Common Structural Rules - Common Structural Rules for Bulk Carriers and Oil Tankers, January 2019 - Part 1 General Hull Requirements - Chapter 10 Other Structures - Section 4 Tanks Subject to Sloshing - 2 Scantling Requirements
2 Scantling Requirements
2.1 Plating
2.1.1 Net thickness
The net thickness of plating, t in mm, subjected to sloshing pressures is not to be less than:
where:
with coefficients defined in Table 1, but not to be taken greater than
Ca-max.
σhg : Hull girder bending stress, in N/mm2, corresponding to the greatest of the sagging and hogging bending moment in absolute value.
Pslh : The greater of Pslh-lng, Pslh-t or Pslh-min as specified in [1.3].
Table 1 : Definition β a, αa and Ca-max
| Acceptance criteria set |
Structural member |
βa |
αa |
Ca-max |
|
|---|---|---|---|---|---|
|
AC-S |
Longitudinal strength members in the cargo hold region including
but not limited to:
•
|
Longitudinally stiffened plating |
0.9 |
0.5 |
0.8 |
|
Transversely or vertically stiffened plating |
0.9 |
1.0 |
0.8 |
||
|
Other strength members including:
|
0.8 |
0 |
0.8 |
||
2.2 Stiffeners
2.2.1 Net section modulus
The net section modulus, Z in cm3, of stiffeners subjected to sloshing pressures is not to be less than:
where:
- fbdg = 12 for stiffeners fixed against rotation at each end. This is generally to be applied for scantlings of all continuous stiffeners.
- fbdg = 8 for stiffeners with one or both ends not fixed against rotation. This is generally to be applied to discontinuous stiffeners.
- For members subject to hull girder stress: coefficient to be taken as defined in Table 2.
- Cs= Cs-max for other cases.
Pslh : The greater of Pslh-ing, Pslh-t or Pslh-min as specified in [1.3].
Cs-max: Coefficient as defined in Table 3.
Table 2 : Permissible bending stress coefficient Cs
|
Sign of hull girder bending stress, σhg (1) |
Lateral pressure acting on(2) |
Stiffener boundary condition(3) |
fbdg |
Coefficient Cs |
|---|---|---|---|---|
|
Tension (positive) |
Stiffener side |
F- F |
12 |
but not to be taken greater than Cs-max |
|
F - S |
8 |
but not to be taken greater than Cs-max |
||
| S - S | 8 | Cs=Cs-max | ||
|
Plate side |
F- F | 12 | Cs=Cs-max | |
| F - S | 8 | Cs=Cs-max | ||
|
S - S |
8 |
but not to be taken greater than Cs-max |
||
|
Compression (negative) |
Stiffener side |
F- F | 12 | Cs=Cs-max |
| F - S | 8 | Cs=Cs-max | ||
|
S - S |
8 |
but not to be taken greater than Cs-max |
||
|
Plate side |
F - F |
12 |
but not to be taken greater than Cs-max |
|
|
F - S |
8 |
but not to be taken greater than Cs-max |
||
| S - S | 8 | Cs=Cs-max | ||
|
(1) σhg is to be considered for the hogging and sagging situations. (2) For primary supporting members located inside the considered tank and for wash bulkheads, the sloshing pressure is to be applied both on stiffener and plate sides. (3) F - F stands for both ends of the stiffener
fixed against rotation
|
||||
Table 3 : Definition β s, αs and Cs-max
| Acceptance criteria set |
Structural member |
βs |
αs |
Cs-max |
|
|---|---|---|---|---|---|
|
AC-S |
Longitudinal strength members in the cargo hold region including but
not limited to:
|
Longitudinal stiffeners |
0.85 |
1.0 |
0.75 |
|
Transverse or vertical stiffeners |
0.7 |
0 |
0.7 |
||
|
Other strength members including: • Stiffeners on transverse bulkheads. • Stiffeners on transverse stringers and web frames. • Stiffeners on tank boundaries and primary supporting members outside the cargo hold region. |
0.75 |
0 |
0.75 |
||
2.3 Primary supporting members
2.3.1 Web plating
The web plating net thickness of primary supporting members, t in mm, is not to be less than:
where:
Pslh : The greater of Pslh-Ing, Pslh-t, Pslh-wf, Pslh-grd and Pslh-min as specified in [1.3]. The pressure is to be calculated at the load application point, defined in Ch 3, Sec 7, [4.1], taking into account the distribution over the height of the member, as shown in Figure 1 and Figure 2.
Ca : Permissible plate bending stress coefficient, as given in [2.1.1].
2.3.2 Stiffeners on web plating
The net section modulus, Z in cm3, of each individual stiffener on the web plating of primary supporting members subjected to sloshing pressures is not to be less than:
where:
Pslh : The greater of Pslh-Ing, Pslh-t, Pslh-wf, Pslh-grd and Pslh-min as specified in [1.3]. The pressure is to be calculated at the load application point, defined in Ch 3, Sec 7, [3.2], taking into account the distribution over the height of the member, as shown in Figure 1 and Figure 2.
Cs : Permissible bending stress coefficient as given in [2.2.1].
fbdg : Bending moment factor as given in [2.2.1].
2.3.3 Tripping brackets supporting primary supporting members
The net section modulus, Z in cm3 in way of the base within the effective length, d, of tripping brackets and net shear area, Ashr in cm2, after deduction of cut-outs and slots, of tripping brackets supporting primary supporting members is not to be less than:
where:
Pslh : The greater of Pslh-Ing, Pslh-t, Pslh-wf, Pslh-grd and Pslh-min as specified in [1.3]. The average pressure may be calculated at mid point of the tripping bracket taking into account the distribution as shown Figure 1 and Figure 2.
strip : Mean spacing, between tripping brackets or other primary supporting members or bulkheads, in m.
h : Height of tripping bracket, see Figure 3, in m.
Cs : Permissible bending stress coefficient for tripping brackets to be taken as 0.75.
Ct : Permissible shear stress coefficient for tripping brackets to be taken as 0.75.
The effective breadth of the attached plate to be used for calculating the section modulus of the tripping bracket is to be taken as h/3.
Figure 3 : Effective length of tripping bracket
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