Structural Engineering & Statics
where the load goes
Concept

Notional load — where it appears

A horizontal force applied to represent a frame's out-of-plumb, equal to the out-of-plumb angle times the vertical load carried. It is an exact statics substitution for a geometry rather than a safety allowance, and it is present in every load combination including the one with no wind in it.

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

00.20.40.60.80246810applied load ÷ buckling load1.1×1.3×1.4×2.0×3.3×10.0×first-order analysis says the answer is always 1×one over one minus the ratio

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.

stability · second order 00.20.40.60.80246810applied load ÷ buckling load1.1×1.3×1.4×first-order analysis says the answer is always 1×one over one minus the ratio

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.

equilibrium · notional load

Named alongside it

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

EccentricityImperfectionP-deltaAmplification factorBracingCritical loadEffective lengthEquivalent horizontal forceErection toleranceFree bodyLateral systemLoad combination

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