Section
3 Longitudinal strength
3.1 General
3.1.2 Longitudinal
strength calculations for the flooded conditions defined in Pt 4, Ch 7, 3.2 Hull vertical bending stresses for flooded conditions to Pt 4, Ch 7, 3.4 Flooded conditions are to be applied for bulk carriers which satsify all of the
following criteria:
- Single skin construction, or double skin construction where any
part of the longitudinal bulkhead is located within B/5 or 11,5 m,
whichever is less, inboard from the ship’s side at right angles
to the centreline at the assigned summer load line.
- Length, L, of 150 m or above.
- Intended for the carriage of cargoes having bulk densities of
1,0 tonne/m3 or above.
3.2 Hull vertical bending stresses for flooded conditions
3.2.1 The
maximum hull vertical bending stresses in the flooded condition at
deck, σDf, and keel, σBf, for use
in Pt 3, Ch 4 Longitudinal Strength are given by the following,
using the appropriate combination of bending moments to give sagging
and hogging stresses:
where
|
M
sf
|
= |
maximum still water bending moment in the flooded condition, in kN m,
at the section under consideration, see
Pt 4, Ch 7, 3.4 Flooded conditions
|
|
M
w
|
= |
design hull vertical wave bending moment, in kN m, as defined in
Pt 3, Ch 4, 5 Hull bending strength at the section under consideration |
|
Z
D,Z
B
|
= |
actual hull section moduli, in m3,
at strength deck and keel respectively, at the section under consideration.
|
3.3 Shear stresses for flooded conditions
3.3.1 The
shear stress, τAf, in the flooded condition to be used
in Pt 3, Ch 4, 6 Hull shear strength, is to be taken
as:
where
|
A
z
|
= |
the first moment, in cm3, about the neutral axis,
of the area of the effective longitudinal members between the vertical
level under consideration and the vertical extremity of the effective
longitudinal members, taken at the section under consideration
|
|
Q
sf
|
= |
maximum hull still water shear force, in kN, in the flooded
condition at the section under consideration |
|
Q
w
|
= |
design hull wave shear force, in kN, as defined in Pt 3, Ch 4, 6.3 Design wave shear force at the section under consideration |
|
I
|
= |
moment
of inertia of the hull about the horizontal neutral axis, in cm4,
at the longitudinal section under consideration
|
|
δi
|
= |
defined in Pt 3, Ch 4, 6.5 Permissible still water shear force. |
3.4 Flooded conditions
3.4.1 For the relevant loading conditions specified in Pt 3, Ch 4, 5.3 Design still water bending moments and Pt 3, Ch 4, 5.4 Minimum hull section modulus, each
cargo hold is to be considered individually flooded up to the equilibrium waterline. The
shear forces and still water bending moments are to be calculated for the most severe
flooded conditions which will significantly load the ship's structure. Harbour
conditions, docking conditions afloat, loading and unloading transitory conditions in
port and loading conditions encountered during ballast water exchange need not be
considered.
3.4.2 For self-unloading bulk carriers where the boundary of the conveyor space between the
bottom of the cargo hold and the top of the conveyor space is not watertight during
seagoing operations, the longitudinal strength in flooded conditions is to be considered
using the extent to which flooding can occur, i.e. both the conveyor space and the cargo
hold are to be assumed to be flooded. See
Pt 4, Ch 7, 3.4 Flooded conditions 3.4.1.
3.4.3 In calculating the weight of ingressed water into the cargo hold under
consideration, the permeabilities and bulk densities given in Table 7.3.1 Permeability and bulk density
factors are to be used.
Table 7.3.1 Permeability and bulk density
factors
| Hold condition
|
Permeability
(see Note 1)
|
Bulk
density
(tonne/m3)
|
| Empty cargo space
|
0,95
|
-
|
| Volume left in loaded cargo spaces
above any cargo
|
0,95
|
-
|
| Iron ore cargo
|
0,3
(see Note 2)
|
3,0
|
| Cement
|
0,3
(see Note 2)
|
1,3
|
Note
1. Bulk cargo permeability is defined as
the ratio of the voids within the cargo mass to the volume occupied by
the cargo.
Note
2. More specific information relating to
the bulk cargo may be used where available, but permeabilities are not
to be less than those given above.
Note
3. For packed cargo, the actual density
of the cargo is to be used with a permeability of zero.
|
3.4.4 In calculating the strength of the ship's structure in the flooded
condition it is to be assumed that the ship's structure will remain fully effective in
resisting the applied loads.
3.5 Additional requirements for ships not built to the IACS Common Structural Rules
3.5.1 Bulk Carriers not built to the IACS Common Structural Rules are to comply with the
requirements of this sub-section.
3.5.2 The safety factor with respect to lateral buckling of longitudinal ordinary
stiffeners required by Pt 3, Ch 4, 7.5 Scantling criteria 7.5.1 is to be
1,265 for the following areas:
- hatchway coaming
- inner bottom
- sloped stiffened panel of topside tanks and hopper tanks (if
any)
- inner side (if any)
- side shell (if directly bounding the cargo hold)
|