On the number of records for structural risk estimation in PBEE

Abstract

Summary Response‐history nonlinear dynamic analysis is an analytical tool that often sees use in risk‐oriented earthquake engineering applications. In the context of performance‐based earthquake engineering, dynamic analysis serves to obtain a probabilistic description of seismic structural vulnerability. This typically involves subjecting a nonlinear numerical computer model to a set of ground‐motions that represent a sample of possible realizations of base acceleration at the site of interest. The analysis results are then used to calibrate a stochastic model that describes structural response as a function of shaking intensity. The sample size of the ground‐motion record set is nowadays usually governed by computation‐demand constraints, yet it directly affects the uncertainty in estimation of seismic response. The present study uses analytical and numerical means to investigate the record sample size, n, required to achieve quantifiable levels of mean relative estimation error on seismic risk metrics. Regression‐based cloud analysis in the context of Cornell's reliability method and incremental dynamic analysis using various intensity measures were employed to derive a relation of the form normalΔ/n, where Δ is a parameter that depends on both the dispersion of structural responses and the shape of the hazard curve at the site. For the cases examined, n can be kept in the 40 to 100 range and achieve 10% mean relative error. The study can contribute to guide engineers towards an informed a‐priori assessment of the number of records needed to achieve a desired value for the coefficient of variation of the estimator of structural seismic risk.

Accounting for the Spatial Variability of Seismic Motion in the Pushover Analysis of Regular and Irregular RC Buildings in the New Italian Building Code

“…Generally, the nonlinear dynamic analysis is considered the most effective way to proceed, because it allows accurately simulation of the response of the buildings under seismic motion. On the other hand, despite the availability of a huge variety of scientific works about this topic, in practice-oriented applications nonlinear dynamic analysis has difficulty finding space for several reasons: the design code provisions about the assessment of existing buildings are still lacking; there is an objective difficulty in the selection of ground-motions (number of accelerograms, efficiency, sufficiency [5]); a detailed characterization of the cyclic behaviour of structural elements is needed, high time-analysis and computational efforts are required.…”

Seismic reliability implied by behavior‐factor‐based design

“…Past research has shown that such IMs are more efficient in predicting inelastic displacement response than single‐spectral‐ordinate IMs, by virtue of accounting for spectral shape beyond the structure's fundamental period 26 . This efficiency is quantified in terms of the dispersion of structural responses given various levels of the conditioning IM and has the practical result of limiting the amount of dynamic analyses required to obtain risk estimates within a target standard error 27,28 . In fact, this period interval contains almost all of the generated ESDoF oscillators, bar a few with , and therefore could be a common IM to express the fragilities of all structures considered 29 .…”

Towards the updated Italian seismic risk assessment: exposure and vulnerability modelling

“…at least 7 signals per 8 intensity levels according to ATC-58-1 (FEMA, 2018)) needs in case of fragility curves' derivation, where special attention has to be paid to response dispersion (Kiani et al 2018). Besides, Baltzopoulos et al (2019) point out that the appropriate number of ground motions is remarkably dependent on the site-specific hazard and influences the achievable level of accuracy.…”