The maximum spacing of vertical stirrups at beam ends (plastic hinge locations) as per IS 13920 is the lesser of
- A0·75d or 300 mm
- B0·55d or 250 mm
- C0·35d or 200 mm
- D0·15d or 150 mmCorrect
Solution
Concept
Close spacing of hoops in the plastic hinge zone (IS 13920)
Formula
s ≤ d/4 (and not more than 100 mm for most cases)
Step-by-step solution
1. IS 13920 requires closely spaced hoops over a length of 2d at beam ends. 2. The spacing is limited to d/4 and a multiple of the smallest bar diameter, with an absolute value around 100 mm. 3. Of the options, the smallest values (0.15d or 150 mm) are closest to this requirement.
Explanation
Closer spacing of stirrups in the hinge region confines the concrete and gives ductility. The options with 0.75d, 0.55d or 0.35d are much more lenient than the code value of about d/4.
Why the other options are wrong
0.75d or 300 mm is the general IS 456 limit for shear reinforcement, which applies outside the hinge region.
Shortcut
Hinge zone: ≤ d/4 and ≈ 100 mm.
Common mistake
Using the IS 456 general limit of 0.75d.
Correct answer: D) 0·15d or 150 mm