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DNV-OS-C103 Structural Design of Column Stabilised Units (LRFD method)
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Sec.5
A. General
Sec.5
A 100 General
Sec.5 A
101 General requirements for the fatigue limit states are given
in DNV-OS-C101 Sec.6. Guidance concerning fatigue calculations are
given in DNV-RP-C203.
Sec.5 A
102 Units intended to follow normal inspection requirements according
to class requirements, i.e. 5 yearly inspection in sheltered waters
or drydock, may apply a Design Fatigue Factor (DFF) of 1.0.
Sec.5 A
103 Units intended to stay on location for prolonged survey period,
i.e. without planned sheltered water inspection, shall comply with
the requirements given in Appendix A.
Sec.5 A
104 The design fatigue life of the unit shall be minimum 20 years.
Sec.5 A
105 The fatigue capacity of converted units will be considered
on a case-by-case basis, and is a function of the following parameters:| — | results and findings form surveys
and assessment of critical details |
| — | service history of the unit and estimated remaining
fatigue life. |
Guidance note:
New structural steel on converted units older than 10 years,
may normally be accepted with minimum 15 years documented fatigue
life from the time of conversion.---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
Sec.5 A
106 Local effects, e.g. due to:| — | slamming |
| — | sloshing |
| — | vortex shedding |
| — | dynamic pressures |
| — | mooring and riser systems. |
shall be included in the fatigue damage assessment when relevant.
Sec.5 A
107 In the assessment of fatigue resistance, relevant consideration
shall be given to the effects of stress concentrations including
those occurring as a result of:
| — | fabrication tolerances, including
due regard to tolerances in way of connections involved in mating
sequences or section joints |
| — | cut-outs |
| — | details at connections of structural sections, e.g.
cut-outs to facilitate construction welding |
| — | attachments. |
Sec.5 A
108 Local detailed finite element analysis of critical connections,
e.g. pontoon and pontoon, pontoon and column, column and deck and
brace connections, should be undertaken in order to identify local
stress distributions, appropriate SCF's, and/or extrapolated
stresses to be utilised in the fatigue evaluation. Dynamic stress
variations through the plate thickness shall be checked and considered
in such evaluations, see DNV-RP-C203, for further details.
Sec.5 A
109 For well known details the local finite element analysis may
be omitted, provided relevant information regarding SCF are available.
Sec.5 A
110 Principal stresses, see DNV-RP-C203 Sec.2.2, should be applied
in the evaluation of fatigue responses.
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