Transcript Preliminary structural model for the wind tower

Seismic design
for the wind turbine tower
(WP1.5 background document presentation)
Institute of Steel Structures
Aristotle Univ. of Thessaloniki
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
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)
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 2nd order & soil-structure
interaction effects (except erecting the towers on rock or very stiff soil).
Seismic design for the wind turbine tower
Elastic spectrum
Seismic design for the wind turbine tower
Elastic spectrum
Seismic design for the wind turbine tower
Design spectrum
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: