COMMON STRUCTURAL RULES FOR BULK CARRIERS BACKGROUND DOCUMENT

PAGE 16 CHAPTER 4: DESIGN LOADS

COMMON STRUCTURAL RULES FOR BULK CARRIERS
SECTION 5 EXTERNAL PRESSURES
1 EXTERNAL PRESSURES ON SIDE SHELL AND BOTTOM
1.1 General
1.1.1
1.1.1.a External pressure used for strength assessment and structural analysis is the total
pressure (p) equal to the sum of the hydrostatic pressure (p
S
) at the position of the
member being examined and the wave pressure (p
W
).
1.1.1.b The wave pressure may be a negative pressure as explained in 1.3, 1.4, and 1.5.
However, the total pressure (p) is not to be taken as a negative value.
1.1.1.c The maximum value from the simplified formulae specified in 1.3, 1.4, and 1.5 is
assigned a value equivalent to the maximum value of wave pressure (long-term
prediction value corresponding to the exceedance probability level of 10
-8
).
1.2 Hydrostatic pressure
1.2.1
1.2.1.a The hydrostatic pressure equivalent to static pressure in various loading conditions
to be studied in still water is considered.
1.3 Hydrodynamic pressures for load cases H1, H2, F1 and F2
1.3.1
1.3.1.a The distribution of wave pressure corresponding to 4 load cases (H1, H2, F1, and
F2) is the distribution in equivalent design waves H and F at which vertical wave
bending becomes maximum. The wave pressure is obtained by multiplying the
response function RAO of wave pressure in equivalent design wave at which the
vertical wave bending moment at midship specified in Section 4 becomes maximum,
by the regular wave height of equivalent design wave of the corresponding
dominant load component.
1.3.1.b The wavelength at which the amplitude of the wave pressure at the centerline of
midship generated in head seas becomes maximum is practically the same as the
wavelength when the vertical wave bending moment becomes maximum. When the
wave pressure at the centerline of midship becomes maximum, the wave pressure
at another location in the same cross section also becomes nearly maximum, and the
phase is almost the same.
1.3.1.c The nonlinear influence coefficient of 0.9 is considered based on the results of model
tank tests for the wave pressure for load cases H1, H2, F1, and F2 at the exceedance
probability level of 10
-8
.
1.4 Hydrodynamic pressures for load cases R1 and R2
1.4.1
1.4.1.a The distribution of wave pressure for load cases R1 and R2 is the distribution in
equivalent design wave R at which the rolling ship motion becomes maximum.
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COMMON STRUCTURAL RULES FOR BULK CARRIERS
1.4.1.b The distribution of wave pressure comprises the fluctuating part of the hydrostatic
pressure from the roll angle (asymmetric component; first term of the formula
specified in 1.4.1, Sec. 5, Ch. 4 of the Rules) and the fluctuating part due to heave
(asymmetric part; 2
nd
term of the formula above).
1.4.1.c A nonlinear influence coefficient of 0.8 is considered for the wave pressure for load
cases R1 and R2 at the exceedance probability level of 10
-8
.
1.5 Hydrodynamic pressure for load cases P1 and P2
1.5.1
1.5.1.a The distribution of wave pressure for load cases P1 and P2 is the distribution of
equivalent design wave P at which the wave pressure at midship becomes
maximum.
1.5.1.b A nonlinear influence coefficient of 0.65 is considered for the wave pressure for load
cases P1 and P2 at the exceedance probability level of 10
-8
.
1.6 Correction to hydrodynamic pressures
1.6.1
1.6.1.a When the wave pressure at the waterline becomes positive (load cases H1, H2, F2,
R1, R2 and P1), the wave pressure at the waterline is converted to head of sea water
and the wave pressure above the waterline is assumed to occur linearly (inclination
of 45 degrees) up to the converted water head position.
1.6.1.b When the wave pressure at the waterline becomes negative (load cases H1, H2, F1,
R1, R2 and P2), the wave pressure below the waterline is taken as the sum of the
wave pressure and the hydrostatic pressure that does not become negative.
2 EXTERNAL PRESSURES ON EXPOSED DECKS
2.1 General
2.1.1
2.1.1.a The pressures specified in 2.2 and 2.3 must be considered regardless of the existence
of water breakers installed on the exposed deck.
2.2 Load cases H1, H2, F1 and F2
2.2.1
2.2.1.a The external pressure p
D
, at any point on the exposed deck for load cases H1, H2, F1
and F2 in head seas and following seas is estimated by the pressure (p
W
) acting on
the exposed deck specified in the LL Convention (or IACS UR S21) and the pressure
coefficient for the exposed deck (, coefficient depending on height of deck
which becomes smaller as the height of deck increases).
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COMMON STRUCTURAL RULES FOR BULK CARRIERS
2.3 Load cases R1, R2, P1, and P2
2.3.1
2.3.1.a The external pressure p
D
at any point on the exposed deck for load cases R1, R2, P1
and P2 in beam seas is estimated using the wave pressure at the side shell position
on the exposed deck described in 1.4, 1.5, and 1.6 (the larger of the values from the
port side and the starboard side is taken), the pressure coefficient () at the exposed
deck and the considered position z.
2.4 Loads carried on exposed deck
2.4.1 Pressure due to distributed load
2.4.1.a When the exposed deck is loaded with distributed cargo load (such as lumber, etc.),
the static and dynamic loads due to such cargo should be considered.
2.4.2 Concentrated forces due to unit load
2.4.2.a When unit load is carried on the exposed deck (such as outfitting items), the static
and dynamic forces due to this unit load must be considered.
3 EXTERNAL PRESSURES ON SUPERSTRUCTURES AND DECKHOUSES
3.1 Exposed decks
3.1.1
3.1.1.a External pressures on exposed deck specified in 2also apply to the exposed decks of
superstructure and deckhouses. However, the external pressures and those
specified in 3.2, 3.3, and 3.4 apply only to the scantling requirements of members
specified in Section 4, Chapter 9.
3.2 Exposed wheel house tops
3.2.1
3.2.1.a The pressure p acting on the tops of exposed wheelhouse is taken as 2.5 kN/m
2
and
greater.
3.3 Sides of superstructures
3.3.1
3.3.1.a The pressure acting on the sides of superstructure is estimated according to the
longitudinal position and height of the location in the superstructure.
3.4 Superstructure end bulkheads and deckhouse walls
3.4.1
3.4.1.a The pressure acting on the superstructure bulkheads and deckhouse walls is
calculated according to the longitudinal position and height on the bulkhead (wall).
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COMMON STRUCTURAL RULES FOR BULK CARRIERS
4 PRESSURE IN BOW AREA
4.1 Bow flare area pressure
4.1.1
4.1.1.a This calculation formula has been corrected to attain consistency with GL Rules
calculation formula that assumes the sea conditions in CSR.
This slamming pressure is applicable only to the scantling requirements of members
specified in 4., Section 1, Chapter 9.
4.2 Design bottom slamming pressure
4.2.1
4.2.1.a This slamming pressure is applicable only to the scantling requirements of specified
members. This calculation formula has been corrected to attain consistency with the
GL Rules calculation formula that assumes the sea conditions in CSR.
4.2.2
4.2.2.a To limit the slamming loads at acceptable level, the smallest design ballast draught
at forward perpendicular should only be undercut in cases where bottom slamming
is not expected.
5 EXTERNAL PRESSURES ON HATCH COVERS
5.1 General
5.1.1
5.1.1.a When cargo is loaded on hatch covers, the static and dynamic loads due to the
loaded cargo are specified in 2.5 according to the type of cargo.
5.2 Wave pressure
5.2.1
5.2.1.a The wave pressure on hatch covers is basically estimated by calculating the pressure
acting on the exposed deck specified in 2.2.1 (according to the regulations of the LL
Convention or IACS UR S21). This wave pressure is applicable only to scantling
requirements of members of hatch covers specified in 4., Section 5, Chapter 9.