Base Isolation systems reduce building vibrations during
earthquakes. This means that the building distorts less, reducing
the chance of damage.
Normally, a building is supported directly on its foundations,
and it is said to have a fixed-base. When base isolation is
used, special structural bearings are inserted
between the bottom of the building and its foundation.
These bearings are not very stiff
in the horizontal direction, so they reduce the fundamental
frequency of vibration
of a building. The frequency becomes so low that the building
does not vibrate as strongly during an earthquake.
During an earthquake, a fixed-base building can sway from
side to side. When a base isolation system is used, the sideways
movement occurs mainly in the bearings, and the building hardly
distorts at all.
There are many types of bearings used for base isolation.
Here are two of them.
Isolating Buildings - 2 Rubber
Isolating Buildings - 3
Friction Pendulum Bearings