1,721,068 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
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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
Dynamic crosswind fatigue of slender vertical structures
No full textWind-excited vibrations of slender structures can induce fatigue damage and cause structural failure without exceeding ultimate limit state. Unfortunately, the growing importance of this problem is coupled with an evident lack of simple calculation criteria. This paper proposes a mathematical method for evaluating the crosswind fatigue of slender vertical structures, which represents the dual formulation of a parallel method that the authors recently developed with regard to alongwind vibrations. It takes into account the probability distribution of the mean wind velocity at the structural site. The aerodynamic crosswind actions on the stationary structure are caused by the vortex shedding and by the lateral turbulence, both schematised by spectral models. The structural response in the small displacement regime is expressed in closed form by considering only the contribution of the first vibration mode. The stress cycle counting is based on a probabilistic method for narrow-band processes and leads to analytical formulae of the stress cycles histogram, of the accumulated damage and of the fatigue life. The extension of this procedure to take into account aeroelastic vibrations due to lock-in is carried out by means of ESDU method. The examples point out the great importance of vortex shedding and especially of lock-in concerning fatigu
Closed form solution of the alongwind-induced fatigue damage to structures
No full textWind-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
Equivalent static wind actions on vertical structures
No full textSince 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
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