An isolated footing of RCC is supporting a pedestal. The critical section for the bending moment should be chosen at:
- Aat the face of the columnCorrect
- Bhalfway between the centre line and the edge
- Ca distance equal to the depth of the column from the face of the column
- Da distance equal to half the depth of the column from the face of the column
Solution
Concept
IS 456 takes the critical section for bending in a footing at the face of the column, pedestal or wall
Step-by-step solution
1. IS 456 gives the rule for the critical section for bending moment in footings. 2. For a footing under a concrete column, pedestal or wall, this section is at the face of the column, pedestal or wall. 3. Here the footing supports a pedestal, so take the section at the face of the pedestal (column). 4. Answer: A.
Explanation
For an RCC footing, the maximum bending moment is taken at the face of the column or pedestal. The section halfway between the centre line and the edge is used only for footings under masonry walls. Distances d and d/2 from the face are used for shear, not for bending.
Why the other options are wrong
B: Halfway between centre line and edge is for footings under masonry walls. C: A distance d from the face is the section for one-way shear, and d is the footing's effective depth, not the column depth. D: A distance d/2 from the face is for punching (two-way) shear.
Shortcut
Bending at face; one-way shear at d; punching shear at d/2.
Common mistake
Mixing up the critical sections for bending and shear.
Correct answer: A) at the face of the column