Consider the following statements regarding the lateral torsional buckling of symmetric sections : 1. The beam has no initial imperfections and its behavior is elastic. 2. It is loaded by unequal and opposite end moments in the plane of the web. 3. The beam have residual stresses and its ends are simply supported vertically and laterally. Which of the above statements is/are correct ?
- A2 and 3
- B3 only
- C1 and 2Correct
- D1 only
Solution
Concept
Assumptions of elastic lateral torsional buckling
Step-by-step solution
1. The ideal beam is perfectly straight with no imperfections and behaves elastically (true). 2. It is loaded by end moments in the plane of the web (true). 3. The classical analysis assumes NO residual stresses, so statement 3 is false.
Explanation
The elastic critical moment is derived for a perfect beam without residual stress; imperfections and residual stresses are accounted for by the design curves.
Why the other options are wrong
Statement 3 introduces residual stresses, which are not part of the ideal model.
Shortcut
Ideal LTB: perfect, elastic, no residual stress.
Common mistake
Accepting residual stresses.
Correct answer: C) 1 and 2