Natural Vibrations - 4

The Natural Frequency of a Building

The natural frequencies of vibration of a building depend on its mass and its stiffness (or how flexible it is).

The natural frequency for each mode of vibration follows this rule:

f = natural frequency in Hertz.
K = the stiffness of the building associated with this mode
M = the mass of the building associated with this mode

Buildings tend to have lower natural frequencies when they are:

• Either heavier (more mass)
• Or more flexible (that is less stiff).

One of the main things that affect the stiffness of a building is its height. Taller buildings tend to be more flexible, so they tend to have lower natural frequencies compared to shorter buildings.

Try some simple experiments with natural frequency.