Earthquakes are clustered in space and time. This means that structures in seismically active regions can be subjected to multiple consecutive instances of base acceleration, with insufficient in-between time for repair operations to take place. In such situations, buildings may experience degradation of their lateral-force-resisting capacity due to damage accumulation. Consequently, the use of seismic fragility functions developed for the intact structure may not be enough, in the context of seismic risk assessment studies that consider the effect of seismic clusters. In these cases, one may employ state-dependent fragility curves, which are separate fragility functions assigned to the same structure, depending on distinct damage states that it may be brought to by prior shocks. State-of-the-art analytical estimation of structure-specific fragility entails the use of dynamic analysis of a numerical model of the structure, for example, incremental dynamic analysis (IDA), which can be computationally laborious, thus motivating the development of simplified, less time-consuming methods, often based on substituting the structural model by equivalent single-degree-of-freedom (SDOF) systems that can be defined via pushover analysis. In fact, existing procedures in the literature, such as back-to-back IDA, that can be used to estimate state-dependent fragility curves, tend to increase computational costs, rendering the development of simplified methodologies for this case a topical issue. In this context, the present paper presents a method for estimating state-dependent seismic fragility functions, based on pushover analysis and a predictive model for constant-ductility residual displacement ratio. This ratio is defined as the absolute value of the of residual-to-peak-transient seismic displacement ratio of an equivalent SDOF structure. The residual displacement model, which considers yielding SDOF systems that exhibit stiffness and strength degradation, with natural periods between 0.3 s and 2.0 s and post-yield hardening ratios from 0 % to 10%, is outlined first. The model also estimates the joint probability distribution of normalized elongated period and strength degradation, for a given ductility demand. This information allows for a probabilistic evaluation of the pushover curve characterizing a damaged structural system, which is then used to obtain state-dependent fragility, when damage states are defined via ductility demand thresholds. The state-dependent fragility curves are estimated via IDA of SDOF oscillators with pushovers that were previously determined from the model. An illustrative application showcases the ability of the proposed methodology to provide state-dependent fragility estimates in an expedient manner.
State-dependent seismic fragility via pushover analysis / Orlacchio, M.; Baltzopoulos, G.; Iervolino, I.. - (2020). (Intervento presentato al convegno 17th World Conference on Earthquake Engineering tenutosi a Sendai (Japan) nel 13-18 September 2020).
State-dependent seismic fragility via pushover analysis
Orlacchio M.;Baltzopoulos G.;Iervolino I.
2020
Abstract
Earthquakes are clustered in space and time. This means that structures in seismically active regions can be subjected to multiple consecutive instances of base acceleration, with insufficient in-between time for repair operations to take place. In such situations, buildings may experience degradation of their lateral-force-resisting capacity due to damage accumulation. Consequently, the use of seismic fragility functions developed for the intact structure may not be enough, in the context of seismic risk assessment studies that consider the effect of seismic clusters. In these cases, one may employ state-dependent fragility curves, which are separate fragility functions assigned to the same structure, depending on distinct damage states that it may be brought to by prior shocks. State-of-the-art analytical estimation of structure-specific fragility entails the use of dynamic analysis of a numerical model of the structure, for example, incremental dynamic analysis (IDA), which can be computationally laborious, thus motivating the development of simplified, less time-consuming methods, often based on substituting the structural model by equivalent single-degree-of-freedom (SDOF) systems that can be defined via pushover analysis. In fact, existing procedures in the literature, such as back-to-back IDA, that can be used to estimate state-dependent fragility curves, tend to increase computational costs, rendering the development of simplified methodologies for this case a topical issue. In this context, the present paper presents a method for estimating state-dependent seismic fragility functions, based on pushover analysis and a predictive model for constant-ductility residual displacement ratio. This ratio is defined as the absolute value of the of residual-to-peak-transient seismic displacement ratio of an equivalent SDOF structure. The residual displacement model, which considers yielding SDOF systems that exhibit stiffness and strength degradation, with natural periods between 0.3 s and 2.0 s and post-yield hardening ratios from 0 % to 10%, is outlined first. The model also estimates the joint probability distribution of normalized elongated period and strength degradation, for a given ductility demand. This information allows for a probabilistic evaluation of the pushover curve characterizing a damaged structural system, which is then used to obtain state-dependent fragility, when damage states are defined via ductility demand thresholds. The state-dependent fragility curves are estimated via IDA of SDOF oscillators with pushovers that were previously determined from the model. An illustrative application showcases the ability of the proposed methodology to provide state-dependent fragility estimates in an expedient manner.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
