Structural Engineering & Statics
where the load goes
Generator

The effective-section generator

Rendered here at the parameters it defaults to, with every essay that calls it — which is the same list as the blast radius of changing it.
The load did not move; the section didA lipped channel 200 by 65 mm at 2 mm thick, drawn twice on top of itself: the outline as fabricated, and the part of it still working once the plates have buckled. The web is held on both edges, so it loses its middle; the flanges are held at the web, so an unlipped one would lose its free edge. What survives is not symmetric with what was drawn, so the centroid moves 8.0 mm — and a load applied along the axis it was designed to arrives 8.0 mm off the section that has to carry it. At the 177 kN this section will take, that is 1.42 kNm of bending nobody applied.8.0 mmas drawnas it workswebλ 2.11 · keeps 43%flangeλ 0.68 · keeps 100%lipλ 0.61 · keeps 100%area left69%eccentricity8.0 mm256 kN of section, 177 kN of it effective, and 1.42 kNm that was not in the load case

The load did not move; the section did. A lipped channel 200 by 65 mm at 2 mm thick, drawn twice on top of itself: the outline as fabricated, and the part of it still working once the plates have buckled. The web is held on both edges, so it loses its middle; the flanges are held at the web, so an unlipped one would lose its free edge. What survives is not symmetric with what was drawn, so the centroid moves 8.0 mm — and a load applied along the axis it was designed to arrives 8.0 mm off the section that has to carry it. At the 177 kN this section will take, that is 1.42 kNm of bending nobody applied.

1 essay calls effective-section. The drawing above is what it returns with no arguments at all; every call below passes it something, because a placement that passes nothing draws whichever member of the family the generator happens to default to rather than the one its essay argues about.

Where it is called

Changing this generator changes every one of these figures.

8.0 mmas drawnas it workswebλ 2.11 · keeps 43%flangeλ 0.68 · keeps 100%lipλ 0.61 · keeps 100%area left69%eccentricity8.0 mm256 kN of section, 177 kN of it effective, and 1.42 kNm that was not in the load case Sections and stress

What is left after it ripples

A thin plate that buckles locally has not failed. It has stopped taking load in its middle and gone on taking it near its edges, so the member is now made of a different section from the one that was drawn — and the new one has its centroid somewhere else, which turns a concentric load into an eccentric one.

The library, page 1 of 6 — where effective-section sits