Environmental Engineering Reference
In-Depth Information
Section 4.3.2). Their effects are calculated according to DIN 1055-4 [12] annex D if the
critical wind speed v
crit
causes relevant resonance effects.
4.5.2.2 Vibration damping
Resonance effects are minimised by damping measures. The total damping
d
is applied
according to DIN 1055-4 annex D [12] as follows:
d ¼ d
s
þ d
a
where
d
s
logarithmic damping decrement of structural damping
d
a
logarithmic damping decrement of aerodynamic damping
It is possible to use the values of the DIBt guideline [9] as an alternative:
a) Structural damping for concrete towers
d
s
¼
0
:
04
b) Aerodynamic damping for concrete towers
d
s
¼
0
:
06
ð
This includes the influence of the rotor blades
!Þ
The aerodynamic damping
d
a
may not be used in connection with action effects due to
vortex-induced transverse vibrations!
4.5.3 Design load cases according to DIBt guideline (onshore)
The design load cases are defined in Tables 4.1 and 4.2.
4.5.3.1 Critical design load cases
The design load cases of groups N (normal and extreme), A (accidental) and T
(transport and erection) must be investigated separately for strength and stability
failure. The internal forces must be assessed in a non-linear analysis according to
second-order theory (for deformation analysis see Sections 3.4 and 4.7.1). Analyses
must be carried out with the most unfavourable of all design load cases for groups N, A
and T. DIN 1045-1 [33] must be used when designing reinforced and prestressed
concrete structures.
When it comes to checking fatigue failure, only those design load case groups
designated with F (fatigue) need to be investigated. In doing so, the actions of the
individual operating conditions are to be accumulated. Difference from DIN 1045-1
[33]: according to the DIBt guideline [9], the fatigue analysis is to be carried out in line
with CEB-FIP Model Code 1990 (DAfStb No. 439 [49]). A detailed analysis of the
concrete is unnecessary when the “simplified analysis” of the DIBt guideline [9] is
adhered to.
