PSI - Issue 78

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

1864

1. Introduction As global demand for clean and sustainable energy continues to rise, the wind energy sector is playing an increasingly critical role in meeting these needs. Research led by the National Renewable Energy Laboratory (NREL) has significantly advanced wind turbine technology, with recent developments focusing on deploying larger Wind Turbine Generators (WTGs) to improve energy efficiency (Fiestas et al., 2025). However, this trend toward larger structures brings increased structural vibrations and stress transmission, underscoring the importance of ensuring adequate protection against both wind and earthquake loads. Despite this need, seismic design provisions for wind turbines remain limited and are not yet formally codified in most regulatory standards (Rostami & Tombari, 2023). Previously, seismic actions were considered secondary in wind turbine design. However, the rapid expansion of wind farms in seismically active regions has emphasized the necessity of robust seismic risk assessment and earthquake resistant design, even in the absence of widespread seismic damage reports (Martinez-Vazquez et al., 2017). As turbine densities increase, so does the potential for significant cumulative risk, making it imperative to incorporate seismic considerations into modern WTG infrastructure planning. To mitigate structural responses under dynamic loads, researchers have explored a wide range of passive control devices. These include Tuned Mass Dampers (TMDs) (Zhang et al., 2016), Tuned Liquid Dampers (TLDs) (Murtagh et al., 2005), Tuned Liquid Column Dampers (TLCDs) (Hemmati et al., 2019; Riascos et al., 2016), and Pendulum TMDs (Chapain & Aly, 2021). A notable contribution by Di Paolo et al. (Di Paolo et al., 2021) introduced a Rotational Friction Damper (RFD) at the tower base, enhancing energy dissipation and reducing base moments. More recently, studies by (Sorge et al., 2023, 2024) (Sorge et al., 2025) evaluated the Hinge-Spring-Friction Device (HSFD) as a passive system for mitigating wind-induced vibrations. Given the increasing installation of WTGs in seismic zones, it is essential to develop control strategies that address both wind and earthquake effects. This study proposes a methodology to optimize the mechanical characteristics of the HSFD, focusing on base moment reduction and device rotation under both service-level wind and seismic conditions. The system will be evaluated under two configurations: (i) a single rated wind load and (ii) seven combined wind-earthquake load cases. The paper is structured as follows: Section 2 introduces the control system, Section 3 describes load characterization, Section 4 presents the design and results, and Section 5 concludes with key findings and future directions. 2. Structural Control for a WTG The HSFD functions as a passive base-isolation joint for WTGs. As shown in Figure 1(b), the mechanism integrates a bearing joint with a circumferential array of pre-compressed springs that furnish a global rotational stiffness and promote recentring once dynamic actions subside. Acting in parallel, multiple friction pads deliver an overturning resistance idealised by a lumped friction moment , , thereby dissipating vibratory energy. Under minor excitations the assembly remains locked, and the tower behaves as a fixed-base cantilever; however, when the external demand exceeds the static friction threshold, the device allows a controlled base rotation ( ) . This self-regulating response caps the transfer of bending demand to both the tower shaft and its foundation, effectively saturating the stress state during extreme loading events.