Advances in Seismic Design Methodologies - Earthquake Engineering for Structural Design - page 407

Advances in Seismic Design Methodologies 407

Because the actual elastic spectra present many peaks which cannot be used in
practice, the constructed elastic spectra must be smoothed (Fig. 9.13a). So, the actual
variation is substituted by a combination of linear or hyperbolic variations. A very
important characteristic of smoothed spectra is the corner period ( Fig. 9.13b), which is
equivalent to the predominant period of the ground motion. It can be determined also
as the period corresponding to peak acceleration associated to the maximum relative
velocity spectrum. It is customary to employ the spectra normalized to the value of the
peak ground acceleration.

Figure 9.13 Smoothes spectra: (a) PGA and EPA values;
(b) Corner period distribution (Gioncu and Mazzolani, 2002)