Triangulation
The count that does not see it
A frame can have exactly as many unknowns as equations and fold up anyway. The count asks whether there are enough equations; it never asks whether they are different from one another.
The triangle that cannot fold, and everything built out of it
A square of pinned bars is a mechanism. A triangle is not, and that single fact is the reason trusses exist and the reason they look the way they do.
The joint that is not a pin
Every truss on this site is analysed as though its joints were frictionless pins. Almost none are. The bending that follows is called secondary, which is a claim about size — and the claim is checkable.
Named alongside it
The objects these essays reach for when they reach for this one.
Method of jointsBracingCritical formEquilibrium matrixIdealisationIndependent equationsJoint rigidityMechanismMoment connectionPanel pointRank deficiencySecondary bending