Synthetic accelerograms for hazard evaluation and response-history analysis of buildings

Non-linear Time History Analysis (NLTHA) of structures is the most sophisticated tool used to understand the real dynamic behaviour of structures (FIB, 2012). The goodness of results relies on an accurate definition of the materials properties, their hysteretic behaviour and the geometry of the structure to be examined, as well as on the definition of the dynamic excitations represented by acceleration time histories. These accelerograms must represent, on average, the hazard of the site under examination, commonly represented by an acceleration response spectrum. Usually the target response spectrum is defined, in a Probabilistic (PSHA) or Deterministic (DSHA) Seismic Hazard Assessment, through Ground Motion Prediction Equations (GMPEs). Therefore, ground motions should have magnitude, source distance and focal mechanism consistent with the sources that control the hazard at the site of interest. Moreover, site soil conditions and the possibility of experiencing near fault effects such as directivity and fling-step needs to be considered (NIST, 2011). Usually, acceleration time histories are selected from databases of records (e.g. the European Strong Motion (ESM) database (Luzi et al., 2016) in order to satisfy all the above-mentioned characteristics and to match, over a defined range of periods, the target response spectrum. As the tolerance on the variability of the selection parameters becomes stronger, the lack of data becomes evident and some modifications (e.g. linear scaling) of the original recorded ground motions are needed if an adequate number of ground motion is to be used. A source of time histories could be the generation of artificial accelerograms (Gasparini and Vanmarke, 1976) or the use of the “response spectrum matching” technique (Al Atik and Abrahamson, 2010; Grant and Diaferia, 2013). However, these techniques have no physical meaning and there are concerns that their use could lead to biased results (Bazzurro and Luco, 2006; Iervolino et al., 2010). A viable alternative is to use synthetic accelerograms generated from a simulation of the source rupture and wave propagation. In this work, a direct link between hazard and response-history analysis is established. Synthetic seismograms are used to define the hazard as described by the Neo Deterministic Seismic Hazard Assessment (NDSHA) (Panza et. al., 2001, 2012; Fasan et al., 2016) and, as a logical consequence, to perform NLTHA on a selected building. A comparison of the results of NLTHAs obtained with natural and synthetic records confirms that physics-based simulations are a valuable tool in structural analysis. Moreover, the NDSHA method is applied to the site of Norcia and predicted spectral acceleration are compared with the recorded one during the event of the 30th of October 2016. Using NLTHAs, structural demands predicted using the real records and the synthetic ones used in the NDSHA are compared, showing that simulated accelerograms can be used to predict real non-linear demands of future earthquakes.