Which one of the following is NOT a difference between the behaviour of the beam-columns subject to the bending moment about minor axis to major axis ?
- AIn the case of slender members under small axial load, there is very little reduction of moment capacity below Mp, since lateral torsional buckling is not a problem in weak axis bending
- BThe moment of magnification is larger in the case of beam-columns bending about their weak axis
- CAs the slenderness decreases, the failure curves in the P/Pn, y-y axis plane change from convex to concave, showing decreasing dominance of minor axis bucking
- DThe failure of short/stocky members is either due to section strength being reached at the ends or at the section of larger magnified momentCorrect
Solution
Concept
Beam-column behaviour: minor versus major axis bending
Step-by-step solution
1. Statements (a), (b) and (c) describe behaviours that differ between weak-axis and strong-axis bending (no LTB, larger magnification, shape of interaction curves). 2. Statement (d) describes the failure of short members in general, whichever axis is bent, so it is not a difference.
Explanation
Short, stocky beam-columns fail by reaching section strength, whichever axis carries the moment.
Why the other options are wrong
(a), (b) and (c) are specific differences of weak-axis behaviour.
Shortcut
Weak axis: no LTB, bigger magnification.
Correct answer: D) The failure of short/stocky members is either due to section strength being reached at the ends or at the section of larger magnified moment