Fragility curves are commonly used in seismic performance assessment of structures. Various endusers/stakeholders have different requirements on this matter: private owners likely need a detailed assessment focused onsingle buildings or small portfolios of buildings,while government agencies or (re)insurance companies might look at large portfolios requiring a lower refinement level and accepting higher uncertainties. In this paper, a multi-level framework for deriving seismic fragility is proposed to fulfil such needs, with particular reference to reinforced concrete (RC) frames. Arefinedapproach based on non-linear time-history analysis is deemed to be appropriate for individual high-importancebuildings (e.g. hospitals, schools) but it may result overcomplicated for assessing individual ordinary (e.g. residential) buildings. Instead, whendealing with large building portfolios,semi-empiricalmethods focused on “archetype” structural models are often the state-of-practice. These simplified approaches may provide a rapid-yet-accurate estimation of the seismic fragility, requiring a relatively small amount of input data. Such approaches often fail tocapture specific deficiencies and/or failure mechanisms that might greatly affect the final assessment outcomes(e.g. shear failure in beam-column joints, in-plane and out-of-plane failure of the infill walls, among others). To overcome these shortcomings, the alternative response analysis methods in the proposed multi-level frameworkare characterised by: 1) a mechanics-based approach; 2) the explicit consideration of spectral shapein modelling seismic input/demands; and3) the explicit consideration of record-to-record variability.Specifically, the proposed framework involves three levels for the seismic response analysis: 1) low refinement -non-linear static analysis (analytical SLaMAor numerical pushover), coupled with the capacity spectrum method; 2) mediumrefinement -non-linear time-history analysis of equivalent single degree of freedom (SDoF)systems calibrated based on either the SLaMA or the pushover curves; 3) highrefinement -non-linear time-history analysis of full numerical models. In all cases, fragility curves are derived through a cloud-based approach employing unscaled real (i.e. recorded) ground motions. The proposed framework is applied to 14four-or eight-storey RC frames showing different plastic mechanismsand distribution of infills.The results show that time-history analysis of SDoF systems is not substantially superior with respect to a non-linear static analysis coupled with the CSM. The estimated median fragility of the simplifiedmethods generally falls within ±20% of thecorresponding estimates from thefull time-history analysis, excluding the uniformly-infilled frames, for which such error range increases up to ±40%due to the (preliminary)choice of a sub-optimal intensity measure. Anumber of limitationsof the study, which are currently being addressedby the authors, are finally highlighted.

A multi-level seismic fragility assessment framework for existing rc buildings / Gentile, Roberto; Galasso, Carmine. - (2020). (Intervento presentato al convegno 17th World Conference on Earthquake Engineering, 17WCEE tenutosi a Sendai, Japan nel September13-18, 2020).

A multi-level seismic fragility assessment framework for existing rc buildings

Gentile Roberto
;
2020-01-01

Abstract

Fragility curves are commonly used in seismic performance assessment of structures. Various endusers/stakeholders have different requirements on this matter: private owners likely need a detailed assessment focused onsingle buildings or small portfolios of buildings,while government agencies or (re)insurance companies might look at large portfolios requiring a lower refinement level and accepting higher uncertainties. In this paper, a multi-level framework for deriving seismic fragility is proposed to fulfil such needs, with particular reference to reinforced concrete (RC) frames. Arefinedapproach based on non-linear time-history analysis is deemed to be appropriate for individual high-importancebuildings (e.g. hospitals, schools) but it may result overcomplicated for assessing individual ordinary (e.g. residential) buildings. Instead, whendealing with large building portfolios,semi-empiricalmethods focused on “archetype” structural models are often the state-of-practice. These simplified approaches may provide a rapid-yet-accurate estimation of the seismic fragility, requiring a relatively small amount of input data. Such approaches often fail tocapture specific deficiencies and/or failure mechanisms that might greatly affect the final assessment outcomes(e.g. shear failure in beam-column joints, in-plane and out-of-plane failure of the infill walls, among others). To overcome these shortcomings, the alternative response analysis methods in the proposed multi-level frameworkare characterised by: 1) a mechanics-based approach; 2) the explicit consideration of spectral shapein modelling seismic input/demands; and3) the explicit consideration of record-to-record variability.Specifically, the proposed framework involves three levels for the seismic response analysis: 1) low refinement -non-linear static analysis (analytical SLaMAor numerical pushover), coupled with the capacity spectrum method; 2) mediumrefinement -non-linear time-history analysis of equivalent single degree of freedom (SDoF)systems calibrated based on either the SLaMA or the pushover curves; 3) highrefinement -non-linear time-history analysis of full numerical models. In all cases, fragility curves are derived through a cloud-based approach employing unscaled real (i.e. recorded) ground motions. The proposed framework is applied to 14four-or eight-storey RC frames showing different plastic mechanismsand distribution of infills.The results show that time-history analysis of SDoF systems is not substantially superior with respect to a non-linear static analysis coupled with the CSM. The estimated median fragility of the simplifiedmethods generally falls within ±20% of thecorresponding estimates from thefull time-history analysis, excluding the uniformly-infilled frames, for which such error range increases up to ±40%due to the (preliminary)choice of a sub-optimal intensity measure. Anumber of limitationsof the study, which are currently being addressedby the authors, are finally highlighted.
2020
17th World Conference on Earthquake Engineering, 17WCEE
A multi-level seismic fragility assessment framework for existing rc buildings / Gentile, Roberto; Galasso, Carmine. - (2020). (Intervento presentato al convegno 17th World Conference on Earthquake Engineering, 17WCEE tenutosi a Sendai, Japan nel September13-18, 2020).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11589/209722
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