Which one of the following is NOT an assumption of impact loading on a beam ?
- AThe falling weight sticks to the beam and moves/vibrates with it
- BNo energy loss takes place
- CThe beam is linearly non elasticCorrect
- DThe deflected shape of the beam is the same under a dynamic load as under the static load
Solution
Concept
Assumptions for impact on beams
Step-by-step solution
1. The falling mass sticks to the beam and vibrates with it (a). 2. No energy is lost (b). 3. The beam behaves linearly elastically (not "non-elastic") (c is not an assumption). 4. The deflected shape under impact is taken the same as under static load (d).
Explanation
The simple impact analysis equates the energy of the falling weight to the strain energy stored by a linearly elastic beam.
Why the other options are wrong
(a), (b) and (d) are the standard assumptions.
Shortcut
Impact analysis: elastic, no losses, static deflected shape.
Common mistake
Missing the word "non" in (c).
Correct answer: C) The beam is linearly non elastic