Why does distortional buckling threaten cold‑formed purlins even when local flange buckling is braced?
Choices
- (A) Half-wavelength distortions rotate the lip-stiffener pair reducing effective section modulus
- (B) Local buckling and distortional buckling never interact
- (C) Cold-formed sections ignore lip stiffeners entirely
- (D) Distortional modes require plate thicknesses above 12 mm only
Correct answer: (A)
Half-wavelength distortions rotate the lip-stiffener pair reducing effective section modulus
Explanation
Distortional waves involve whole flange-lip systems rotating together.