Site based stochastic seismic spectra

• Stochastic response spectra by simulation of site-dependant earthquake process.
• Process envelope is consistent with energy characteristics of real accelerogram.
• Spectrum is the plot of the maximum response of system to the input process.

In this paper, a method to develop stochastic response spectra on the basis of the random vibration theory is proposed. The main innovation of this study with respect to previous ones in literature is to derive response spectra in stochastic way, starting from a seismological consistent stochastic model of the seismic motion, trying to increase in this way the accuracy in response peak evaluation to future earthquakes at a given site. In fact, the approach evaluates the maximum of structural response, namely the response spectrum, without requiring the use of repeated time history analyses, but directly, by obtaining the peak response of a single degree of freedom system subject to a site based stochastic model of ground motion. A nonstationary stochastic model for the ground motion is adopted, defined by a temporal function and by a set of parameters that describe, respectively, the evolution of the amplitude during the time and the frequency content of the record. These are selected on the basis of the information contained in a data bank of real seismic events by means of a regression analysis. In this way, it is possible to formulate relations between stochastic model parameters and seismological parameters.After the stochastic model of the earthquake is constructed and the peak response of a single degree of freedom is evaluated by means of random vibration theory, the stochastic response spectra are finally obtained. A parametric analysis is then performed to evaluate the influence of seismological parameters, such as epicentral distance and magnitude, on stochastic spectra. A comparison with Eurocode 8 spectrum is also evaluated. The possibility to construct by means of this approach site based stochastic energy spectra adds value and novelty to the proposed method.