Accounting for earthquake‐induced ground‐motion duration in building‐portfolio loss assessment

Abstract Earthquake‐induced ground‐motion duration can have a non‐negligible impact on the nonlinear seismic performance of structures. However, in current seismic risk assessment practice, hazard and vulnerability analyses generally only consider ground motion's amplitude and frequency‐content features, often relegating duration to implicit considerations. This study introduces a simulation‐based framework to explicitly quantify the impact of ground‐motion duration on building‐portfolio direct economic losses. Case‐study synthetic building portfolios located at different distances from a case‐study seismic source (i.e., fault) are assembled considering – individually and in combination – three building typologies representing distinct vulnerability classes in Southern Italy. Such typologies correspond to non‐ductile moment‐resisting reinforced concrete (RC) infilled frames designed to only sustain gravity loads (i.e., pre‐code infilled frames), and ductile moment‐resisting RC infilled and bare frames designed considering seismic provisions for high‐ductility capacity (i.e., special‐code infilled and bare frames). Event‐based probabilistic seismic hazard analysis is performed explicitly simulating duration jointly with spectral‐shape‐related intensity measures (IMs), accounting for their spatial and cross‐correlation. Sets of ground‐motion records are selected to conduct cloud‐based nonlinear time‐history analyses (NLTHAs) and derive fragility models for each considered building typology through archetype structures, simulating their structural response using computational models that account for stiffness and strength cyclic and in‐cycle deterioration as well as destabilising effects. Fragility models are derived using average pseudo‐spectral acceleration (in a range of periods of interest) as the primary IM and alternatively: (1) the dissipated hysteretic energy as an engineering demand parameter (EDP), implicitly accounting for duration given the cumulative nature of such an EDP and the adopted nonlinear modelling strategy, in a scalar format; (2) the dissipated hysteretic energy as an EDP, as before, explicitly considering duration as an IM together with spectral shape, in a vector‐valued format. Vulnerability models are then derived using the fragility models and appropriate building‐level damage‐to‐loss models. The portfolio loss exceedance curves and expected annual losses computed for each combination of exposure, hazard, and vulnerability models are critically assessed and discussed. Depending on the portfolio's size, exposure composition, location relative to the fault, site conditions and the seismic source model, the impact of duration on the loss estimates can be significant. For the considered settings, relative variations up to 200% between the scalar‐ and vector‐valued‐based portfolios expected annual losses are observed, attaining the highest discrepancies as the fault‐to‐portfolio distance increases.