For what reason, we would expect local buckling of W-shape section before global buckling in design?

[mador]

Hello! Everyone,
I have a quick question here about steel design.
For what reason, we would expect that the local buckling in section (let us say, W-shape) occurs before the global buckling in both axial compression design and flexural design?
I am thinking of this because, in my mind, if the local buckling comes out first, it probably affects the stability of the structure and reduces the global buckling load (critical load).
Although I believe it is true that local buckling may cause much smaller damage than the influence by global buckling. But if it is like that, the global buckling strength might not get developed, do you agree with me? Thanks in advance,
Matthew

 

[KootK]

I agree with you. Local buckling is precluded with standard steel sections by limiting width to thickness ratios (b/t). Most of the common steel sections are proportioned such that local buckling would not precede yielding of the overall cross section.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.