Environmental Engineering Reference
In-Depth Information
The flexural tension reserve - under the condition
e
pd
e
p0.1d
(see above) - gives us the
following maximum reserve for the bending moment that can be accommodated by the
cross-sectional area of prestressing steel:
D
M
p0d
Ds
p0d
A
p
r
p
=
2
where
A
p
total cross-sectional area of external tendons inside tower
r
p
radius of circumcircle of external tendons
All in all, it should be pointed out that with respect to ensuring adequate reserves of flexural
tension at the ultimate limit state, it is not a good idea to select an excessively high level of
prestress for the concentric tendons in the tower.
An example of a calculation for an antenna support structure can be found in
Beton-Kalender 2006 [8]. The tower for a wind turbine wouldbeanalysedina
similar way.
4.7.2 Linear analysis of internal forces
DIN 1045-1 [33] 8.6.1 stipulates that verifying the equilibrium state of loadbearing
structures with bar-type members or walls subjected to axial compression (and in
particular the equilibrium state of these members themselves taking into account the
effects of member deformations) is essential when deformations reduce the load-
carrying capacity by more than 10%.
By implication, this means that in all other cases the internal forces at the ultimate limit
state may be calculated using a linear analysis (to first-order theory), which in turn
means that the internal forces due to the individual independent actions may be
combined linearly according to the superposition principle [44].
This requirement is generally satisfied in power production.
The following applies to onshore wind turbines [9] for group N (normal and extreme),
or to offshore wind turbines [11] for groups N (normal), E (extreme) and T (transport/
erection):
E
d
¼
X
E
Gk
;
j
þ g
P
E
Pk
þ
X
j
1
g
G
;
j
i
1
g
Q
;
i
E
Qk
;
i
The normal wind profile model (NWP) is combined with a design wave for design load
case 1.15 (see Table 4.4). The following applies in particular for an explicit considera-
tion of the design load cases:
E
d
¼
X
h
i
j
1
g
G
;
j
E
Gk
;
j
þ
1
:
00
E
Pk
þ
1
:
20
E
QV
r
or V
out
Þ
þ
E
QH
s
ðÞ
or H
max
;
1
Þ
þ
Q
N
;
k
ð
ð
