Civil Engineering Reference
In-Depth Information
Figure 5.3
Dynamic excitation frequencies of
structures by wind and earthquake.
At this point, it is worth noting the essential differences between dynamic response of
structures to wind and earthquake. The main differences between the excitation forces
due to these two natural phenomena are:
• Earthquakes are of much shorter duration than wind storms (with the possible exception
of the passage of a tornado) and are thus treated as transient loadings.
• The predominant frequencies of the earthquake ground motions are typically 10-50
times those of the frequencies in fully developed wind storms. This means that
structures will be affected in different ways, e.g. buildings in a certain height range
may not experience significant dynamic response to wind loadings, but may be prone
to earthquake excitation.
• The earthquake ground motions will appear as
fully
correlated equivalent forces acting
over the height of a tall structure. However, the eddy structure in wind storms results
in
partially
correlated wind forces acting over the height of the structure. Vortex-
shedding forces on a slender structure are also not fully correlated over the height.
Figure 5.3 shows the various frequency ranges for excitation of structures by wind and
earthquake actions.
