Friction dampers are designed to have moving
parts that will slide over each other during a strong earthquake.
When the parts slide over each other, they create friction
which uses some of the energy from the earthquake that goes
into the building.
This is a Pall Friction Damper installed in the Webster Library
of Concordia University in Montreal, Canada. The damper is
connected to the centre of some cross-bracing.
The damper is made up from a set of steel plates, with slotted
holes in them, and they are bolted together. At high enough
forces, the plates can slide over each other creating friction.
The plates are specially treated to increase the friction