Hysteretic energy-based state-dependent fragility for ground-motion sequences

Received: 9 July 2020 Revised: 7 September 2020 Accepted: 19 October 2020 DOI: 10.1002/eqe.3387 RESEARCH ARTICLE Hysteretic energy-based state-dependent fragility for ground-motion sequences Roberto Gentile 1, 2 Carmine Galasso 1, 3 1 Department of Civil, Environmental and Geomatic Engineering, University College London, London, UK 2 Institute for Risk and Disaster ReductionUniversity College London, London, UK 3 Scuola Universitaria Superiore (IUSS) Pavia, Pavia, Italy Correspondence Roberto Gentile, Department of Civil, Environmental and Geomatic Engineer- ing, University College London, London, United Kingdom. Email: [email protected] Funding information H2020 Marie Skłodowska-Curie Actions, Grant/Award Number: 843794 Abstract A framework to derive state-dependent fragility relationships of structures subjected to ground-motion sequences (e.g. mainshock-aftershock (MS-AS) or trig- gered earthquakes) is proposed. The hysteretic energy dissipated in the sequence is adopted as the main demand parameter, as it is a cumulative measure mono- tonically increasing with the length of the excitation. For a structure subjected to earthquake-induced ground motions, it is not possible to define a closed-form representation of the hysteretic energy as a function of the peak deformation. However, based on theoretical considerations, the hysteretic energy-peak deformation trend is discussed, highlighting that (a) the significant duration of the ground motion explains the variability of the hysteretic energy for a given peak deformation; (b) the hysteretic energy dissipated in an AS decreases (for a given AS peak displacement) if the peak displacement in the MS increases. A vector- valued probabilistic seismic demand model consistent with these considerations is proposed in the form of a surface relating the hysteretic energy in the sequence to the peak deformation in the MS and a ground-motion intensity measure of the AS. This is calibrated via sequential cloud-based time-history analyses. The framework is demonstrated for 14 reinforced concrete frame buildings with dif- ferent height, plastic mechanisms, and infill distributions. The results show the feasibility of the proposed approach, effectively capturing damage accumulation without inconsistencies in the obtained statistical model. The framework may be used for risk-assessment applications explicitly incorporating ground-motion sequences. The hysteretic energy versus peak deformation relationship may also be exploited in problems involving long-duration ground motions or soft soils. KEYWORDS ground-motion sequences, hysteretic energy versus peak deformation, mainshock-aftershock, probabilistic seismic demand model, reinforced concrete frames, seismic fragility This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2020 The Authors. Earthquake Engineering & Structural Dynamics published by John Wiley & Sons Ltd. Earthquake Engng Struct Dyn. 2020;1–17. wileyonlinelibrary.com/journal/eqe 1

Hysteretic energy-based state-dependent fragility for ground-motion sequences

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groundmotion sequences

hysteretic energy versus

mainshockaftershock

probabilistic seismic

reinforced concrete

seismic fragility