138 research outputs found
Cycle counting methods for bi-modal stationary Gaussian processes
No full textThe cycle counting procedure is a fundamental step in the fatigue analysis of structures. This paper is devoted to cycle counting methods, starting from the spectral properties of the loading process. Cycle counting methods for stationary Gaussian narrow-band and broad-band processes proposed in literature are discussed. Focusing attention on bi-modal processes, which are usual in dynamic response of structures, the cycles histograms obtained by the Peak and Peak-Valley Counting methods are expressed in closed form. From these, a couple of upper and lower bounds for the mean total damage and for the mean fatigue life are obtained. Then, an advanced formulation of the cycle counting is developed, obtaining a new closed form solution of the cycles histogram which better approximate the Rainflow Counting results. The proposed method is finally applied to several different bi-modal processes, comparing the results with other criteria and with solutions based on simulated time-histories
Neutral and non-neutral atmosphere: probabilistic characterization and wind-induced response of structures
No full textFatica indotta dal vento su strutture verticali snelle caratterizzate da densità di potenza spettrale di risposta bimodale
No full textDynamic alongwind fatigue of slender vertical structures
No full textThe wind-excited vibration of structures induce fluctuating stresses around mean deformation states that lead to fatigue damage accumulation and can determine structural failure without exceeding design wind actions. This paper proposes a mathematical model aimed at deriving a histogram of the stress cycles, the accumulated damage and the fatigue life of slender vertical structures (e.g. towers, chimneys, poles and masts) in alongwind vibrations. The formulation, integrally in closed form, is based on a probabilistic counting cycle method inspired by narrow-band processes. An example illustrates the proposed procedure and shows, through the comparison with Monte Carlo simulations, the entity of the approximations involved by treating the response as narrow-banded instead of broad-banded
PREDICTION OF THE WIND-INDUCED FATIGUE OF SLENDER STRUCTURES
No full textA major shortcoming in the structural and wind engineering sectors concerns
wind-induced fatigue design and verification procedures. Despite wind-induced fatigue is a
critical phenomenon which may lead many slender structures to damage and collapses, suitable engineering and standards procedures are still fragmentary and almost lacking. Structural typologies sensitive to this problem are, for example, wind turbines, bridges, cranes, poles
and towers. A method was proposed by one of the authors, which allows to evaluate in closed
form the mean damage in the unit time induced by alongwind turbulence effect on steel slender structures or steel structural elements. The procedure is suitable for engineering calculations and code provisions. The present paper describes the more recent advance in
generalizing the procedure for determining the wind-induced fatigue damage of slender structures, taking into account simultaneous alongwind and crosswind structural responses due to
turbulence and discussing the main analytical features and the simplifying hypotheses adopted. The set of input parameters is coherent with standard format. An application of the proposed generalized procedure to a real case study is reported and discussed, showing the
capability of the proposed method to catch the main feature of the fatigue damage phenomenon with quite simple calculation procedure
Wind-induced fatigue collapse of real slender structures
No full textThis 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
Closed-Form Prediction of the Alongwind-Induced Fatigue of Structures
No full textWind‐induced fatigue is a crucial topic in the design of wind‐sensitive structures. In spite of this, methods proposed in literature are mainly addressed to research, or they are too much simplified for engineering applications. Thus, suitable engineering and standards procedures are almost totally lacking, this being a major shortcoming in structural and wind engineering. Starting from a closed form solution recently proposed by 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 formulae, referred to as the I and II level closed form solutions (CFS) are obtained and critically discussed with special concern for input parameters. The I level CFS implies three further simplifications joined together by the common aim of providing refined approximations of the reference target solution. The II level CFS implies three different simplifications joined together by the common aim of providing easy solutions on the safe side. This set of CFS are framed within a general procedure that any country or any society or any engineer can easily personalize to its own situation and requirement, this ranging from numerical tools up to manual engineering calculations and code provisions
The role of parameter uncertainties in the alongwind-induced fatigue damage prediction
No full textThe paper is part of a research project aimed at the probabilistic description of the fatigue life, suitable for risk analyses and safety evaluations. One of the authors of this paper has carried out many researches connected with the definition of the current wind distribution and with the probabilistic nature of the wind-excited response of structures deriving the distribution of the uncertainties in their evaluation. Starting from an analytical model of the fatigue analysis , this study identifies a set of input quantities which are described in terms of mean value and variance. Adopting a suitable uncertainty propagation technique, the paper discusses the influence of the selected parameters on the fatigue life evaluation
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