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Structure response
| A simple and widely used approach for the representation of
the structure response is the so-called "response spectrum"
method. Response spectra form the basis of seismic regulation
codes, such as the USAEC, US building code in the United States
and the EC 8 in Europe. In this context the structure is supposed
to behave like a simple oscillator, such as a spring or pendulum.
The characteristic parameters of this model are the natural
frequency and the damping, which are determined by size, configuration
and material makeup of the structure. Earthquake ground motion
will excite the building and cause it to "resonate"
according to its preferred frequency. The calculation of response
spectra consists of several steps. First, select the natural
period and damping, then calculate the relative displacement
of the oscillator, i. e. its "response" with respect
to ground, and note the maximum amplitude of the response. This
is repeated for a set of natural frequencies in order to get
a "spectrum" of responses. A dangerous situation arises
if the natural frequency of a structure falls in the frequency
range of major seismic radiation. In this case the accelerations
in the structure may be several times higher than the peak ground
acceleration measured at the surface. |
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