Section 5 Design loading
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Ships, July 2022 - Part 3 Ship Structures (General) - Chapter 3 Structural Design - Section 5 Design loading

Section 5 Design loading

Parent topic: Chapter 3 Structural Design

5.1 General

5.1.1 This Section contains the design heads/pressures to be used in the derivation of scantlings for decks, tank tops and transverse bulkheads. These are given in Table 3.5.1 Design heads and permissible cargo loadings.

Table 3.5.1 Design heads and permissible cargo loadings

Structural item and position Component Standard stowage rate C, in m3/tonne Design loading p, in kN/m2 Equivalent design head h i in metres Permissible cargo loading in kN/m2 Equivalent permissible head, in metres
Design heads and permissible cargo loadings (SI units)
Weather deck (general cargo)       h 1    
(a) Loading for minimum scantlings            
Forward of 0,075L from F.P. Beams and longitudinals 1,39 12,73 1,8 8,5 1,2
Primary structure 29,64 + 14,41E 4,2 + 2,04E
Between 0,12L and 0,075L from F.P. Beams and longitudinals 1,39 10,61 1,5 8,5 1,2
Primary structure 22,59 + 14,41E 3,2 + 2,04E
Aft of 0,12L from F.P. Beams and longitudinals 1,39 8,5 + 14,41E 1,2 + 2,04E 8,5 1,2
Primary structure
(b) Specified cargo loading            
Forward of 0,075L from F.P. Beams and longitudinals 1,39 2,47p a + 14,41E or as (a),
whichever is larger

(Note 1)

 0,35p a + 2,04E

(Note 1)


 p a 0,14p a
Primary structure 3,5p a + 14,41E or as (a),
whichever is larger

(Note 1)

 0,5p a + 2,04E

(Note 1)

    
Between 0,12L and 0,075L from F.P. Beams and longitudinals 1,39 1,98p a + 14,41E or as (a),
whichever is larger

(Note 1)

0,28p a + 2,04E

(Note 1)

    
Primary structure 2,67p a + 14,41E or as (a),
whichever is larger

(Note 1)

0,38p a + 2,04E

(Note 1)

 p a 0,14p a
Aft of 0,12L from F.P. Beams and longitudinals 1,39 p a + 14,41E

(Note 1)

0,14p a + 2,04E

(Note 1)

 p a 0,14p a
Primary structure
Cargo decks       h 2    
General cargo (standard loads) All structure 1,39 7,07H td H td 7,07H td H td
Special cargo (specified loads) C p a
p a
Machinery space, workshop and stores 1,39 18,37 2,6 - -
Ship stores 1,39 14,14 2,0 - -
Accomodation decks
(clear of tanks) 		All structure 1,39 8,5 h 3 - -
1,2
Superstructure decks (Note 2)       h 3    
1st tier Beams and longitudinals — — 0,9 Where the deck is exposed to the weather, add 2,04E — —
2nd tier 0,6
3rd tier and above 0,45
Decks forming crown of tunnels and deep tanks Plating and stiffeners C
h 4 — —
h
where h = ½ height of stand pipe above crown
(c) Bulk carrier (see Pt 3, Ch 3, 1.1 Application 1.1.3) with topside tanks              
Weather deck outside line of hatchways in way of cargo hold region, when topside tanks empty Beams and longitudinals 1,39 — — 7,06h h = the lesser of
(i) 0,22B
(ii)
where
W b = weight of water ballast in the topside tank per frame space, in kN
A = Corresponding area, (m2), of deck in way over one hold frame space
Primary Structure 1,39 — —
Cargo hatch covers (standard loading)       h H    
Steel cover Webs, stiffeners and plating 1,39 7,07H td H td 7,07H td H td
Wood cover — 1,39 — — 7,07H td H td
Inner bottom       H    
Ship without heavy cargo notation Plating and stiffeners 1,39 — — 9,82T 1,39T
Ship with heavy cargo notation C but ≤ 0,865
H
H
Watertight bulkheads Plating and stiffeners 0,975 10,07h 4 h 4 from Fig 3.5.2 — —
Deep tank bulkhead Plating and stiffeners C but ≤ 0,975 h 4 from Fig 3.5.2 — —

Note 1. In the case of beams and longitudinals, the equivalent design head is to be used in conjunction with the appropriate formulæ.

Note 2. For forecastle decks forward of 0,12L from F.P., see Weather decks.

Note 3. For hatch covers of non-CSR bulk carriers, ore carriers and combination carriers, see Pt 4, Ch 7, 12 Steel hatch covers.

Note 4. For hatch covers of ship types excluding non-CSR bulk carriers, ore carriers and combination carriers, see Pt 3, Ch 11, 2 Steel hatch covers.

Note 5. For pontoon hatch covers, see Pt 3, Ch 11, 2.17 Pontoon covers.

5.2 Symbols

5.2.1 The symbols used in this Section are defined as follows:

L, L pp, C b, B, D and T as defined in Pt 3, Ch 1, 6.1 Principal particulars

h i = appropriate design head, in metres
e = span of stiffener
p = design loading, in kN/m2
p a = applied loading, in kN/m2
C = stowage rate, in m3/tonne
= generally
= volume of the hold, in m3 excluding the volume contained within the depth of the cargo hatchway, divided by the weight of cargo, in tonnes, stowed in the hold, for inner bottom
E = correction factor for height of platform
= , but not less than zero nor more than 0,147
H = height from tank top to deck at side, in metres
H c = 'tween deck height measured vertically on the centreline of the ship from 'tween deck to underside of hatch cover stiffeners on deck above, in metres
H td = cargo head in 'tween deck, in metres, as defined in Figure 3.5.1 Heads for 'tween decks.

Figure 3.5.1 Heads for 'tween decks

Figure 3.5.2 Heads for watertight and deep tank bulkheads

5.2.2 The following symbols and definitions apply in particular to the design pressures for partially filled tanks:

Lpp and C b as defined in Pt 3, Ch 1, 6.1 Principal particulars

b = height of internal primary bottom members, in metres
F = fill height, in metres
F r = effective filling ratio
=
GM = transverse metacentric height, in metres, including free surface correction, for the loading condition under consideration
H t = tank depth, in metres, measured from the bottom of the tank to the underside of the deck at side. In the case of holds, the depth is measured from the inner bottom to the underside of the deck at hatch side, except in double skin ships with hatch coaming in line with the inner skin, in which case, the depth is measured to the top of the hatch coaming
n = number of internal primary bottom members
L s = the effective horizontal free surface length, in metres, in the direction of angular motion (i.e. tank breadth for roll, tank length for pitch)
S nr = ship's natural rolling period
= seconds
= for ships for which either r or GM varies significantly between loading conditions (for example, bulk carriers and tankers, see Pt 3, Ch 3, 1.1 Application 1.1.3), S nr should be evaluated for each representative loading condition considered
r = radius of gyration of roll, in metres, and may be taken as 0,34B
S np = ship's natural pitching period
= seconds
= for ships for which either T or C b varies significantly between loading conditions (for example, bulk carriers and tankers, see Pt 3, Ch 3, 1.1 Application 1.1.3), S np should be evaluated for each representative loading condition considered
T np = fluid natural period of pitch
= seconds
T nr = fluid natural period of roll
= seconds
θmax = maximum `lifetime' pitch angle, in degrees:
=
φmax = maximum `lifetime' roll angle, in degrees:
=

5.3 Stowage rate and design loads

5.3.1 Unless it is specifically requested otherwise, the following standard stowage rates are to be used:

  1. 1,39 m3/tonne for weather or general cargo loading on deck and inner bottom.

  2. 0,975 m3/tonne for liquid cargo of density of 1,025 tonne/m3 or less on watertight and tank divisions. For liquid of density greater than 1,025 tonne/m3 the corresponding stowage rates are to be adopted.

5.3.2 Proposals to use a stowage rate greater than 1,39 m3/tonne for permanent structure will require special consideration, and will normally be accepted only in the case of special purpose designs such as fruit carriers, etc.

5.3.3 The design head and permissible cargo loading are shown in Table 3.5.1 Design heads and permissible cargo loadings.

5.4 Design pressure for partially filled tanks

5.4.1 When partial filling of tanks or holds is contemplated for sea-going conditions, the risk of significant loads due to sloshing induced by any of the ship motions is to be considered. An initial assessment is to be made to determine whether or not a higher level of sloshing investigation is required, using the following procedure which corresponds to the Level 1 investigation outlined in the SDA Procedure for Sloshing loads and scantling assessment, on tanks partially filled with liquids.

5.4.2 In general, significant dynamic magnifications of the sloshing pressures are considered unlikely for the following cases:

  1. For internally stiffened tanks:

    1. Where two (or more) deck girders (in the case of rolling) or deck transverses (in the case of pitching) are located not more than 25 per cent of the tank breadth or length respectively from the adjacent tank boundary, and the fill level is greater than the tank depth minus the height of the deck girders or transverses;

    2. Where the deck girders or transverses, at any location, are less than 10 per cent of the tank depth, and the fill level is greater than the tank depth minus the height of the deck girders or transverses;

    3. Where the fill level is less than the height of any bottom girders or transverses.

  2. For smooth tanks:

    where the fill level is less than 10 per cent or more than 97 per cent of the tank depth.

5.4.3 Significant dynamic magnification of the fluid motions, and hence the sloshing pressure, can occur if either of the following conditions exist:

  1. The natural rolling period, Tnr, of the fluid and the ship's natural rolling period, Snr, are within five seconds of each other.

  2. The natural pitching period, Tnp, of the fluid is greater than a value of three seconds below the ship natural pitching period, Snp.

These values define the limits of the critical fill range for each tank.

5.4.4 The critical fill range, Fcrit, is to be determined using the following formula:

where
= natural logarithm to base e
η = for fill level at Snr - 5 seconds upper bound roll critical fill level
or η = for fill level at Snr + 5 seconds lower bound roll critical fill level
or η = for fill level at Snp - 3 seconds upper bound pitch critical fill level
or η = for fill level at Snp seconds

The lower bound pitch critical fill level is 0,1 per cent fill. The value of F crit is limited to the range 0 to 100 per cent, see also Pt 3, Ch 3, 5.4 Design pressure for partially filled tanks 5.4.6.

5.4.5 The natural periods of the ship for a given motion type are to be determined for the service loading conditions agreed between the Shipbuilder and Clasifications Register. From this aspect, the storm-ballast and the segregated ballast conditions and the condition with all tanks partially filled could be the most critical.

5.4.6 When a ship is to be approved for Unrestricted Filling Levels - Unspecified Loading Conditions, many arbitrary ship loading conditions are possible. In order to cover the complete range of loading conditions, the fully loaded and ballast conditions are to be considered. These two conditions give an upper and lower limit for the possible range of natural periods of the ship as shown in Figure 3.5.3 Natural periods diagrams. Both the roll and pitch motion modes are to be examined.

Because of the unrestricted filling level requirement, the critical sloshing ranges extend from [SnrBallast - 5] to [S nrLoaded + 5] seconds in roll and from [SnpBallast - 3] to [SnpLoaded] in pitch. Also, because of unrestricted filling levels, the ship natural period range extends from [S nBallast] to [S nLoaded] for both pitch and roll.

For sloshing in the roll motion mode shown in Figure 3.5.3 Natural periods diagrams, the critical fill range extends from F 1 to F4. All fill levels between F1 and F4 are to be investigated:

  • For fill levels between F1 and F2, SnrBallast is to be used.
  • For fill levels between F3 and F4, SnrLoaded is to be used.
  • For fill levels between F2 and F3, Snr is to be equal to T nr.

Similarly, for sloshing in the pitch motion mode shown in Figure 3.5.3 Natural periods diagrams, the critical fill range extends from F1 to F4. All fill levels between F1 and F4 are to be investigated.

  • For fill levels between F1 and F2, SnpBallast is to be used.
  • For fill levels between F2 and F3, Snp is to be equal to Tnp.
  • For fill levels between F3 and F4, Snp loaded is to be used.

Figure 3.5.3 Natural periods diagrams

5.4.7  When a ship is to be approved for Restricted Filling Levels - Unspecified Loading Conditions, many arbitrary ship loading conditions are possible within the restrictions imposed. In order to cover the complete range of loading conditions, the fully loaded and ballast conditions are to be considered. These two conditions give an upper and lower limit for the possible range of ship natural period. It is recognised that there might be ship natural period bands which will not be applicable as a result of the limitations on the fill levels. However, it is recommended that the Unrestricted Filling Levels - Unspecified Loading Conditions procedure outlined in Pt 3, Ch 3, 5.4 Design pressure for partially filled tanks 5.4.6 be applied.

5.4.8 When a ship is to be approved for Unrestricted Filling Levels - Specified Loading Conditions, each specified loading condition is to be examined for the complete fill ranges to determine the critical sloshing fill range for each tank in both roll and pitch motion modes.

5.4.9 When a ship is to be approved for Restricted Filling Levels - Specified Loading Conditions, each specified loading condition is to be examined for the restricted fill ranges to determine the critical sloshing fill range for each tank in both roll and pitch motion modes.

5.4.10 Where the assessment indicates that all the intended fill levels are outside the critical fill ranges and, therefore, significant sloshing will not occur, no further evaluation is required with regard to sloshing pressure. In such cases, the scantlings of the tank boundaries are to be determined in accordance with the relevant Rule requirements.

5.4.11 Where the separation of periods defined in Pt 3, Ch 3, 5.4 Design pressure for partially filled tanks 5.4.3 is not met, other levels of assessment will be required as given in the SDA Procedures for sloshing loads and scantling assessment, on tanks partially filled with liquids.

5.4.12 The structural capability of the tank boundaries to withstand the dynamic sloshing pressures is to be examined. The magnitude of the predicted loads, together with the scantling calculations may be required to be submitted.

5.5 Flooded loads

5.5.1 The distance to the flooded load point, ZFD, is to be calculated as follows;
ZFD = Tf + ΔTh,t

where

ΔTh,t is the increase in draught due to heel and trim, in metres
  • ΔTh,t =
ΔTh is the increase in draught due to heel, in metres
ΔTt is the increase in draught due to trim, in metres
Tf is the flooded draught, in metres, to be taken as

see also Figure 3.5.4 Damage waterline at any location

5.5.2 For passenger ships, where the damage waterlines, see Pt 3, Ch 1, 6.10 Damage waterlines, have not been provided, the distance from the baseline to the deepest equilibrium/intermediate waterline, whichever is the greater, and the intermittent waterline can be estimated in accordance with Pt 3, Ch 3, 5.5 Flooded loads 5.5.1 using the flooding angles and coefficients given in Table 3.5.3 Flooding angles and coefficients for passenger ships. The flooded load point is to be measured perpendicular to the damage waterline.

Table 3.5.2 Flooding angles and coefficients

Ship type Heel angle, θ Trim coefficient, χ Flooding coefficient, ϕ
Forward Aft Forward Aft
General cargo ships 30 2 3 1,10 1,10
Container ships 30 1,5 2 1,05 1,05
Ore carriers and bulk carriers 30 3 1,5 1,05 1,10
Ro-Ro cargo ships 30 3 2,5 1,10 1,30
Gas Carriers 30 1 2,5 1,10 1,05
Tankers 30 1 2 1,05 1,05
Special purpose ships carrying 200 personnel or fewer, see Note 1 12, see Note 2 2 2 1,10 1,10
Other cargo ships 30 3 3 1,10 1,10
Note 1 Special purpose ships are as defined in the Code of Safety for Special Purpose Ships – Resolution A.534(13). For special purpose ships carrying more than 200 personnel, seeTable 3.5.3 Flooding angles and coefficients for passenger ships
Note 2 The heel angle is to be taken 7 degrees for locations aft of 0,5L

Table 3.5.3 Flooding angles and coefficients for passenger ships

Ship type Final/intermediate heel angle, θ Intermittent heel angle, θ Trim coefficient, χ Flooding coefficient, ϕ
Forward Aft Forward Aft
Ro-Ro passenger ships/ferries 15 26 3,5 3,5 1,15 1,15
Multi-decked passenger ships 15 22 0 0 1,15 1,15
Other passenger ships and ferries 15 22 0 0 1,15 1,15
Special purpose ships carrying more than 200 personnel, see Note 15 N/A 0 0 1,15 1,15
Note Special purpose ships are as defined in the Code of Safety for Special Purpose Ships – Resolution A.534(13)

Figure 3.5.4 Damage waterline at any location

5.5.3 The heel angles and flooding coefficients given in Table 3.5.2 Flooding angles and coefficients are based on one compartment damage. If required by the Owner, additional flooding can be considered where the flooded load point is to be determined based on the equilibrium damage waterline resulting from the damage stability calculations, see Pt 3, Ch 1, 6.10 Damage waterlines. The flooded load point is to be measured perpendicular to the damage waterline.

5.5.4  Where the damage waterlines, see Pt 3, Ch 1, 6.10 Damage waterlines, have been provided by the designer, the methodology used to determine the damage waterlines is also to be submitted as supporting information.

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