P-delta — where it appears
Named by 3 essays across 2 fields — each of them below, with the objects they name alongside it.
The load that makes itself worse
A structure that has leaned carries its weight off the axis, which makes it lean further. The amplification is one over one minus the load ratio, and it runs away long before the buckling load.
The load that is really a lean
No frame is ever plumb. The columns are out of upright by something like a three-hundredth, and every tonne of gravity load standing on that lean has a horizontal component. The force that represents it is not a safety allowance — it is an exact statics substitution for a geometry nobody drew.
The stiffness the load takes away
Buckling is usually taught as an event — a critical load, a bifurcation, a mode. Written as a matrix it stops being an event at all. A compressive load subtracts a stiffness from the structure, the subtraction grows with the load, and the critical load is simply where what is left reaches zero.
Named alongside it
The objects these essays reach for when they reach for this one.
Critical loadEccentricityEffective lengthImperfectionNotional loadSecond orderAmplificationAmplification factorBracingBucklingCompatibilityDegrees of freedom