ANS:C - 15 cm

he choice of a maximum thickness of 15 cm for the reinforced concrete footing on piles at its edges, as per I.S. 456: 1978, likely stems from several engineering considerations and practical constraints associated with foundation design and construction. Here's an explanation of why this maximum thickness is specified:

1. Load Distribution: The primary function of a footing is to distribute the loads from the superstructure (building or structure) to the underlying soil or pile foundation. Excessive thickness at the edges of the footing can lead to uneven stress distribution, potentially causing differential settlement or overstressing of certain areas. By limiting the edge thickness to 15 cm, engineers aim to achieve a more uniform distribution of loads, minimizing the risk of structural issues due to differential settlement.
2. Economic Considerations: In engineering design, it's essential to optimize material usage and construction costs while ensuring adequate structural performance. Keeping the edge thickness of the footing within a reasonable range, such as 15 cm, helps control material quantities and construction expenses without compromising the integrity and stability of the foundation system.
3. Construction Practicality: Thicker sections of concrete can be more challenging to construct and may require additional formwork, labor, and equipment. By specifying a maximum thickness of 15 cm for the edges of the footing, the design accommodates practical construction considerations, facilitating efficient and cost-effective construction processes on-site.
4. Structural Performance: The structural behavior of the footing, including its load-carrying capacity, settlement characteristics, and interaction with the underlying soil or piles, is influenced by various factors, including footing geometry and dimensions. Limiting the edge thickness to 15 cm helps ensure that the footing behaves predictably under applied loads and environmental conditions, enhancing overall structural performance and durability.
5. Code Compliance: Engineering standards and building codes, such as I.S. 456: 1978, provide guidelines and requirements for the design and construction of reinforced concrete elements, including footings. Adhering to these code provisions helps ensure that the foundation design meets established safety and performance criteria, promoting structural integrity and compliance with regulatory standards.

Overall, the maximum thickness of 15 cm for the edges of reinforced concrete footings on piles represents a balance between structural requirements, construction practicality, and economic considerations, aimed at achieving safe, reliable, and cost-effective foundation solutions for various building and infrastructure projects.