MAIN ASPECTS RELATED TO THE DESIGN OF STEEL WIND TURBINES

An eco-friendly alternative to non-renewable energy sources, such as oil, to produce electrical energy, is certainly represented by the wind farms. Wind farms consist of a series of towers, or vertical elements, generally made of steel, whose dimensions are really important: they can reach 100 meters in height and, in the case of tubular towers, the diameter can exceed 3 meters. Although the structural scheme is quite simple (cantilever beam with concentrated mass on top) their design hides many issues, not always known to those approaching these structures for the first time, which if neglected can lead to very dangerous effects. The dynamic actions acting on steel wind towers cause a limitation of the fatigue life of the construction details which, if not adequately designed, will show the classic signs of premature deterioration (e.g. cracks on welds). The foundations are very different case to case, depending on the considered wind turbines. Onshore steel turbines are generally realized employing hollow circular steel profiles presents a unique huge reinforced concrete foundation with eventually the adjunction of piles. In this case, it can be underlined that these enormous concrete foundations are particularly hard to dispose of once the steel tower is removed. The following paper presents the main aspects to be checked in the design of these structures, providing a minimum framework in the estimation of structural safety. Furthermore, one chapter is also dedicated to the problem of structure-rotor resonance which leads to the total block of the entire system. Along with the problem itself, some mitigation strategies are also presented. The reported steel wind tower can be considered as representative of many solutions already installed both in Italy and abroad.