Ground motion sample size vs estimation uncertainty in seismic risk

In the context of seismic risk assessment as per the performance-based earthquake engineering paradigm, a probabilistic description of structural vulnerability is often obtained via dynamic analysis of a nonlinear numerical model. It typically involves subjecting the structural model to a suite of ground-motions that are representative, as a sample, of possible seismic shaking at the site of interest. The analyses results are used to calibrate a stochastic model describing structural response as a function of seismic intensity. The sample size of ground motion records used is, nowadays, usually governed by computation-time constraintson the other hand, it directly affects the estimation uncertainty which is inherent in risk analysis carried out in this way. Recent studies have suggested methodologies for the quantification of estimation uncertainty, to be used as tools for determining the appropriate number of records for each application on an objective basis. The present study uses one of these simulation-based methodologies, based on standard statistical inference methods and the derivation of structural fragility via incremental dynamic analysis, to investigate the accuracy of the risk estimate (e.g., the annual failure rate) vs the size of ground motion samples. These investigations consider various scalar intensity measures and confirm that that the number of records required to achieve a given level of accuracy for annual failure rate depends not only on the dispersion of structural responses, but also on the shape of the hazard curve at the site. This indicates that the efficiency of some frequently-used intensity measures is not only structure-specific but also site-specific.The study presented in this paper was developed within the activities of ReLUIS (Rete dei Laboratori Universitari di Ingegneria Sismica) for the project ReLUIS-DPC 2014–2018, as well as within the H2020-MSCA-RISE-2015 research project EXCHANGE-Risk (Grant Agreement Number 691213)

REXELweb: a tool for selection of ground-motion records from the Engineering Strong Motion database (ESM)

This paper illustrates REXELweb, an updated online version of REXEL, which is a tool for the automatic selection and scaling of spectrum-compatible ground- motions for dynamic analysis of structures. REXELweb allows to define target spectra according to user-definition or design provisions (Eurocode 8 and Italian building code), as well as to uniform hazard spectra (UHS) based on a European hazard model. REXELweb implements all functionalities and options of REXEL through web-services that are accessible either via a MATHWORKS-MATLAB script or a user-friendly web-interface. The program selects records from the Engineering Strong Motion database (ESM), which is a daily-updated Pan-European repository of high-quality ground-motion records. These features make REXELweb a potentially useful tool for researchers and practitioners.Associazione Geotecnica ItalianaPublishedRome5T. Sismologia, geofisica e geologia per l'ingegneria sismic

La selezione di registrazioni accelerometriche a due componenti secondo le NTC18 e la circolare applicativa

Le moderne normative sismiche come l’Eurocodice 8 (EC8) o le Norme Tecniche per le Costruzioni (NTC), consentono la verifica del progetto strutturale tramite analisi dinamiche, utilizzando modelli tridimensionali delle strutture, sollecitate da due o tre componenti del moto del suolo (due componenti orizzontali ed una componente verticale). Tali registrazioni del moto sismico vanno scelte in modo che siano rappresentative della sismicità del sito di costruzione e gli spettri di risposta elastica, eventualmente scalati, devono rispettare alcuni requisiti di compatibilità con lo spettro elastico di progetto (spettro obiettivo). Le NTC impongono, come criterio di spettrocompatibilità, che la media degli spettri elastici delle componenti orizzontali dei segnali selezionati debba approssimare lo spettro elastico obiettivo entro una fissata soglia tolleranza in un determinato intervallo di periodi: tale prescrizione implicitamente permette che le due componenti orizzontali di una registrazione selezionata possano avere di fattori di scala diversi. La circolare applicativa delle NTC ha invece introdotto, similmente a quanto prescritto nello EC8–parte 2 (progettazione sismica di ponti), una procedura per cui preliminarmente vengono combinati gli spettri delle componenti orizzontali della singola registrazione tramite la radice quadrata della somma dei quadrati (SRSS) delle ordinate spettrali, viene poi calcolata la media degli spettri SRSS opportunamente scalati e confrontata con lo spettro obiettivo incrementato di una fissata quantità. Obiettivo di questo lavoro è valutare la compatibilità tra i risultati ottenuti con la procedura prescritta dalle nuove NTC e le indicazioni esposte in circolare. Un’ulteriore analisi condotta ha confrontato separatamente le medie delle componenti orizzontali con lo spettro obiettivo (e non complessivamente, come precedentemente esposto). I risultati ottenuti suggeriscono che le due procedure portano a selezioni tra loro compatibili. Inoltre, nella grande maggioranza dei casi trattati il soddisfacimento del criterio di compatibilità considerando la media complessiva di tutte le componenti delle registrazioni porta al soddisfacimento della compatibilità per componenti separate

Dynamic analysis of single-degree-of-freedom systems (DYANAS): A graphical user interface for OpenSees

Non-linear dynamic response of SDOF systems enjoys widespread application in earthquake engineering, sometimes as a testing ground for cumbersome analytical procedures, but often as a direct proxy of first-mode-dominated structures, within the family of simplified, pushover-based methods for seismic structural assessment and/or design. This article presents DYANAS, a MATHWORKS MATLAB®-based graphical user interface that uses the OpenSees finite element platform to perform nonlinear dynamic analysis of single-degree-of-freedom (SDOF) oscillators. The scope of this open-source, freely distributed software is to serve as a tool for earthquake engineering research. The main advantages offered by the DYANAS interface are ease in the definition of the required analysis parameters and corresponding seismic input, efficient execution of the analyses themselves and availability of a suite of convenient, in-built post-processing tools for the management and organization of the structural responses. The types of dynamic analysis frameworks supported are incremental, multiple-stripe and cloud. Simultaneous consideration of pairs of uncoupled dynamic systems gives the possibility for intensity measures to refer to bidirectional ground motion. In the paper, an outline of the types of dynamic analysis frameworks typically used in performance-based earthquake engineering is provided, followed by a detailed description of the software and its capabilities, that include an array of post-processing tools. In order to properly place this software tool within its natural performance-based earthquake engineering habitat, some example applications are provided at the end of the paper

Seismic Fragility of Italian Code-Conforming Buildings by Multi-Stripe Dynamic Analysis of Three-Dimensional Structural Models

The RINTC (2015–2017) project was a three-year research program aimed at assessing the seismic reliability of code-conforming structures in Italy. It dealt with five structural typologies of residential and industrial buildings: reinforced concrete, masonry, precast reinforced concrete, steel, and base isolated reinforced concrete. To reach its goals, several tens of structures featuring the same configuration were designed at different sites, characterized by different seismic hazard and considering two soil site conditions. The failure risk (i.e. the failure rate) of the buildings was evaluated by means of non-linear dynamic analysis of three-dimensional numerical models. The study herein presented parametrized the vulnerability models of the considered structures; in other words, it provides the seismic fragility curves for code-conforming Italian buildings analyzed in the RINTC project. Lognormal fragilities refer to global collapse failure and usability preventing damage, which are the performances considered in the project, and are derived via state-of-the-art methods, including consideration of the uncertainty in the estimation of their parameters. The curves are made available to be possibly used for further risk analyses and enable a discussion of the fragility fitting issues as a function on the site’s hazard