Appendices 
99 
Note: 
For verifications concerning the cyclic loads pertaining to deep foundations that are mainly 
subject to axial loading, it is sufficient to calculate loads for a 50 year cycle: 
• Both in the case of a simplified marginal value analysis of the load range, resp. the load am 
plitudes, according to the criteria described in EA-Pfahle as a result of the limiting value 
criterion: F’ zyk < 10% of R k 
• As well as in an explicit verification control process because the loads during the 100 year 
cycle would otherwise be considered twofold, namely first in the form of a degradation of 
the deep foundation and then as a decisive effect within the scope of the verification control 
process. 
In the case of the verification control process for heavyweight foundations, this is different in 
so far as the extreme event is only considered once in the verification control process. In this 
connection, the reduction of the shear strength as a result of the accumulation of pore water 
pressure during the design storm shall be determined. The load spectrum shall then be accor 
dingly verified. 
The determination of the wave distribution during the design storm (wave height and period 
with the respective number of cycles) is conducted using statistical extreme value distribu 
tions (e.g. Rayleigh distributions). A stress spectrum that is appropriately quantified for foun 
dation elements can be determined by establishing the chronological progression of the foun 
dation loads for the varying wave heights between the phases of significant wave height at the 
beginning and the end of the storm, and the maximum wave height during the strong wind 
phase. For offshore stations, a five-hour strong wind phase shall be considered, whereby the 
ULS incident is to be integrated into the stress spectrum of the design storm. 
In order to establish the wave distribution and achieve a simplified determination of the stress 
spectrum, the distribution according to Hansteen may be consulted for locations in the North 
Sea as represented by Andersen [1]. The result of transferring a Hansteen distribution related 
to a five-hour strong wind phase (Table 1) to a five-phase storm event of 35 hours duration 
according to [1] is, in the case of an ascending and descending arrangement of the standar 
dised wave heights that are determined for each of the phases of storm, a distribution of the 
standardised wave height and the load on the foundation elements that is standardised with 
regard to the extreme load as it is shown in Figure 3-I.3. The standardised wave height is the 
ratio of the wave height to the significant wave height during the strong wind phase. 
For further information, please refer to Andersen [1].