Which of the following statements is true?
Try it first: pick an option, then read the explanation.
Asked in SSC JE 22/01/2018 (Morning)
Detailed Explanation
A footing spreads a concentrated column or wall load over a larger area of soil. Each projecting part of the footing acts like a cantilever pushed upward by the soil pressure.
Why “To ensure uniform pressure distribution, the thickness of the foundation is decreased gradually towards the edge” Is Correct
The bending moment and shear in this cantilever are largest at the face of the column and fall to zero at the free edge. So the footing needs its full depth near the column but can be made gradually thinner towards the edge (sloped or stepped footings). This keeps the footing stiff where it matters, so it spreads the load evenly, while saving material. That is statement (c).
Why the Other Options Are Wrong
- A. To ensure uniform pressure distribution, the thickness of the foundation is kept uniform throughout: A uniform thickness works but wastes material near the edges; it is not what the statement asks.
- B. To ensure uniform pressure distribution, the thickness of the foundation is increased gradually towards the edge: Thickening towards the edge is the reverse of what the bending moment requires.
- D. To ensure uniform pressure distribution, the thickness of the foundation is kept zero at the edge: Zero thickness at the edge is impossible; a minimum edge depth (e.g. 150 mm for RCC footings on soil) is always kept.
Key Point
Footing depth: maximum at the column face, reduced towards the edge (sloped/stepped).
Key Concepts for Students
- Critical section for bending: face of the column.
- Critical sections for shear: d and d/2 from the column face (one-way and punching).
- IS 456 minimum edge thickness for footings on soil is 150 mm.
Practice more: this is question 29 in Shallow and Deep Foundation MCQs – Part 2. Try the whole set and check every answer instantly.