Fragility curves for Italian residential masonry buildings with retrofit interventions

The earthquakes of the last decades have shown that the Italian residential masonry built her-itage has high seismic vulnerability, in particular when considering structures built before 1919. For this reason, it is necessary to develop effective large-scale risk mitigation strategies in order to reduce the huge losses that could occur in the aftermath of an earthquake. In this paper some retrofit interventions applicable mainly to old buildings are presented, explaining their advantages and potential. These interventions are then implemented, through Vulnus 4.0 software, on a database of 205 buildings built before 1919, previously analyzed in their as-built state. Fragility curves are then developed for each building, and are processed in order to create a vulnerability model for different construction periods that takes into account the possible ret-rofit intervention strategies. Therefore, this procedure allows a comparison between pre and post retrofit intervention fragility, and the results in terms of curves can be used for large scale damage and risk simulations

Evaluation of the seismic vulnerability of masonry churches on a territorial scale. Empirical and analytical fragility assessment

Gli eventi sismici verificatisi negli ultimi decenni in Italia hanno evidenziato l’elevata vulnerabilità delle chiese. La risposta sismica di questi edifici è legata a meccanismi di rottura ricorrenti di parti della struttura che dimostrano un comportamento quasi indipendente, chiamati macroelementi. Studi specifici volti alla comprensione dei meccanismi di danneggiamento delle chiese sono stati avviati a seguito del sisma del Friuli del 1976, ma solo a partire dal terremoto dell’Umbria-Marche del 1997 sono state condotte indagini sistematiche post-sisma. I dati relativi al danno sono molto importanti per la comunità scientifica, in quanto consentono di creare curve di vulnerabilità e fragilità per gruppi tipologicamente omogenei di chiese e di effettuare valutazioni di rischio. La scheda di rilievo attualmente utilizzata fin dal 2006 è la scheda A-DC che analizza la risposta sismica di una chiesa considerando 28 meccanismi di collasso relativi ai diversi macroelementi che la compongono (facciata, abside, transetto, ecc.). La prima fase dello studio riguarda il confronto dei dati di attivabilità dei meccanismi di collasso e della presenza del relativo macroelemento ottenuti da due sopralluoghi relativi alla stessa chiesa. In particolare, data la presenza di frequenti differenze interpretative, sono state analizzate nel dettaglio 225 chiese ispezionate due volte da tecnici diversi durante la sequenza sismica che ha colpito il Centro Italia nel 2016/2017 per individuare le situazioni problematiche ricorrenti e le cause delle diverse criticità. Una volta individuate le carenze, ma anche le potenzialità della scheda A-DC, lo studio si è concentrato sulle analisi di vulnerabilità empiriche. I dati raccolti durante la fase emergenziale dei terremoti di L’Aquila 2009, Emilia 2012 e Centro Italia 2016/2017, relativi a un totale di 1391 chiese, sono stati utilizzati per produrre set di curve di vulnerabilità e fragilità, dopo una dettagliata analisi tipologica preliminare. Al fine di produrre un modello di vulnerabilità tipologico, è stato proposto un nuovo approccio semplificato per determinare gli indici di vulnerabilità delle chiese sulla base di diversi modificatori di vulnerabilità, definiti evidenziando i parametri tipologici che maggiormente influenzano la vulnerabilità. Queste osservazioni hanno permesso anche di individuare quali parametri meritano di essere raccolti durante i sopralluoghi, migliorando l’efficienza delle future campagne di indagine. In conclusione viene presentato una set di curve di vulnerabilità e fragilità. Successivamente, è stato selezionato un sotto-campione omogeneo del database precedentemente esaminato, costituito da 633 chiese a navata unica colpite dalla sequenza sismica del Centro Italia 2016/2017, per effettuare analisi di dettaglio. Sono state quindi condotte analisi specifiche per valutare prima l’influenza del materiale della muratura e poi l’effetto dei singoli meccanismi di rottura sulla definizione dell’indice di danno complessivo, con l’obiettivo di fornire valutazioni qualitative e curve di vulnerabilità e fragilità specifiche dei meccanismi di collasso più ricorrenti e significativi. Infine, sono state derivate per via numerica curve di fragilità relative al meccanismo di ribaltamento della facciata. Sono state effettuate analisi cinematiche lineari e non lineari mediante simulazione Monte Carlo, calibrata su dati osservazionali al fine di ottenere risultati rappresentativi sia in termini di valori medi che di dispersione. Quindi, la probabilità di superamento di ciascuno stato di danno è stata identificata attraverso l’utilizzo degli spettri accelerazione-spostamento, andando poi a derivare i set di fragilità per le chiese semplici a una navata. Inoltre, sono stati eseguiti confronti e analisi di sensitività per stabilire l’influenza sulla vulnerabilità del meccanismo di ribaltamento di alcuni parametri tipologici e geometriciThe seismic events that occurred in the last decades in Italy highlighted the high vulnerability of churches. Indeed, the seismic response of this particular type of building can be related to the recurring failure mechanism of parts of the structure that demonstrate an almost independent behaviour, called macro-elements. Specific studies aimed at understanding the damage mechanisms of churches have been undertaken since the 1976 Friuli earthquake, but only since the Umbria-Marche earthquake in 1997 a systematic series of post-earthquake surveys have been carried out to evaluate the damage suffered by churches. Damage data is essential for the scientific community as it allows the creation of vulnerability and fragility curves for typologically homogeneous groups of churches and to carry out risk assessment. The survey form currently used for churches since 2006 is the A-DC form that analyses the seismic behaviour of a church by considering 28 collapse mechanisms related to the different macro-element that compose it (i.e. façade, nave, apse, transept, etc.). The first step of the study concern comparing the data related to the identification of the possibility of activation of the collapse mechanisms and the related macro-element of two inspections of the same church. In particular, 225 churches inspected twice by different technicians during the 2016-2017 Central Italy seismic sequence were investigated. The analysis highlighted the presence of frequent interpretative differences. Therefore, each of the 225 churches was carefully analysed to identify the recurring situations that caused these critical issues. Once the weaknesses, but also the potential of the A-DC form, had been identified, the study focused on empirical vulnerability analyses. The data collected during the emergency phase of the three last significant earthquakes (L’Aquila 2009, Emilia 2012, Central Italy 2016/2017), related to a total of 1391 churches, were used to propose typological sets of vulnerability and fragility curves, after a preliminary detailed typological analysis. In order to produce a typological vulnerability model, a new simplified approach to determining vulnerability indexes of churches was proposed based on several vulnerability modifiers, defined pointing out which typological parameters effectively affect the overall vulnerability. These observations also allowed identifying which parameters deserve to be collected on-site, improving the efficiency of future survey campaigns. In conclusion, vulnerability and fragility curves are presented, starting from the vulnerability modifiers. Subsequently, a sub-sample of the previously examined database consisting of 633 single-nave churches affected by the 2016/2017 Central Italy seismic sequence was selected to carry out more detailed vulnerability analyses on a homogeneous sample. So, specific analyses are carried out first to assess the influence of the masonry material and then the effect of single failure mechanisms on the definition of the overall damage index, with the focus of providing qualitative evaluations and explicit vulnerability and fragility curves related to the most recurring and significant collapse mechanisms. Lastly, the numerical derivation of fragility curves related to the mechanism of the overturning of the façade was presented. In particular, linear and non-linear kinematic analyses were performed using Monte Carlo simulation, calibrated on observational data to obtain representative results both in term of mean values and dispersion. Then, the limit state exceedance probability correlated to the displacement related to each damage state was identified using acceleration-displacement spectra, and then fragility sets for simple single-nave churches were derived. In addition, comparisons and sensitivity analyses were performed to establish the influence of specific typological and geometrical parameters on the vulnerability of the overturning mechanism

Vulnus Web 5.1 Procedura automatica per analisi di vulnerabilità di edifici in muratura / Automatic procedure for seismic vulnerability analysis of masonry buildings

Vulnus è una procedura automatica per l’analisi della vulnerabilità sismica di edifici di muratura isolati o aggregati, valevole per una verifica globale preliminare di capacità strutturale. Il modello di vulnerabilità si basa sulla valutazione di parametri adimensionali, due dei quali riferiti al comportamento fuori piano (combinazione di meccanismi cinematici) e nel piano (resistenza delle pareti a taglio), computati su un piano tipico dell’edificio, e un terzo valutato sulla somma pesata dei punteggi ricavati dalla scheda GNDT di II livello. Attraverso la teoria del random and fuzzy set e l’integrazione di informazioni qualitative del rilievo in sito, vengono definite le curve di probabilità di collasso e i relativi valori di aspettazione, e un giudizio qualitativo complessivo della vulnerabilità

Vulnus Web: A Web-Based Procedure for the Seismic Vulnerability Assessment of Masonry Buildings

Masonry is a widespread construction system, but it is very prone to seismic damage. In Italy, almost 60% of residential buildings are constructed in masonry, and 85% of them were built before 1980 without specific design regulation; thus, there is the need for large-scale vulnerability assessment. When large stocks of residential buildings (>50–100) are involved, also in historical centers, seismic vulnerability analysis must resort to simplified and computer-aided methods. Among these, the best known analyze (i) the overall shear strength normalized to the weight; (ii) the activation coefficient of local mechanisms; and (iii) dimensionless indexes obtained from the weighted sum of scores associated with a set of vulnerability factors. The Vulnus procedure proposes a vulnerability function in the 3D space defined by these factors, namely VIP, VOP and VV. The ‘mechanical’ indexes VIP and VOP determine the capacity of the building (in-plane and out-of-plane, respectively), whereas the ‘empirical’ index VV sets the pace at which this capacity is reached and the uncertainty in its final value. The procedure considers the confidence level of the indexes by means of fuzzy set theory, which enables expression of the vulnerability in linguistic terms (e.g., ‘high’ or ‘low’), as well as through a fragility curve. In this paper, a web toolbox based on the Vulnus procedure, namely, Vulnus Web, is proposed. It enables the central archiving of data, improved interaction with the program code and a wider dissemination. The new procedure was applied to a masonry building hit by the Central Italy 2016 earthquake; both the vulnerability level assessed numerically and the damage prediction were in good accordance with the actual seismic performance of the building

Comparison of Fragility Sets to Assess the Effectiveness of Retrofit Interventions on Masonry Buildings in Italy

Seismic events that have occurred in Italy in recent decades have shown the significant vulnerability of the Italian building stock. In particular, residential masonry buildings have suffered serious damage, highlighting the need to plan effective mitigation strategies as soon as possible. In this context, this study aims to evaluate the effectiveness of possible retrofit interventions for masonry buildings. Fragility curves of macro-classes of residential masonry buildings have been developed in both as-built and retrofitted conditions within the DPC-ReLUIS agreement (Department of Civil Protection—Network of University Laboratories for Earthquake Engineering). In particular, three sets of fragility curves, developed by the University of Padova (UniPD) and the University of Genova (UniGEa and UniGEb) are discussed and compared herein. The three models show similar estimates of the expected structural improvements for the examined retrofit interventions when applied to the building macro-classes, although some differences, due to the different analysis approaches, can be observed

Derivation of mechanical fragility curves for macro-typologies of Italian masonry buildings

Seismic risk mitigation at national scale requires the vulnerability assessment of the built stock, which is generally based on the definition of appropriate fragility curves by means of different methods. A first type of methods uses an empirical approach with calibration from observed damage. A second group of methods uses mechanical models suitable to describe the structural behavior; however, because an in-depth geometric and structural characterization of the buildings is very time-consuming at the territorial level, these models must remain “as simple as possible” to limit the number of input parameters. The aim of this work is to estimate the fragility of the Italian masonry buildings stock grouped in macro-typologies ISTAT (National Institute of Statistics), i.e. defined by construction age and number of stories; this is essential for deriving damage scenarios at territorial scale based solely on ISTAT information. Vulnus Vb 4.0 (2009), a software developed at the University of Padova, was found to be very useful for this purpose as it provides fragility curves of masonry buildings assessing the in-plane (IP) failure, the principal out-of-plane (OOP) mechanisms and the main typological-structural characteristics; judgments on the quality of information are also used to provide an upper and lower fragility limit. More than 500 buildings were examined with this software, appropriately chosen to guarantee a good statistical representation of the built stock. The information for each building was retrieved directly from the related projects and, in the case of missing information, reference was made to design manuals and codes, and to specific literature. Finally, the fragility results were processed to provide a mean fragility curve (representing the trigger of an IP - OOP mechanism) and a range of possible dispersion for each ISTAT macro-typology. These results can also be used to calibrate macro-seismic models of vulnerability in the literature, if the will is to represent this mechanical fragility in a more distributed way, i.e. with more damage states