The type of footing in which load-bearing members share a common rectangular or trapezoidal footing is called:
Try it first: pick an option, then read the explanation.
Asked in SSC JE 14/11/2022
Detailed Explanation
Usually each column has its own isolated footing. Sometimes two columns are so close, or one is so near the property line, that separate footings would overlap or be badly eccentric.
Why “combined footing” Is Correct
Then one footing is provided for both columns: a combined footing. Its shape is chosen so that the centre of the footing area coincides with the resultant of the column loads, giving uniform soil pressure. With equal loads it is rectangular; with unequal loads, or limited space beside the heavier column, it is made trapezoidal.
| 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. stepped footing: A stepped footing is a single footing made in steps of decreasing width.
- B. eccentric footing: An eccentric footing has the load off-centre; it is not shared by columns.
- D. isolated footing: An isolated footing carries only one column.
Key Point
Combined footing: one footing, two or more columns; rectangular (equal loads) or trapezoidal (unequal).
Key Concepts for Students
- A strap footing is an alternative: two footings joined by a stiff beam.
- Combined footings are designed as inverted beams loaded by soil pressure.
- Centroid of footing area = line of action of the resultant load.
Practice more: this is question 19 in Shallow and Deep Foundation MCQs – Part 2. Try the whole set and check every answer instantly.