The parameters have certain characteristics that are of practical interest.
Pseudo-spectral
acceleration
Consider a quantity A for a SDOF system
Let A/g be called
base shear coefficient or lateral force coefficient. It is used in building
codes to represent the coefficient by which structural weight is multiplied to
obtain the base shear. A is the peak pseudo-acceleration. A
pseudo-acceleration response spectrum is a plot of A as functions of T_{n}.
The parameters have certain
characteristics that are of practical interest. The pseudo-spectral velocity S_{pv}
is close to spectral velocity S_{v} for short period structures
and is almost equal to the intermediate periods but is different for long
period structures. A comparison of the NS component of the Northridge
earthquakes is made in Fig. 17.14 for spectral velocity and spectral
acceleration for ς = 0.05.
For zero damping, pseudo-spectral acceleration is identical to spectral
acceleration S_{a}. However, for damping other than zero these
two are slightly different. Nevertheless, for damping levels encountered in
most engineering applications the two may be considered to be practically
equal.
Evaluation of spectral displacement S_{d} by
the use of Eq. 17.9a after numerical integration of Eq. 17.2 is to be carried
out to obtain the time history response u(t). The corresponding
pseudo-spectral velocity S_{pv} and pseudo-spectral acceleration
S_{pa} can readily be established from Eq. 17.19 and 17.21.