Environmental Engineering Reference
In-Depth Information
5.4 Extreme load cases
The main parameter resulting from the natural frequency check is the pile diameter.
For the part of the support structure that is submerged, the diameter determines the
hydrodynamic loads: waves and currents. The extreme load cases on an offshore
wind turbine and the soil reaction to support those loads are shown in Fig. 31.
The rest of the loads are aerodynamic loads on the turbine and the tower. The
combinations of these loads under different conditions are prescribed in the design
standards. To take the probability of occurrence into account, several load combi-
nations are prescribed: maximum 50-year wave load combined with a reduced
50-year gust event and the reduced maximum 50-year wave load combined with
the full 50-year gust. An overview of load combinations is shown in Table 3.
5.5 Foundation design
Now that the global structural dimension and the design load cases are known, the
foundation design can be detailed.
Wind
=
Waves
+
Current
Soil
F soil
Figure 31: Extreme load cases on the offshore wind turbine and the soil reaction
to support those loads.
Table 3: Load combinations [ 3 ].
Environmental load type and return period to defi ne
characteristic value of corresponding load effect
Water
level
Limit
state
Load
combination
Wind
Waves
Current
Ice
ULS
1
50 years
5 years
5 years
50 years
2
5 years
50 years
5 years
50 years
3
5 years
5 years
50 years
50 years
4
5 years
5 years
50 years
5
50 years
5 years
50 years
 
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