Energy-compatible modulating functions for the stochastic generation of fully non-stationary artificial accelerograms and their effects on seismic site response analysis

The reliability of non-linear dynamic analysis aimed to predict the seismic performance of structural and geotechnical systems, as well as their dynamic interaction, is significantly affected by the selection of suitable input motions. Several procedures for selecting actual earthquake records compatible with the seismic hazard at the site of interest and for evaluating synthetic accelerograms consistent with a seismological framework are available in the literature. However, the degree of uncertainty affecting these approaches might lead to unreliable performance predictions especially for strongly non-linear problems, such as those involving the response of soils to cyclic and dynamic loading. In this vein, the paper presents a procedure for generating fully non-stationary ground motions ensuring energy compatibility with a target motion. Two different approaches have been introduced: i) the time window method based on the central finite difference approach and ii) the simplified intensity-compatible approach in which a closed form expression is provided to evaluate a modulating function that depends on the Arias intensity and on the strong motion duration of a target motion. To highlight the reliability and the accuracy of the proposed procedure, several sets of spectrum-compatible artificial accelerograms, generated starting from a rock outcropping motion, were used as input motions in a series of one-dimensional site response analyses. The analysis results are presented and discussed in the paper highlighting the influence of the main features of the proposed generation procedure on the variability of the computed site response.