OS-C501
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Offshore Standard DNV-<strong>OS</strong>-<strong>C501</strong>, November 2013<br />
Sec.6 Failure mechanisms and design criteria – Page 121<br />
shall be performed as described in Sec.9 [11]. Reduction of mechanical properties due to local failure such as<br />
matrix cracking or delamination shall be taken into account.<br />
8.4.11 If the condition described in Sec.9 [11.2.5] is satisfied, the analysis may be performed without<br />
geometric non-linearity provided the load effect modelling factor is increased as specified. In such a case the<br />
geometrical imperfections must still be included.<br />
8.4.12 Sec.9 [11.2.4] provides an approximate way of estimating the combined influence of imperfections and<br />
in-plane or axial loading, based on the use of linear analysis.<br />
8.4.13 The calculated resistance is to be considered as a mean strength from a probabilistic point of view.<br />
8.4.14 Variability to the mean strength is introduced by:<br />
— uncertainties in the stiffness parameters that are used in the buckling calculations<br />
— uncertainties in geometric parameters<br />
— uncertainties in size of imperfections and how imperfections are considered.<br />
8.4.15 To reflect the uncertainty introduced by geometrical imperfections, the partial load effect model factor<br />
for checks on failure mechanisms referred to in [8.4.8] shall be based on a COV of 15% unless lower values<br />
can be justified.<br />
9 Displacements<br />
9.1 General<br />
9.1.1 Maximum displacements shall be defined as extreme values with a small probability of being exceeded<br />
and without uncertainties or tolerances associated with them. The following design criterion shall be fulfilled:<br />
where,<br />
d n<br />
d spec<br />
γ F<br />
γ Sd,<br />
γ .γ<br />
characteristic value of the local response of the structure (here displacement)<br />
specified requirement on maximum displacement<br />
partial load effect factor<br />
load model factor<br />
Displacements may also be defined as maximum strains, curvatures etc.<br />
d<br />
F Sd<br />
. <<br />
n<br />
9.1.2 Displacements shall be calculated as described in Sec.9 or shall be measured directly. A reduction of<br />
stiffness of the structure due to material non-linearity or due to time dependent effects on the elastic constants<br />
shall be considered. Plastic deformations due to permanent static or fatigue loads shall also be considered.<br />
9.1.3 The failure type (Sec.2 [3.4]) associated with a displacement requirement shall be decided on an<br />
individual basis.<br />
Guidance note:<br />
If the displacement requirement requires that:<br />
- the structure should never touch the neighbouring structure locally, the failure type would be brittle<br />
- the structure can touch the neighbouring structure locally at low loads, the failure type would be plastic<br />
- the structure can touch the neighbouring structure locally at loads that may cause some permanent damage the<br />
failure type would be ductile.<br />
If the structures may touch each other slightly, the corresponding loads and possible damage effects shall be analysed.<br />
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9.1.4 If the criterion is used in combination with a linear non-degraded analysis according to Sec.9 [2.4], all<br />
strains and stresses in fibre direction above the level to initiate matrix cracking shall be multiplied by the<br />
analysis factor γ a from Sec.9 [3.2].<br />
d<br />
spec<br />
DET NORSKE VERITAS AS