OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.3 Design input – Page 33
S
S
S s
S s1
S s2
t
t
S
S
S s1
S s
S s2
t 1 t 2
t
t
S
S s1
t
S s2
t 1 t 2
Figure 3-2
Examples of division into time intervals and definition of the sustained values S si for different load
effects.
9.6 The fatigue load effects
9.6.1 All load effect fluctuations, e.g. stress or strain fluctuations, imposed during the entire design life, shall
be taken into account when determining the long-term distribution of stress or strain ranges. All phases shall
be included and both low-cycle fatigue and high-cycle fatigue shall be considered.
9.6.2 Fatigue may be analysed for load effects in terms of either stress or strain. Strain is preferred for
composite laminates.
9.6.3 The characteristic distribution of load effect amplitudes shall be taken as the expected distribution of
amplitudes determined from available data representative for all relevant loads. This is a long-term distribution
with a total number of stress/strain cycles equal to the expected number of stress/strain cycles over a reference
period such as the design life of the structure.
9.6.4 For fatigue analysis the mean and amplitude of the stress or strain fluctuations shall be specified.
Basically a table of the following form given in Table 3-3 should be established.
Table 3-3 Definition of fatigue loads
Number of cycles Mean load Amplitude
DET NORSKE VERITAS AS