A steel chimney 3 m in diameter is situated in a region where the intensity of uniform wind pressure is 1200 N/m². If the shape factor is 0·7 and the intensity of wind pressure is uniform, the shear due to wind load at a level of 15 m below the top of the chimney will be
- A37·8 kNCorrect
- B34·6 kN
- C31·8 kN
- D27·6 kN
Solution
Concept
Wind force on a cylindrical structure
Formula
F = p × Cf × D × h
Step-by-step solution
1. Projected area of the chimney above the section = D × h = 3 × 15 = 45 m². 2. F = 1200 × 0.7 × 45 = 37 800 N = 37.8 kN.
Explanation
The shear at a level equals the wind force on the part of the chimney above it: pressure × shape factor × projected area.
Why the other options are wrong
The other values do not equal 1200 × 0.7 × 3 × 15.
Shortcut
F = p Cf D h.
Common mistake
Using the circumference instead of the projected width.
Correct answer: A) 37·8 kN