Concept

Capacity design — where it appears

Choosing where a structure will yield and then making everything else strong enough for that choice to come true. The forces the protected members are designed for come from the yielding element's own capacity rather than from the applied load.

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

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.

dynamics · ductility demand

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.

structures · eccentric brace

Named alongside it

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

Ductility Energy dissipation Hysteresis Plastic hinge Behaviour factor Buckling Eccentric brace Equal displacement rule Lateral system Link Load path Plastic moment

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