OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.2 Design philosophy and design principles – Page 23
3.6.13 The load model factors depend on the method used for the structural analysis. See Sec.8 [3] and Sec.9
[12].
3.6.14 The resistance model factors depend on the uncertainties in the material strength properties caused by
manufacturing, installation and degradation. See Sec.8 [2].
3.7 Structural Reliability Analysis
3.7.1 As an alternative to design according to the LRFD format specified and used in this Standard, a
recognised Structural Reliability Analysis (SRA) based design method in compliance with Classification Note
No. 30.6 “Structural Reliability Analysis of Marine Structures” or ISO 2394 may be applied provided it can be
documented that the approach provides adequate safety for familiar cases as indicated in this Standard.
3.7.2 The Structural Reliability Analysis is to be performed by suitably qualified personnel.
3.7.3 As far as possible, target reliabilities are to be calibrated against identical or similar designs that are
known to have adequate safety. If this is not feasible, the target reliability is to be based on the limit state
category, the failure type and the Safety or Service Class as given in Table 2-3 and Table 2-4.
Table 2-3 Target annual failure probabilities P FT
Failure consequence
Failure type
LOW
NORMAL
HIGH SAFETY CLASS
SAFETY CLASS SAFETY CLASS
Ductile failure type (e.g. as for steel)
P F = 10 -3 P F = 10 -4 P F = 10 -5
Brittle failure type
(basis case for composite) P F = 10 -4 P F = 10 -5 P F = 10 -6
Table 2-4 Target reliabilities in the SLS expressed in terms of annual
probability of failure
SERVICE CLASS
SERVICE FAILURES
Normal 10 -3
High 10 -4
4 Design approach
4.1 Approaches
4.1.1 The structure can be designed according to three different approaches:
— An analytical approach, i.e. the stress/strain levels at all relevant parts of the structures including the
interfaces and joints are determined by means of a stress analyses (e.g. a FEM-analyses, see Sec.9) and
compared with the relevant data on the mechanical strength.
— Design by component testing only, i.e. full scale or scaled down samples of the structure or parts of the
structure are tested under relevant conditions (see Sec.10) such that the characteristic strength of the
complete structure can be determined.
— A combination of an analytical approach and testing, i.e. the same approach specified in Sec.10 for
updating in combination with full scale component testing.
4.1.2 The structure shall be designed such that none of the failure mechanisms, identified in the design analysis
(see Sec.3 and Sec.6), will occur for any of the design cases specified in Sec.3. The design against each
individual failure mechanism can be checked with the help of one of the three approaches mentioned in [4.1.1].
4.2 Analytical approach
4.2.1 The level of all stress (strain) components in all relevant areas of the structure, including stress
concentrations, shall be determined according to Sec.9.
4.2.2 Failure criteria and safety factors are applied to the load effects, i.e., the local stresses or strains.
4.2.3 The analysis provides the link between load and load effect. If non-linear effects change the mean,
distribution type and COV of the load effect relative to the load itself, the properties of the load effect shall be
used to determine safety factors.
4.2.4 The partial factors in Sec.8 shall be used.
DET NORSKE VERITAS AS