Advances in Seismic Design Methodologies - Earthquake Engineering for Structural Design - page 413

Advances in Seismic Design Methodologies 413

Spectral amplification

Intraplate
earthquakes

(b) T(s)

Figure 9.18 Elastic response spectra for soil classes: (a) Interplate (Type 1)
earthquakes; (b) Intraplate (Type 2) earthquakes (Gioncu, 2006, after Sabetta and
Bommer, 2002)

In Figures 9.17b and 9.18b, corresponding to the intraplate earthquakes (M <5.5), a
very important increasing in acceleration amplification is observed, larger than for the
interplate one. But the influence of soil conditions on corner periods is very reduced,
contrary to the observed increasing in case of interplate earthquakes.
Inelastic response spectra. Following the design philosophy for structures in
seismic area, the sizing of individual members, connections and supports is typically
based on the distribution of internal forces, which are computed by means of the
design response spectrum, substantially reduced from the elastic one, determined using
the recorded ground motions. As a result of this reduction, the severe ground motions
demand large deformations in the structural systems and, therefore, inelastic structural
response and energy dissipation are inevitable requirements. As a consequence, the
elastic response spectrum has a limited capability to predict the structure behavior
during severe earthquakes and an inelastic response spectrum must be considered. The
inelastic response spectrum is obtained by reducing the elastic response spectrum,
taking into account the structure capacity to dissipate seismic energy (Fig. 9.19). So,