1. Seismic design for the wind turbine tower (WP1.5 background document presentation) Institute of Steel Structures Aristotle Univ. of Thessaloniki

2. Seismic design for the wind turbine tower Relevant Codes:  EC8-1 : Design of structures for earthquake resistance – General rules, seismic actions and rules for buildings  EC8-6 : Design of structures for earthquake resistance – Towers, masts and chimneys  GL Wind 2003 IV – Part 1

3. Seismic design for the wind turbine tower Methods of analysis:  Spectral response analysis is used (EC8.6 §3.2.2 & EC8.1 §3.2.2)‏  Lateral force method of analysis is not applicable (more than one modes are participating)‏  Time history analysis can be used supplementary for the verification of spectrum analysis results  Non linear static (pushover) analysis may be applied for verification purposes only (EC8.1 §4.3.3.4.2.1)‏

4. Seismic design for the wind turbine tower Earthquake motion representation  Represented by the “Elastic response spectrum”  Alternatively, the “Design spectrum” may be used (ductile behaviour of the structure)‏  Since wind is the dominant load case, “Elastic response spectrum” can be used  Translational spectra are taken into account  Rotational spectra are taken into account (EC8-6 §3.1) when: Structures taller than 80 m in regions where the peak ground acceleration exceeds the 25% of gravity acceleration Structures with height > 5 * max base dimension (pile foundations excluded) Combination of rotational component to the corresponding translational (SRSS method)  Foundation has to be modeled together with the tower for 2 nd order & soil-structure interaction effects (except erecting the towers on rock or very stiff soil).

5. Seismic design for the wind turbine tower Elastic spectrum

6. Seismic design for the wind turbine tower Elastic spectrum

7. Seismic design for the wind turbine tower Design spectrum

8. Seismic design for the wind turbine tower Combinations of seismic actions: The sum of the effective modal masses taken into account must amount to at least 90% of the total mass of the structure. Combination: SRSS method when combining independent vibration modes (Tmin <= 0.9*Tmax). Else more accurate combinations as CQC must be used. Combination of the horizontal & vertical components of the seismic excitation: