The foundation in which a concrete beam is provided to join two footings, is known as

Explanation:

Strap Footing

A strap footing is a type of foundation that is used to connect two isolated footings, typically when the available space is limited, or the soil bearing capacity is uneven under the footings. The strap beam helps in balancing the loads and transferring them evenly, reducing the chances of differential settlement. This type of footing is commonly used in construction where the columns are placed close to the property boundaries.

Analyzing the Given Options

1. "Strip Footing." (Incorrect)

   • Strip footing is used for supporting walls or a series of columns. It is a continuous strip of concrete foundation and is not used to join two footings.

2. "Strap Footing." (Correct)

   • Strap footing involves a concrete beam that connects two isolated footings to balance loads and reduce differential settlements.

   • This type of footing is used when one footing is near a boundary and cannot spread uniformly.

3. "Combined Footing." (Incorrect)

   • Combined footing is used when two or more columns are close enough that their footings overlap. It is a single footing supporting multiple columns and does not involve a connecting beam.

4. "Raft Footing." (Incorrect)

   • Raft footing, also known as mat footing, is used when the entire structure is supported by a single large slab. It is not used to join two isolated footings.

Conclusion:

The correct answer is Option 2: Strap Footing, as it involves a concrete beam connecting two footings to distribute loads evenly and prevent differential settlement.