In the case of an I-section beam maximum shear stress is at
- AThe junction of the top flange and web
- BMiddle of the webCorrect
- CEither (A) or (B)
- DNone of the above
Solution
Concept
Maximum shear stress location in I-section beam
Formula
NONE
Step-by-step solution
1. The shear stress distribution across a cross-section varies parabolically with depth. 2. In an I-section beam, the web resists most of the vertical shear force. 3. The maximum shear stress occurs at the neutral axis, which lies at the middle of the web. Answer: B
Explanation
Shear stress distribution across a beam cross-section varies parabolically with distance from the neutral axis. In an I-section beam, the thin vertical web carries almost all the vertical shear force, reaching its maximum intensity at the neutral axis located at the middle of the web. Moving away from the middle toward the flanges causes the shear stress intensity to decrease rapidly.
Why the other options are wrong
A) Shear stress at the flange-web junction undergoes a sudden change, but is not the maximum. C) Maximum shear stress occurs strictly at the neutral axis in the middle of the web. D) Option B is the correct answer.
Shortcut
Maximum shear stress in an I-section occurs at the neutral axis, which is the middle of the web.
Common mistake
Assuming maximum shear stress occurs at the flange-web junction rather than at the neutral axis in the middle of the web.
Correct answer: B) Middle of the web