1,721,195 research outputs found
Approccio semplificato al problema NaTech generato da sismi.
No full textIncidenti tecnologici causati da eventi sismici costituiscono una tipologia specifica di eventi NaTech, in cui non si ha una semplice coesistenza di rischi di diversa natura che devono essere ricomposti, ma l’interazione di eventi pericolosi e la concatenazione di danni che genera una tipologia di rischio integrato da affrontare con strumenti specifici. Infatti, quando differenti tipi di rischio coesistono possono generarsi eventi interagenti che provocano danni ancora più severi di quelli che si possono manifestare in caso di singoli eventi. In questo contributo viene presentata una procedura semplificata di screening sviluppata utilizzando una metodologia di analisi decisionale multi-criterio (AHP, Analytic Hierarchy Process). La metodologia è stata utilizzata per supportare i processi decisionali tramite la definizione di possibili alternative d’intervento all’interno di un framework di multi-criteri pesati
Coupling of differential evolution algorithm and quadratic approximation for dynamic identification
No full textIn the present paper, dynamic identification problem of a FE structure with unknown parameters is solved by global search method. Response surface methodology is introduced in Differential Evolution algorithm to improve the performance of the algorithm. Differential evolution (DE) is a evolutionary algorithm where N different vectors collecting the parameters of the system are chosen randomly or by adding weighted differences between vectors obtained from two populations. In the modified algorithm, the new parameter vector is defined as the minimum of a second-order polynomial surface, approximating the cost function. Performance in term of speed rate is strongly improved by introducing the second-order approximation; nevertheless, robustness of DE algorithm for global minimum search of cost function is preserved, since mul-tiple search points are used simultaneously. A numerical examples is presented, concerning identification of mechanical parameters of a steel-concrete bridge with unknown values of concrete elastic modulus, mass, and bearing stiffnesses
Il fenomeno della delaminazione nel placcaggio con FRP di strutture di conglomerato cementizio armato
No full textIdentificazione dinamica attraverso algoritmi di ottimizzazione evolutiva
No full textIn questa memoria sono presentati i risultati ottenuti dall’identificazione dinamica di un modello agli Elementi Finiti di un ponte in struttura mista acciaio-calcestruzzo. I valori ottimi di massa e rigidezze sono stati ottenuti mediante un algoritmo evolutivo, il Differential Evolution Algorithm
Differential evolution algorithm in dynamic structural identification
No full textIn the present paper, a Differential Evolution algorithm is used to perform a structural identification of mass and stiffness properties of a frame structure. Identification is performed starting from exact data and, alternatively, from pseudo-experimental data, obtained by adding some statistic scattering to exact data. Different object functions are adopted and results are compared with those obtained adopting classical gradient method. Numerical results confirm that adopting both frequencies and modal shapes instead of fre-quencies only strongly increases the sensitivity of object function to identification parameters. Results ob-tained are then much less scattered, with coefficient of variation of the same order of magnitude of that of pseudo-experimental data
Improving the speed performance of an Evolutionary Algorithm by a second-order cost function approximation
No full textIn the present paper, dynamic identification problem of a FE structure with unknown parameters is solved by global search method. Response surface methodology is introduced in Differential Evolution algorithm to improve the performance of the algorithm. Differential evolution (DE) is an evolutionary algorithm where N different vectors collecting the parameters of the system are chosen randomly or by adding weighted differences between vectors obtained from two populations. In the modified algorithm, the new parameter vector is defined as the minimum of a second-order polynomial surface, approximating the cost function. Performance in term of speed rate is strongly improved by introducing the second-order approximation; nevertheless, robustness of DE algorithm for global minimum search of cost function is preserved, since multiple search points are used simultaneously. A numerical examples is presented, concerning identification of mechanical parameters of a steel truss girder bridge with unknown values of masses and stiffnesses of bracing and bearing
Stabilità di tralicci PREM in prima fase
No full textThe results of a numerical and analytical investigation on hybrid steel truss RC beams are described. Hybrid steel truss RC beams are beams where, during the construction phase and the concrete casting (Phase I), the steel truss system only carries the vertical loads. The steel truss of the beams may have different shapes, depending on the technology adopted, the span and the load. In this report, Steel trusses constituted by upper and diagonal bars and a steel plate at the bottom are considered. In construction phase, the verification against failure due to the safety against instability of the upper steel bars in compression or the diagonal elements is the most important design requirement. In the present study, four different beams are considered, with different steel trusses in Phase I condition. Finite Element modelizations of the beams are made and the failure loads are obtained, taking into account second-order effects due to large displacements. It is shown that the stability of the steel truss strongly depends on the lateral stiffness of the diagonal elements of the truss, as well as on the torsional rigidity of the lower steel plate. Starting from results of the numerical model, some design criteria are illustrated and discussed
Effects of data uncertainty on the quantitative risk assessment of an industrial plant under seismic action
No full textThis paper describes a fuzzy set based approach for dealing with uncertainies in the assessment of “NaTech” events triggered by earthquakes. The methodology has been integrated within a general framework developed for the assessment of external hazard factors in industrial sites.
The starting point is the Probabilistic Seismic Hazard Assessment (PSHA) at the site considered, in order to evaluate probabilities of occurrence of ground motions of different severity. Fragility curves are then derived for atmospheric storages, corresponding to different damage levels. For both seismic hazard and fragility curves, confidence intervals are derived, and fuzzy numbers are used to model uncertainties.
The effects of these uncertainties on the Quantitative Risk Assessment (QRA) of local and societal risk indexes, caused by accidental scenarios triggered by seismic events, are evaluated for a case study refinery. The adopted QRA methodology allows for identification and the consequence assessment of all the possible scenarios, including possible domino events. The procedure has been implemented in a GIS-based software tool in order to manage the high number of event sequences that are likely to be generated in large industrial facilities. The developed methodology requires a limited amount of additional data with respect to those used in a conventional QRA
La qualificazione degli FRCM
No full textEntro la fine dell'anno, il Ministero delle Infrastrutture e dei Trasposrti emanerà le Linee Guida per la qualificazione di compositi rinforzati a matrice inorganica da utilizzare per il consolidamento strutturale di costruzioni esistenti. Ecco una sintesi dei principali contenuti del documento
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