Researchers carry out tests on real structures, like bridges
and dams, to find out how they
Their vibrations can be measured under naturally occurring
forces, like the wind. Alternatively, the structures can be
forced to vibrate using machines, or by hitting them with
a special hammer.
Every structure has special properties that describe the
way it vibrates, called its natural
frequencies and mode shapes.
These properties generally remain the same regardless of what
is making the structure move, e.g. the wind or a vibrating
Researchers can measure these properties from real structures
when they are vibrating. They use these measurements to check
that computer simulations of the
structure behave in the same way as the real structure.
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