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DNV-OS-C201 Structural Design of Offshore Units (WSD method) |
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| Sec.6: Section Scantlings |
| — | plate thicknesses and local strength of panels |
| — | simple girders |
| — | calculations of complex girder systems. |
| tm | = | 7 mm for primary structural elements |
| = | 5 mm for secondary structural elements | |
| fy | = | minimum yield stress in N/mm2, defined in Sec.4 Table D1. |
| ka | = | correction factor for aspect ratio of plate field | |
| = | (1.1 - 0.25 s/l)2 | ||
| maximum 1.0 for s/l = 0.4 | |||
| minimum 0.72 for s/l = 1.0 | |||
| s | = | stiffener spacing in m, measured along the plating | |
| p | = | lateral pressure in kN/m2 as given in Sec.3 D | |
| sp1 | = | permissible bending stress (N/mm2), taken as the smaller of: | |
| 1.3 (sp-sj) and sp = h0 fy | |||
| sj | = | equivalent stress for global in-plane
membrane stress
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| h0 | = | basic usage factor, see Sec.2 Table E1 | |
| fy | = | minimum yield strength, see Sec.4 Table D1 | |
| kpp | = | fixation parameter for plate | |
| = | 1.0 for clamped edges | ||
| = | 0.5 for simply supported edges. | ||
Guidance note: ---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
The design bending stress sp1 is
given as a bi-linear capacity curve for the plate representing the
remaining capacity of plate when reduced for global in-plane membrane
stress.
| l | = | stiffener span in m |
| km | = | bending moment factor, see Table C1 |
| sp2 | = | permissible bending stress dependent on the type of loading condition, see Sec.2 D100 |
| = | 0.6 fy - sj (N/mm2) for loading condition a) | |
| = | 0.8 fy - sj (N/mm2) for loading condition b) | |
| kps | = | fixation parameter for stiffeners |
| = | 1.0 if at least one end is clamped | |
| = | 0.9 if both ends are simply supported. |
Guidance note: ---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
The section modulus Zs will
typically be calculated for plate side and stiffener flange side.
The permissible bending stress sp2 for plate side is given as
a linear capacity curve for the plate representing the remaining
capacity of plate when reduced for global in-plane membrane stress
(longitudinal, transverse and shear stresses).
The permissible bending stress for stiffener flange side is
given as a linear capacity curve for the stiffener flange representing
the remaining capacity of stiffener when reduced for global longitudinal
membrane stress.
| j | = | angle between the stiffener web plane and the plane perpendicular to the plating. |
In such cases the section modulus of the stiffener calculated as indicated in 401 is normally to be based on the following parameter values:
| km | = | 8 |
| kps | = | 0.9 |
The stiffeners should normally be snipped to an angle of maximum 30°.
Guidance note: ---e-n-d---o-f---G-u-i-d-a-n-c-e---n-o-t-e---
For typical sniped end details as described above, a stress
range lower than 30 MPa can be considered as small dynamic stress.
| Ce | = | parameter given in Fig.1 for various numbers of evenly spaced point loads (Np) on the girder span |
| b | = | full breadth of plate flange in m, e.g. span
of the supported stiffeners, or distance between girders, see also 602. |
| l0 | = | distance between points of zero bending moments in m |
| = | Sg for simply supported girders | |
| = | 0.6 Sg for girders fixed at both ends | |
| Sg | = | girder span as if simply supported, see 602. |
Fig. 1 Graphs for the effective flange parameter C
| — | section modulus according to 602 |
| — | web area according to 603. |
| Sg | = | girder span in m. The web height of in-plane girders may be deducted. When bracket(s) are fitted at the end(s), the girder span Sg may be reduced by two thirds of the bracket arm length(s), provided the girder end(s) may be assumed clamped and provided the section modulus at the bracketed end(s) is satisfactory. |
| b | = | breadth of load area in m (plate flange), b may be determined as: |
| = | 0.5 (l1 + l2) where l1 and l2 are the spans of the supported stiffeners on both sides of the girder, respectively, or distance between girders | |
| km | = | bending moment factor km-values in accordance with 605 |
| sp2 | = | bending stress, see B401. |
| kt | = | shear force factor, see 605 |
| Ns | = | number of stiffeners between considered section and nearest support. The Ns-value shall in no case be taken greater than (Np + 1)/4 |
| Np | = | number of supported stiffeners on the girder span |
| Pp | = | average "point load" (kN) from stiffeners between considered section and nearest support |
| tp | = | 0.39 fy (N/mm2) for loading condition a) |
| = | 0.46 fy (N/mm2) for loading condition b). |
| sp2 | = | 0.91 fy (N/mm2) in 602 |
| tp | = | 0.5 fy (N/mm2) in 603. |
Sec.6 C
| Table C1 Values of km and kt | ||||||||||||||||||||||||||||||||||||||||||||||||||
| Load and boundary conditions | Bending moment and shear force
factors | Positions | 1 | km1 kt1 2 | km2 - 3 | km3 kt3 1 | Support 2 | Field 3 | Support
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12 | 0.5 24 | 12 | 0.5
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- | 0.38 14.2 | 8 | 0.63
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- | 0.5 8 | - | 0.5
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15 | 0.3 23.3 | 10 | 0.7
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- | 0.2 16.8 | 7.5 | 0.8
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- | 0.33 7.8 | - | 0.67 | ||||||||||||||||||
| — | shear area variation, e.g. due to cut-outs |
| — | moment of inertia variation |
| — | effective flange |
| — | lateral buckling of girder flanges. |
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