Loadbearing structures and detailed design - Concrete Structures for Wind Turbines - page 121

- In doing so, the composite structure consisting of foundation, tower and wind turbine
is considered in the three-dimensional turbulent wind field.
- Owing to the linear-elastic simulation, the dynamic actions are verified with the
partial safety factor g F ¼ 1.00.

- On the other hand, the verification of the cross-sections is carried out with partial
safety factors

g F 1.00 depending on the design load case group according

to [9].
- At the ultimate limit state, the increase in the internal forces as a result of non-linear
influences (e.g. second-order theory, cracked state) has to be taken into account
(quasi-static calculation with g F 1.00).

Details of the total dynamic analysis are described in Section 4.9.1.1.

4.5.2 Simpli ed analysis
A simplified analysis may only be carried out when resonance effects play only a minor
role, that is with the condition that the first natural frequency deviates by at least 10%
from the excitation due to the 1x rotational frequency of the rotor (see Campbell
diagram, Figure 4.7). Furthermore, the simplified analysis is characterised by the
following points:
- The collective loads resulting from the prior aeroelastic simulation calculations are
applied to the machinery/tower interface as actions.
- These and the other actions are considered as quasi-static actions, that is given
partial safety factors g F 1.00, depending on the design load case group according
to [9].
- At the ultimate limit state, the increase in the internal forces as a result of non-linear
influences (e.g. second-order theory, cracked state) has to be taken into account.

4.5.2.1 Sensitivity to vibration
Wind turbine towers should generally be classed as sensitive to vibration. In doing so
we must distinguish between wind-induced vibrations of the tower in the direction of
the wind and transverse to the direction of the wind.
Tower vibrations in the direction of the wind are taken into account as follows:
- Turbine not in operation
a) Applying the turbulent extreme wind speed model (EWM): internal forces
as a result of the average wind speed (10-min mean) are multiplied by the
gust response factor G according to DIN 1055-4 [12] annex C (see
Section 2.3.1).
b) Applying the steady extreme wind speed model (if the tower is not vulnerable
to vibration) with the internal forces as a result of the gust wind speed
(3 s average), but without the gust response factor G.
- Turbine in operation
The gust response does not need to be considered in this case.
Vortex-induced transverse vibrations are of minor significance in reinforced and
prestressed concrete towers and therefore may be ignored in most cases (see also