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Thunderstorms winds are localized and transient phenomena characterized by three-dimensional non-stationary velocity fields. While numerous studies investigated the wind loading on cantilevered structures under thunderstorm downburst winds, there is a lack of fundamental research on the behavior of simple circular cylinders subjected to downburst-like outflows. This paper investigates the pressure distribution and aerodynamic coefficients of two cylinders with different diameters immersed in three different types of wind: (1) isolated downburst (DB); (2) downburst embedded in an atmospheric boundary layer (ABL) wind (DBABL); and (3) steady ABL wind. The focus of this study is to provide a comparative analysis between aerodynamic coefficients (drag and lift) and surface pressures that result from these three different wind systems. The ABL winds caused a higher drag on the thinner cylinder than the two DB-like outflows. The lift coefficients during the primary vortex passage in the DB-like outflows were negative at the base of the cylinders and approached zero or to slightly positive values close to the cylinders' top. The location of the cylinders in DB-like outflows is the dominant factor for their aerodynamics. [ABSTRACT FROM AUTHOR]

This paper is part of a research project that started from the consideration that thunderstorms are transient phenomena with short duration and the structural response to transient phenomena, most notably to earthquakes, is traditionally evaluated by the response spectrum technique. Based on this consideration, a “new” method is formulated that generalizes the “old” response spectrum technique from earthquakes to thunderstorms. A previous paper addressed this problem for ideal point-like Single-Degree-Of-Freedom systems subjected to wind actions perfectly coherent over the exposed structural surface. The present paper generalizes this formulation to real space Multi-Degree-Of-Freedom systems subjected to partially coherent wind fields with assigned velocity profile and turbulence properties; for sake of simplicity, in this stage of the research, the structure is modeled as a continuous slender vertical cantilever beam. Analyses are carried out by making recourse to the equivalent wind spectrum technique, a method developed for synoptic stationary winds, the use of which is extended here to non-synoptic non-stationary conditions. In spite of a rather complex formulation, the application of the thunderstorm response spectrum technique is straightforward: the equivalent static force is the product of the peak wind loading by a non-dimensional quantity, the equivalent response spectrum, given by a simple diagram. Its derivation represents one of the most typical features of this method: it is based on the joint numerical processing of a set of measured thunderstorm records and an analytical model that conceptually reconstructs the complete wind field around the measured data. In virtue of its characteristics, the thunderstorm response spectrum technique is particularly suitable for rapid engineering calculations and simple code applications. [ABSTRACT FROM AUTHOR]

Thunderstorms are transient phenomena characterized by short duration. Engineering is usual to evaluate the structural response to such phenomena, most notably to earthquakes, by the response spectrum technique, a method extensively applied in both the scientific and technical fields. This paper represents the first stage of a research project aimed at introducing a “new” method that generalizes the “old” response spectrum technique from earthquakes to thunderstorms. In such a framework, it establishes the fundamentals of the structural response of ideal point-like Single-Degree-Of-Freedom systems subjected to thunderstorm wind actions perfectly coherent over the exposed structural surface. A general definition of thunderstorm response spectrum is introduced, which allows a straightforward evaluation of the maximum structural response and the equivalent static force. A new definition of thunderstorm base response spectrum is also provided. Several forms of representation and parameterization of these response spectra are studied, showing the merits and the shortcomings of each of these. The general properties of the response spectra are investigated, pointing out some relevant analogies with the seismic case and the classical analysis of synoptic events. In particular, while wind engineering is usual to express the wind loading starting from wind velocity models, the method proposed herein, similarly to seismic engineering, involves the use of real thunderstorm records. The records adopted in this paper to illustrate the new method come from the wind monitoring campaign conducted for the European project “Wind and Ports”. Despite the application to this case study, the methods and the definitions presented are fully general and may be applied in any context. [ABSTRACT FROM AUTHOR]

The study aims to estimate the maximum dynamic response of linear elastic SDOF systems subjected to thunderstorm outflows. Starting from a recently developed Evolutionary Power Spectral Density (EPSD) model for the wind velocity, the dynamic response is decomposed into a time-varying mean and a non-stationary random fluctuation. The EPSD and the Non-Geometrical Spectral Moments (NGSMs) of the random fluctuation are derived both accounting and neglecting the transient dynamics due to the modulating function of the load. The mean value of the maximum nonstationary fluctuating component of the response is estimated based on the definition of an equivalent stationary process following an approach proposed in the literature. In order to mitigate the overestimations of the maximum dynamic response due to the Poisson approximation, analogously to the formulation developed by Der Kiureghian for withe noise excitation, an equivalent expected frequency is introduced for thunderstorm excitation. Finally, the maximum dynamic response to thunderstorms is estimated as the sum of the maximum mean and fluctuating parts and a numerical validation of the results against real recorded thunderstorms is provided, highlighting the reliability of adding up the mean and fluctuating contributions and the advantages and limits of neglecting the transient dynamics. • Response is derived starting from a consistent EPSD model of thunderstorm velocity. • The expected value of the maximum response is derived trough equivalent parameters. • A correction for the overestimations due to Poisson approximation is introduced. • The approach is validated against time-domain solutions from recorded thunderstorms. • Neglecting the transient dynamics may be overconservative. [ABSTRACT FROM AUTHOR]

Abstract: The International Association for Wind Engineering (IAWE) was born in 1975, at the 4th International Conference on Wind Engineering (ICWE), London, UK, in a pioneering stage of wind engineering. It operated, mostly informally, until 1999, when the IAWE Steering Committee Meeting at the 10th ICWE, Copenhagen, Denmark, decided to open a wide debate and study new tools to make the IAWE coherent with the impressive development in wind engineering. Following this decision, new IAWE by-laws were compiled and a renewed organisation was proposed to and accepted by the Steering Committee Meeting at the 11th ICWE, Lubbock, TX, 2003. This decision promoted several actions aimed at offering the international wind engineering community a more operative and efficient service and support. In particular, an Executive Board was constituted to drive the Association and its activities between two subsequent ICWEs; a Secretariat was established to administer the IAWE and to represent a reference point for the wind engineering community; several associations and societies were accepted into IAWE membership, and a wide network of links and cooperations was created among member organisations, supporting members and other individual contacts spread to all parts of the world; the official IAWE web site—www.iawe.org—was created; renewed liaisons were made operative with international organisations working in wind engineering and similar fields; IAWE Awards were instituted in the broad field of wind engineering; a better sequence of dates and venues of the most important wind engineering conferences was planned. This paper provides a general framework and some critical remarks on the progress and the prospects of the IAWE. [Copyright &y& Elsevier]

Abstract: The gust buffeting of long span bridges is analysed by the Double Modal Transformation, a method consisting in the joint transformation into principal coordinates of the structural displacements (modal analysis) and of the loading exciting the bridge (Proper Orthogonal Decomposition, POD). Even if an accurate representation of the turbulent field producing the loading requires a high number of modes, thanks to the orthogonality of structural and turbulence modes, a satisfactory estimate of the structural response can be achieved representing the turbulence field through only a few modes. Based on this observation, an effective turbulence field is defined as that part of the actual turbulence which really influences the structural response, i.e. the turbulence reconstructed using only the necessary POD modes. The analysis of the spectral properties of the effective turbulence field shows that its harmonic content is strongly reduced and concentrated in a restricted frequency band with respect to the actual turbulence; moreover, it is highly correlated also for large distances. These observations allow a critical selection of the time and space discretizations to adopt for numerical analyses, strongly reducing their computational burden. [Copyright &y& Elsevier]

Few mathematical methods attracted theoretical and applied researches, both in the scientific and humanist fields, as the Proper Orthogonal Decomposition (POD) made throughout the last century. However, most of these fields often developed POD in autonomous ways and with different names, discovering more and more times what other scholars already knew in different sectors. This situation originated a broad band of methods and applications, whose collation requires working out a comprehensive viewpoint on the representation problem for random quantities. Based on these premises, this paper provides and discusses the theoretical foundations of POD in a homogeneous framework, emphasising the link between its general position and formulation and its prevalent use in wind engineering. Referring to this framework, some applications recently developed at the University of Genoa are shown and revised. General remarks and some prospects are finally drawn. [ABSTRACT FROM AUTHOR]

The Proper Orthogonal Decomposition (POD) is a statistical method particularly suitable and versatile for dealing with many problems concerning wind engineering and several other scientific and humanist fields. POD represents a random process as a linear combination of deterministic functions, the POD modes, modulated by uncorrelated random coefficients, the principal components, it owes its popularity to the property that only few terms of the series are usually needed to capture the most energetic coherent structures of the process, and a link often exists between each dominant mode and the main mechanisms of the phenomenon. For this reason, POD modes are normally used to identify low-dimensional subspaces appropriate for the construction of reduced models. This paper provides a state-oil the-art and some prospects on POD, with special regard to its framework and applications in wind engineering. A wide bibliography is also reported. [ABSTRACT FROM AUTHOR]

Original studies on gust factor buffeting dealt with the alongwind displacement of structures. Research on this topic carried out since the nineties followed two distinct lines: the first determines the maximum effects due to the alongwind response; the second extends the original method from the alongwind response to crosswind and torsional responses. This paper represents the junction point of these research lines with reference to cantilever slender vertical structures. It derives the most relevant effects associated with the three-dimensional (3-D) wind-excited response of this structural type and shows that a suitable definition of one non-dimensional quantity, referred to as the 3-D gust effect factor, provides such effects at any level through a wide set of experimental, numerical and analytical procedures. A new definition of a 3-D equivalent static force consistent with this method is also introduced and critically compared with previous analogous statements. [Copyright &y& Elsevier]

An adequate education in a discipline as vast and articulated as wind science and engineering cannot fail to recognize its origins, developments, fundamentals, advancements and prospects. This paper analyses and discusses the actual state of education by identifying its limits, gaps and strengths, as well as the hard core of knowledge that should constitute the common basis for a mature and modern discipline capable of generating figures endowed with broad views and specialized skills. Pursuing this vision in a rational and homogeneous framework, it also points out the role of new strategies aiming to exploit technological evolution and communication systems, to rationalize co-operative educational programs on broad territorial scales, to involve different competences as in-depth as they are varied in the wind science and engineering community. Meanwhile, it highlights the necessity of reaching those who need to establish and consolidate this culture, but do not have the opportunity to personally experience the manifold initiatives in the discipline, to seize the interest of people towards wind science and engineering, to disseminate its culture and know-how into everyday life and society. • Education in wind science and engineering should recognize its origins, developments, fundamentals and advancements. • Its state should identify its limits, gaps, strengths and the core of knowledge that should constitute its common basis. • This vision should be supported by new strategies exploiting technological evolution and communication tools. • It is essential to spread the knowledge of wind towards a wider public, bringing it into everyday life and society. • Giovanni Solari is the sole author of this paper, so he carried out the work leading to this contribution. [ABSTRACT FROM AUTHOR]

This paper presents a new approach for modelling the evolutionary power spectral density (EPSD) of thunderstorm outflows based on a database of 129 real-scale thunderstorm time-histories. Two equivalent methods of decomposition of the wind velocity are investigated, outlining the derivation of the EPSD. The analyses are based on the hypothesis that the residual turbulent fluctuations can be treated as a uniformly modulated process, whose reliability is verified studying the steadiness of its up-crossing rate. The assumption of considering a constant turbulence intensity is checked through the evaluation of the dynamic response of a set of SDOF systems in time-domain and through the response spectrum technique. Two models for the time-modulating function of the EPSD are proposed that include the parameters characteristic of both the thunderstorm event and the background wind. Finally, the steps for the derivation of the EPSD are outlined pointing out the limits of the representation of the PSD of the reduced turbulent fluctuations through spectral models commonly adopted in wind engineering. The final aim of this research is finalising a triad of complementary methods for evaluating the dynamic response of structures to thunderstorm outflows - EPSD, time-domain and response spectrum - consistent with real-scale time-history records. • The non-stationarity of turbulent fluctuations is analysed through their up-crossing rate. • The residual turbulent fluctuations can be dealt with a uniformly modulated process. • Assuming steady turbulence intensity causes overestimations in the dynamic response. • The models proposed for the time-modulating functions encase a physical meaning. • Two different ways of modelling the evolutionary power spectral density are outlined. [ABSTRACT FROM AUTHOR]

Most verifications at the ultimate and serviceability limit states involve the evaluation of the maximum value of a structural parameter and its comparison with a threshold. This evaluation has thus a dominant impact on engineering, design and codes that reflects on the safety and economy of built environment and society. The distribution of the maximum value of the wind-excited response of structures is usually determined by the Davenport’s model assuming that the structural response is a random stationary Gaussian process and the up-crossings of high response thresholds are rare independent events. The hypothesis that wind actions are stationary limits the analysis to synoptic phenomena. The hypothesis that wind actions are Gaussian implies that turbulence is small and the atmospheric stratification is neutral. The hypothesis that the up-crossings of high response thresholds are rare independent events raises some doubts on its application to flexible and low-damped structures, just those structures most susceptible to dynamic wind actions. This paper aims at inspecting this topic with special regard for some aspects almost ignored in literature, namely the properties of real wind velocity records and their influence on the distribution of the maximum value, the simulation of wind velocity histories with particular concern for the length of the signals, and the classic use of some theoretical models of the maximum value with special attention to the aprioristic acceptance of the representativeness of its mean value. Analyses are here carried out in the classic framework of stationary Gaussian processes. The results achieved point out some shortcomings in the classic engineering practice and provide some remarks for future research. [ABSTRACT FROM AUTHOR]