Structural Engineering & Statics
where the load goes
Concept

Torsional buckling — where it appears

Buckling in which a member rotates about its own longitudinal axis instead of deflecting sideways, resisted by the section's torsional and warping stiffness. It governs sections with a low torsion constant, and the same equation restrained by a continuous spring gives distortional buckling.

Named by 2 essays across 2 fields — each of them below, with the objects they name alongside it.

the same, laid flatr = 4.3 mmλ = 9247 kNsquarer = 15.8 mmλ = 25397 kNtall rectangler = 57.7 mmλ = 691295 kNI-sectionr = 90.0 mmλ = 443146 kNthe dashed pair is ±r about the centroidthe bar is the Euler load at 4 m, to scale

The one length a section takes into a column

A section has an area, a second moment, two section moduli, a shear centre and a torsion constant. A column has heard of exactly one of them, and it is none of those — it is the length √(I/A), which is where the whole area would have to sit to give the section the stiffness it has.

sections · radius of gyration 32100316100031620200400600800half-wavelength (mm, logarithmic)buckling stress (N/mm²)localdistortionalglobalyield287 at 689 mmthe distortional minimum is 2√(EC_wk_φ) + GJ over I₀, at π(EC_w/k_φ)^¼

The mode between the two that get checked

A thin-walled strut has three ways of buckling and two of them have design rules. The third has a half-wavelength several times the section depth, a shape in which the fold lines themselves move, and an elastic stress that no effective-width calculation can produce.

stability · distortional buckling

Named alongside it

The objects these essays reach for when they reach for this one.

SlendernessAsymmetric sectionBucklingBuilt up columnBuilt up sectionCold formed sectionDistortional bucklingEffective lengthEffective widthElastic foundationEuler loadHalf wavelength

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