Sect.4 -Design Loads

7/29/2019 Sect.4 -Design Loads

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Section 4 - Design Loads B 4 - 1

Section 4

Design Loads

A. General, Definitions

1. General.

This Section provides data regarding design loads for

determining the scantlings of the hull structural elements

by means of the design formula given in the following

Section or by means of direct calculations. The dynamic

portions of the design loads are design values which can

only be applied within the design concept of this Volume.

2. Definitions

2.1 Load centre2.1.1 For plates:

Vertical stiffening system:

0,5@stiffener spacing above the lower support of

plate field, or lower edge of plate when the thickness

changes within the plate field.

Horizontal stiffening system:

Midpoint of plate field.

2.1.2 For stiffeners and girders:

Centre of span R.

2.2 Definition of symbols

v0 = ship's speed according to Section 1, H.5.

c = density of cargo as stowed in [t/m3]

= density of liquids in [t/m3]

= 1,0 t/m3

for fresh water and sea water

z = vertical distance of the structure's load centre

above base line in [m]

x = distance from aft end of length L in [m]

p0 = basic external dynamic load

= 2,1@(CB + 0,7)@c0@cL@f@cRW [kN/m2]

for wave directions with or against the ships

heading

p01 = [kN/m2]( )2 6 0 7 0, . , . .C c cB L+

for wave directions transverse the ships heading

CB = moulded block coefficient according to Section

1, H.4., where CB is not to be taken less than

0,60.

c0 = wave coefficient

= for L < 90 mL

25%4,1

c0 = for 90 L 300 m10,75 S300 S L

100

1,5

cRW = service range coefficient

= 1,00 for unlimited service range

= 0,90 for service range P

= 0,75 for service range L

= 0,60 for service range T

f = probability factor

= 1,0 for plate panels of the outer hull (shell

plating, weather decks)= 0,75 for secondary stiffening members of the

outer hull (frames, deck beams), but not less than

fQ according to Section 5, D.1.

= 0,60 for girders and girder systems of the outer

hull (web frames, stringers, grillage systems),

but not less than fQ/1,25

cD, cF = distribution factors according to Table 4.1.

B. External Sea Loads

1. Load on weather decks

1.1 The load on weather deck is to determined accordingto the following formula:

pD = p0 [kN/m2]

20 @T

(10 %z - T) HcD

1.2 For strength decks which are to be treated asweather decks as well as for forecastle decks the load is

not to be less than the greater of the following two values:

pDmin = 16@f [kN/m2]

or

pDmin = 0,7@p0 [kN/m2]


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Section 4 - Design Loads B4 - 2

Table 4.1Distribution factors for sea loads on ship's sides and weather decks

Range Factor cD Factor cF1)

A 0 < 0,2 1,2 -


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Section 4 - Design Loads B 4 - 3

Aft of 0,1 L from F.P. up to 0,15 L from F.P. the pressurebetween pe and ps is to be graded steadily.

The design load for bow doors is given in Section 6, H.3.

2.3 Load on stern structures

The design load for stern structures from the aft end to 0,1 Lforward of the aft end ofL and above the smallest designballast draught at the centre of the rudder stock up toT+ c0/2 is to be determined according to the following

formula:

pe = cA@L [kN/m2]

with Lmax = 300m.

cA = 0,3 @c $ 0,36

c = see 2.2

pe = must not be smaller than ps according to 2.1.1

or 2.1.2 respectively

3. Load on the ship's bottom

The external load pB of the ship's bottom is to be determined

according to the following formula:

pB = 10 @T + p0 @cF [kN/m2].

4. Design bottom slamming pressure

4.1 The design bottom slamming pressure may bedetermined by the following formula:

pSL = [kN/m2]162 L @c1 @cSL @cA @cs

forL 150 m 150 m

c1 = 3,6 - 6,5Tb

L

0,2

c1max = 1,0

Tb = smallest design ballast draught at F.P for normal

ballast conditions in [m],according to which the

strengthening of bottom forward, see Section.6,E. has to be done.

This value has to be recorded in the Class

Certificate and in the loading manual.

Where the sequential method for ballast water

exchange is intended to be applied, Tb is to be

considered for the sequence of exchange.

Note

With respect to the observation of the smallestdesign ballast draught Tb, an exception is

possible, if during the exchange of ballast waterweather conditions are observed the parametersof which are put down in the annex to theCertificate of Class.

cSL = distribution factor, see also Fig. 4.2

Fig. 4.2 Distribution factor cSL

cSL = 0 for 0,5x

L


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Section 4 - Design Loads D4 - 4

b = breadth of deckhouse

B = largest breadth of ship at the position considered.

Except for the forecastle deck the minimum load is:

pDAmin

= 4 [kN/m2]

5.2 For exposed wheel house tops the load is not to betaken less than

p = 2,5 [kN/m2]

C. Cargo Loads, Load on Accommodation Decks

1. Load on cargo decks

1.1 The load on cargo decks is to be determined

according to the following formula:

pL = pc (1 + av) [kN/m2]

pc = static cargo load in [kN/m2]

if no cargo load is given: pc = 7 @h for 'tween decks butnot less than 15 kN/m

2.

h = mean 'tween deck height in [m].

In way of hatch casings the increased height of cargo is

to be taken into account

av = acceleration factor as follows:

= F @m

F = 0,11v0

L

m = mo - 5 (mo - 1) for 0 0,2x

L


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Section 4 - Design Loads E 4 - 5

p1 = [kN/m2]9,81@ [h1@cosn%(0,3@b%y)sinn]%100@pv

h1 = distance of load centre from tank top in [m]

av see C.1.1

n = design angle of heel in degrees for tanks

= arctan in generalfbk@H

B

fbk = 0,5 for ships with bilge keel

= 0,6 for ships without bilge keel

n $ 20o for hatch covers of holds carrying liquids

b = upper breadth of tank in [m]

y = distance of load centre from the vertical

longitudinal central plane of tank in [m]

pv = set pressure of pressure relief valve in [bar], if

a pressure relief valve is fitted

= working pressure during ballast water exchange

[bar]

=z2,5

10%p

v

z = distance from top of overflow to tank top [m]

pv = pressure losses in the overflow line [bar]

pvmin = 0,1 [bar]

pvmin = 0,1 [bar] during ballast water exchange for both,

the sequential method as well as the flow-through method

= 0,2 bar (2,0 mWS) for cargo tanks of tankers

(see also Rules for Machinery Installations,

Volume III, Section 15).

Smaller set pressures than 0,2 bar may be accepted in special

cases. The actual set pressure will be entered into the class

certificate.

1.2 The maximum static design pressure is:

p2 = 9,81 @h2 [kN/m

2

]

h2 = distance of load centre from top of overflow or

from a point 2,5 m above tank top, whichever

is the greater. Tank venting pipes of cargo tanks

of tankers are not to be regarded as overflow

pipes.

For tanks equipped with pressure relief valves and/or for

tanks intended to carry liquids of a density greater than

1 t/m3, the head h2 is at least to be measured to a level at

the following distance hp above tank top:

hp

= 2,5 @ [mWS], head of water in [m],

or

= 10 @pv [mWS], where pv > 0,25 @.

Regarding the design pressure of fuel tanks and ballast tanks

which are connected to an overflow system, the dynamic

pressure increase due to the overflowing is to be taken into

account in addition to the static pressure height up to the

highest point of the overflow system, see also Regulation

for Construction, Equipment and Testing of Closed Fuel

Overflow Systems.

2. Design pressure for partially filled tanks

2.1 For tanks which may be partially filled between 20%and 90% of their height, the design pressure is not to be

taken less than given by the following formulae:

2.1.1 For structures located within 0,25 Rt from thebulkheads limiting the free liquid surface in the ship's

longitudinal direction:

pd = [kN/m2]4 & L150

Rt @ @nx %100 pv

Rt = distance in [m] between transverse bulkheads

or effective transverse wash bulkheads at the

height where the structure is located.

2.1.2 For structures located within 0,25 bt from thebulkheads limiting the free liquid surface in the ship's

transverse section:

pd = [kN/m2]5,5 -

B

20bt @ @ny %100 @pv

bt = distance in [m] between tank sides or effective

longitudinal wash bulkhead at the height where

the structure is located.

nx = 1 &4

Rtx1

ny = 1 &4

bty1

x1 = distance of structural element from the tanks

end in the ships longitudinal direction in [m]

y1 = distance of structural element from the tankssides in the ships transverse direction in [m]

2.2 For tanks with ratios Rt/L > 0,1 or bt/B> 0,6 a directcalculation of the pressure pd may be required.

E. Design Values of Acceleration Components

1. Acceleration components

The following formulae may be taken for guidance whencalculating the acceleration components owing to ship's

motions.


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Section 4 - Design Loads E4 - 6

Vertical acceleration:

az = a0 1%5,3-45

L

2 x

L-0,45

2 0,6

CB

1,5

Transverse acceleration:

ay = a0 0,6%2,5x

L-0,45

2

%k 1%0,6@kz-T

B

2

Longitudinal acceleration:

ax = a0 0,06 %A2 - 0,25 A

where

A = 0,7 !L

1200%5

z - T

L

0,6

CB

The acceleration components take account of the followingcomponents of motion:

Vertical acceleration (vertical to the base line) due toheave, and pitch.

Transverse acceleration (vertical to the ship's side) dueto roll, yaw and sway including gravity component of roll.

Longitudinal acceleration(in longitudinal direction) dueto surge and pitch including gravity component of pitch.

ax, ay and az are maximum dimensionless accelerations (i.e.,

relative to the acceleration gravity g) in the related direction

x, y and z. For calculation purposes they are consideredto act separately.

a0 = 0,2v0

L0

%3 @c0 @cL @cRW

L0

fQ

L0 = length of ship L [m], but for determination ofa0 the length L0 shall not be taken less than 100m

k =13 @GM

B

= metacentric height in [m]GM

kmin = 1,0

fQ = probability factor depending on probability level

Q as outline in Table 4.2.

Table 4.2 Probability factor fQ for a straightlinespectrum of seaway-induced stress ranges

Q fQ

10-8

10-7

10-6

10-5

10-4

1,000

0,875

0,750

0,625

0,500

2. Combined acceleration

The combined acceleration amay be determined by means

of the "acceleration ellipse" according to Fig. 4.3 (e.g. y-z-

plane).

Fig. 4.3 Acceleration ellipse

Sect.4 -Design Loads

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