Question

In an isolated square concrete footing, the critical section for two-way shear occurs at

• A. at face of column
• B. at a distance d / 3 from face of column
• C. at a distance d from the face of the column
• D. at a distance d / 2 from periphery of column face

Hint:

Remember the critical sections for shear in footings:
- One-Way Shear (like a beam) $\rightarrow$ at distance d from the column face.
- Two-Way Shear (punching) $\rightarrow$ at distance d/2 from the column face.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify the location of the critical section for checking two-way shear (also known as punching shear) in an isolated footing.

Step 2: Detailed Explanation:
In the design of footings, shear is checked in two ways:

• One-Way Shear (or Wide-Beam Shear): This is checked at a critical section located at a distance

$d$ from the face of the column, where $d$ is the effective depth of the footing. The footing is treated like a wide beam cantilevering from the column.

• Two-Way Shear (or Punching Shear): This is the tendency of the column to "punch" through the footing. The shear failure occurs along a truncated pyramid shape. According to IS 456:2000 (Clause 31.6.1.1), the critical section for two-way shear is taken at a distance of

$d/2$ from the periphery (or face) of the column. The shear is checked along this perimeter.


Option (D) correctly describes the location for the critical section for two-way shear.

Step 3: Final Answer:
The critical section for two-way shear in an isolated footing occurs at a distance d/2 from the periphery of the column face.