Structural Engineering & Statics
where the load goes
Concept

Moment — where it appears

The turning effect of a force about a point, equal to the force times its perpendicular distance from that point. It has no meaning until the point is named, and half the arithmetic errors in statics are a moment taken about a centre nobody wrote down.

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

200 kN200 kNthe chord — and the line of action1.20 mbending moment = P × offsetpeak 240 kNmbending stress is 24.0 times the axial stress at the worst section

The member with only one direction

If a body is in equilibrium under forces applied at exactly two points, those forces are equal, opposite and along the line joining the points. It is three conclusions from two equations, it is the shortest real theorem in statics, and nearly everything on this site depends on it without saying so.

equilibrium · two force member 2700 kNthe leaf, 900 kN3600 kN on the trunnionno moment, at any angle9 mW·a = 8100 kNm and C·r = 8100 kNm — a product, not a weightinertia 9908 t·m² against 7431 for the leaf alone

Balanced, and four times as heavy

A counterweight cancels a moment about a pivot, and that is the only thing it cancels. The bearing beneath carries both weights, the inertia rises as the square of the radius, and a load that moves cannot be balanced at more than one position at all.

equilibrium · counterweight

Named alongside it

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

EquilibriumFree bodyBalanceBearingCentre of gravityCounterweightDead loadEccentricityFunicularImperfectionLever armLine of action

All concepts