The correct answer is D. All the above.
An isolated footing is a type of foundation that is used to support a single column or pier. It is typically made of concrete and is designed to transfer the load from the column to the soil below. The footing may have steps or projections in the concrete base to increase its bearing area and distribute the load more evenly. Heavily loaded column bases must be provided with steel reinforcement in both directions to prevent cracking.
Here is a more detailed explanation of each option:
- Option A: Isolated footing is provided under column to transfer the load safely to soil bed.
This is true. The purpose of an isolated footing is to transfer the load from the column to the soil below in a safe and efficient manner. The footing is designed to be larger than the column so that it has a greater bearing area. This allows the load to be spread out over a larger area of the soil, which reduces the pressure on the soil and prevents it from sinking.
- Option B: Column footings may have steps or projections in the concrete base.
This is also true. Steps or projections in the concrete base of a column footing are called “haunches.” They are used to increase the bearing area of the footing and distribute the load more evenly. Haunches are typically used in footings that support heavy loads.
- Option C: Heavily loaded column base must be provided steel reinforcement in both directions.
This is also true. Steel reinforcement is used in concrete footings to prevent cracking. Heavily loaded column bases are more likely to crack than lightly loaded column bases, so they must be provided with steel reinforcement in both directions to prevent cracking.
In conclusion, all of the options are correct. Isolated footings are provided under columns to transfer the load safely to the soil bed. Column footings may have steps or projections in the concrete base. Heavily loaded column bases must be provided with steel reinforcement in both directions.