For tanks of this type the following applies:
-
.1 The effects of all dynamic and static loads should
be used to determine the suitability of the structure with respect to:
plastic deformation
buckling
fatigue failure
crack propagation.
Statistical wave load analysis in accordance with 4.3.4,
finite element analysis or similar methods and fracture mechanics analysis or an
equivalent approach, should be carried out.
-
.2 A three-dimensional analysis should be carried out
to evaluate the stress levels contributed by the ship's hull. The model for this
analyses should include the cargo tank with its supporting and keying system as
well as a reasonable part of the hull.
-
.3 A complete analysis of the particular ship
accelerations and motions in irregular waves and of the response of the ship and
its cargo tanks to these forces and motions should be performed unless these data
are available from similar ships.
-
.4 A buckling analysis should consider the maximum
construction tolerances.
-
.5 Where deemed necessary by the Administration,
model tests may be required to determine stress concentration factors and fatigue
life of structural elements.
-
.6 The cumulative effect of the fatigue load should
comply with:
- where:
|
n
i
|
= |
number of stress cycles at each stress level during the life
of the ship |
|
N
i
|
= |
number of cycles to fracture for the respective stress level
according to the Wöhler (S-N) curve |
|
N
j
|
= |
number of cycles to fracture for the fatigue loads due to
loading and unloading |
- C
w should be less than or equal to 0.5, except that the
Administration may give special consideration to the use of a value greater
than 0.5 but not greater than 1.0, dependent on the test procedure and data
used to establish the Wöhler (S-N) curve.