Reliability-based design of wind-turbine rotor blades against failure in ultimate loading

A probabilistic model for analysis of the safety of a wind-turbine rotor blade against failure in ultimate loading is presented. Only failure in flapwise bending during the normal operating condition of the wind turbine is considered. The model is based on an extreme-value analysis of the load response process in conjunction with a stochastic representation of the governing tensile strength of the rotor blade material. The model is applied to an analysis of the reliability of a site-specific wind turbine of a prescribed make. A 20 yr design life is considered. The probability of failure in flapwise bending of the rotor blade is calculated by means of a first-order reliability method, and contributions to this probability from all local maxima of the load response process over the operational life are integrated. 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 design.