In a fixed beam subjected to downward loads, the maximum bending moment is given by the greater fixing moment. This is true
- Aif load is only central point load
- Bif load is only eccentric point load
- Cif load is only distributed load
- Dfor any combination of downward loadsCorrect
Solution
Concept
Location of the maximum moment in a fixed beam
Step-by-step solution
1. For a central point load the fixing moment (Wl/8) equals the sagging moment, and for a UDL the fixing moment (wl²/12) is twice the midspan moment (wl²/24). 2. For eccentric point loads the greater fixing moment exceeds the sagging moment under the load. 3. In every downward-load case the numerically greatest moment is at a fixed end, so the statement holds for any combination of downward loads.
Explanation
In a fixed beam with downward loads, the hogging moments at the fixed ends are never smaller than the sagging moments in the span. So the maximum bending moment is the greater fixing moment in all cases.
Why the other options are wrong
Options (a), (b) and (c) are only particular cases of the general rule in (d).
Shortcut
Fixed beam: the greatest moment is at a support.
Common mistake
Thinking the midspan moment can govern.
Correct answer: D) for any combination of downward loads