1,721,085 research outputs found
On reliability perception of seismic hazard estimates used in structural design
No full textState-of-the-art approaches for the seismic hazard assessment of a site of interest are mainly based on the development of the classical probabilistic seismic hazard analysis (PSHA). A PSHA allows defining the values of a set of ground shaking intensity measures at a site of interest, given an acceptable exceedance probability in a fixed time interval. In this way, structures are designed to bear uniform hazard spectra derived from PSHA results, as prescribed by most of the seismic codes adopted worldwide. However, PSHA estimates are often subject to debate every time a severe earthquake occurs. For this reason, in the framework of the PSHA methodology, the main aim of this study is to propose a reliability-based approach for assessing seismic hazard estimates subsequently used in structural design. The time-exposure of the structure was revealed to be a crucial parameter, evidencing why classical PSHA is representative of the “long-run case” in which the time interval of the earthquake catalogue goes to infinity
Risk-based catastrophe bond design for a spatially distributed portfolio
No full textCatastrophe bonds (CAT bonds) are risk-linked securities used by the insurance industry to transfer risks associated with the occurrence of natural disasters to the capital markets. Despite their growing importance, connected with the higher exposures to potential natural disasters, relatively few studies on CAT bond pricing, design and their application are available in the literature. In particular, the existing pricing formulations for pricing analysis do not account for uncertainties in model parameters and are not contextualized in a more general CAT bond coverage design procedure for an area of interest. For these reasons, this paper presents a general procedure for designing a CAT bond-based coverage for a spatially distributed portfolio against losses due to natural hazards, accounting also for model parameters uncertainties in CAT bond pricing process. The procedure is then applied to a case study represented by the residential building portfolio in Italy, proposing an ad-hoc CAT bond-based coverage against losses induced by earthquake occurrences, defined on the basis of the most recent version of the seismic risk map of Italy currently proposed in scientific literature
Impact of epistemic and aleatory uncertainties on the seismic reliability assessment of existing structures
Full text linkSeismic reliability assessment of structural systems is commonly done via the convolution of seismic hazard and structural fragility to get resulting failure rate, and later compute seismic reliability index. Within this frame, many uncertainty sources have to be handled by the risk analyst, who is asked to make some reasonable assumptions in order to carry out his/her seismic safety quantification. However, slight changes in the definition of input parameters and/or the use of different empirical or analytical models can strongly impact the final reliability outcomes. The present work aims therefore to investigate the impact of different sources of uncertainties by comparing together key parameters to be defined in both hazard and fragility analysis, considering a casestudy represented by an existing multi-span steel-concrete composite bridge to better understand which of these sources is more impacting on the final estimates. Results show how uncertainties associated to hazard and fragility are as a whole of the same order of magnitude and thus how both uncertainty sources have to be properly considered. In addition, a detailed sensitivity analysis was carried out for ranking the uncertainty sources in relation to their impact on the overall reliability index dispersion. Results showed that the choice of a suitable Ground Motion Prediction Equation (GMPE) model, the non-linear modelling technique and the number of the accelerometric records adopted for the structural analysis seem to be the factors that mostly contribute to the seismic reliability index variability, representing the uncertainty related to these parameters the majority of the overall reliability index dispersion
Model Uncertainty Assessment for the Anchorage Length Formulation of fib Model Code 2020
No full textIn the design of pre-tensioned concrete elements, it is important to avoid the anchorage failure of tendons. This can be done by predicting the anchorage length through any of the empirical or semiempirical models provided by the main design codes. However, the models in these codes are based on experimental evidence gathered many years ago, when the 7-wire strands manufacturing process was significantly different from now. The objective of this contribution is to evaluate the model uncertainty for the anchorage length formulation of the last draft of the fib Model Code 2020 and to ensure that all the main influencing factors are properly considered. Since a direct measure of anchorage length is not experimentally feasible, a large data set of flexural tests has been gathered from the scientific literature, and each failure mode has been compared to the corresponding anchorage length prediction, to obtain a censored sample of the model uncertainty from which an appropriate probability distribution could be estimated. Then, the minimum values of the partial safety factors that consider both model and material uncertainties and ensure the achievement of the target reliability in anchorage length predictions have been derived through Monte Carlo Simulations. Finally, these results have been validated through a FORM approach for some case studies and compared to the current fib Model Code 2020 proposed partial safety factors, showing that they guarantee the achievement of the expected level of reliability in all the evaluated situations
A CAT bond-based coverage scheme proposal for Italy
Full text linkCatastrophe bonds (CAT bonds) are risk-linked securities used by the insurance industry to transfer risks associated with the occurrence of natural disasters to the capital markets. Despite their growing importance, relatively few studies on CAT bond pricing, design and their application are available in the literature. Indeed, existing pricing formulations for pricing analysis do not account for uncertainties in model parameters and are not contextualized in a more general CAT bond coverage design procedure for an area of interest with a distributed portfolio. For these reasons, this paper presents a general procedure for designing a CAT bond-based coverage for a spatially distributed portfolio against losses due to natural hazards. The procedure is then applied to a case study represented by the residential building portfolio in Italy, aiming to design a CAT bond-based coverage scheme against losses induced by seismic events all over the entire national borders
L' utilizzo della mappa di rischio sismico nella valutazione della sostenibilità finanziaria di piani di riduzione del rischio in Italia
No full textLo sviluppo di mappe del rischio sismico tramite l’adozione di procedure scientificamente-basate, permette di fornire agli enti governativi un quadro quantitativo della distribuzione spaziale dello stesso per una nazione. Saper redigere una mappa del rischio sismico risulta fondamentale qualora si debba andare a delineare un piano nazionale di riduzione del rischio sismico, in quanto, a tal proposito, risulta necessario quantificare il rischio sismico ante e post operam, quantificandone così i relativi benefici. Il prezzo da pagare per l’ottenimento di tali benefici è rappresentato dai costi da sostenere per la realizzazione di interventi strutturali volti al rinforzo antisismico dell’asset immobiliare oggetto di interesse. Risulta pertanto evidente come il problema si possa ricondurre alla trattazione finanziaria applicabile alla classica casistica di un investimento, e pertanto, si debba procedere ad un’attenta analisi della sua sostenibilità finanziaria. Nel presente contributo viene brevemente illustrata l’applicazione di tali concetti al caso di studio rappresentato dal patrimonio edilizio nazionale adibito a destinazione residenziale, proponendo come esempio l’implementazione di un possibile piano di mitigazione del rischio sismico, ed illustrando dal punto di vista metodologico i passi da seguire per analizzarne la sostenibilità finanziaria
Nuove leggi di correlazione tra parametri di sintesi del moto sismico e osservazioni di intensità macrosismica attribuite con l'uso della scala macrosismica europea EMS-98
No full textLo studio della correlazione tra intensità macrosismiche osservate a seguito di evento sismico e le stime dei parametri di sintesi del moto sismico derivabili dai segnali accelerometrici registrati in corrispondenza delle stazioni accelerometriche risulta essere tuttora di rilevante interesse nell’ambito delle applicazioni di ingegneria sismica orientate all’analisi degli effetti alla scala territoriale di scenari sismici. A tal riguardo, differenti formulazioni sono state proposte nel corso degli scorsi decenni da vari autori internazionali, con l’obiettivo di cogliere la relazione funzionale tra i parametri di sintesi più comunemente utilizzati (ad esempio PGA, PGV, PGD) e le stime di intensità macrosismica attribuite con le diverse scale
macrosismiche esistenti (tra le varie, le scale MCS, MM, MSK). Una revisione dello stato dell’arte sui modelli proposti in letteratura scientifica negli ultimi 70 anni è stata presentata nello studio di Zanini et al., 2019. Tuttavia, emergono alcune criticità rilevanti dall’analisi dello stato dell’arte: in primis, la maggior parte delle relazioni non sono invertibili, ovvero sono state calibrate tramite classici procedimenti di regressione lineare e pertanto forniscono solo un’applicazione univoca (ovvero da intensità macrosismica a parametri di sintesi del moto sismico, le cosiddette IGMCE - Intensity to Ground Motion Conversion Equations, oppure da parametri di sintesi del moto sismico a intensità macrosismiche, le GMICE - Ground Motion to Intensity Conversion Equations). Oltre a tale aspetto, allo stato attuale non sono disponibili leggi di conversione in grado di trasformare parametri di sintesi del moto sismico in valori di intensità macrosismica in accordo alla più recente versione della Scala Macrosismica Europea EMS-98. Se da un lato, tale questione potrebbe essere superata facendo leva sul fatto che per livelli di intensità intermedi i gradi di intensità tra le principali scali macrosismiche sembrerebbero
ragionevolmente potersi considerare equivalenti (Musson et al., 2010), e altresì vero che è stato dimostrato in letteratura come per livelli di intensità maggiori possano verificarsi significative discrepanze tra le assegnazioni di intensità formulate utilizzando differenti scale. Pertanto, partendo da questo stato di fatto, il presente contributo illustra i risultati originali ottenuti dagli autori che hanno portato alla costruzione del primo database di coppie di valori di parametri di sintesi del moto sismico e intensità macrosismiche formulate con la scala EMS-98, ed alla successiva calibrazione di un set di leggi di conversione tramite l’uso di una procedura di regressione ortogonale, ottenendo in tal modo leggi di conversione completamente invertibili (ovvero contemporaneamente GMICE ed IGMCE)
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