Concept
Portal frame — where it appears
2 essays name this object, across 2 fields. What follows is each of them, and the objects they name alongside it.
The frame that leans, and what stops it
A rectangle of pinned bars folds flat. Make the corners rigid instead of adding a diagonal and it does not — which buys an unobstructed opening and costs bending in every member of it.
The moment that goes round the corner
At a rigid knee the bending moment does not stop at the end of the beam. It turns and runs down the column, and in the same instant the beam's shear becomes the column's axial force — while the block of steel that has to carry the turn appears on no member diagram anywhere.
Named alongside it
The objects these essays reach for when they reach for this one.
Moment connectionContinuityContraflexureFree body diagramHaunchJoint rigidityMoment diagramPanel zoneStiffnessStiffness distributionSway