive strength = M25

Step 1 : Size of the footing

Assume self weight of footing equal to 10% of super imposed load

Step 2 : Net upward pressure

Step 3 : Depth of footing on the basis of B.M

The maximum B.M at the base of the column is given by,

By thumb rule we take 2.5 times higher value of d for shear check

Step 4 : Area of reinforcement

Step 5 : Check for one way shear

For one way shear, critical section is located at a distance ‘d’ from the face of the column

Hence OK for one way shear

Step 6 : Check for two way shear (punching shear)

For two way shear, The section lies at a distance d/2 from the column face all around

RESULT :

By using the given details the square footing is designed