A fixed beam of span l is subjected to a central concentrated load W. The bending moment at the supports will be
- AWl/4
- BWl/8Correct
- CWl²/4
- DWl²/8
Solution
Concept
Fixed end moment for a central load
Formula
M = W l / 8
Step-by-step solution
1. For a fixed beam with a central point load, both end moments are Wl/8 (hogging). 2. The midspan moment is also Wl/8 (sagging).
Explanation
The simply supported midspan moment Wl/4 is shared equally between the supports and the centre in a fixed beam.
Why the other options are wrong
Wl/4 is the simply supported moment; Wl²/4 and Wl²/8 have wrong dimensions.
Shortcut
Fixed beam, central load: Wl/8 at supports and at centre.
Common mistake
Giving Wl/4.
Correct answer: B) Wl/8