DNV-OS-C102 Structural Design of Offshore Ships

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App.A: Conversion of Tanker to Floating Offshore Installation

DNV-OS-C102 Structural Design of Offshore Ships

App.B: Longitudinal Strength according to the LRFD Method

APPENDIX B
Longitudinal Strength according to the LRFD Method

App.B
A. Introduction

App.B
A 100 General

App.B A
101   This appendix explains the Load and Resistance Factor Design (LRFD) method. This method may be used for the strength check instead of the Working Stress Method (WSD) as described in Sec.5 C.

App.B A
102   Using the LRFD method will replace the a) and b) combinations given in Sec.3 Table C1. Transit condition shall comply with the requirements to longitudinal strength (Pt.3 Ch.1 Sec.5) in Rules for Classification of Ships and the extreme condition will be similar to the WSD method as the load factor and material factor of 1.0 shall be used.

App.B A
103   According to the LRFD format, see DNV-OS-C101, two sets of partial coefficient combinations shall be analysed. These combinations are referred to as the a) and b) combinations, see Table B1.

App.B A
104   The material factor to be used in the longitudinal strength assessment of the hull girder is 1.15.

App.B A
105   The capacity assessment in the longitudinal strength condition shall include buckling and yield checks.

App.B A
106   Buckling capacity checks shall be performed in accordance with Sec.5 C500.

App.B
B. Hull Girder Longitudinal Strength

App.B
B 100 Hull girder bending and shear checks

App.B B
101 The hull girder bending and shear capacity in the operating conditions shall be checked according to B200 and B300. The capacity checks are based on the two equations below:

raster

Where:
M_g	=	characteristic bending moment resistance of the hull girder
M_S	=	characteristic design still water bending moment based on actual cargo and ballast conditions
M_w	=	characteristic wave bending moment based on an annual probability of exceedance of 10^-2
Q_g	=	characteristic shear resistance of a longitudinal shear element in the hull girder
Q_S	=	characteristic design still water shear force in the longitudinal shear element based on actual cargo and ballast conditions
Q_W	=	characteristic wave shear force in the longitudinal shear element based on an annual probability of exceedance of 10^-2
g_m	=	material factor
g_f,G,Q	=	partial load factor for still water loads (permanent + variable functional loads)
g_f,E	=	partial load factor for environmental loads.

Guidance note:
Typical longitudinal shear elements are unit's side, inner side and longitudinal bulkheads that contribute to the global shear capacity of the hull girder. Each of such elements should be considered separately subjected to the shear force in the element.

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App.B B
102 The partial load coefficients for assessment of global capacity are given in Table B1.

App.B B
Table B1 Partial coefficients for the longitudinal strength
Combination Load category
Still water loads Environmental loads
a) 1.2 0.7
b) 1.0 1.15

App.B B
103   The environmental loads for hull girder global response are mainly wave induced loads. Other environmental loads may normally be neglected.

App.B B
104   The dimensioning condition for different M_w/M_s ratios is shown in Figure 1. Offshore units also complying with the main class requirements will typically have M_w/M_s ratios of 1.4 to 1.6. In such cases the b) combination is dimensioning.

App.B B
105   Combination a) need not be assessed for the hull girder capacity if:

raster

Guidance note:
Note that the M_s in the equations given above include the global effect of top side loads.

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raster

Fig. 1 Dimensioning combination

App.B
B 200 Hull girder yield check

App.B B
201 The global hull and main girder system nominal stresses derived from direct strength calculations shall comply with the yield criteria given below:

for survival conditions (100 years return period for environmental loads)

s_e	=	nominal equivalent stress
g_m	=	material factor = 1.15
f_y	=	yield stress of the material

App.B
B 300 Hull girder buckling capacity

App.B B
301 Hull girder buckling capacity shall be determined according to the principles given in Sec.5 C600 using a usage factor of:

raster , where g_m = 1.15

App.B B
302 All stresses and pressure shall be based on an annual probability of exceedance of 10^-2.

App.B B
303 The ultimate buckling capacity of each stiffened panel shall be determined according to DNV-RP-C201 Buckling Strength Analysis.

Table B1 Partial coefficients for the longitudinal strength
Combination	Load category
Combination	Still water loads	Environmental loads
a)	1.2	0.7
b)	1.0	1.15

DNV-OS-C102 Structural Design of Offshore Ships

APPENDIX B Longitudinal Strength according to the LRFD Method

App.B A. Introduction

App.BA 100 General

App.B B. Hull Girder Longitudinal Strength

App.BB 100 Hull girder bending and shear checks

App.BB 200 Hull girder yield check

App.BB 300 Hull girder buckling capacity

APPENDIX B
Longitudinal Strength according to the LRFD Method

App.B
A. Introduction

App.B
A 100 General

App.B
B. Hull Girder Longitudinal Strength

App.B
B 100 Hull girder bending and shear checks

App.B
B 200 Hull girder yield check

App.B
B 300 Hull girder buckling capacity