PSI - Issue 78

Ettore Sorge et al. / Procedia Structural Integrity 78 (2026) 1863–1870

1869

lasts only marginally longer than one-minute, appreciable free vibration persists well after the strong-motion window, indicating limited intrinsic damping. When the HSFD is engaged (Figure. 5b), the corresponding extrema are curtailed to +208 MN·m and – 73 MN·m, equating to a base-moment reduction of approximately 52 %. This improvement is obtained despite the multi-hazard, dynamic environment characteristic of modern 5-MW WTGs. The results substantiate the HSFD’s capacity to suppress both peak and residual responses, thereby extending structural longevity and reliability under combined wind – earthquake excitation.

Figure 5. Time history of the WTG (a) and WTG-HSFD (b) systems.

5. Conclusions This study establishes a benchmark for multi-hazard design of utility-scale wind turbines by proving that a purpose tuned Hinge-Spring-Friction Device (HSFD) can simultaneously mitigate wind- and earthquake-induced demands without compromising day-to-day energy production. Through 63 coupled simulations that combined seven turbulent, rated-wind records with seven spectrum-compatible earthquakes representative of the Avellino site, the optimized HSFD consistently reduced peak base moments by ≈52 %. Furthermore, the HSFD performance suggests tangible gains in fatigue life, reduced cumulative damage, and shorter inspection outages after extreme events. Equally significant is the clarification of load-combination practice. The results confirm that widely used uncoupled SRSS formulations underestimate demand, whereas the linear rule recommended in IEC 61400-1, with a 0.75 interaction factor, reproduces fully coupled responses with acceptable conservatism. Operationally, the HSFD behaves as a “smart” passive joint: it remains locked under minor disturbances, yields and dissipates energy during strong transients, and then self-recenters — offering a low-maintenance, fail-safe alternative to active or semi-active controls often deemed impractical for remote wind-farm settings. Because the mechanism is modular, retrofitting existing towers or scaling to forthcoming platforms is straightforward; only the spring stiffness and friction capacity require re-optimization for the conditions of the WTG. Acknowledgements The authors acknowledge the support of the ReLUIS 2024-26 project for having financed this research, in the framework of the work package No. 15 “Isolation and dissipation devices and systems”. References

Asareh, M. A., Schonberg, W., & Volz, J. 2016a. Effects of seismic and aerodynamic load interaction on structural dynamic response of multi megawatt utility scale horizontal axis wind turbines. Renewable Energy , 86 , 49 – 58. https://doi.org/10.1016/J.RENENE.2015.07.098