Structural Engineering & Statics
where the load goes
Concept

Load combination — where it appears

A set of loads considered together, each at a factored value, representing one state the structure has to survive. Which combination governs is rarely the one with the largest total, because a structure responds to the arrangement of a load and imposed loads may be absent.

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

02468101214161820-200-100100distance along the beam (m)bending moment (kNm, sagging up)the sagging envelopethe hogging envelopeeach case exact to 3e-16 · the envelope out by 23%

The envelope is not a structure

A continuous beam whose imposed load may sit on any span has eight load cases, and every one of them is a genuine state of equilibrium. The curve the design is made against is not one of them — it is assembled from different cases at different stations, and it fails the identity all eight satisfy exactly.

equilibrium · load arrangement 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.

Free bodyBending momentBracingContinuityCritical loadEccentricityEnvelopeEquilibriumEquivalent horizontal forceErection toleranceImperfectionImposed load

All concepts