Identification of groups of uniform hazard time-histories for performance based seismic design applications

Within a Performance Based Seismic Design framework, the choice of the reference design seismic input (commonly referred to as “earthquake bins”) is deeply rooted upon their probabilistic identification. Typically, the earthquake bins are identified by means of earthquake “intensity measures” consisting of scalar or vector-valued combinations of selected ground motion parameters associated to a given probability. This paper focuses on the identification of groups of uniform hazard (acceleration) time-histories for Performance Based Seismic Design applications. In detail, on the basis of a peculiar Probabilistic Seismic Hazard Analysis, the characteristics that a group of earthquake inputs must possess in order to be associated to a given exceedance probability are obtained. The proposed procedure takes advantage of the information carried by the “epsilon” parameter, and is rooted on a separate treatment of the aleatory variability and the epistemic uncertainty considered in the hazard analysis. The analytical developments allow to identify a condition for the spectral ordinates of the acceleration time histories, which is valid for a number of structural periods at once, and to quantify (in terms of co-efficient of variation of the spectral ordinates) the randomness associated to the epistemic uncertainty (error in the spectral acceleration prediction law).