Design of Shallow Foundation (Isolated Footings)

AIM:

To design a square footing for a column size of 400x400 for given constraints and do following check:

• 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 the column-footing joints is within 0.45 times the maximum concrete compressive strength.
• Also, to provide a sketch showing the details of geometric and structural features of footing.

INTROUDUCTION:

• Footing is a part of the foundation which is constructrd with cocrete or brickwork masonary and acts as a base for the floor columns and floor walls.
• The main function of footing is to transfer the vertical lads directly to the soil.
• The four main types of footing is to transfer the vertical loads directly to the soil.
• A wall footing or stripfooting is a continous strip of concrete that serves to spread the weight of a load-bearing wall across an area of the overall column to the area of the property
• Spreading footing is provided when two columns are closely placed or when the column is at the property line.
• Raft footing is provided for very weak soil or when the area of the overall column to the area of the site footprint exceeds 50%.
• Isolated footing is an individual footing that transfers the load to the underground soil. It is provided when a single column is to be provided.

PROCEDURE:

Given Data,

• Column size = 400mm x400mm
• Compression axial load for the load combination of (1.5DL+1.5LL) is 2000KN
• Safe bearing capacity at a depth of 2 meter below E.G.L is 150KN/m^2
• Assuming the self-weight of the footing and soil above it as a 10% load
• Grade of concrete = 25KN/m^2
• Assuming fy = 415 N/mm^2

• Gross bearing capacity
• Assuming the unit weight of the soil to be 18KN/m^3
• Load on the footing = 1333.33KN
• Weight of the footing = 3.5 x 3.5 x25 x 0.8 = 245KN
• Weight of the soil = 3.5x 3.5 (2-0.8) x 18 = 261.6KN
• Total load = 1852 KN
• Gross bearing capacity = 1852/3.5 x 3.5 = 257 KN/m^2
• As 257 KN/m^2 > 150KN/m^2, hence safe
• Corrected net soil pressure = 2000/3.8 x 3.8 = 138.5KN

Reinforcement Bars Placement Plan

Section of the Footing

Result:-

Sloped isolated footing for the square column is designed for the given conditions and also checked.