32 research outputs found
Thee issues concerning the statistics of mean and extreme wind speeds
No full textIn the calibration of statistical models for mean and extreme wind speeds, data coming from historical series measured at meteorological stations are used. In most of the cases, these do not comply with characteristics of the model to be calibrated. In particular, this is due to a finite onset wind speed of anemometers and to the discontinuous sampling. As a result, the mean wind speeds are often underestimated. In addition, when the extreme wind speeds are described through the Gumbel model, these are overestimated due to the non-perfect fitting of the data. In this paper the three issues related to the existence of a measurement threshold of anemometers, of the discontinuous sampling of mean wind speed, and of the appropriateness of the Gumbel distribution for the description of extreme wind speeds are discussed, based on the analysis of the historical records available to the Meteorological Service of the Italian Air Force, using an empirical approach. An estimate of the inaccuracies associated with each of the approximations above, is given
Wind risk assessment of structures based on Monte Carlo simulation of peak wind speeds and peak wind pressures
No full textA reliable assessment of structural safety under wind actions needs of a probabilistic approach
in order to take into account the uncertainty involved in the characterization of hazard, vulnerability and aerodynamic
interaction. In this context, the concepts of Performance-Based Wind Engineering (PBWE) can be
usefully adopted and a probabilistic methodology based on Monte Carlo simulation of peak wind speeds and
peak wind pressures is proposed aiming at the evaluation of the annual probability of achievement a fixed limit
state due to wind actions. In particular, using the Proper Orthogonal Decomposition (POD), the multi-variate
random fields can be decomposed and described in a simplified way as a combination of a few low-order dominant
eigenvectors (modes) generated by a Monte Carlo simulation. The methodology enables the probabilistic
assessment of structural performances for a set of loading scenarios, which can simulate all possible critical
events during the entire lifetime of the structure. By integrating the structural fragility and the hazard for the site,
the methodology allows to estimate the annual risk associated to the achievement of a specific limit state due
to wind actions and, hence, provides a tool for assessment and retrofit of existing structures and for design of
new structures. The methodology can also be employed in a multihazard perspective in order to investigate the
performance of a structure under different critical events and improve structural safety. In the paper, as a case
study, the probabilistic methodology has been applied to an existing steel aircraft hangar
Probabilistic assessment of seismic behaviour of an existing RC building retrofitted with BRBs
No full textThe paper presents the seismic performance assessment of a four-storey reinforced concrete
(RC) existing framed structure designed for gravity loads only. The sample structure exhibits high seismic
vulnerability, i.e. lowlateral resistance and limited translation ductility.The structural assessment and retrofitting
was deemed necessary due to a variation of the building occupancy. Natural frequencies and damping ratios are
experimentally investigated by operational modal analysis; the estimated modal properties were employed to
calibrate the numerical finite element structural model.The retrofitting strategy encompasses the use of Buckling
Restrained Braces (BRBs). Such braces can be conveniently installed along the perimeter frames of the multistorey
buildings to lower the seismic demand on the existing structure and regularize its dynamic response. Local
strengthening can, however, be necessary. Comprehensive nonlinear static (pushover) and dynamic (response
history) analyseswere carried out for both the as-built and retrofitted structures to investigate the efficiency of the
adopted intervention strategy.Asuite of code-compliant natural strong motion recordswas selected and employed
to perform inelastic response history analyses. A probabilistic approach has been employed to investigate the
performance of the structure under critical events and to ensure its acceptable performance during its entire
lifetime. The seismic fragility is calculated by implementing an Incremental Dynamic Analysis (IDA) using
the method of multiple-stripe analysis. The outcomes of the inelastic analyses show that the existing structure
exhibits extremely poor strength capacity and energy dissipation. It is also demonstrated that, under moderate
and high magnitude earthquakes, the damage experienced by the retrofitted structural system is located in the
added dampers; the response of the existing RC structure is chiefly elastic
Multi-hazard assessment of steel hangar structures subjected to seismic and wind loads
No full textThe Italian wind climate is characterized by rather low annual average wind velocity, and moderately high extremes; on the other hand, Italy is one of the most seismic countries in the Mediterranean area, both in terms of frequency and intensity of earthquake occurrences . These events have to be examined to define a reliable prediction of extreme loads, and a probabilistic multi-hazard approach can be employed to investigate the performance of a structure under critical events and to ensure its acceptable performance during its entire lifetime. This paper examines the case of steel airport hangars located in areas with low seismicity, where the contribution of the wind risk can represent the most important hazard. In this framework the wind vulnerability has to be characterized with a probabilistic approach and all possible failure mechanism induced by wind loads have to be analyzed. The main objective of this paper is to provide a tool for assessment and retrofit of existing structures, as well as for the design of new structures
The Cruel Radiance of What Is
No full textNeglected by the critics and omitted in many bibliographies, probably due to its semi-clandestine publication almost thirty years after its composition, Les Yeux invisibles is one of Nanni Balestrini’s most singular and unclassifiable books, starting with the paradoxical definition of “roman” that appears on its cover. Structured as a complex sequence of texts and images, it occupies a position halfway between the literary and poetic texts and the visual production of the author; cut up, collage, and montage impose a discontinuous rhythm to its pages, with continuous jumps and deviations which in appearance discourage any claim of coherent narration. The essay offers a critical account of Les Yeux invisibles in the context of Nanni Balestrini’s personal and literary life
WIND RISK ASSESSMENT IN A MULTIHAZARD PERSPECTIVE: THE CASE OF STEEL AIRCRAFT HANGARS
No full textIn the field of structural engineering, current design procedures use the envelope of individual hazard demands on a structure to ensure safety against multiple hazards. With regard to wind and seismic hazard, these actions can reasonably considered uncorrelated and, therefore, the design can be carried out separately; however, a difficulty in multi-hazard design for wind and earthquake is that the
load and resistance factor method makes use of different design philosophies developed by different subdisciplines. Seismic design explicitly allows for inelastic behavior. In contrast, wind design assumes that the structures behaves in elastic range both for damage limit state (DLS) and ultimate limit state (ULS), although ULS typically refers to return periods shorter than those used for seismic design. In this context, a probabilistic multi-hazard approach can be employed to investigate the performance of a structure under critical events and to ensure its acceptable performance during its entire lifetime. Following the approach proposed by the Pacific Earthquake Engineering Research Center (PEER) for Performance-Based
Earthquake Engineering, the purpose of the thesis is to define a reliable methodology for probabilistic estimation of the annual wind risk associated to the achievement of specific limit states. Such approach must be implemented in
probabilistic terms due to the stochastic nature of both resistance and loading parameters. These uncertainties affect the wind field, the structural response and
also the aerodynamic interaction between the environment and the structure. Therefore, a reliable evaluation of structural performances needs the statistical treatment of recorded data, that is the first step towards the investigation of the performance of wind-exposed structures, the characterization of the interaction by
wind tunnel testing or computational fluid dynamics (CFD) techniques and also the knowledge of the structural behavior, i.e. the analysis of all possible failure
mechanism induced by wind loads. Starting from this point, the main statistical methods for treatment of extreme wind speeds are presented in the Chapter 2, including the methods for correction of non-standard conditions in terms of roughness and orography. The theoretical background is then applied by performing the statistical analyses of observed data collected starting from 1951 by the Air Force meteorological service. Some of the results are presented in the Chapter 3 whereas the detailed results in terms of fitted parameters, 50-year return period wind speeds, directional and seasonal coefficients estimated by different
methods are presented in the Appendixes. The effect of the dowsampling is also investigated and the underestimation of 50-year return period wind speeds is quantified for all the stations available. A further step of the research activity has consisted in the characterization of the structural vulnerability. In fact, the Chapter 4 provides a brief review of properties of materials, structural details and structural types adopted in the past for steel hangars, that are considered as representative wind-exposed structures. These structural types are characterized by large spans and, in some cases, have borrowed design solutions from other industrial buildings. The attention is focused on historical evolution of structural types and adopted design standards; some failure cases which occurred during the last years due to extreme wind events are illustrated. Hence the main elements of vulnerability are
discussed. Furthermore, the aerodynamic interaction is investigated; the role of the location and size of the openings is outlined and, in particular, the main theories
about the propagation of the internal pressure due to a dominant opening are examined. In fact, due to their particular use, the steel aircraft hangars have a
dominant opening that allows increased internal pressures to occur. By assembling of all the previously mentioned tools, a methodology for assessing wind risk is
proposed aiming at the evaluation of the annual probability of achievement a fixed limit state due to wind actions. In a multihazard framework, the resulting value can
be compared with the same probability referred to seismic actions obtained by applying the IDA approach. Finally, in order to implement and explain the multihazard risk assessment, two case studies are presented and briefly discussed
Modeling virtual fuels for HCCI-like internal combustion engines development
No full textEfficiency and cleanliness of internal combustion engines can be easily improved with better after-design agents like cleaner lubricants and fuels, tribo-coatings and innovative materials or complex exhaust after-treatment systems, but it is above all a matter of well-planned design from the beginning of engine development itself.
The rush for the zero-emission vehicle sets on the table the old chimaera of automotive engineers: the HCCI combustion engine. This particular engine has very high efficiency and produces neither PM nor NOx but, however, for its development, it cannot be simulated trustfully and completely with current virtual tools yet (because of the complexity of that kind of combustion) nor tested on real benches (because of the that kind of combustion is still hard to control).
Supported by QuickSim©, a Virtual Engine (VE) used in FKFS/IVK for series/motorsport/educational purposes, a better description of the combustion characteristics of gasoline surrogates has been developed by means of Virtual Reactors (VR), as far as flame speed and ignition point are concerned, and the results are presented in this work, as extract from the PhD final work of the author.
This way, innovative combustions can be investigated and developed involving also unconventional fuels and following operations at real test benches where slight differences among traditional gasolines do affect tests results
A Software Tool for the Exponential Power Distribution: The normalp Package
No full textIn this paper we present the normalp package, a package for the statistical environment R that has a set of tools for dealing with the exponential power distribution. In this package there are functions to compute the density function, the distribution function and the quantiles from an exponential power distribution and to generate pseudo-random numbers from the same distribution. Moreover, methods concerning the estimation of the distribution parameters are described and implemented. It is also possible to estimate linear regression models when we assume the random errors distributed according to an exponential power distribution. A set of functions is designed to perform simulation studies to see the suitability of the estimators used. Some examples of use of this package are provided.
Il ruolo della Corte di giustizia dell’Unione europea e il suo rapporto con gli altri organi dell’Unione
No full textThis article examines the role of the ECJ as “power” among the other powers of the EU legal system. The analysis is construed through the examination of the ECJ case-law, which serves to explain the contribution by the ECJ to the establishment of the rule of law as a fundamental principle of the EU legal system, this being the most important instrument to govern the inter-institutional balance among EU powers and to allow individual to enforce rights granted by EU norms vis-à-vis other individuals and especially the EU (and member States) institutions. In doing this, the author contends that the apparent lack of full legal protection in respect of some areas of EU law, such as in the CFSP arena, or the jurisdiction for review of legality of acts by natural or legal persons, may be interpreted as a flaw in the system; on the other hand, problems can be envisaged in the Commission practice to adopt atypical acts (as in the competition law field) and non-legislative documents, as well as in the more recent development of agencies, whose growing powers deserve particular attention also from the point of view of establishing proper principles and rules for jurisdictional control of their activity
“Pel di Carota” Proposta di traduzione dal russo di un racconto per l’infanzia di Sergej Alekseev
No full textThis work aims at providing a possible translation into Italian of a short story for children called "Ryžik" by Russian author Sergej Alekseev. The first chapter and second chapter are, respectively, an overview of the Soviet children's literature during the 20th century and an overview of the Soviet works translated and published in Italy in the period after WW2. The third chapter focuses on the topic of translating for children and its inherent challenges. The fourth chapter provides a short biography of the author and a description of his main works and his style. The fifth chapter consists of the suggested translation, followed by the sixth chapter, which is an analysis of the challenges encountered during the translation which deserve to be discussed more in depth. The main goal of this work is to introduce a new author into the Italian literary landscape, while giving children the chance to get in touch with the Russian culture and history since an early age
