Reinforcement details of spread footing
Among various types of foundations, the isolated footing is considered as one of the most recognized and easiest types of foundations that is extensively utilized all through the globe. Foundation is very crucial for the building since the total load of the building is transmitted to ground via the foundation.
Isolated footings are very useful for Reinforced cement concrete column as it is trouble-free and very inexpensive. The purpose of an isolated footing is to support a single column. Isolated footings stands for independent footings which are placed for each column.
This type of footing can be used under the following situations :-
• Columns are not placed narrowly.
• Loads on footings are fewer.
• The safe bearing strength of the soil is normally higher.
The Isolated footings basically comprises of a bottom slab. There exist three basic types of bottom slabs:
• Pad footing (having identical thickness)
• Stepped footing (with inconsistent thickness)
• Sloped footing (trapezoidal section)
Footings experience the impact of upward soil pressure, under such situation footings twist in a dish-shaped form. So, applicable reinforced steel mesh is placed to withstand the two important internal forces alias shear force and bending moment.
Where footing is to be place at the boundary of land or a road where it becomes difficult to stand your footing in neighbors property, footings will be designed as combined footings or even eccentric footing can be applied as a substitute of isolated footings.
The Design of Isolated Footing:
The Isolated Footings is designed to find out the followings:
1. Area of footing
2. Thickness of footing
3. Reinforcement Details of footing with a satisfying moment and shear force consideration.
4. Inspect development length and shearing stresses.
All the above things are performed based on the loads on footings, safe bearing strength (SBC) of the soil, grade of concrete and Steel. Minimum cover to main reinforcement should not be lower than 50mm on the surface of the contact with the earth face. The diameter of main reinforcement should not be under 10mm.
The design of footings is based on the following steps :-
• Determine an area of footings depending on factored loads.
• Guess proper thickness of footing
• Determine critical section for flexure and shear
• Determine bending moment and shear forces at critical section
• Verify the suitability of the assumed thickness
• Ascertain reinforcement detail
• Verify bearing stresses
• Check for development length