Nonlinear static analyses based on either inelastic or elastic spectra with equivalent viscous damping: A parametric comparison

In the last decade, nonlinear static procedures emerged as the reference practice-oriented analysis method for structures under seismic actions. These procedures are generally based upon two key steps: (i) performing a nonlinear static (pushover) analysis under lateral forces and (ii) evaluating the seismic demand through the so-called capacity spectrum obtained at the end of the previous step. This paper specifically deals with the latter and proposes a parametric comparison between two wide classes of methods formally based on conceptually alternative approaches for defining the demand spectra in nonlinear static analyses of dissipative structures. First of all, the paper outlines the main conceptual aspects of such alternative methods and reports their key operational details. Particularly, it proposes a dimensionless formulation of their relationships and demonstrates that both methods are based upon a small and almost common set of dimensionless parameters. Therefore, a wide parametric analysis is proposed to compare the ductility demand obtained by means of these two alternative methods with the aim of describing and quantifying the different predictions obtained by applying such methods. Finally, the results of nonlinear time-history analyses are proposed for assessing the two aforementioned methods.