Design Detail of Isolated Footing
Isolated Footings (Par or spread footings) are
commonly used for shallow foundations in order to carry and transfer
concentrated loads, caused for example by column or pillar. Isolated footings
are consists either of reinforcement or non-reinforcement.
 |
| Isolated Footing |
1.
Pad Footing (
Uniform Thickness)
2.
Sloped Footing
Bearing Capacity of Soil
The size of footing
depends on bearing capacity of soil. The load on unit area below footing should
less than bearing capacity of soil to prevent settlement of footing.
Total pressure acting at
base of footing including self-weight of footing, weight of column, over burden
pressure of soil above footing etc. is called gross bearing capacity of soil.
The net pressure at base
of footing after deduction the weight of excavated soil safe bearing capacity
of soil.
Soil Bearing Capacity of
different types of soils are as under:
Types of Soil / Rock
|
S.B.C (KN/M2)
|
(1)
Rocks
(2)
Non-cohesive soils
(Gravel,
Coarse sand, medium sand, fine sand etc.)
(3)
Cohesive soils
(Soft, hard or
stiff clay)
|
450-3000
100-450
50-450
|
Isolated Footing
Reinforcement Detailing
Reinforcement
detailing of footing is as much important as site investigation for the
structural design of footing. A good detailing reflect the design requirement
of the footing for structural stability.
A
good detailing of reinforcement covers topics live cover to reinforcement based
on environmental consideration, minimum reinforcement and bar diameters, proper
dimensioning of footing. It is desirable foundation should be detailed in both
plan and elevation in drawing.
Reinforcement detailing
of isolated footing include:
1.
Concrete cover of
reinforcements – 75 mm
2.
Minimum
reinforcement and bar diameter
Reinforcement
shall not be less than 0.12 % of the total cross sectional area. The minimum
diameter for main reinforcement should not be less than 12 mm.
3.
Reinforcement
distributing in isolated footing
Square
Footing: The reinforcement
extending in both directions is distributed uniformly across the full width of
the footing.
Rectangular
Footing: reinforcement is
distributed across the full width of footing in long direction.
4. Soil Bearing Capacity.
5. Load on the Structure.
6. Type of Structure.
Sample Design of Isolated Footing With Reinforced Detailing
|
| Isolated Footing |
0 Comments