Common Structural Rules for Bulk CarriersRule Change Notice 3

Common Structural Rules for
Bulk Carriers, January 2006

Rule Change Notice 3(Ch 8 Sec 2, 2.3 Equivalent notch stress range)
Notes: (1) These Rule Changes enter into force on 12 September 2008.

Copyright in these Common Structural Rules for Bulk Carriers is owned by:American Bureau of Shipping
Bureau Veritas
China Classification Society
Det Norske Veritas
Germanischer Lloyd
Korean Register of Shipping
Lloyd's Register
Nippon Kaiji Kyokai
Registro Italiano Navale
Russian Maritime Register of Shipping
Copyright © 2006

The IACS members, their affiliates and subsidiaries and their respective officers, employees or agents are, individually andcollectively, referred to in this clause as the ‘IACS Members’. The IACS Members, individually and collectively, assume no
responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or
advice in this document or howsoever provided, unless that person has signed a contract with the relevant IACS Member
entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms
and conditions set out in that contract.

Page 1 of 15

Rule Change Notice 3

Common Structural Rules for Bulk Carriers

For technical background for Rule Changes in this present document, reference is made toseparate document Technical Background for Rule Change Notice 3

Chapter 8 Fatigue Check of Structural Details

Section 2 – FATIGUE STRENGTH ASSESSMENT
2. Equivalent notch stress range
2.3 Equivalent notch stress range
2.3.1 Equivalent notch stress range
The equivalent notch stress range, in N/mm2, for each loading condition is to be calculated with the following
formula:∆σ eq, j = K f ∆σ equiv, jwhere:∆σequiv , j : Equivalent hot spot stress range, in N/mm2, in loading condition “j” obtained by [2.3.2].
Kf: Fatigue notch factor defined in Tab 1.
Table 1:

Fatigue notch factors Kf

Subject

KfNot Grinding
Without weld grinding

Butt welded joint
Fillet welded joint
Non welded part

1.25
1.30
1.00

Grinding
With weld grinding(not applicable forordinary stiffeners andboxing fillet welding*1)
1.10
1.15 *2-Note:*1 Boxing fillet welding is defined as a fillet weld around a corner of a member as an extension of the principal
weld.
*2 This is applicable for deep penetration welding, or full penetration welding only.
In case where grinding is performed, full details regarding grinding standards including the extent,smoothness particulars, final welding profiles, and grinding workmanship as well as quality acceptancecriteria are to be submitted to the Society for approval.
It is preferred that any grinding is carried out by rotary burrs, is to extend below plate surfaces in orderto remove any toe defects and ground areas are to have sufficient corrosion protection.
Such treatments are to procedure smooth concave profiles at weld toes with the depth of these
depressions penetrating into plate surfaces to at least 0.5mm below the bottom of any visible
undercuts.
The depth of any grooves produced is to be kept to a minimum and, in general, kept to a maximum of
1mm.
Under no circumstances is grinding depth to exceed 2mm or 7 % of plate gross thickness, whicheveris smaller.
Grinding has to extend to 0.5 longitudinal spacing or 0.5 frame spacing at the each side of hot spot
locations.

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Common Structural Rules for Bulk CarriersRule Change Notice 3

2.3.2 Equivalent hot spot stress range
The equivalent hot spot stress range, in N/mm2, is to be calculated for each loading condition with the following
formula:∆σ equiv , j = f mean, j ⋅ ∆σ W , jwhere:
fmean , j

: Correction factor for mean stress :• for hatch corners fmean , j = 0.77
• for primary members and longitudinal stiffeners connections, fmean , j corresponding to the condition“j” taken equal to:0.25⎧⎡⎛ 1 − ln 10 − 4 σ m , j ⎞⎤ ⎫⎪⎪⎟⎥ ⎬f mean, j = max ⎨0.4, ⎢max⎜ 0, +
⎜ 2
⎟⎥
∆
4
σ
⎢
W
j
,
⎪⎩
⎝
⎠⎦ ⎪⎭
⎣

(

σm ,1

)

: Local hot spot mean stress, in N/mm2, in the condition “1”, obtained from the following formulae:•

If 0.6∆σ W ,1 ≥ 2.5 ReH :0.6∆σ m ,1 = −0.18∆σ W ,1•σm , jIf 0.6∆σ W ,1 < 2.5 ReH :σ m ,1 = ReH − 0.6∆σ W ,1for

0.6∆σ W ,1 > ReH − σ res − σ mean,1

σ m ,1 = σ mean,1 + σ resfor

0.6∆σ W ,1 ≤ ReH − σ res − σ mean,1: Local hot spot mean stress, in N/mm2, in the condition “j”, obtained from the following formulae:•

If 0.24σ W , j ≥ ReH :σ m , j ( j ≠1) = −0.18∆σ W , j•

If 0.24σ W , j < ReH :σ m , j ( j ≠1) = − ReH + 0.24∆σ W , j

for 0.24∆σ W , j > ReH + σ m ,1 − σ mean,1 + mean, j

σ m, j ( j ≠1) = σ m,1 − σ mean,1 + σ mean, j for 0.24∆σ W , j ≤ ReH + σ m ,1 − σ mean,1 + σ mean, jσmean , j : Structural hot spot mean stress, in N/mm2, corresponding to the condition “j”
σres: Residual stress, in N/mm2, taken equal to: obtained from the following formulae:

σ res = max{σ res, j ,σ res = 0.25ReH}

j = 1,2,3,4

for stiffener end connection

Page 3 of 15

Rule Change Notice 3

Common Structural Rules for Bulk Carriers

σ res = 0

for non welded part and primary members(cruciform joint or butt weld)

[

{

]

}

⎧max − ReH , min R eH , σ res 0 + σ mean, j + 0.6∆σ W , j − σ mean, j − 0.6∆σ W , j⎪for σ mean, j ≥ 0⎪
σ res , j = ⎨⎪min ReH , max − R eH , σ res 0 + σ mean, j − 0.24∆σ W , j − σ mean, j + 0.24∆σ W , j⎪for σ mean, j < 0⎩[⎧0.25 ReH
⎩0σ res 0 = ⎨

{

for

}

welded joint

for non welded part

Page 4 of 15]

Common Structural Rules for Bulk carriers

Technical Background for Rule Change Notice 3

Common Structural Rules for
Bulk Carriers, January 2006

Technical Background forRule Change Notice 3(Ch 8 Sec 2, 2.3 Equivalent notch stress range)

Copyright in these Common Structural Rules for Bulk Carriers is owned by:American Bureau of Shipping
Bureau Veritas
China Classification Society
Det Norske Veritas
Germanischer Lloyd
Korean Register of Shipping
Lloyd's Register
Nippon Kaiji Kyokai
Registro Italiano Navale
Russian Maritime Register of Shipping
Copyright © 2006

The IACS members, their affiliates and subsidiaries and their respective officers, employees oragents are, individually and collectively, referred to in this clause as the ‘IACS Members’. The
IACS Members, individually and collectively, assume no responsibility and shall not be liable toany person for any loss, damage or expense caused by reliance on the information or advice in thisdocument or howsoever provided, unless that person has signed a contract with the relevant IACS
Member entity for the provision of this information or advice and in that case any responsibility or
liability is exclusively on the terms and conditions set out in that contract.

Page 5 of 15

Technical Background for Rule Change Notice 3

Common Structural Rules for Bulk Carriers

Technical Background for the Changes Regarding Equivalent notch
stress range:
1. Reason for the Rule Change in Ch 8 Sec 2 2.3:
As specified in Appendix 1, almost all damages are occurred in ballast hold.
The reasons that the majority of damage caused by cracks occurs in ballast holds are as follows.
Structural members in ballast holds are subject to high internal pressure due to ballast water.
However, since they are subject to relatively low external pressure, high tensile stresses (both themean stress and stress range are large) are placed on those structural members susceptible to low
fatigue life such as lower stool connections and bilge knuckle connections as shown in Fig. 3.1,
while, the stresses placed on structural members in cargo holds that are other than ballast holds are
relatively small or compressive even in cases where their value is large.
Therefore, the majority of damage caused by cracks occurs in ballast holds. In the case of bilge
knuckle connections in ballast holds under heavy ballast conditions, since the sum of the tensile
mean stress and 0.6 times stress range are greater than ReH, the term σ res 0 does not affect any
formula specified in CH 8 Sec 2 [2.3.2] of the current CSR (See the background for the treatment ofresidual stress specified in Appendix 2.
This means that any fatigue assessment results for structural members such as those bilge knuckle
connections in which damage occurs are not affected by the value of residual stress.
On the other hand, with respect to those structural members in empty and loaded holds that areother than ballast holds, excessive compressive mean stresses or the mean stresses in four loading
conditions are compressive or relatively low.
Therefore, any fatigue assessments performed according to current rules give results which are far
from our experience that less damage caused by cracks of primary members (bilge knuckles andlower stools) in empty and loaded holds other than ballast holds occur
The reasons for obtaining such results are due to the assumptions that (1) the tensile residual
stresses are generated after any excessive compressive loads are removed, and (2) the existence ofinitial weld residual stresses of 0.25 ReH.
In some cases, the weld residual stress is released due to certain reasons for the primary
members. The factors which are the cause of stress release are (i) assembly process (ii) tank test (iii)internal and external loads etc. And we obtained the remark that the weld residual stress is released
even if the large compressive load is applied
Based on the above knowledge, the calculation formula of the equivalent hot spot stress range
is corrected to make weld residual stress zero except the case for ordinary stiffener. Moreover, it isalso known that when excessive compression loads are imposed on the welded structure and thenremoved, it does not lead to production of tensional residual stress. This knowledge has beenreflected in the formula.
However, the assumption of initial weld residual stress is kept for longitudinal stiffeners,
because longitudinal stiffeners penetrate transverse webs at so many locations that the estimation
should be left on the safer side.
Furthermore, the stress concentration at the hot spots subjected to fatigue strength assessment
can be mitigated by grinding as can the stress concentration in primary members. As the CSR for
tankers reflects this information, the effects of stress mitigation by grinding have been included in
the assessment of primary members except the connection of side frames which the boxing fillet
welds are adopted, considering the actual and practical construction procedure.

2. Summary of the Rule Change
2.1
Improvement of the calculation of the equivalent hot spot stress range of primary
members to include weld residual stress and excessive compressive stress(1) The current assumption of the initial weld residual stress is to be applied to the fatigue strength
assessment for longitudinal stiffeners.
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Common Structural Rules for Bulk Carriers

σ res = 0.25ReH

Technical Background for Rule Change Notice 3

for ordinary stiffener(2) As the effects of weld residual stress do not need to be considered for primary members, theassumption of the initial weld residual stress is to be added in a similar way to the current
assumption for non welded parts in which the residual stress does not exist.
σ res = 0 , (for non welded part and primary members (cruciform and butt weld)
2.2 Consideration of the effects of grinding
In the calculation of hot spot stress, the coefficient for the grinding effect is to be defined withreference to the ‘International Institute of Welding (IIW) Recommendation of IIW “Fatigue design
welded joint and component”’ and added to Ch8 Sec2 Table1.
According to the post welds improvements specified in “IIW Recommendations on Post Weld
Improvements of Steel and Aluminum Structures, XIII-1965-00, 2004”, grinder finishing for the
purpose of removing any undercut and /or smoothing any welding beads is recommended to be
carried out.
The recommended practice for grinder finishing is to the plate surface to a depth of at least
0.5mm from the bottom of the visible undercut but not to exceed 1.0mm.
According to the results of experiments specified in several technical papers, the grinder effecton fatigue life is estimated to have a value of 1.3. If a value of 1.0 is used for those surfaces that are
not subjected to grinder finishing then this is an improvement.
According to “IIW Recommendations for Fatigue Design of Welded Joints and Components,
2004, IIW Document XIII-1965-03/XV-1127-03” the grinder effect value is to be taken as 1.25 inorder to be on the safe side. For example, (extract of IIW Rec.) No. 511

Two-sided fillets, toe ground: 100MPa
Fillet weld(s) as welded : 80MPa(100/80=1.25)
The recommended value is based on the results of experiments that used specimens in wellcontrolled conditions.
Considering that any actual grinding work on structures is not so well controlled, we feel that, tobe even more on the safe side, the grinder effect value should be even further lowered to 1.15 as
proposed in Rule Change Notice 3.
Table 1 Fatigue notch factors Kf
Subject

Butt welded joint
Fillet welded joint
Non welded part

Grinding
KfNot Grinding
With weld grinding
Without weld grinding (not applicable and boxing
fillet welding*1)
1.25
1.10
1.30
1.15*2
1.00
-

Note:
*1 Boxing fillet welding is defined as a fillet weld around a corner of a member as an extension of the principal weld.
*2 This is applicable for deep penetration welding, or full penetration welding only.

However, to avoid any risk of root cracking, the application of this technique is limited to deep
penetration welding or full penetration welding.
Furthermore, in order to ensure the effects of the grinding, procedures specified by the International
Institute of Welding have been added to the Rules.

3. Effects due to this change
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Technical Background for Rule Change Notice 3

Common Structural Rules for Bulk Carriers

To see the effects of the change to the calculation formulae of the equivalent hot spot stressrange for primary members, the fatigue strength assessment of the connections of the inner bottom
plate with the bilge hopper sloping plate and the lower stool side plate was carried out. For
reference, all the lower stool side plates have slanted configuration.

A
B
C
D
E

Table 3.1 Considerable ships and cargo holds
Type of ship
Type of cargo holds
Cape (DSS) 170K
Ballast hold
Empty hold
Loaded holdCape (SSS) 180K
Ballast hold
Loaded holdPanamax (SSS) 82K
Ballast hold
Empty holdPanamax (SSS) 110K
Ballast hold
Loaded hold
Handymax (SSS) 57K
Ballast hold
Empty hold

The equivalent hot spot stress range and mean stress obtained by FEA are shown in Figure 3.1
The following cumulative fatigue damage was calculated from the above equivalent hot spot stressrange and mean stress.
(1) The cumulative fatigue damage according to the current CSR(2)(a) The cumulative fatigue damage according to the corrected formulae in 2.1 (“mod_1” inFigure 3.2)(b) The cumulative fatigue damage according to the corrected formulae in 2.1 with the effect ofgrinding in 2.2 (“mod_1(G) in Figure 3.2)
The results of the cumulative fatigue damage are shown in Figure 3.2.
From the results in Figure 3.2, the following can be said about the corrected formulae in 2.1.
(1) There is no effect on the cumulative fatigue damage at the fatigue assessment points in ballast
holds where there was high tensional mean stress.
(2) In cargo holds other than ballast holds, the cumulative fatigue damage at the fatigue assessment
points was less than that of the current CSR, when there was compressive or low tensional meanstress and the hot spot stress range was large.
(3) The relative tendency of the cumulative fatigue damage at the fatigue assessment points inballast holds and other holds was consistent with the damage record specified in the Appendix.
(4) The cumulative fatigue damage with grinding was about 60% of that without grinding.
4. Impact on scantlings
Since the results of the fatigue strength assessment depend on various countermeasures such as
grinding, additional reinforcement, inset plate or local thickness increase, and other fabrication
improvements, the scantling impact due to this change cannot be estimated directly. However, thecorrection of the calculation formulae mitigates the excessive result on fatigue damage in cargoholds other than ballast holds, where less fatigue cracks have been found in the damage record.

Page 8 of 15

Common Structural Rules for Bulk Carriers

Technical Background for Rule Change Notice 3

Fig. 3.1 Hot spot stress range and hot spot mean stress

A (DSS Cape)
max
min
mean

710
355
0
-355
-710
-1065

Heavy
Homo
Normal
Alt
Heavy
Homo
Alt
Normal
Heavy
Homo
Alt
Normal
Alt
Homo
Heavy
Normal
Heavy
Homo
Alt
NormalAlt
HomoNormalHeavy
HomoNormal
Heavy
Alt
Homo
Heavy
Alt
Normal
Homo
Heavy
Alt
NormalStress (N/mm2)

1065

Bilge
(Ballast)

Lstool_Aft(Ballast)

Lstool_Fore(Ballast)

Bilge(Loaded)

Lstool_Aft(Loaded)

Lstool_Fore(Loaded)

Bilge(Empty)Lstool_Aft(Empty)Lstool_Fore(Empty)B (SSS Cape)
max
min
mean

710
355
0
-355

Bilge (Ballast)

Lstool_Aft (Ballast)

Lstool_Fore(Ballast)

Bilge (Loaded)

Lstool_Aft (Loaded)

Normal

Alt

Homo

Heavy

Heavy

NormalAlt

HomoNormal

Heavy

Homo

Alt

Normal

Alt

Homo

Heavy

Alt

Normal

Homo

Heavy

Alt

Heavy

-1065

Normal-710
Homo

Stress (N/mm2)

1065

Lstool_Fore(Loaded)Fig. 3.1 Hot spot stress range and hot spot mean stress (continued)

C (SSS Panamax)
max
min
mean

710
355
0
-355

Bilge (Ballast)

Lstool_Fore(Ballast)

Lstool_Aft(Ballast)

Bilge (Ballast)Page 9 of 15

Bilge (Empty)

Lstool_Aft(Empty)Heavy

Normal

Alt

Homo

Heavy

Normal

Alt

Homo

Alt

Normal

Heavy

Homo

Normal

Alt

Homo

Heavy

Normal

Alt

Homo

Heavy

Alt

Normal

Homo

Heavy

Alt

Homo

-1065

Normal-710
Heavy

Stress (N/mm2)

1065

Lstool_Fore(Empty)Technical Background for Rule Change Notice 3

Common Structural Rules for Bulk Carriers

D (SSS Panamax)
max
min
mean

710
355
0
-355

Bilge (Ballast)

Lstool_Aft (Ballast)

Lstool_Fore(Ballast)

Bilge (Loaded)

Lstool_Aft(Loaded)

Heavy

NormalAlt

HomoNormal

Heavy

Alt

Homo

Heavy

NormalHomo

Alt

Normal

Alt

Homo

Heavy

Normal

Alt

Homo

Heavy

Alt

Normal

-1065

Homo

-710
Heavy

Stress (N/mm2)

1065

Lstool_Fore(Loaded)E (SSS Handymax)
max
min
mean

710
355
0
-355

Bilge (Ballast)

Lstool_Aft(Ballast)

Lstool_Fore(Ballast)

Bilge (Empty)

Lstool_Aft(Empty)Heavy

NormalAlt

HomoNormal

Heavy

Alt

Homo

Alt

Heavy

NormalHomoNormal

Alt

Homo

Heavy

Normal

Homo

Alt

Heavy

Normal

Homo

-1065

Alt

-710
Heavy

Stress (N/mm2)

1065

Lstool_Fore(Empty)*"Lstool_Aft" and "Lstool_Fore" mean the lower stool of the aft end and fore end of the cargo hold.

Page 10 of 15

Common Structural Rules for Bulk Carriers

Technical Background for Rule Change Notice 3

Fig. 3.2 Cumulative fatigue damage

A (DSS Cape)
Cumulative fatigue damage

2
CSR-B
mod_1
mod_1(G)

1.5
1
0.5
0
Bilge
(Ballast)

Lstool_Aft Lstool_Fore(Ballast)(Ballast)

Bilge(Loaded)

Lstool_Aft Lstool_Fore(Loaded)(Loaded)

Bilge(Empty)Lstool_Aft Lstool_Fore(Empty)(Empty)B (SSS Cape)
Cumulative fatigue damage

3
CSR-B
mod_1
mod_1(G)

2.5
2
1.5
1
0.5
0
Bilge (Ballast)

Lstool_Aft(Ballast)

Lstool_Fore(Ballast)

Bilge (Loaded)

Lstool_Aft(Loaded)

Lstool_Fore(Loaded)C (SSS Panamax)
Cumulative fatigue damage

4
CSR-B
mod_1
mod_1(G)

3.5
3
2.5
2
1.5
1
0.5
0
Bilge (Ballast)

Lstool_Fore(Ballast)

Lstool_Aft(Ballast)

Bilge (Ballast)Page 11 of 15

Bilge (Empty)

Lstool_Aft(Empty)Lstool_Fore(Empty)Technical Background for Rule Change Notice 3

Common Structural Rules for Bulk CarriersFig. 3.2 Cumulative fatigue damage (Continued)

Cumulative fatigue damage

D (SSS Panamax)
5
4.5
4
3.5
3
2.5
2
1.5
1
0.5
0

CSR-B
mod_1
mod_1(G)

Bilge (Ballast)

Lstool_Aft(Ballast)

Lstool_Fore(Ballast)

Bilge (Loaded)

Lstool_Aft(Loaded)

Lstool_Fore(Loaded)E (SSS Handymax)
Cumulative fatigue damage

2
CSR-B
mod_1
mod_1(G)

1.5
1
0.5
0
Bilge (Ballast)

Lstool_Aft(Ballast)

Lstool_Fore(Ballast)

Bilge (Empty)

Lstool_Aft (Empty)

Lstool_Fore(Empty)*"Lstool_Aft" and "Lstool_Fore" mean the lower stool of the aft end and fore end of the cargo hold.

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Common Structural Rules for Bulk Carriers

Technical Background for Rule Change Notice 3

Appendix 1 Damage record
The members and locations specified in Ch 8 Sec 1 of CSR for Bulk Carriers are those that have apotential risk of fatigue damage regardless of the type of hold or damage frequency.
We surveyed damage data of the primary members listed below that require fatigue strength
assessment in order to comprehend the exact risk of fatigue damage:• Connections between inner bottom plating and sloping and/or vertical plate of lower stool(IB/slant of LS)• Connections between inner bottom plating and sloping plate of hopper tank
(IB/sloping of BH)• Connections between inner hull plating and sloping plate of hopper tank
(IS/sloping of BH)• Connections between transverse bulkhead and sloping plate of lower stool (TB/LS)• Connections between transverse bulkhead and sloping plate of upper stool (TB/US)• Connections between hold frames and sloping plate of lower wing tank (HF/BH)• Connections between hold frames and sloping plate of upper wing tank (HF/TST)The survey was carried out according to the following conditions.
(1) Crack damage data reported between 1996 and 2007 in the 3015 ships constructed
between 1958 and 2007
(2) Damage that occurred due to design, fatigue, or unknown causes(3) For hold frames, damage of ships complying with IACS S12 (1992)
Damage data is classified by the type of hold (ballast hold and cargo hold) and the number ofcases of damage is normalized by the number of classified holds per a ship.
The results are given in Table A1.
Table A1 Number of cases of damage *Ballast hold
Cargo hold(No. of cases of damage / No. of cargoholds)
365
0
173
0.4
9
0
92
0.2
63
0.5
15
0
31
0
748
1.1

IB/slant of LS
IB/sloping of BH
IS/sloping of BH
TB/LS
TB/US
HF/BH
HF/TST
Total
Note* The number of cases of damage per cargo hold is the quotients of number of cargo damage
divided by number of cargo holds.
As given in Table A1, the damage to members in ballast hold is 99.8% of the total number ofthe case of damage for primary members and the damage to holds other than ballast hold is 0.2%.
About 72% of damage occurred at the connection between inner bottom plating and the sloping
plate of the hopper tank and between inner bottom plating and the sloping and/or the vertical plateof the lower stool.

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Common Structural Rules for Bulk carriers

Technical Background for Rule Change Notice 3

Appendix 2 Technical Background for the treatment of mean stress andresidual stress
1. It is well and widely known that any initial residual stresses (σres), which are tensile and havemagnitudes that are normally close to the yield stresses of materials, exist in welded joints (hotspots) or their periphery thereof.
In cases where loads are imposed onto hot spots and stresses at such hot spots reach locallyyield stresses, any initial residual stresses are relaxed after the removal of such loads. Thisphenomenon is called the shake-down effect. This shake-down effect occurs in those perfectly
elasto plastic models introduced in the Rules.
Furthermore, it is also known that static mean stresses (structural mean stresses) influence thefatigue strengths.
The effect of any mean stresses influencing the fatigue strengths can be evaluated by the sum of
any residual stresses and structural mean stresses.
Since the S-N curves with slopes equal to 3, as given by UK-HSE standards, express fatigue
strengths of welded structures in those cases where residual welds close to the yield stresses ofmaterials exists, it cannot be used to evaluate the effects of mean stresses.
2. The relaxation of any initial residual stresses at hot spots can be evaluated by using shake-down
models based on the assumptions of perfectly elasto plastic models. Those loads to be considered
are hydrostatic loads (structural mean stresses) and hydrodynamic loads induced by waves.
Since those stress ranges due to hydrodynamic loads induced by waves are random variables inwhich wave heights are subject to the Gaussian process, any stresses contributing to shake-down
effects depend on the periods of duration in navigating under specific loading conditions.
Assuming that ships are imposed upon by significant hydrodynamic pressure only in cases
where such ships are at sea, these periods of duration for one loading condition can be set to about
10 days (105 cycles).
In this case, the magnitude of any stress ranges σ S dominating mean stress conditions during
this period can be expressed by 0.96∆σ 5 (Ref. SNAJ 190, November 2001), where ∆σ 5 is definedas the maximum stress range corresponding to these 105 cycles loads.
In those fatigue strength assessment procedures specified in the Rules, reference stresses
correspond to 104 cycle loads. In cases where ∆σ 5 is defined as the maximum stress range
corresponding to 105 cycles loads, the relationship between ∆σ 5 and ∆σ 4 is:∆σ 5 = 1.25∆σ 4Then, we can get the following relationship：
σ S = 0.96∆σ 5 = 1.2∆σ 4
The model regarding initial residual stresses σ res , mean stresses σ mean and σ S can beillustrated as given in Fig. A1 and σ max is used, in order to evaluate any shake-down effects.
From the relationship illustrated by the above figure, we can get the following equation:
σ max = σ res + σ mean + 0.5σ S = σ res + σ mean + 0.6∆σ 4
3. As specified above, shake-down effects are to be considered in cases where the σ max exceeds theyield stress of material (ReH).
In such cases, any considered mean stresses can be expressed by the following equation:
σ m = ReH − 0.6∆σ 4
In those cases where 0.5σ S + σ res + σ mean is less than ReH:
σ m = σ mean + σ res

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Common Structural Rules for Bulk Carriers

Technical Background for Rule Change Notice 3

The above cases are applicable to “Condition 1” which is defined the condition in which
maximum stress is the largest on the tension side among the loading conditions “homogeneous”,“alternate” “normal ballast” and “heavy ballast”
According to experience as well as some studies regarding fatigue damages of side
longitudinals in single hull tankers, initial weld residual stresses for welded joints such as
longitudinals are conservatively given the value of 0.25 ReH.

σ mean0.6∆σ 4σ S = 1.2∆σ 4

σ max

σ res
0
Fig. A1 Illustration of the relationship of σ res , σ mean and σ S
4. However, in the cases of fatigue strengths of any of the welded joints of primary members,
initial residual stress values of 0.25 ReH are too conservative considering the tendency of fatigue
damage, especially, in those cases where mean stresses of all loading conditions are compressions.
In the case of weld joints of primary members, any residual stresses after removal of applied
loads can be still evaluated by the following equation in order to consider shake-down effects.
σ res ' = σ m1 − σ mean1
Where,
σ m1 : the mean stress of the “Condition 1” considered the shake-down effectσ mean1 : the structural mean stress in the “Condition 1”.
However, in cases where σ mean1 is a compression, σ res ' should be taken to equal 0 considering thedamage tendencies of the welded joints of primary members.
5. In conclusion, the treatment of residual stresses of primary members is to be changed as
specified by this Rule Change Notice 3.

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