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Studies carried out on gust buffeting and aerodynamic admittance show that mode shape represents a sort of watershed. If the mode does not change sign along the structure axis, the problem admits a robust conceptual interpretation based on energy cascade and a simple closed-form solution. If, instead, the mode changes sign, the solution calls for numerical tools, and its physical interpretation definitely is unclear. The companion paper investigated this issue within the novel framework of the enhanced equivalent spectrum technique and derived a closed-form solution of the aerodynamic admittance that can be applied to any mode using quasi-steady theory. This solution is precise and simple for modes with a few changes of sign, but it becomes laborious with increasing mode shape complexity; in addition, it provides a partial conceptual interpretation. Both these limitations were overcome in this paper, in which the application of proper orthogonal decomposition led to a full conceptual interpretation of aerodynamic admittance and to a simple and general closed-form solution. Analyses were limited here to single modes; multiple arbitrary modes are left for future research, as is the generalization of these concepts to arbitrary influence functions. [ABSTRACT FROM AUTHOR]

The loading and response of structures due to gust buffeting is a dominant topic of wind engineering. One of its crucial aspects is the shape of vibration modes. Although numeric solutions are available for any mode, conceptual interpretations and closed-form solutions mainly are limited to the case in which the sign of the mode does not change along the structural axis. For modes that change sign, it is difficult, if not impossible, to recognize the physical role of the parameters that govern the problem and judge analysis results in qualitative form. This paper addressed this issue in the framework of quasi-steady theory by clarifying the relationship linking aerodynamic admittance with mode shape, showed that any mode may be brought back to a piecewise ensemble of regular modes with constant sign, and used this concept to obtain a closed-form expression for any aerodynamic admittance. This solution is simple for modes with few changes of sign, but becomes laborious as mode complexity increases. In addition, it provides a partial conceptual interpretation. Both of these limits were overcome in the companion paper, in which the use of proper orthogonal decomposition led to a full conceptual interpretation of aerodynamic admittance and a simple and general closed-form solution. [ABSTRACT FROM AUTHOR]

Thunderstorm outflows are usually analysed by decomposing their horizontal velocity into a slowly-varying mean part and a residual fluctuation; in this framework the wind direction is often examined qualitatively but disregarded quantitatively. This is incoherent with the traditional analysis of synoptic wind speeds, where the mean velocity and direction are first determined, then the fluctuations are decomposed in terms of longitudinal and lateral turbulence components. Aiming to overcome these shortcomings, a novel directional decomposition strategy is formulated here, which makes the study of thunderstorm outflows and synoptic winds fully coherent. The results provided by the classic and novel decomposition rules are first compared and elucidated with reference to a couple of real thunderstorm and synoptic wind velocity records. Later on, they are applied to a broad class of thunderstorm outflow records whose statistical properties are investigated. The novel approach is strategic to carry out directional analyses of the dynamic behaviour of structures in terms of alongwind and crosswind response. • The classical decomposition rule of thunderstorm outflows disregards wind direction. • Classical synoptic wind and thunderstorm outflow decomposition rules are incoherent. • A novel directional rule is formulated that overcomes the above shortcomings. • The novel rule is strategic to carry out directional analyses of the structural response. [ABSTRACT FROM AUTHOR]

Highlights • Design wind velocity and wind-induced damage are often related to thunderstorms. • Research on thunderstorm loading of structures is still fragmentary and uncertain. • Calibration and advance are provided of response spectrum technique and time-domain analysis. • The response spectrum technique is a suitable tool for engineering calculations. • Time-domain analysis is highly efficient with a limited computational burden. Abstract Thunderstorms are transient events. Design wind velocity and wind-induced damage are often related to them. Despite this, research on thunderstorm loading of structures is still fragmentary and uncertain due to their complexity, short duration and small size. These issues make it difficult to set physically realistic and simple models as well as to gather real data. This favoured the implementation of refined methods based on limited measurements. The European Projects "Wind and Ports" and "Wind, Ports and Sea" realised an extensive monitoring network from which many thunderstorm outflow records were extracted. They were analysed to inspect their characteristics and to formulate methods coherent with measurements. Firstly, the response spectrum technique conceived for earthquakes was extended to thunderstorms. Then, a hybrid simulation strategy was proposed and time-domain integrations of the structural response were applied. This paper provides a joint calibration and advancement of these two methods, leading to results that substantially agree, especially faced with their conceptual and operative diversities. This confirms the potential of the response spectrum technique to become a suitable tool for calculating the thunderstorm loading of structures and the efficiency of hybrid simulations and time-domain analyses to investigate, with a limited computational burden, advanced structural issues. [ABSTRACT FROM AUTHOR]

The study of thunderstorm outflows and their loading and response of structures is a key topic in modern wind engineering. This paper provides a new contribution to this research by analyzing a wide dataset of 277 wind velocity records characterized by strong transient properties and labeled by thunderstorm outflow. These records have been detected for up to 6 years by 14 anemometers belonging to an extensive in-site monitoring network distributed in the Northern Mediterranean ports. Analyses are carried out in order to extract the parameters of major interest for evaluating the wind loading effects of structures and furnishing a comprehensive statistical characterization of the huge amount of data recorded. Results lead to a novel classification of thunderstorm outflows with reference to the time scale of the gust front passage and their intensity; a refined interpretation of the differences involved by the turbulence intensity, the integral length scale and the gust factor of mesoscale downbursts and synoptic low-pressure systems; a confirmation of the substantial independence of these quantities with respect to the ratio between the height above ground of the sensor and the roughness length of the terrain, together with their correlation with the wind velocity; a new parameterization of the harmonic content of the turbulent fluctuations. [ABSTRACT FROM AUTHOR]

The meteorological services of mid-latitude countries record wind speeds averaged over 10 min or 1 h periods and peak wind speeds for the same averaging period or a full day. Design wind speeds based on the statistical analysis of this data in a mixed wind climate may prove to be imprecise and unsafe due to the occurrence of intense, small and rapid extreme wind events such as thunderstorm outflows. Considering the 6 year continuous high-frequency records registered in two Port areas of the Upper Tyrrhenian Sea, a preliminary but representative analysis of the extreme wind speed distribution has been carried out in a mixed wind climate area frequently struck by thunderstorms. Results show that wind speeds with a high return period are always related to thunderstorm outflows. The mixed extreme distribution asymptotically overlaps with that for thunderstorms for high return periods and always provides the highest wind speeds. Gathering the ensemble of all extreme values into a single set leads to underestimating of the extreme wind speed. The Italian code provides conservative estimates of the extreme wind speed that protect designers from thunderstorms as well. However, refined analyses of the local wind climate that ignore thunderstorm events may lead to severe underestimations of the design wind velocity. [ABSTRACT FROM AUTHOR]

Free-standing lattice towers are structures used for various purposes such as radio and television broadcasting, electric power and microwave transmission, meteorological measurements, wind energy production and so on. Due to their properties, they are mainly sensitive to wind loads. A longstanding discussion on the wind loading effects on this structural type has been carried out in the literature. This paper investigates the alongwind load effects on free-standing lattice towers by introducing specific influence functions of displacements, shear forces, bending moments and axial forces in leg elements. Such influence functions are first derived, calibrated and validated for the most typical structural types, then they are used within the framework of the gust effect factor technique. Comparative studies with reference to both the traditional use of cantilever beam approaches and finite element methods point out the role of the bracing pattern and, more precisely, of the level of the crossing of diagonals in tower panels. All the applications developed here refer to real structures with different properties. Results are interpreted and compared with those provided by previous studies on this structural type. Engineering and design issues are discussed focusing on the most critical aspects concerning dynamic wind loads. [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]

The analysis of wind actions and effects on structures involves the knowledge of the parent population and extreme value distributions of the mean wind velocity. In spite of an impressive amount of measurements, refined probabilistic models and detailed applications to the study of specific sites, there is an equally disheartening lack of available probabilistic information at the territorial scale, and, therefore, of tools effectively applicable in the engineering and codification sectors. Almost all of the international standards and codes report sufficiently reliable maps of the mean wind velocity with 50-year return periods. On the other hand, there are still few regulations that provide the distribution of the yearly maximum value of the mean wind velocity or such value as a function of the return period. Furthermore, no regulations provide the distribution of the parent population of the mean wind velocity that may be very important for serviceability and fatigue analyses. This paper introduces a joint representation of the parent population and extreme value distributions of the mean wind velocity of synoptic extratropical cyclones; starting from this model, simple but reliable expressions are derived, directly applicable in the engineering and codification sectors, aimed at bridging the gap described. The obtained expressions are critically examined, pointing out their advantages but also some apparent critical issues. A preliminary application of these expressions is carried out with reference to the Italian territory. [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]

There are many metallic structures, taken as a whole or at level of individual elements - including lighting poles, telecommunication towers, pylons, wind turbines, containers unloder, structures supported by cables - with relevant slenderness, flexibility, lightness and low dissipative capacity. These structures, inevitably exposed to wind dynamic actions, have been occuring an endless series of collapses and failures of welded joints. The analysis of the collapses show a phenomenon almost completely ignored in the past: fatigue caused by wind actions. In many cases, the collapse takes place from a few days to a few months of structure completion. It is partly due to lack of expertise in weld execution, but it is mainly a consequence of lack of knowledge of wind-fatigue. The article presents an overview of the physical phenomena and structural properties that determine this kind of failure. The prospects, now ripe, to spread calculation procedures for estimating such failure and avoid it are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: The Journal of Wind Engineering and Industrial Aerodynamics published a paper (Steenbergen et al., 2012) providing a wide parametric analysis aimed at comparing the results by procedures 1 and 2 of Eurocode 1, in order to evaluate the dynamic alongwind response of buildings. Based on such analysis, that paper pointed out that the differences between the two procedures and the theoretically correct values are small with reference to the structural factor. For the comfort level, instead, larger differences occur and procedure 2 is preferable. This discussion shows that procedures 1 and 2 involve variations typical of different approximations and calculation methods and that such differences are almost negligible with respect to the variations obtained when taking duly into account crosswind and torsional accelerations. A wider prospect on the code evolution is also drawn. [Copyright &y& Elsevier]

Wind-induced fatigue is a crucial topic in the design of wind-sensitive structures. Despite this, methods proposed in literature are mainly addressed to research, or they are too simplified for engineering applications. Thus, suitable engineering and standards procedures are almost totally lacking, which is a major shortcoming in structural and wind engineering. Starting from a closed-form solution (CFS) recently proposed by the authors, this paper develops a novel engineering approach to evaluate the alongwind-induced fatigue of structures and structural elements. This approach is based on a hierarchy of hypotheses that lead to a progressive simplification of the basic formulation. Two classes of formulas, referred to as Levels I and II CFSs, are obtained and critically discussed with special concern for input parameters. Level I CFS implies three further simplifications joined together by the common aim of providing refined approximations of the reference target solution. Level II CFS implies three different simplifications joined together by the common aim of providing easy solutions on the safe side. This set of CFSs is framed within a general procedure that any country, society, or engineer can easily personalize to a situation and requirement, ranging from numerical tools to manual engineering calculations and code provisions. [ABSTRACT FROM AUTHOR]

Abstract: This paper illustrates the research activities linked with the European Project “Wind and Ports: The forecast of wind for the management and the safety of port areas”, which involves the Department of Civil, Environmental, and Architectural Engineering of the University of Genova, and the Port Authorities of Genova, La Spezia, Livorno, Savona (Italy) and Bastia (France). The project is based on three tools, namely the historical databases, the global meteorological data and forecasting system, and the data provided by a wide seaport monitoring network that represents also the first product of the project. These tools are processed by a set of numerical models that represents the second product and the key tool to derive three further products, namely the statistical mapping of seaport areas, a medium-term forecasting system and a short-term forecasting system. A web-based GIS system is being realized to make the products of this project directly available to port operators, within a global system for a safe management of port areas. Downstream of these products, this paper provides some insights of the wide validation procedure that is going to be implemented to check and to improve the quality of the results. Further prospects for new research projects using the results of the Wind and Ports Project as starting point are also discussed. [Copyright &y& Elsevier]

Abstract: This paper analyzes the fatigue collapse of two slender structures due to wind-induced vibrations. The analysis is based on a complete procedure for the wind-induced fatigue analysis proposed by the authors. The application of the proposed method, compared with the real cases examined, leads to accurate fatigue life prediction; moreover, it gives a complete picture of the stress state and damage of the structures, furnishing useful information on the structural behavior and a key for the interpretation of collapses and damage causes. In particular, the analysis highlights the critical aspects of the aerodynamic behavior of the considered structures and suggests some remarks on the current state-of-the art on design against wind-induced actions. [ABSTRACT FROM AUTHOR]

Abstract: Wind-induced fatigue is a crucial topic in the design of several structural types. Despite this, the methods proposed in the literature have been developed mainly for research purposes. As a consequence, reliable engineering and standard methods for wind-induced fatigue analyses are still very limited and mainly addressed to the crosswind-induced fatigue caused by vortex shedding. Based on these considerations, this paper proposes a novel approach to evaluate the alongwind-induced fatigue of slender structures and structural elements. Starting from the procedure recently proposed by the authors, a hierarchy of hypotheses is introduced and critically discussed, which leads to a progressive simplification of the basic formulation. Two levels of formulae are derived, namely a closed form solution and an approximated closed form expression of the wind-induced damage; these represent a solid base from which to derive suitable methods for engineering calculations and standards. Application of the proposed solutions shows good agreement with numerical results. [Copyright &y& Elsevier]

• A mathematical model to evaluate motion-induced forces on slender structures subjected to thunderstorm outflows is proposed. • Time-varying aerodynamic damping matrix and aerodynamic stiffness matrix of the system are defined. • Three levels of analysis are addressed, according to the characteristics of the wind event. • The classical solution for synoptic winds is found as a particular case. • Suitable wind fields compatible with single-point records are rebuilt and applied on two configuration of a structure, estimating the motion-induced forces. • The effects of the transient aeroelasticity are analysed and critically commented. • Motion-induced forces are evaluated on slender real structures. Literature is rich about studies which concern the insurgence of instability of structural systems under the action of steady flows, which have led to well-consolidated methods to assess the structural safety with regard to aeroelastic phenomena induced by synoptic winds. On the other hand, there are no clear references regarding aeroelasticity induced by the effect of thunderstorm outflows, events characterised by irregular variations of the wind speed and direction in a limited duration of time, which prevent the furnishing of a long time interval for the structure and the fluid to synchronise. This paper, based under the hypothesis of applicability of the classic strip and quasi-steady theory, illustrates a mathematical model able to consider the aeroelastic effects of thunderstorm outflows into the dynamic response of slender structures, from which the methodology for synoptic winds may be found as a particular case. After defining three different levels of analysis, applications regarding the Endless Column by Constantin Brâncuși under the action of ten thunderstorm outflows are proposed, whose outcomes are critically analysed and commented. [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]

Alongwind actions on structures may produce a great number of stress cycles and lead to significant damage accumulation. A critical analysis of the pertinent methods proposed in the literature provides evidence of the necessity of improving the level of approximation, taking into account the bandwidth spectral properties of the stress processes. This paper pursues this aim by establishing an advanced broadband formulation. Applying the cycle counting method based on the narrow-band assumption, two discrete cycles histogram expressions are first suggested, which lead to an upper and lower bound of the fatigue damage. As the gap between the two bounds may be very large, a more refined counting method is formulated, based on a bimodal representation of the alongwind induced stress power spectral density functions; the low- and high-frequency spectral contents are associated, respectively, with the quasistatic and the resonant parts of the response. Some examples highlight the properties of the proposed procedure and show the good agreement between the bimodal approach and the numerical results. [ABSTRACT FROM AUTHOR]

Abstract: Monte Carlo simulation is becoming a fundamental tool for the design of complex and important wind-excited structures. A common application regards the time-domain dynamic analysis of multi-dof nonlinear structures whose excitation is calculated on the base of simulated wind velocity time-histories. The present paper describes a methodology for the simulation of wind velocity fields over large domains, possibly in zones characterised by complex topography. The modelling of turbulence in non-homogeneous flow condition and some computational aspects related to its simulation are discussed, proposing some strategies for reducing the calculation time. The simulation procedure is applied to the case of the Messina Strait bridge for which the three components of turbulence are simulated over a domain composed by 351 nodes. [Copyright &y& Elsevier]

The modeling and simulation of the wind field along structures is a fundamental step in the analysis of their wind-excited response. The proper orthogonal decomposition (POD) provides efficient tools to formulate a model of the turbulence field based on principal components. This paper proposes a representation of turbulence based on a double application of the proper orthogonal decomposition. Considering a linear domain and generalizing an analogous previous solution concerning the classical components, closed form expressions for the eigenvalues and eigenfunctions of the principal turbulence field are obtained. Based on this representation, a very efficient simulation scheme for the three correlated turbulence components along a linear domain is introduced. [ABSTRACT FROM AUTHOR]

The wind-excited vibrations of structures induce fluctuating stresses that lead to fatigue damage accumulation and may determine structural failure without exceeding ultimate strength. This paper proposes a mathematical model aimed at deriving the histogram of the stress cycles, the accumulated damage, and the fatigue life of slender vertical structures exposed to simultaneous alongwind and crosswind vibrations. Wind climate is modeled by the joint density function of the mean wind velocity and direction. Wind-induced actions consist of aerodynamic forces on the stationary structure and of aeroelastic forces due to the structural motion. Aerodynamic actions on the stationary structure are caused by the turbulence of the oncoming flow, dealt with through quasisteady theory, and by the vortex wake, considered as independent from turbulence. Aeroelastic forces are aimed at reproducing the lock-in phenomenon. The static and the quasistatic parts of the structural response are evaluated by the influence function technique, taking all modes of vibrations into consideration. The resonant part of the response is related to the fundamental alongwind and crosswind modes only. The probabilistic accumulation of damage due to aerodynamic actions on stationary structures is estimated by a counting cycle method inspired by narrow band processes. The damage in lock-in conditions is superimposed by counting stress cycles deterministically. The examples illustrate the application and the effectiveness of the proposed procedure, focusing attention on the role of upper modes and wind directionality. [ABSTRACT FROM AUTHOR]

Since the pioneering studies developed by Alan G. Davenport, the equivalent static actions on structures are a key topic of the wind engineering research. Two main methods have been proposed. The former, referred to as the gust factor (GF) technique, defines wind actions through a unique load distribution scaled by a non-dimensional coefficient eventually depending on the effect considered. The latter, referred to as the load combination (LC) technique, defines wind actions, till now in the alongwind direction, as a combination of three distinct load distributions associated with the static, quasi-static and resonant parts of the response. This paper provides a rational scheme and a generalisation of these procedures with reference to cantilever vertical structures. As for the GF technique, also the LC technique is initially extended to the 3-D response, discussing critically a set of alternative models for the quasi-static part of the loading. A new method is also proposed, referred to as the global loading technique, where equivalent static wind actions are assigned as a unique load distribution independent of the load effect considered. All problems dealt with in this paper are solved in closed form. [Copyright &y& Elsevier]

This paper illustrates and discusses the progress and the prospects of analytical methods for estimating the wind-induced response of structures, with special regard to cantilever vertical structures. Also in this era of large facilities and super-computers, closed form solutions, eventually assisted by user-friendly numerical programs, electronic sheets and symbolic calculus tools, imply relevant significance and great potentialities. Their use may be divided into two operative lines, referred to as direct applications and integrated procedures. Direct applications concern those analyses that pursue their aims by applying analytical methods autonomously; they comprehend two broad classes of procedures addressed, respectively, to solve specific engineering problems and to assess general tendencies. Integrated procedures concern those analyses that pursue their aims through articulated flow-charts whose logical blocks imply analytical methods, numerical algorithms and experimental measurements; embedded in such a context, analytical methods are powerful tools to establish reliable procedures for the aerodynamic identification of structures and to solve complex wind engineering problems, among which the propagation of uncertainties, structural reliability and wind-induced fatigue, otherwise almost prohibitive. [Copyright &y& Elsevier]

The 3-D gust effect factor (GEF) technique is an efficient method to determine the maximum displacements and internal forces of vertical structures subjected to alongwind, crosswind and torsional gust-excited vibrations. All these effects and the related equivalent static forces may be evaluated through one non-dimensional quantity referred to as the 3-D GEF, whose expression was found in closed form. This property makes very attractive the use of functional analysis to establish general tendencies and classification strategies. Confirming some previous results limited to alongwind vibrations, this paper shows that such tendencies are mainly related to the shape of the fundamental modes of vibration. Structures are thus classified into homogeneous categories and general rules are provided to assess a priori the distribution of internal forces. Errors inherent the determination of internal forces by the classical gust response factor technique are also discussed. Among several aspects of engineering interest, those concerning wind actions on the foundation and the stress state for wind-induced fatigue deserve particular attention. [Copyright &y& Elsevier]

Literature on turbulence modeling is rich in empirical, semi-empirical and theoretical spectral equations whose parameters assume deterministic values. Starting from a critical review of the state of the art, a unitary model of the 3-D atmospheric turbulence was proposed where all parameters are defined by first- and second-order statistical moments derived from a wide selection of experimental measurements. Analyses based on Monte Carlo simulation of the model parameters show that the propagation of turbulence uncertainties over the wind-excited response of structures gives rise to a relevant scatter. The passage from Monte Carlo simulations to Taylor series expansions addressed to apply the first-order second-moment technique provides systematic rules to deal with the structural response in a full probabilistic environment. It also allows appreciation of the role of each uncertain parameter. The joint application of this procedure and a closed form solution of the response drastically reduces the computational burden and makes these analyses operatively possible. The proposed approach is a step forward towards the formulation of a unitary probabilistic model of the wind-excited response of structures, comprehensive of model errors, parameter uncertainties and parameter randomness. [Copyright &y& Elsevier]

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]

This paper discusses different strategies for the extraction of the time-varying mean from wind speed time histories. Due to the advantage of allowing analytical evaluations, the attention is focused on kernel regression techniques, considering different weighting functions, namely a constant, a Gaussian and a cardinal sine weighting function. The problem is firstly treated analytically, and the frequency-domain properties of the filter associated to different kinds of weighting functions in the definition of the slowly varying mean through kernel regression are analysed. Then, different weighting functions are adopted for the analysis of digitally-simulated stationary wind speed time histories and for the time histories of thunderstorm outflows recorded by a tri-axial anemometer. The consequences of the adoption of different weighting functions on the harmonic content and statistical properties of turbulence are studied. The same features are found also for thunderstorm outflow records. • Kernel regression techniques for the time-varying mean extraction are studied. • The properties of the filter associated to various weighting functions are analysed. • The statistical moments of the reduced turbulent fluctuation are estimated. • Applications to stationary and nonstationary wind speed time histories are provided. [ABSTRACT FROM AUTHOR]

Wind actions are crucial for the safety and sustainability of structures. The wind climate of Europe and many other parts of the world is dominated by synoptic extra-tropical cyclones and mesoscale thunderstorms. Thunderstorms are frequent events that cause wind speeds and damage often greater than those of cyclones. This paper describes a wide research activity including an extensive monitoring network, an unprecedented database of transient wind speed recordings, a broad spectrum of numerical tools for elaborating data and extracting their statistical properties relevant to the wind loading of structures, the development of wind tunnel tests and CFD simulations, investigations on weather scenarios and damage surveys aiming to complete the information provided by field measurements. Based on these resources, a new generation of wind loading models is being developed – response spectrum technique, time-domain integration, evolutionary spectral density - robustly coherent with measured data and intrinsically coherent with each other. These studies are being carried out in the framework of the project THUNDERR, funded by the European Research Council (ERC) with an Advanced Grant 2016 in order to produce outcomes physically correct, transferable to design and standards, suitable to modify the current wind loading format and make constructions wind-safer and cost-efficient. • THUNDERR project studies thunderstorm outflows and their impact on structures. • Outflows are studied by real measurements, CFD simulations and wind tunnel tests. • New wind loading models are being developed to account for thunderstorm effects. • Design practices will benefit of THUNDERR outcomes to make constructions wind-safer. [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]

Summary: This paper studies the wind load on 1,000 m‐high super‐tall buildings and provides basic reference for design, including the utilization of passive and active control devices. High‐frequency force balance wind tunnel tests of super‐tall buildings with different height are carried out to investigate the effects of building height and wind flow on the wind load. Both monsoon and typhoon climate wind flows are simulated based on target models suggested in literatures. The simulation of typhoon climate wind flows is carried out by a newly developed technique. The analysis of the experimental results confirms that the aerodynamic force is very sensitive to both building height and wind flow. In monsoon climate, the turbulence intensity decreases on increasing the height above ground. Thus, on increasing the building height, vortex shedding becomes increasingly intense and excites stronger structural vibrations in the across‐wind direction, though the across‐wind fluctuating overturning moment coefficient is almost the same. In typhoon climate, both the mean and the fluctuating overturning moment coefficients increase with the building height. This is mainly caused by the decreasing mean wind speed. The vortex excitation becomes weaker on increasing the building height, and this phenomenon is different from that observed in the monsoon climate. In order to better explain vortex‐shedding excitation, a new parameter referred to as the characteristic turbulence intensity is defined herein as a weighted mean value of the turbulence intensity in the range of the building height. It provides a robust interpretation of the vortex excitation of super‐tall buildings located in different wind flow and climate conditions. [ABSTRACT FROM AUTHOR]

The Mediterranean is a 'hot spot' for the genesis of different types of severe weather events, including potentially damaging wind phenomena like downbursts, whose occurrence and evolution in this geographical region have not been documented in the literature. This paper is part of an interdisciplinary collaboration between atmospheric scientists and wind engineers with the objective of conducting a comprehensive analysis of the field measurements and weather scenarios related to nonsynoptic wind systems in this area. The downburst that struck the Livorno coast of Italy at about 1310 local time 1 October 2012 is investigated as a relevant test case for such severe wind events. The wind velocity records detected by ultrasonic anemometers, part of a monitoring network created for the European 'Wind and Ports' and 'Wind, Ports and Sea' projects, are analyzed and decomposed in order to inspect the main statistical features of this transient event. The analysis of the meteorological precursors to this event is carried out making use of model analyses, standard in situ measurements, remote sensing techniques, proxy data, and direct observations. The results obtained bring new insights into a downburst's onset and detection in the Mediterranean, its evolution at the local scale, and possible connections to specific synoptic-scale weather conditions like secondary cyclogenesis in the lee of the Alps. [ABSTRACT FROM AUTHOR]

The statistical modeling of the extreme mean wind speed is a very controversial subject. Several models are currently being applied in the literature, based on different assumptions and supplying quite different results. This paper takes a step back towards the common root of many extreme value models: the Annual Rate of Independent Events (ARIE). Starting from an analysis of large datasets of synthetic wind observations, the ARIE is inspected from a new point of view and some features so far hidden are brought to light. Based on that, a new effective approach to model the distribution of the extreme mean wind speed is proposed. The reliability of the proposed model is discussed processing both large datasets of synthetic wind observations, and small-sized datasets representative of real conditions. ARIE sensitivity to uncertainties in the parent distribution is also evaluated and critically discussed. [ABSTRACT FROM AUTHOR]

This paper presents analytical and experimental investigations aimed at evaluating the aeroelastic instability and wind-excited response of slender vertical cantilever structures, in particular complex lighting poles and antenna masts with distributed eccentricities. The application of the methods herein presented to a real structure emphasizes the significance of aerodynamic eccentricities, upper vibration modes and coupling between the translational components of the motion. In such a framework, particular sets of the parameters and specific structural configurations may cause very low critical galloping velocities. Additionally, the hypothesis of polar symmetry commonly used in technical calculations may lead to relevant underestimations of the wind-excited response. From this point of view, this paper provides possible interpretations for a number of damage and collapses of this structural type without clear and suitable explanations. [ABSTRACT FROM AUTHOR]

The authors have recently developed a Monte Carlo simulation algorithm able to generate thousands of years of synthetic wind speed values. In this study, however, two points have not received adequate attention: the presence of underlying periodic deterministic components embedded into the time series of the velocity and the generation of time series having exactly the desired marginal distribution. In principle, both these issues may have relevant consequences on the distribution of extreme values. This paper investigates and discusses the presence of underlying deterministic components in the wind records, develops a refined simulation algorithm for non-Gaussian colored wind speed stationary processes, and finally inspects how much these advances affect the analysis of extreme values. An extensive simulation consisting of more than 12,740 years of synthetic wind speeds is performed, based on the synoptic wind climatology of the central part of Italy. The results demonstrate that the use of a refined simulation algorithm improves the quality of extreme values analysis. On the other hand, it is not easy to express a definite opinion on the random or deterministic nature of some periodic cycles; it is shown, however, that dealing with such cycles as random or deterministic has very limited consequences on extreme values analysis. [ABSTRACT FROM AUTHOR]

Abstract: This study proposes a novel methodology to create a large sized synthetic dataset of wind velocities and adopts this to discuss the probability distributions commonly used for extreme winds. A large number of long-term time series of mean wind speed are generated by a numerical procedure that faithfully reproduces the macro-meteorological component of wind velocity, while guaranteeing sample functions with random extremes. Through application of this technique, a large sized dataset of synthetic extreme wind observations has been extracted, of a size unprecedented in literature. Commonly applied extreme value (EV) methods are then used to process the dataset produced. In the first instance, the effectiveness of these models is tested to exclude any false effects due to the limited period covered by current wind measurements. Following this, interval estimations of design wind speeds are derived by analyzing EVs from records of different lengths in order to explore the applicability of EV distributions to real situations. The comparison between analytical and numerical results provides many interesting and intriguing points of discussion, and opens the way to new research horizons in EV analysis. [Copyright &y& Elsevier]

Abstract: This paper introduces a procedure for the simulation of long-term time series of the mean wind speed. A series of meteorological records are used to describe the probabilistic distribution and the spectrum of the process to be simulated. In particular, a complete description of the macro-meteorological spectrum of the wind speed is obtained, piecing together spectral portions deriving from different records. Then, an advanced simulation algorithm is introduced, based on existing iterative methods for simulating non-Gaussian processes via memoryless transformations, revised in order to obtain random extreme values of the simulated time-histories. The outlined procedure is finally applied for generating sample functions of the mean speed process. The availability of a large number of realizations permits the ability of the new algorithm to produce functions with desired features to be investigated in terms of ensemble statistics. This robust database could be useful for further studies. [Copyright &y& Elsevier]

Abstract: Gust buffeting of structures is analyzed by Double Modal Transformation, a method consisting in the joint transformation into principal components of structural displacements (modal analysis) and of wind loading (proper orthogonal decomposition). It commonly occurs that modal truncation applies to both the series of structural and loading modes; besides, many loading modes are almost orthogonal respect the dominant structural modes, so they do not contribute to structural response. This set of conditions allows the introduction of an effective action, defined as the loading process reconstructed retaining only those loading modes that excite the structure. This paper discusses this method and the related concepts by analyzing a set of simple ideal structures in closed form; this approach allows the formulation of general criteria aimed at defining the effective wind action as a function of non-dimensional structural and wind parameters. The numerical analysis of a real structure confirms the tendencies pointed out by the analytical solutions. [Copyright &y& Elsevier]

Presents a study which proposed a double modal transformation method, by which the dynamic analysis of a linear structure is carried out through the simultaneous transformation of the equations of motion and the loading process. Covariance and spectral proper transformation; Wind engineering applications; Conclusions.

The urban atmospheric boundary layer (UABL) is complex due to the heterogeneous underlying city surface. The nine anemometers installed at different heights along the 325 m meteorological tower provide an opportunity to carry out a refined study of wind properties in the UABL in central Beijing, China. Based on the recent 5-year high-resolution measured data, in total, 229,488 10-min length segments of wind records related to each anemometer are reliable for further analyses. Accordingly, the statistical properties of the wind speed and direction are first analyzed to present the local wind climate in a comprehensive way. Moreover, the pattern of the wind profiles related to two typical synoptic intense events are illustrated in order to give a preliminary perspective, then the statistical properties corresponding to a series of intense windstorms are described. Here, the deviations in the wind direction occur between 200 m and 280 m of the atmosphere, which might be due to the existence of an Ekman spiral; besides this, the laws of wind profiles based on open terrain are not suitable for the UABL, and the aerodynamic characteristic parameters of the UABL based on vertical stratified structures have to be considered. The results contribute to the establishment of revised models for the wind profile and are useful for the further understanding of the structure of UABL wind. [ABSTRACT FROM AUTHOR]

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]

A "downburst" is defined as a diverging wind system that occurs when a strong downdraft induces an outflow of damaging winds on or near the ground. Severe wind damage in many parts of the world are often due to thunderstorm outflows and their knowledge is therefore relevant for structural safety and design wind speed evaluation. Nevertheless, there is not yet a shared model for thunderstorm outflows and their actions on structures. In this paper, an analytical model that simulates the horizontal mean wind velocity originated from a travelling downburst is proposed. The horizontal wind velocity is expressed as the vector summation of three independent components: the stationary radial velocity generated by an impinging jet over a flat surface, the downdraft translating velocity, which corresponds to the parent cloud motion, and the boundary layer background wind field at the surface where the downburst is immersed. A parametric analysis is also developed and coupled with the analytical model aiming to investigate two observed downburst events and extract their main parameters – e.g. downdraft diameter, touch-down position, translating downdraft speed and direction, intensity and decay period - in order to reconstruct the space-time evolution of these events and validate the model itself. • An analytical model is developed to simulate thunderstorm outflows. • Downburst parameters are estimated through a parametric analysis. • Two real-scale thunderstorm outflows are simulated. [ABSTRACT FROM AUTHOR]

The dynamic complexity and the limited spatiotemporal structure of thunderstorms make the collection of reliable and systematic measurements of this phenomenon, which are definitely needed to evaluate its action on structures, challenging. The Northern Tyrrhenian is a "hot-spot" for the genesis of severe potentially damaging wind phenomena, such as downbursts. In the context of the European projects "Wind and Ports" and "Wind, Ports and Sea", a large and complex wind monitoring network has been installed just in this area. Here, three LiDAR profilers provide a vertical scanning of the atmosphere up to 250 ​m above the ground level. From their continuous recordings, a method to extract thunderstorm events is herein proposed, based on an automated procedure involving systematic quantitative controls and specific qualitative judgments. Starting from it, this paper provides a comprehensive investigation and comparison of the main parameters ruling the outflow vertical profiles of a selected subset of thunderstorms. The nose shape of the wind profiles appears mainly during the velocity ramp-up and peak stages. During the downburst, the wind direction is systematically invariant with height. The capability of LiDAR to measure the wind speed turbulence component is also discussed and its properties along the vertical profile are shown. • Thunderstorm wind profiles are extracted from LiDAR databases. • Signals are processed by means of the classical and directional decomposition methods. • The nose shape of the wind profiles appears during the velocity ramp-up and peak stages. • The wind direction is observed to be invariant with height during the outflow. • The maximum values of turbulence intensity occur prior to those of horizontal wind speed. [ABSTRACT FROM AUTHOR]

The study of thunderstorm outflows and their actions on structures is a dominant topic of wind engineering. This paper contributes to knowledge in this field through a systematic analysis of the thunderstorm outflows recorded by 9 anemometers installed at different heights along the 325 m high Beijing Meteorological Tower. Analyses are carried out through a directional decomposition strategy. The characteristics of a wide dataset of thunderstorm signals are analysed in a statistical environment coherent with the traditional one for synoptic winds; in this stage of the research, estimations of the mean wind speed and direction, the turbulence parameters and gust factor are carried out considering the records as disjoint from each other. Based on this choice, the results are compared with those obtained in the northern Mediterranean, providing a preliminary answer to the crucial question whether thunderstorms have similar properties in different areas, or, better, what of their properties are similar and what depend on the area itself. Besides to previous researches, the time evolution of the wind speed and direction profile is investigated with reference to a thunderstorm test case event. The systematic analysis of the full dataset of thunderstorm outflow fields is postponed to future researches. • A series of thunderstorm outflow records are detected in Beijing urban area. • A novel directional decomposition strategy recently formulated is implemented. • The characteristics of a wide dataset of thunderstorm signals are analysed in a statistical environment. • The results are compared with those obtained in the northern Mediterranean preliminarily. • The time evolution of the wind speed and direction profile is investigated condidering a test case. [ABSTRACT FROM AUTHOR]