Fatigue analysis of on-shore wind turbine towers

Abstract

A procedure for estimation of fatigue lives of bolts in flange connections of tubular steel wind turbine towers is developed in this research. The procedure includes numerical calculation of aerodynamic forces, and finite element modeling of the bolted connection. Changes of wind variables are taken into consideration by representative values which are obtained from their probability density functions which are calibrated by wind measurements in the field. Bolt stress time-series calculated numerically and measured by sensors are in agreement in the aspects of fatigue damage and power spectra. The amount of fatigue damage experienced by a bolt is greatly affected by its position in the connection. This procedure uses a limited number of loading cases that represent the long-term variability of the wind parameters, and therefore it requires a reasonable computation effort. Moreover, the influence of reduction of bolt preload on the fatigue damage expe rienced by the bolts is evaluated. Results of finite element analyses are used for fatigue calculations. According to the results of this study, loss of bolt preload increases the stress ranges, and consequently increases the fatigue damage. However, this effect is more significant as the bolt preload is reduced to 25 % of the design value.