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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
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
WIND RISK ASSESSMENT IN A MULTIHAZARD PERSPECTIVE: THE CASE OF STEEL AIRCRAFT HANGARS
Get PDFIn 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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