ABSTRACT
The beginning of modern seismic design may be fixed during the 1950s, when the
dissipation of seismic energy through plastic deformations was considered by Housner.
His method develops a limit design type analysis for ensuring a sufficient energy-
absorbing capacity to guarantee an adequate safety factor against collapse in case of
extremely strong ground motions. The first study on the inelastic response spectrum
was made by Velestos and Newmark in 1960. They obtained the maximum response
deformation for elastic-perfectly plastic structures. Since this first application in
seismic design, the response spectrum has become a standard measure of the demand
of ground motion. The utility of the response spectrum lies in the fact that it gives a
simple and direct indication of the overall displacement and acceleration demands of
the earthquake ground motion, for structures having different period and damping
characteristics, without needing to perform detailed numerical analysis. A new concept
was proposed in 1969 by Newmark and Hall, by constructing spectra based on
accelerations, velocities, and displacements, in the short, medium and long period
ranges, respectively (Gioncu and Mazzolani, 2002).
