Structural Engineering & Statics
where the load goes
Concept

Half wavelength — where it appears

The length of one buckle in a member that buckles into waves, and the variable a buckling stress is minimised over. Each mode of a thin-walled section has its own, so plotting critical stress against half-wavelength separates modes that a single check would merge into one.

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

1968 kNthe restraint: 0.35 N/mm per mmtwo half-waves, each 6000 mmunrestrained 173 kN in one half-wave, drawn faintly · effective length 3555 mm

Held everywhere, and it forgets its length

A brace at a point divides a member's buckling length. A restraint spread along the whole member does something else — the member chooses its own number of half-waves, and past a few of them the critical load stops depending on the length at all.

stability · continuous restraint 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.

Elastic foundationSlendernessBracingBucklingCold formed sectionCompression flangeContinuous restraintCritical loadDistortional bucklingEffective lengthEffective widthEigenvalue

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