3.6.1 GeneralTransverse vertically corrugated watertight bulkheads are generally
to be fitted with a lower stool and an upper stool below the deck.
The corrugation angle shown in Fig 1 is to be not less than 55°.
3.6.2 Span of corrugationsThe span lC of the corrugations (to be used for carrying out the strength checks according to Pt B, Ch 7, Sec 2 or Pt B, Ch 8, Sec 4, as the case may be) is to be taken as the distance shown in Fig 2. For the definition of lC, the internal end of the upper stool may not be taken at a distance from the deck at centreline greater than:
3.6.3 Lower stoolThe lower stool is to have a height in general not less
than 3 times the depth of the corrugations.
The thickness and material of the stool top plate are to be not less than those required for the bulkhead plating above. The thickness and material properties of the upper portion of vertical or sloping stool side plating within the depth equal to the corrugation flange width from the stool top are to be not less than the required flange plate thickness and material to meet the bulkhead stiffness requirement at the lower end of corrugation.
The ends of stool side ordinary stiffeners are to be attached to brackets at the upper and lower ends of the stool.
The distance from the edge of the stool top plate to the surface of the corrugation flange is to be in accordance with Fig 3.
The stool bottom is to be installed in line with double bottom floors and is to have a width not less than 2,5 times the mean depth of the corrugation.
The stool is to be fitted with diaphragms in line with the longitudinal double bottom girders for effective support of the corrugated bulkhead. Scallops in the brackets and diaphragms in way of the connections to the stool top plate are to be avoided.
Where corrugations are cut at the lower stool, the weld connections of corrugations and stool side plating to the stool top plate are to be in accordance with [7.1]. The weld connections of stool side plating and supporting floors to the inner bottom plating are to be in accordance with [7.1].
3.6.4 Upper stoolThe upper stool is to have a height in general between
2 and 3 times the depth of corrugations. Rectangular stools are
to have a height in general equal to twice the depth of corrugations,
measured from the deck level and at the hatch side girder.
The width of the upper stool bottom plate is generally to be the same as that of the lower stool top plate. The stool top of non-rectangular stools is to have a width not less than twice the depth of corrugations.
The thickness and material of the stool bottom plate are to be the same as those of the bulkhead plating below. The thickness of the lower portion of stool side plating is to be not less than 80% of that required for the upper part of the bulkhead plating where the same material is used.
The ends of stool side ordinary stiffeners are to be attached to brackets at the upper and lower end of the stool.
The stool is to be fitted with diaphragms in line with and effectively attached to longitudinal deck girders extending to the hatch end coaming girders for effective support of the corrugated bulkhead. Scallops in the brackets and diaphragms in way of the connection to the stool bottom plate are to be avoided.
3.6.5 AlignmentStool side plating is to align with the corrugation flanges; lower stool side vertical stiffeners and their brackets in the stool are to align with the inner bottom longitudinals to provide appropriate load transmission between these stiffening members. Lower stool side plating may not be knuckled anywhere between the inner bottom plating and the stool top plate.
3.6.6 Effective width of
the compression flangeThe effective width of the corrugation flange to be considered
for the strength check of the bulkhead is to be obtained, in m,
from the following formula:
bEF = CE A
|CE||:||Coefficient to be taken equal to: |
|b||:||Coefficient to be taken equal to:|
|A||:||Width, in m, of the corrugation flange (see Fig 1)|
|tf||:||Net flange thickness, in mm|
|ReH||:||Minimum yield stress, in N/mm2, of the flange material, defined in Pt B, Ch 4, Sec 1, .|
3.6.7 Effective shedder platesEffective shedder plates are those which:
3.6.8 Effective gusset platesEffective gusset plates are those which:
3.6.9 Section modulus at
the lower end of corrugations
Except in case e), if the corrugation webs are not supported by local brackets below the stool top plate in the lower part, the section modulus of the corrugations is to be calculated considering the corrugation webs 30% effective.
Provided that effective shedder plates, as defined in [3.6.7], are fitted (see Fig 4 and Fig 5), when calculating the section modulus of corrugations at the lower end (sections 1 in Fig 4 and Fig 5), the area of flange plates may be increased by the value obtained, in cm2, from the following formula:
without being taken greater than 2,5 A tF ,
A : Width, in m, of the corrugation flange (see Fig 1) tSH : Net shedder plate thickness, in mm tF : Net flange thickness, in mm.
Provided that effective gusset plates, as defined in [3.6.8], are fitted (see Fig 6 to Fig 8), when calculating the section modulus of corrugations at the lower end (cross-sections 1 in Fig 6 to Fig 8), the area of flange plates may be increased by the value obtained, in cm2, from the following formula:
IG = 7 hG tF
hG : Height, in m, of gusset plates (see Fig 6 to Fig 8),
to be taken not greater than (10/7)SGU SGU : Width, in m, of gusset plates tF : Net flange thickness, in mm, based on the as-built condition.
Sloping stool top plate
If the corrugation webs are welded to a sloping stool top plate which has an angle not less than 45° with the horizontal plane, the section modulus of the corrugations may be calculated considering the corrugation webs fully effective. For angles less than 45°, the effectiveness of the web may be obtained by linear interpolation between 30% for 0° and 100% for 45°.
Where effective gusset plates are fitted, when calculating the section modulus of corrugations the area of flange plates may be increased as specified in d) above. No credit may be given to shedder plates only.
3.6.10 Section modulus at sections other than the lower end of corrugationsThe section modulus is to be calculated with the corrugation webs considered effective and the compression flange having an effective flange width, bEF , not larger than that obtained in [3.6.6].
3.6.11 Shear areaThe shear area is to be reduced in order to account for possible non-perpendicularity between the corrugation webs and flanges. In general, the reduced shear area may be obtained by multiplying the web sectional area by (sin ), being the angle between the web and the flange (see Fig 1).