Accounting for directivity-induced pulse-like ground motions on building-portfolio seismic loss

Earthquake-induced pulse-like ground motions are often observed in near-source conditions due to forward-directivity. Recent worldwide earthquakes have emphasized the severe damage potential of such pulse-like ground motions. This paper introduces a framework to quantify the impact of directivity-induced pulse-like ground motions on economic losses for building portfolios. To this aim, a simulation-based probabilistic risk modelling framework is implemented for various syntheticbuilding portfolios located either in the fault-parallel or fault-normal orientationswith respect to an idealstrike-slip fault. Those portfolios consist of two building typologies representative of distinct vulnerability classes in the Mediterranean region: non-ductile moment-resisting reinforced concrete (RC) frames with masonry infills, mainly designed to sustain gravity loads (i.e.pre-code frames); and ductile moment-resisting RC infilled frames designed according to the Eurocode 8 (EC8) seismic provisions for high ductility class (i.e.special-code frames). Monte Carlo-based probabilistic seismic hazard analysis (PSHA) is first performed, specifically modifying conventional PSHA to account for the pulse-occurrence probability and for the spectral amplification due to near-source directivity effects. Hazard curves for sites/buildings located at different distances from the fault areobtained, and the spatial distribution of the spectral amplification is investigated and critically discussed. A set of pulse-like ground motions and a set of spectrally-equivalent ordinary records are used to perform non-linear dynamic analysis (NLDA) and derive fragility relationships for index buildings representative of each considered building class. A vulnerability model is finally built by combining the derived fragility relationships with a (building-level) damage-to-loss model specifically calibrated for Italy.Results of the study are presented in terms of average annual loss (AAL) for various portfolios of different sizes. These results show that the influence of near-source directivity effects is significant when estimating losses of individual buildings or small portfolios located very close to a fault. Nevertheless, the impact of pulse-like ground motions on losses for larger portfolios can be considered minimal and can be neglected in most of the practical large-scale seismic risk assessment applications.