Spacing between longitudinal bars measured along the periphery of RCC columns should not exceed 300 mm.

Explanation:

1. Importance of spacing between longitudinal bars in RCC columns:
The spacing between longitudinal bars in reinforced concrete (RCC) columns plays a crucial role in ensuring the structural integrity and strength of the column. The correct spacing ensures proper distribution of load, prevents cracking, and enhances the overall performance of the column.

2. Significance of measuring spacing along the periphery:
Measuring the spacing between longitudinal bars along the periphery of the RCC column is important because it helps in ensuring uniform distribution of reinforcement throughout the column's circumference. This uniform distribution is necessary to resist the bending and shearing forces acting on the column.

3. Maximum allowable spacing:
The correct answer to the given question is option 'C', which states that the spacing between longitudinal bars measured along the periphery of RCC columns should not exceed 300 mm. This means that the distance between any two adjacent bars along the periphery should not be more than 300 mm.

4. Reason for the maximum spacing limit:
The maximum spacing limit is defined to prevent excessive displacement, cracking, and failure of the RCC column. If the spacing between bars exceeds the specified limit, it may lead to inadequate reinforcement, reduced load-carrying capacity, and compromised structural stability.

5. Impact of spacing on structural behavior:
The spacing between longitudinal bars affects the behavior of the RCC column under various loading conditions. Smaller spacing provides better resistance against bending and shear forces, reduces the risk of cracking, and improves the overall strength and durability of the column.

6. Other considerations:
In addition to the maximum spacing limit, it is also important to adhere to other design and construction guidelines while placing longitudinal bars in RCC columns. These include proper cover to the reinforcement, adequate lap lengths, and proper anchorage to ensure the bars are effectively bonded with the surrounding concrete.

Conclusion:
To ensure the structural integrity and strength of RCC columns, the spacing between longitudinal bars measured along the periphery should not exceed 300 mm. Adhering to this maximum spacing limit helps in achieving the desired load-carrying capacity, resistance against bending and shear forces, and overall durability of the column.