Environmental Engineering Reference
In-Depth Information
4.6.5 Partial safety factors according to GL guideline
At the serviceability limit state the partial safety factors for all actions are
g
F
¼
1.00,
likewise at the fatigue limit state ([11] 4.3.7.2.2).
4.7
Ultimate limit state
4.7.1 Deformation calculations according to second-order theory
The internal forces for the tower and the foundation of a wind turbine are generally
calculated according to the following scheme for the ultimate limit state:
1. Conception of structural model according to Section 4.2 with imperfections.
The following must be taken into account according to DIBt guideline [9] 6.4.1:
a) Vertical misalignment as a result of fabrication and erection inaccuracies and
the influence of asymmetric solar irradiation:
w
a
¼
5mm
=
m or 0
:
005
b) Vertical misalignment as a result of differential settlement of the subsoil:
A differential settlement between the outer edges of the foundation amounting to
40mm or a vertical misalignment of the tower amounting to 3mm/m is a reasonable
value that can be assumed for standard calculations. The correctness of this
assumption should be confirmed by a soil mechanics specialist in individual cases.
2. Calculation of the internal forces for the tower and the foundation according to
second-order theory when the conditions stated in DIN 1045-1 [33] 8.6.1 apply (for
details see Section 3.1).
a) According to [33] 8.6.1 (6), the theoretical mean values are to be used for the
material strengths. According to [33] 8.5.1 (4), these amount to
8)
Concretes up to C 50/60:
f
cR
¼
0.85
a
f
ck
¼a
f
ck
/
g
Cm
¼a
f
ck
/1.20
Concretes grade C 55/67 and higher:
f
cR
¼
0
85
a
f
ck
=g
0
C
¼ a
f
ck
=ðg
Cm
g
0
C
Þ
¼ a
f
ck
=ð
1
:
20
g
0
C
Þ
:
Reinforcing steel:
f
yR
¼
1.1
f
yk
Prestressing steel:
f
p0.1R
¼
1.1
f
p0.1k
The member cross-sections (concrete dimensions, cross-sectional area of reinforc-
ing steel and, if applicable, prestressing steel) are to be designed in advance in such
a way that the uniform partial safety factor may not be lower than
g
R
¼
1.30
(groups N, E, F and T) or
g
RA
¼
1.10 (group A) according to [33] 8.5.1 (4) for the
design value of the ultimate resistance.
8)
According to [36], the additional partial safety factor
g
0
C
is unnecessary for high-strength
concretes.
