Damage Evaluation and Control for Fatigue under Stochastic Excitation

In this paper we consider the problem of fatigue damage arising on light alloy space frame towers subjected to wind induced vibration during the service lifetime. In order to mitigate the fatigue damage, a passive control technique is proposed, based on the implementation of viscoelastic dampers. A full stochastic formulation is adopted for wind loading, vibration calculation and fatigue analysis. Among the many methods available in the literature for fatigue analysis, the Rayleigh method is selected for calculations. However, some comparisons made with the Rainflow algorithm show that in order to achieve an unbiased life evaluation, the intrinsic error of the Rayleigh approximation must be accounted for with a numerical calibration. The obtained results show that aluminum lattice towers may be very sensitive to fatigue problem. In this paper a design procedure is outlined that allows to estimate the expected fatigue life of the structure and to assess the optimal damping ratio required in order to extend the structure service lifetime.