4.5.1.1 For integral tanks,
allowable stresses should normally be those given for hull structure
in Recognized Standards.
4.5.1.2 For membrane tanks,
reference is made to the requirements of 4.4.2.5.
4.5.1.3 For type A independent
tanks primarily constructed of plane surfaces, the stresses for primary
and secondary members (stiffeners, web frames, stringers, girders)
when calculated by classical analysis procedures should not exceed
the lower of R
m/2.66 or R
e/1.33
for carbon-manganese steels and aluminium alloys, where R
m and R
e are defined in 4.5.1.7. However, if detailed calculations
are carried out for the primary members, the equivalent stress σC as defined in 4.5.1.8 may
be increased over that indicated above to a stress acceptable to the
Administration; calculations should take into account the effects
of bending, shear, axial and torsional deformation as well as the
hull/cargo tank interaction forces due to the deflection of the double
bottom and cargo tank bottoms.
4.5.1.4 For type B independent
tanks, primarily constructed of bodies of revolution, the allowable
stresses should not exceed:
where
|
σm
|
= |
equivalent
primary general membrane stress |
|
σL
|
= |
equivalent
primary local membrane stress |
|
σb
|
= |
equivalent
primary bending stress |
|
f
|
= |
the
lesser of 
|
|
F
|
= |
= the lesser of 
|
with R
m and R
e as
defined in 4.5.1.7. With regard
to the stresses σm, σL and σb see also the definition of stress categories in 4.13. The values A, B, C and D should be shown on the International Certificate
of Fitness for the Carriage of Liquefied Gases in Bulk and should
have at least the following minimum values:
| Nickel steels and carbon-manganese steels
|
Austenitic steels
|
Aluminium alloys
|
|
A
|
3
|
3.5
|
4
|
|
B
|
2
|
1.6
|
1.5
|
|
C
|
3
|
3
|
3
|
|
D
|
1.5
|
1.5
|
1.5
|
4.5.1.5 For type B independent
tanks, primarily constructed of plane surfaces, the Administration
may require compliance with additional or other stress criteria.
4.5.1.6 For type C independent tanks the maximum allowable
membrane stress to be used in calculation according to 4.4.6.1.1 should be the lower of:
where:
- R
m and R
e are as defined in 4.5.1.7.
4.5.1.7 For the purpose of 4.5.1.3, 4.5.1.4 and 4.5.1.6 the following
apply:
- .1
-
|
R
e
|
= |
specified minimum yield stress at room temperature
(N/mm2). If the stress-strain curve does not show a defined
yield stress, the 0.2% proof stress applies. |
|
R
m
|
= |
specified minimum tensile strength at room temperature
(N/mm2). |
For welded connections in aluminium alloys the respective values of
R
e or R
m in annealed conditions should be used.
-
.2 The above properties should correspond to the
minimum specified mechanical properties of the material, including the weld metal
in the as-fabricated condition. Subject to special consideration by the
Administration, account may be taken of enhanced yield stress and tensile strength
at low temperature. The temperature on which the material properties are based
should be shown on the International Certificate of Fitness for the Carriage of
Liquefied Gases in Bulk provided for in 1.5.
4.5.1.8 The equivalent stress σC(von Mises, Huber) should be determined by:
where:
|
σx
|
= |
total
normal stress in x-direction |
|
σy
|
= |
total
normal stress in y-direction |
|
τxy
|
= |
total
shear stress in x-y plane. |
4.5.1.9 When the static and
dynamic stresses are calculated separately and unless other methods
of calculation are justified, the total stresses should be calculated
according to:
where:
|
σx·st, σy·stand τxy·st
|
= |
static stresses |
|
σx·dyn, σy·dyn and τxy·dyn
|
= |
dynamic stresses |
all determined separately from acceleration components and hull
strain components due to deflection and torsion.
4.5.1.10 For internal insulation
tanks, reference is made to the requirement of 4.4.7.2.
4.5.1.11 Allowable stresses
for materials other than those covered by chapter
6 should be subject to approval by the Administration in each
case.
4.5.1.12 Stresses may be
further limited by fatigue analysis, crack propagation analysis and
buckling criteria.