Environmental Engineering Reference
In-Depth Information
Fig. 4.15 Safety analysis according to normative regulations
4.6.3.2 Combined sea state and wind
According to the applicable normative regulations, the design situations are investi-
gated for the limit states to be verified by combining all independent actions linearly
with the help of partial safety factors. The actions due to sea state and wind are
determined independently of each other (Figure 4.15).
Using statistically evaluated measurements (e.g. measured at FINO-1) as a basis, an
ongoing research project [62] is aiming to determine adapted extreme value distribu-
tions and the critical statistical influencing parameters for the actions due to sea state
and wind. On the one hand, the aim is to consider the directional dependence, on the
other, the correlation between wind and sea state.
A distinction is necessary here (see Section 4.6.2):
- There is a strong correlation between the significant wave height H
s
and the dynamic
pressure q
ref
dependent on the 10-min average of the wind speed V
ref
.Alinear
combination may be considered as a conservative approximation.
- There is only a weak correlation between the maximum wave height (H
max
) and the
peak dynamic pressure q
gust
averaged over a gust duration of 2-4 s. A non-
conservative approximation would be to consider this as actions not dependent
on stochastics.
This results in the following combination rules (with partial safety factors
g
H
and
g
W
plus combination factors
c
W
and
c
H
for sea state and wind):
a) E
1
(H, q)
¼g
H
E(H
max
)
þg
W
[E (q
ref
)
þc
W
E(q
gust
q
ref
)]
b) E
2
(q, H)
¼g
W
E(q
gust
)
þg
H
[E (H
s
)
þc
H
E(H
max
H
s
)]
