For a number of columns constructed in a row, the type of foundation provided is:
Try it first: pick an option, then read the explanation.
Asked in SSC JE 27/01/2018 (Evening); SSC JE 2008
Detailed Explanation
A strip (continuous) footing is long compared with its width. It is the normal foundation under a load-bearing wall, and it is also used under a line of closely spaced columns.
Why “Strip” Is Correct
When several columns stand in a single row, their isolated footings would come close together or overlap. Joining them into one continuous strip footing along the row is simpler and spreads the load evenly. Terzaghi's strip footing equation, qu = cNc + γDfNq + ½γBNγ, applies to it directly.
| Foundation | When it is used |
|---|---|
| Isolated (spread) footing | One column on reasonably good soil |
| Strip (continuous) footing | A wall, or several columns in one row |
| Combined footing | Two or more columns on one footing (rectangular or trapezoidal), e.g. a column near the property line |
| Strap (cantilever) footing | Two footings joined by a strap beam to balance an eccentric outer column |
| Raft (mat) foundation | Footings would cover more than about 50% of the plan area; weak soil; differential settlement must be limited |
| Pile / well / caisson | Deep foundations: good bearing stratum lies deep, or loads are very heavy |
Why the Other Options Are Wrong
- A. Footing: ‘Footing’ is too general; it does not name the type.
- B. Raft: A raft covers the whole building area, not one row.
- C. Strap: A strap footing links just two footings with a beam, usually to balance an eccentric column.
Key Point
Row of columns or a wall → strip (continuous) footing.
Key Concepts for Students
- Strip footing analysis is two-dimensional (plane strain).
- Square and circular footings use shape factors in Terzaghi's equation.
- If strips under several rows merge, the result is a raft.
Practice more: this is question 24 in Shallow and Deep Foundation MCQs – Part 2. Try the whole set and check every answer instantly.