Hysteresis — where it appears
Named by 3 essays across 2 fields — each of them below, with the objects they name alongside it.
The only thing that stops it
Drive a structure at its own frequency and the amplitude grows without limit unless something takes energy out. What takes it out is damping, and damping is the one structural property that is never designed, never drawn, and never known until the thing is built.
The earthquake asks for a displacement
A structure a quarter as strong as the elastic demand does not deflect four times as far. It deflects almost exactly as far, yields on the way, and survives — which is why no ordinary building is designed for the force an earthquake would apply if it stayed elastic.
The part that is meant to be weak
A braced frame is stiff and has nowhere to yield. A moment frame yields everywhere and is soft. Move the two diagonals a metre apart along the beam and the whole storey shear has to pass through the segment between them — which keeps most of the stiffness and puts every yielding in one member the designer chose.
Named alongside it
The objects these essays reach for when they reach for this one.
Energy dissipationCapacity designDuctilityPlastic hingeBehaviour factorBucklingDampingDamping ratioEccentric braceEqual displacement ruleFree vibrationLateral system