Reliability-based fatigue design of wind-turbine rotor blades

A probabilistic model for analysis of the safety of a wind-turbine rotor blade against fatigue failure in flapwise bending is presented. The model is based on a Miner's rule approach to cumulative damage and capitalizes on a conventional S-N curve formulation for fatigue resistance in conjunction with a new 'distorted Weibull' distribution for representation of wind-induced bending moment ranges. The model accounts for inherent variability and statistical uncertainty in load and resistance, and model uncertainties are also included. The model is applied to an analysis of the reliability of a site-specific wind turbine of a prescribed make. A 20-year design lifetime is considered. The probability of fatigue failure in flapwise bending of the rotor blade is calculated by means of a first-order reliability method. It is demonstrated how the reliability analysis results can be used to calibrate partial safety factors for load and resistance for use in conventional deterministic fatigue design. (C) 1999 Elsevier Science Ltd. Ail rights reserved.