Advances in Seismic Design Methodologies - Earthquake Engineering for Structural Design - page 415

Advances in Seismic Design Methodologies 415

Figure 9. 20 Inelastic response spectra: (a) Using a constant q factor;
(b) Using a variable q factor (Gioncu and Mazzolani, 2002)

the dissipative capacity of the structure up to failure. The two ways to transform the
elastic response spectrum into the inelastic one are presented in Figure 9.20: by
reducing the elastic response spectra by means of a reduction factor q, which can be
constant or variable, in function of the structure natural period and considering some
equivalence conditions (based on energy or displacement).

9.4.4 Displacement Response Spectra

The conventional seismic design is entirely a force-based approach, which assumes
that an acceleration response spectrum reliably provides, for a given degree of
damping, the elastic force level acting on the structure and, therefore, it represents an
adequate indicator of the seismic design. Recently, however, displacement-based
design has attracted growing interest among engineers, because it is recognized that
displacements describe in a more explicit way the structural response under seismic
actions, compared to forces (Priestley, 1997, Tolis and Faccioli, 1999). The correlation
between acceleration and displacement spectra is presented in Figure 9.14.