Strap Footing

A strap footing is a type of foundation system used to connect two or more independent spread footings of columns with a beam. It is also known as a connecting footing or a combined footing. The purpose of a strap footing is to distribute the load from the columns evenly to the soil, ensuring stability and preventing excessive settlement.

Here are the key points to explain why the correct answer is option 'C' - Strap footing:

1. Definition: A strap footing is a type of combined footing that consists of a strap beam connecting two or more spread footings of columns. The strap beam acts as a tie beam and transfers the load from the columns to the soil.

2. Load Distribution: The strap beam distributes the load from the columns to the individual spread footings, which in turn transfer the load to the soil. This helps in reducing the stress on the soil and prevents excessive settlement.

3. Stability: By connecting the independent spread footings with a strap beam, the stability of the entire foundation system is increased. The strap beam resists the overturning and sliding forces, ensuring the columns remain stable.

4. Design Considerations: The design of a strap footing involves determining the size and depth of the spread footings, the thickness and width of the strap beam, and the reinforcement required. The load distribution and the soil bearing capacity are important factors in the design process.

5. Types: Strap footings can be classified into two types based on the arrangement of the columns and the strap beam:
a) Parallel Strap Footing: In this type, the strap beam is parallel to the columns, and the spread footings are aligned in a straight line.
b) Inclined Strap Footing: In this type, the strap beam is inclined to the columns, and the spread footings are arranged in a staggered manner.

6. Advantages: Strap footings offer several advantages, including:
- Efficient load distribution
- Cost-effective compared to individual footings for each column
- Reduced differential settlement
- Enhanced stability and structural integrity

In conclusion, when the independent spread footings of two columns are connected by a beam, it is referred to as a strap footing. The strap footing system ensures proper load distribution, stability, and prevents excessive settlement.