OS-C501

Offshore Standard DNV-OS-C501, November 2013
Sec.9 Structural analysis – Page 155
10.3.8 If core failure of type brittle occurs due to core fracture (in tension or compression), E core shall be
reduced to 0 (default value) or to a positive value as described in [10.3.11].
10.3.9 If core failure of type ductile or plastic occurs due to core shearing , G core * shall be set equal to the
secant modulus at the corresponding τ level; E core * shall be proportionally reduced by the same amount. If τˆcore
is reached, G core and E core shall be reduced to 0 (default value) or to positive values as described in [10.3.11].
10.3.10 If core failure of type brittle occurs due to core shearing, G core shall be reduced to 0 (default value) or
to a positive value as described in [10.3.11].
10.3.11 Instead of using the default value 0 for the parameters in [10.3.7]-[10.3.10], gradual degradation of the
material properties can be used, provided experiments document the validity of values larger than 0 for the
material used.
10.3.12 In numerical calculations certain problems arise, e.g. lack of inversion possibility of the structure
stiffness matrix, when setting degraded material properties equal to 0. Thus, one should apply small values, i.e.
1% of the non-degraded values, instead of 0.
10.3.13 If the non-linear behaviour of the core cannot be modelled properly, the core shall not be used beyond
its yield point and the yield criterion in Sec.6 shall be applied as the ultimate limit state for sandwich failure.
10.4 3-D progressive failure analysis
10.4.1 If the through thickness stresses and through width strains are significant, see [10.1.3], a 3-D
progressive analysis shall be carried out.
10.4.2 A similar progressive failure analysis as presented for monolithic structures in [2.3], shall be carried
out. However, failure mechanisms related to the core, see Sec.6 and [10.3], shall be included.
10.5 Long term damage considerations
10.5.1 The same progressive failure analysis as the one presented in [2.2] and [2.3] shall be carried out using
degraded (long-term) material properties as described in Sec.5 [3].
10.5.2 Degraded material properties shall be used in the calculations of stresses and strains and in the
determination of the strength used in the failure criteria.
11 Buckling
11.1 General
11.1.1 The need for special buckling analysis shall be assessed carefully in every case. In particular the
following aspects shall be considered in making this assessment:
— presence of axial compressive stresses in beam or column-type members or structural elements
— presence of in-plane compressive or shear stresses in flat, plate-like elements
— presence of in-plane compressive or shear stresses in shell-like elements.
11.1.2 Two alternative approaches may be used in analysing buckling problems:
— analysis of isolated components of standard type, such as beams, plates and shells of simple shape
— analysis of an entire structure (or of an entire, complex structural component).
11.2 Buckling analysis of isolated components
11.2.1 When a member or component that is a part of a larger structure is analysed separately a global analysis
of the structure shall be first applied to establish:
— the effective loading applied to the member/component by the adjoining structural parts
— the boundary conditions for the structural member, in terms of translational and rotational stiffness
components in all relevant directions.
11.2.2 For simple members or components standard formulae or tables may be used to estimate elastic critical
loads (P e ), critical stresses (σ e ) or critical strains (ε e ), and the corresponding elastic buckling mode shapes.
Alternatively these quantities may be calculated using analytical or numerical methods. It shall always be
checked that the buckling mode shape is consistent with the boundary conditions.
11.2.3 An assessment shall be made of the shape and size of initial, geometrical imperfections that may
influence the buckling behaviour of the member. Normally the most critical imperfection shape for a given
buckling mode has a similar form to the buckling mode itself. However, any geometrical feature (including
DET NORSKE VERITAS AS