PSI - Issue 78

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

1867

3.2. Earthquake load (E) The seismic response of the NREL 5 MW WTG was evaluated by analyzing the data collected at the installation site in Avellino, Italy (latitude 41°1′22.2′′ , longitude of 15°17′35.2′′ ). This region has both high wind energy deployment and a notable seismic hazard. A total of seven ground motion records were selected for the purpose of this study, with the selection process conducted using the REXEL v.3.5 software (Iervolino et al., 2010). This selection process was undertaken in compliance with the provisions set out in the NTC2018 (Norme Tecniche per Le Costruzioni, 2018) and (Eurocode 8, 2005) for performance-based seismic design. The design conditions stipulated a service life of 50 years, importance class IV, and a 10% probability of exceedance, corresponding to a return period of 949 years. Local site conditions were defined as topography category T1 and ground type C. The target spectrum was defined with 5% damping, and selected records were scaled to fall within 90–130% of the target spectrum across the range between 1 =0.2 0 and 2 =2 0 , where the fundamental period 0 =3.57 . For practicality, 2 was fixed at 4 s. Table 2 presents key metadata of the selected records, including country, station, event date, propagation direction, magnitude, scale factor, and duration. All records exhibit peak ground acceleration (PGA) values around 0.55 g.

Table 2. List of earthquakes compatible with the design spectral target.

ID Event

Country

Station

Date

Direction

Magnitude [-]

Factor

Duration

Scale [-]

[seconds]

1 2 3 4 5 6 7

Duzce Alkion

Turkey Greece Turkey Greece Turkey Turkey Turkey

ST553 ST121 ST271 ST122 ST549 ST271 ST772

12/11/1999 24/02/1981 01/10/1995 24/02/1981 27/06/1998 01/10/1995 17/08/1999

E-W N-S N-S N-S E-W E-W N-S

7.2 6.6 6.4 6.6 6.3 6.4 7.6 6.7

0.82 1.82 1.54 1.45 1.55 1.31 1.41 1.41

41.9 25.9 27.7 36.9 29.2 28.0

Dinar

Alkion Adana

Dinar Izmit

135.8

Mean

46.5

As illustrated in Figure. 3 (a), the time history envelope of the scaled records highlights the variability among events, with Record ID 1 showing the largest acceleration. The Figure. 3 (b) comparison of individual response spectra shows that the average spectrum (blue line) closely matches the target spectrum (red line) within the defined period range.

(a) (b) Figure 3. Seismic data overview: (a) envelopment of data records and record with ID 1, and (b) spectral portrayal.

4. WTG response under W+E load A fundamental step in the seismic design of WTGs is the combination of wind and earthquake effects. In practice, the peak base moment caused by wind alone, , is combined with the peak base moment induced by the earthquake