Engineering ground motion selection based on displacement-spectrum compatibility C. Smerzini & R. Paolucci Dipartimento di Ingegneria Strutturale, Politecnico di Milano, Italy C. Galasso & I. Iervolino Dipartimento di Ingegneria Strutturale, Università degli Studi di Napoli Federico II, Italy SUMMARY: In this paper we address the selection of displacement-spectrum compatible natural accelerograms for displacement-based seismic design and assessment by nonlinear dynamic analysis. This involved: i) the definition of a target displacement spectrum for Italian sites, that fits the results of probabilistic seismic hazard analyses both at short and at long periods, ii) the construction of an ad hoc high quality strong ground motion database, namely SIMBAD, and iii) the development of the software REXEL-DISP to select suites of real accelerograms compatible with target displacement spectra. Illustrative applications of REXEL-DISP are presented to underline some interesting features of displacement-based ground motion selection, namely the good performance of unscaled records and the possibility to achieve broadband spectral compatibility, given the availability of tools for computer aided record selection. Keywords: Displacement-Based Design, earthquake strong motion database, ground motion selection 1. INTRODUCTION Recent performance-based approaches to seismic design have given an increasing emphasis on the proper definition of the seismic demand at long periods. This is even more important when one refers to the definition of seismic demand in terms of displacement response spectra, such as in the capacity- spectrum (FEMA, 2005) and the direct displacement-based design approaches (Priestley et al., 2007), where the availability of reliable earthquake ground motions up to long periods is required. This has stimulated several research works concerning, on one side, the development of improved displacement design spectra based on independent evaluations of long period spectral ordinates rather than on the use of the standard pseudo-spectral rule (Faccioli et al., 2004) and, on the other side, the definition of simple criteria to assess the reliability of digital strong motion data (Paolucci et al., 2008). Such advances have supported the calibration of up-to-date empirical ground motion prediction tools extending to long periods (Cauzzi and Faccioli, 2008), the improved quantification of site effects at long periods (Manou et al., 2007; Figini and Paolucci, 2009), the formulation of new seismic hazard maps at long periods in Italy (Faccioli and Villani, 2009). In the framework of performance-based seismic design and assessment, a relevant issue is the selection of a suitable set of ground motion records to represent the design seismic excitation for nonlinear dynamic analysis (NLDA). According to the vast majority of international codes, such as the Eurocode 8, or EC8 (CEN, 2004), the current Italian seismic code, or NTC08 (CS.LL.PP., 2008), and US ASCE 7-10 provisions (ASCE, 2010), the selected suite of records needs to match, within prescribed tolerance limits, the target design spectrum. Moreover, appropriate acceleration histories shall be obtained from records having magnitudes, distances and source mechanisms consistent with those controlling the target spectrum in the range of periods of interest for a given application. While tools designed for the selection of earthquake ground motions compatible with design acceleration response spectra for earthquake engineering purposes are progressively becoming available, e.g., REXEL (Iervolino et al., 2010) and REXELite (Iervolino et al., 2011), the instruments apt for the selection of displacement-spectrum compatible accelerograms are still very limited and at research stage (e.g., Corigliano et al., 2012).