What is refuted here — page 18
Safe rather than true — continued
Not a misconception so much as a simplification that has stopped being labelled as one. Each of these errs on the safe side in the case it was chosen for — and each has a direction in which it does not. 5 claims in this group.
Quoting k = 4 for a long plate is an approximation, so it could be wrong in either direction.
What decides it: It is the floor of the envelope and not an average through it. Every scallop rises above 4 and none falls below it, so the quoted value understates the critical stress by up to 12.5 per cent and never overstates it — and past an aspect ratio of 1.60 the error can never exceed 5 per cent again.
Tested in Four was never a fact about plates, at the figure it turns on · the essays about plate buckling.
One pass of the effective-width calculation is enough, because the correction is small.
What decides it: It is small in the moment and not in the width. One pass reports 278 mm of web removed against the converged 323, understating the loss by 16 per cent, while the moment capacity it reports is 10,079 kNm against 9,999 — an error of 0.8 per cent. The two errors differ by a factor of twenty because the width that goes missing sits near the neutral axis.
Tested in Classified by a gradient it does not have, at the figure it turns on · the essays about plate buckling.