[A] Hull Girder Ultimate Strength

1.2.1.2 The magnitudes of the partial safety factors in Section 9/1.4 have been calibrated for this single step method.
DRAFT – OCTOBER 05
©American Bureau of Shipping, Det Norske Veritas and Lloyd’s Register 2005
The hull girder ultimate bending moment capacity, MU, is defined as the maximum bending capacity of the hull girder beyond which the hull will collapse. Hull girder failure is controlled by buckling, ultimate strength and yielding of longitudinal structural elements.
κ
=
θ l
Where: θ
l
the relative angle rotation of the two neighbouring crosssections at transverse frame positions
the transverse frame spacing, i.e. span of longitudinals
net area of the stiffened deck panel, in m2
ultimate capacity of stiffened deck panel, in N/mm2. To be calculated for each stiffened panel using:
• the advanced buckling analysis method, see Section 10/4
MU = Zredσ yd ⋅ 103 kNm
Where: Zred Ired
Aeff
Anet50 σU
σyd zdk-mean zNA-red
reduced section modulus of deck (to the mean deck height)
=
I red
z − z dk−mean
NA−red
vertical distance to the mean deck height, taken as the mean of the deck at side and the deck at centre line, measured from the baseline, in m
failure modes of all main longitudinal structural elements. For tankers, in sagging,
the critical mode is generally inter-frame buckling of deck structures, as shown in F STRUCTURAL RULES FOR OIL TANKERS
2 CALCULATION OF HULL GIRDER ULTIMATE CAPACITY
2.1 Single Step Ultimate Capacity Method
2.1.1 Procedure
2.1.1.1
The single step procedure for calculation of the sagging hull girder ultimate bending capacity is a simplified method based on a reduced hull girder bending stiffness accounting for buckling of the deck, see Figure A.2.1. The hull girder ultimate bending moment capacity, MU, is to be taken as:
1.1.1.2
The sagging hull girder ultimate capacity of a hull girder section, is defined as the
maximum value on the static non-linear bending moment-curvature relationship M-κ, see Figure A.1.1. The curve represents the progressive collapse behaviour of
hull girder under vertical bending.
Figure A.1.1 Bending Moment - Curvature Curve M-κ
M
MU
κ
1.1.1.3 The curvature of the critical inter-frame section,κ, is defined as:
1.3.1.2
Structures compressed beyond their buckling limit have reduced load carrying capacity. All relevant failure modes for individual structural elements, such as: plate buckling, torsional stiffener buckling, stiffener web buckling, lateral or global stiffener buckling; and their interactions, are to be considered in order to identify the weakest inter-frame failure mode.
m3
reduced hull girder moment of inertia, in m4. The inertia is to be calculated in accordance with Section 8/1.2.2.1, using:
• a hull girder net thickness of tnet50 for all longitudinally effective members
1.2 Application
1.2.1 General
1.2.1.1 The sagging hull girder ultimate bending capacity is to be assessed by the single step procedure described in Sub-Section 2. This is only applicable to longitudinally framed double hull tankers in the sagging bending condition.
APPENDIX A.1/PAGE 1
APPENDIX A - HULL GIRDER ULTIMATE STRENGTH
COMMON STRUCTURAL RULES FOR OIL TANKERS
1.3 Assumptions
1.3.1 General
1.3.1.1
The method for calculating the ultimate hull girder capacity is to identify the critical
DRAFT – OCTOBER 05
©American Bureau of Shipping, Det Norske Veritas and Lloyd’s Register 2005
APPENDIX A.1/PAGE 2
APPENDIX A - HULL GIRDER ULTIMATE STRENGTH
• the net thicknesses tnet50
specified minimum yield stress of material, in N/mm2, for
deck structure applied in determining hull girder section modulus, see Section 8/1.2.3
that is effectively able to be stressed to yield:
=
σU σ yd
Anet 50
m2
Note
The effective area of deck girders is to be taken as the net area of the girders using a thickness of tnet50.
Figure A.1.2 Ship in Extreme Sagging Inter-Frame Buckling Failure
θ Buckled region
M
M
1.4 Alternative Methods
1.4.1 General
1.4.1.1 Principals for alternative methods for the calculation of the hull girder ultimate
bending capacity; e.g. incremental-iterative procedure and non-linear finite element analysis, are given in Sub-Section 3.
1.4.1.2