Guide for the Hull Structures

Reassessment of in Service Ships

Effective from 1 January 2003

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Guide for the hull structures reassessment of in service ships

INDEX

1 GENERAL................................................................................................................................................................................. 1

2 FIELD OF APPLICATION......................................................................................................................................................... 1

3 DEFINITIONS AND SYMBOLS ................................................................................................................................................ 1

4 PARTIAL SAFETY FACTORS ................................................................................................................................................. 2

4.1 General .......................................................................................................................................................................... 2
4.2 Partial safety factors based on the increased knowledge of the structure..................................................................... 2
4.2.1 General............................................................................................................................................................... 2
4.2.2 Partial safety factors γK1, γK2, γK3 and γK4 for plating ........................................................................................... 2
4.2.3 Partial safety factor γK5 for ordinary stiffeners .................................................................................................... 2
4.2.4 Partial safety factors γK6, γK7, γK8 and γK9 for primary supporting members........................................................ 2

5 ACCEPTANCE CRITERIA FOR THE HULL GIRDER STRENGTH......................................................................................... 2

6 ACCEPTANCE CRITERIA FOR PLATING .............................................................................................................................. 2

6.1 Application ..................................................................................................................................................................... 2
6.1.1 General............................................................................................................................................................... 2
6.1.2 Specific cases .................................................................................................................................................... 2
6.2 Renewal thicknesses ..................................................................................................................................................... 2
6.2.1 Overall renewal thickness................................................................................................................................... 2
6.2.2 Minimum renewal thickness ............................................................................................................................... 2
6.2.3 Renewal thickness of plating subjected to lateral pressure or wheeled loads.................................................... 4
6.2.4 Shear buckling renewal thickness ...................................................................................................................... 4
6.2.5 Rule gross thickness .......................................................................................................................................... 5

7 ACCEPTANCE CRITERIA FOR ORDINARY STIFFENERS.................................................................................................... 5

7.1 Applications ................................................................................................................................................................... 5
7.2 Renewal scantlings........................................................................................................................................................ 5
7.2.1 Renewal section modulus................................................................................................................................... 5
7.2.2 Renewal web and face plate thicknesses........................................................................................................... 5
7.2.3 Rule gross section modulus ............................................................................................................................... 5

8 ACCEPTANCE CRITERIA FOR PRIMARY SUPPORTING MEMBERS.................................................................................. 6

8.1 Application ..................................................................................................................................................................... 6
8.2 Work ratios .................................................................................................................................................................... 6
8.2.1 Reassessment work ratio ................................................................................................................................... 6
8.2.2 As-built work ratio ............................................................................................................................................... 7
8.2.3 Yielding work ratio .............................................................................................................................................. 7
8.2.4 Buckling work ratio ............................................................................................................................................. 7
8.3 Renewal scantlings........................................................................................................................................................ 9
8.3.1 Overall renewal thickness................................................................................................................................... 9
8.3.2 Yielding renewal thickness ................................................................................................................................. 9
8.3.3 Buckling renewal thickness ................................................................................................................................ 9

I
Guide for the hull structures reassessment of in service ships

1 GENERAL [1.3.1] of the Rules. This thickness is to be

The aim of this guide is to specify the criteria for the calculated as specified in [6.2.4]
reassessment of the hull structural elements of ships in tR4 : Shear buckling renewal thickness, in mm,
service, which may be carried out by RINA, at the request i.e. the thickness that the plating of a ship in
of the Owner. service is to have in order to fulfil the shear
The reassessment analysis is to be planned by the Owner buckling check, according to the strength
and RINA before commencing a Class survey requiring principles in Pt B, Ch 4, Sec 3, [1.3.1] of the
thickness gauging. Rules. This thickness is only to be
The reassessment is carried out by checking the strength considered for ships equal to or greater than
of the ship in her actual state, as shown by the thickness 90 m in length and is to be calculated as
gauging, against the acceptance criteria stated in this specified in [6.2.5]
guide for the hull girder, plating, ordinary stiffeners and tG : Rule gross thickness, in mm, of plating,
primary supporting members. defined in [6.2.6]
The strength checks are also carried out to identify tA,W : As-built thickness of ordinary stiffener web,
possible "hot spot items" (see [3]) to address the following in mm
close-up surveys. Other “hot spot items” may result from tA,F : As-built thickness of ordinary stiffener face
fatigue analyses and surveyors inspections. plate, in mm
This guide is also intended to provide the criteria for a local tM,W : Measured thickness of ordinary stiffener
strength assessment of structural elements based on the web, in mm
measured thicknesses, to be carried out on the occasion of tM,F : Measured thickness of ordinary stiffener face
a CAP survey as required by the RINA “ Guide for the Ship plate, in mm
3
Condition Assessment Programme (CAP) ”. wM : Section modulus, in cm , of ordinary
stiffeners, to be calculated as specified in Pt
2 FIELD OF APPLICATION B, Ch 4, Sec 3, [3.4] of the Rules on the
basis of the measured thicknesses of web,
This guide applies to all types of ships to which the Rules face plate and attached plating
(as defined in 3) apply. wR : Renewal section modulus, in cm , of
3

ordinary stiffeners i.e. the section modulus

3 DEFINITIONS AND SYMBOLS that an ordinary stiffener of a ship in service
“Rules” means the Rules for the Classification of Ships in is to have to fulfil the yielding check,
force at the time of reassessment. according to the strength principles in Pt B,
“As-built thickness” means the thickness indicated on the Ch 4, Sec 3, [1.2.1] of the Rules
drawings for the ship at the time of construction. tR,W : Renewal thickness, in mm, of ordinary
“Rule thickness” and “Rule section modulus” mean the stiffener web, i.e. the web thickness that an
thickness of plating and the section modulus of ordinary ordinary stiffener of a ship in service is to
stiffeners, as required by the Rules. have in order to fulfil the buckling check,
“Hot spot items” means those items that are to be closely according to the strength principles in Pt B,
inspected during surveys. Ch 4, Sec 3, [1.3.2] of the Rules. This
tA : As-built thickness of plating, in mm thickness is to be calculated as specified in
tM : Measured thickness of plating, in mm [7.2.2]
tC : Corrosion additions, in mm, defined in Pt B, tR,F : Renewal thickness, in mm, of ordinary
Ch 4, Sec 2, [3] of the Rules stiffener face plate, i.e. the face plate
tC1, tC2 : Corrosion additions, in mm, defined in Pt B, thickness that an ordinary stiffener of a ship
Ch 4, Sec 2, [3] of the Rules for the two in service is to have in order to fulfil the
compartments separated by the plating buckling check, according to the strength
under consideration. For internal plating of a principles in Pt B, Ch 4, Sec 3, [1.3.2] of the
compartment, tC1 = tC2 = tC Rules. This thickness is to be calculated as
tR : Overall renewal thickness, in mm, of plating, specified in [7.2.2]
3
in mm, defined in: wG : Rule gross section modulus, in cm , of
[6.2.1] in general ordinary stiffeners, defined in [7.2.3]
[8.3.1] for the plating which constitutes W RR : Reassessment work ratio, defined in [8.2.1]
primary supporting members W RA : As-built work ratio, defined in [8.2.2]
tR1 : Minimum renewal thickness, in mm, of tRY : Yielding renewal thickness, in mm, of
plating defined in [6.2.2] primary supporting members, i.e. the
tR2 : Renewal thickness, in mm, of plating thickness that the plating which constitutes
subjected to lateral pressure or wheeled primary supporting members of a ship in
loads, i.e. the thickness that the plating of a service is to have in order to fulfil the yielding
ship in service is to have in order to fulfil the check, according to the strength principles in
strength check, according to the strength Pt B, Ch 4, Sec 3, [1.2.2] of the Rules. This
principles in Pt B, Ch 4, Sec 3, [1.1] of the thickness is to be calculated as specified in
Rules. This thickness is to be calculated as [8.3.2]
specified in [6.2.3] tRB : Buckling renewal thickness, in mm, of
tR3 : Compression buckling renewal thickness, in primary supporting members, i.e. the
mm, i.e. the thickness that the plating of a thickness that the plating which constitutes
ship in service is to have in order to fulfil the primary supporting members of a ship in
compression buckling check, according to service is to have in order to fulfil the
the strength principles in Pt B, Ch 4, Sec 3, buckling check, according to the strength

1
Guide for the hull structures reassessment of in service ships

principles in Pt B, Ch 4, Sec 3, [1.3.1] of the • [8.3.3] for buckling strength checks (γK9)
Rules. This thickness is to be calculated as
specified in [8.3.3]
2 5 ACCEPTANCE CRITERIA FOR THE HULL GIRDER
E : Young’s modulus, in N/mm , to be taken
STRENGTH
equal to:
5 2
E = 2,06.10 N/mm : for steels in general The hull girder section modulus calculated considering the
5 2
E = 1,93.10 N/mm : for stainless steels: measured thicknesses is to be not less than 90% of the
ν : Poisson’s ratio. Unless otherwise specified, hull girder section modulus required by the Rules for new
a value of 0,3 is to be taken into account ships.
ReH : Minimum yield stress, in N/mm , of the
2 Where this check is not complied with, steel renewals of
material, defined in Pt B, Ch 4, Sec 1, [2] of the continuous longitudinal elements in the deck and
the Rules bottom zones are to be carried out as far as deemed
γm, γR, γK1,..., γK9 : Partial safety factors, defined in [4]. necessary to fulfil the above requirement.

4 PARTIAL SAFETY FACTORS 6 ACCEPTANCE CRITERIA FOR PLATING

4.1 General 6.1 Application

The partial safety factors γm and γR are defined in:
• Pt B, Ch 7, Sec 1, [1.2] or Pt B, Ch 8, Sec 3, [1.2] of the 6.1.1 General
Rules, as applicable, for plating The acceptance criteria for measured thicknesses of
• Pt B, Ch 7, Sec 2, [1.2] or Pt B, Ch 8, Sec 4, [1.2] of the plating, together with the application procedure to be
Rules, as applicable, for ordinary stiffeners adopted during the reassessment of hull structures, are
• Pt B, Ch 7, Sec 3, [1.3] or Pt B, Ch 8, Sec 5, [1.3] of the represented in the flow chart in Fig 1.
Rules, as applicable, for primary supporting members. The meaning of the symbols utilised in the flow chart is
specified in [6.2].
4.2 Partial safety factors based on the increased
knowledge of the structure 6.1.2 Specific cases
For the specific cases indicated in Tab 1, the acceptance
4.2.1 General criteria to be applied, in lieu of those in [6.1.1], are those
specified in the Rules to which reference is made in the
The partial safety factors γK1, γK2, … to γK9 take into same table.
account the increased knowledge of the structural
behaviour obtained through surveys carried out on the
6.2 Renewal thicknesses
structures of ships in service and verification of their
performance. Therefore, they have values equal to or less
than 1,0 and apply to reduce the partial safety factor on 6.2.1 Overall renewal thickness
resistance, *R, adopted in the strength checks of new The overall renewal thickness is to be obtained, in mm,
ships (see Part B, Chapter 7 or Part B, Chapter 8 of the from the following formula:
Rules, as applicable).
tR = max (tR1, tR2, tR3, tR4)
4.2.2 Partial safety factors γK1, γK2, γK3 and γK4 for
plating 6.2.2 Minimum renewal thickness
The partial safety factors γK1, γK2, γK3 and γK4 are to be The minimum renewal thickness is to be obtained, in mm,
from the following formula:
calculated as specified in:
• [6.2.2] for minimum thickness checks (γK1) tR1 = t1 γK1
• [6.2.3] for the strength checks of plate panels subjected where:
to lateral pressure or wheeled loads (γK2) t1 : Minimum net thickness, in mm, to be
• [6.2.4] for compression buckling strength checks (γK3) calculated as specified in Pt B, Ch 7, Sec 1,
• [6.2.5] for shear buckling strength checks (γK4) [2.2] or Pt B, Ch 8, Sec 3, [2.2] of the Rules,
as applicable
4.2.3 Partial safety factor γK5 for ordinary stiffeners γK1 : Partial safety factor for minimum thickness
The partial safety factor for yielding strength checks (γK5) is checks:
to be calculated as specified in [7.2.1].
γK1 = NP ψ1
4.2.4 Partial safety factors γK6, γK7, γK8 and γK9 for without being greater than 1,0
primary supporting members
Np : Coefficient defined in Tab 2
The partial safety factors γK6, γK7, γK8 and γK9 are to be
calculated as specified in: t C1 + t C2
ψ1 = 1 +
• [8.2.1] for reassessment structural analyses (γK6, γK7) t1
• [8.3.2] for yielding strength checks (γK8)

2
Guide for the hull structures reassessment of in service ships

Figure 1 : Acceptance criteria for measured thicknesses of plating and application procedure

YES
Thickness measurements tM tM < t R Steel renewal required

NO

YES No steel renewal

tM > tR + 0.5 (t G- tR) required

NO

HOT SPOT
ITEM

Table 1 : Renewal thicknesses for plating in specific cases

Ship type Item Rules to be applied
Ships with the service notation bulk carrier ESP, of Plating of vertically corrugated Part A of the Rules
single side skin construction, having L≥150 m, intended transverse watertight bulkheads
for the carriage of bulk cargoes having dry bulk density
3
equal to or greater than 1,0 t/m , contracted for
construction on or after 1 July 1998
Ships with the service notation bulk carrier ESP, Hatch cover plating Part A of the Rules
contracted for construction on or after 1 July 1998
Ships with the service notation bulk carrier ESP, of Plating of vertically corrugated Pt A, Ch 6, App 1 of the Rules
single side skin construction, having L≥150 m, intended transverse watertight bulkhead
for the carriage of bulk cargoes having dry bulk density between cargo holds No. 1 and 2
3
equal to or greater than 1,78 t/m , contracted for
construction prior to 1 July 1998

Table 2 : Coefficient NP
Plating Coefficient NP
L < 90 m L ≥ 90 m
In general, including that which constitutes the web of primary 0,75 0,80
supporting members
Plating which constitutes the face plate of primary supporting 0,80 0,85
members
Bottom primary supporting members of ships with one of the 0,80 0,85
service notations bulk carrier ESP, ore carrier ESP or
combination carrier ESP
Hatch coaming brackets 0,70 0,75
Cross ties of ships with the service notation oil tanker ESP 0,80 0,85

3
Guide for the hull structures reassessment of in service ships

6.2.3 Renewal thickness of plating subjected to girder transverse sections as being constituted
lateral pressure or wheeled loads by elements (plating, ordinary stiffeners,
primary supporting members) with measured
The renewal thickness of plating subjected to lateral pres- thicknesses and scantlings
sure or wheeled loads is to be obtained, in mm, from the
following formula: ε1, K1 : Coefficients defined in Pt B, Ch 7, Sec 1,
[5.3.1] or Pt B, Ch 8, Sec 3, [5.3.1] of the
tR2 = t2 γK2
Rules, as applicable
where:
γK3 : Partial safety factor for compression buckling
t2 : Net thickness, in mm, to be calculated as strength checks:
specified in:
γK3 = NP ψ3
• Pt B, Ch 7, Sec 1, [3] or Pt B, Ch 8, Sec 3,
[3] of the Rules, as applicable, for plating without being greater than 1,0
subjected to lateral pressure
• Pt B, Ch 7, Sec 1, [4] or Pt B, Ch 8, Sec 3, Np : Coefficient defined in Tab 2
[4] of the Rules, for plating subjected to
t C1 + t C2
wheeled loads ψ 3 = 1+
where the hull girder stresses are to be t3
calculated considering the hull girder
transverse sections constituted by elements 6.2.5 Shear buckling renewal thickness
(plating, ordinary stiffeners, primary supporting
members) having their measured thicknesses The shear buckling renewal thickness is to be obtained, in
and scantlings mm, from the following formula:
tR4 = t4 γK4
γK2 : Partial safety factor for the strength checks of
plate panels subjected to lateral pressure or t4 : Net thickness to be obtained, in mm, from the
wheeled loads: following formulae:
γK2 =NP ψ2 R eH
for γ m γ R τ1 ≤ :
without being taken greater than 1,0 2 3
Np : Coefficient defined in Tab 2
t4 =
b (
τ1 γ R γ m 12 1 - ν 2
103
)
t +t π EK 2
ψ 2 = 1 + C1 C2
t2
R eH
6.2.4 Compression buckling renewal thickness for γ m γ R τ1 > :
2 3
The compression buckling renewal thickness is to be
obtained, in mm, from the following formula:
b (
3 1 - ν 2 ReH ) 2

( )10
3
t4 =
tR3 = t3 γK3 π EK 2 ReH − 3 τ1 γ R γ m
where:
t3 : Net thickness to be obtained, in mm, from the b : Length, in m, of the plate panel side, defined
following formulae: in Pt B, Ch 7, Sec 1, [5.1.3] of the Rules
ReH τ1 : In plane hull girder shear stress, in N/mm , to
2
for γ m γ R σ x1 ≤ :
2 be calculated as specified in Pt B, Ch 7, Sec
1, [5.2.3] of the Rules, considering the hull
t3 =
b ( )
σ x1 γ R γ m 12 1 - ν 2
103
girder transverse sections as being constituted
π EK1 ε by elements (plating, ordinary stiffeners,
primary supporting members) with measured
ReH thicknesses and scantlings
for γ m γ R σ x1 > :
2 K2 : Coefficient defined in Pt B, Ch 7, Sec 1, [5.3.2]
of the Rules

t3 =
b ( )
3 1 - ν 2 R eH
2
103 γK4 : Partial safety factor for shear buckling strength
π EK1 ε (R eH − σ x1 γ R γ m ) checks:
b : Length, in m, of the plate panel side, defined γK4 = NP ψ4
in Pt B, Ch 7, Sec 1, [5.1.2] or Pt B, Ch 8, Sec
3, [5.1.2] of the Rules, as applicable without being greater than 1,0

σx1 : In plane hull girder normal stress, in N/mm to

2 Np : Coefficient defined in Tab 2
be calculated as specified in Pt B, Ch 7, Sec t C1 + t C2
1, [5.2.2] or Pt B, Ch 8, Sec 3, [5.2.2] of the ψ 4 = 1+
Rules, as applicable, considering the hull t4

4
Guide for the hull structures reassessment of in service ships

6.2.6 Rule gross thickness α, β : Parameters, depending on the type of ordinary

The Rule gross thickness is to be obtained, in mm, from stiffener, defined in Pt B, Ch 4, Sec 2, Tab 1 of
the following formula: the Rules.
tG = max (t1, t2, t3, t4) + tC1 + tC2 Table 3 : Coefficient NS
where t1, t2, t3 and t4 are the net thicknesses defined in Ordinary Coefficient NS
[6.2.2], [6.2.3], [6.2.4] and [6.2.5], respectively. stiffeners L < 90 m L ≥ 90 m
Flat bars and bulb profiles 0,75 0,80
7 ACCEPTANCE CRITERIA FOR ORDINARY
Flanged profiles 0,80 0,81
STIFFENERS

7.1 Applications 7.2.2 Renewal web and face plate thicknesses

The acceptance criteria for measured scantlings of
ordinary stiffeners, together with the application procedure The renewal web and face plate thicknesses are to be
to be adopted during the reassessment of hull structures, obtained, in mm, from the following formulae:
are represented in the flow chart in Fig 2.
tR,W = hW / CW
The meaning of the symbols utilised in the flow chart is
specified in [7.2]. tR,F = bF / CF
where:
7.2 Renewal scantlings
hw : Web height, in mm
7.2.1 Renewal section modulus bf : Face plate breadth, in mm
3
The renewal section modulus is to be obtained, in cm , CW , CF : Coefficients depending on the type and
from the following formula: material of ordinary stiffeners, defined in Tab
wR = wY γK5 4.
where: In any case, the renewal web and face plate thicknesses
3
wY : Net section modulus, in cm , to be calculated are to be not less than those obtained according to Pt A,
as specified in Pt B, Ch 7, Sec 2, [3] or Pt B, Ch 2, App 3, [4] of the Rules.
Ch 8, Sec 4, [3] of the Rules, as applicable,
where the hull girder stresses are to be 7.2.3 Rule gross section modulus
calculated considering the hull girder
transverse sections constituted by elements 3
(plating, ordinary stiffeners, primary supporting The Rule gross section modulus is to be obtained, in cm ,
members) with measured thicknesses and from the following formula:
scantlings w Y + βt C
wG =
γK5 : Partial safety factor for yielding strength 1 − αt C
checks: where:
γK5 = NS ψ5 α, β : Parameters, depending on the type of ordinary
stiffener, defined in Pt B, Ch 4, Sec 2, Tab 1 of
without being greater than 1,0 the Rules
NS : Coefficient defined in Tab 3 wY :
3
Net section modulus, in cm , defined in [7.2.1].
βt C
1+
wY
ψ5 =
1 − αt C

5
Guide for the hull structures reassessment of in service ships

Figure 2 : Acceptance criteria for measured scantlings of ordinary stiffeners and application procedure

WM< W R

OR
Scantling measurements t <t YES
M,W R,W Steel renewal required
t t t
M' M,W' M,F
OR
t <t
M,F R,F

NO

WM>W
_ R +0,25(WG - WR)

AND
t >t
_ + 0,25 (t -t ) YES
M,W R,W A, W R,W No steel renewal required
AND
t >t + 0,25 (t -t )
M,F _ R,F A,F R, F

NO

HOT SPOT ITEM

Table 4 : Coefficients CW and CF

CW CF
Type of ordinary
stiffeners ReH = 235 ReH = 315 ReH = 355 ReH = 235 ReH = 315 ReH = 355
2 2 2 2 2 2
N/mm N/mm N/mm N/mm N/mm N/mm
Flat bar 20 18 17,5 Not applicable
Bulb 56 51 49 Not applicable
With symmetrical face 56 51 49 34 30 29
plate
With non-symmetrical 56 51 49 17 15 14,5
face plate

8 ACCEPTANCE CRITERIA FOR PRIMARY The meaning of the symbols utilised in the flow chart is
SUPPORTING MEMBERS specified in [8.2] and [8.3].

8.1 Application 8.2 Work ratios

The acceptance criteria for measured scantlings of primary
supporting members, together with the application 8.2.1 Reassessment work ratio
procedure to be adopted during the reassessment of hull The reassessment work ratio is to be obtained from the
structures, are represented in the flow chart in Fig 3. following formula:

6
Guide for the hull structures reassessment of in service ships

WRR = max (γK6WRY, γK7WRB) γ R γ m τb

WR B2 =
where: τC
γK6, γK7 : Partial safety factors for reassessment WRB3 : Compression, bending and shear buckling
structural analyses: work ratio:
γK6 = 0,85 F
WR B3 =
γK7 = 1,00 FC

WRY : Yielding work ratio, defined in [8.2.3] WRB4 : Bi-axial compression and shear buckling work
ratio:
WRB : Buckling work ratio, defined in [8.2.4].
1
 n n n
8.2.2 As-built work ratio   σa   σb  
WR B 4 = γR γm   + 

The as-built work ratio is to be obtained from the following   R a σ c,a  R σ
  b c,b


formula:
 
WRA = max (WRY, WRB) σa, σb, τb : Normal and shear stresses, in N/mm2, defined
where: in Pt B, Ch 7, Sec 1, [5.4] of the Rules
2
WRY : Yielding work ratio, defined in [8.2.3] σc, τc : Critical buckling stresses, in N/mm , defined in
Pt B, Ch 7, Sec 1, [5.3] of the Rules
WRB : Buckling work ratio, defined in [8.2.4].
F : Coefficient defined in Pt B, Ch 7, Sec 1, [5.4.4]
8.2.3 Yielding work ratio of the Rules
The yielding work ratio is to be obtained from the following Fc : Coefficient to be obtained from the following
formula: formula:
γ R γ m σ VM
WR y = σ c om b R eH
Ry for ≤ : Fc = 1
F 2γ R γ m
where:

σVM :
2
Equivalent stress, in N/mm , to be calculated σ c om b R eH
for > :
as specified in Pt B, Ch 7, App 1, [5.1.2] of the F 2γ R γ m
Rules, considering the hull structure as being
constituted by elements (plating, ordinary
stiffeners, primary supporting members) with 4σ comb  σ comb 
Fc = 1 − 
measured thicknesses and scantlings ReH γ R γ m  ReH γ R γ m 
2
Ry : Minimum yield stress, in N/mm , of the
2 2
material, to be taken equal to 235/k N/mm σcomb : Combined stress in N/mm , defined in Pt B,
Ch 7, Sec 1, [5.4.4] of the Rules
k : Material factor, defined in Pt B, Ch 4, Sec 1,
[2.3] of the Rules. σc,a, σc,b : 2
Critical buckling stresses, in N/mm , defined in
Pt B, Ch 7, Sec 1, [5.4.5] of the Rules
8.2.4 Buckling work ratio
n, Ra, Rb: Coefficients defined in Pt B, Ch 7, Sec 1,
The buckling element work ratio is to be obtained from the [5.4.5] of the Rules.
following formula:
The above quantities are to be calculated considering the
WRB = max (WRB1, WRB2, WRB3, WRB4)
hull structure as being constituted by elements (plating,
where: ordinary stiffeners, primary supporting members) with
WRB1 : Compression buckling work ratio: measured thicknesses and scantlings.
γ R γ mσb
WR B1 =
σC
WRB2 : Shear buckling work ratio:

7
Guide for the hull structures reassessment of in service ships

Figure 3 : Acceptance criteria for measured scantlings of primary supporting members and application procedure

Scantling measurements
tM

STRUCTURAL ANALYSIS

WR > 0,975
NO R
OR
t < 0,7 t
M A

YES

Damage found? tM> tR

YES YES

NO Reinforcement
NO Definition

tM> tR
YES NO
STRUCTURAL ANALYSIS
UPDATE

WR A > 1,0
YES for the item affected
by the damage

NO

No steel renewal HOT SPOT Steel renewal Repair with

required ITEM required reinforcement

8
Guide for the hull structures reassessment of in service ships

8.3 Renewal scantlings 0,25(t C1 + t C2 )

ψ Y = 1+
ty
8.3.1 Overall renewal thickness
The overall renewal thickness is to be obtained, in mm, 8.3.3 Buckling renewal thickness
from the following formula:
The buckling renewal thickness is to be obtained, in mm,
tR = max (tRY, tRB, 0,75tA) from the following formula:
tRB = tB γK9
8.3.2 Yielding renewal thickness
where:
The yielding renewal thickness is to be obtained, in mm,
from the following formula: tB : Net thickness to be obtained, in mm, from the
tRY = tY γK8 following formula:

t B = [t A − 0,5(t C1 + t C2 )]
3
where: WR B
tY : Net thickness to be obtained, in mm, from the WRB : Buckling work ratio, defined in [8.2.4]
following formula:
tY = [tA - 0,5 (tC1 + tC2)] WRY γK9 : Partial safety factor for buckling strength
checks:
WRY : Yielding work ratio, defined in [8.2.3]
γK9 = NP ψB
γK8 : Partial safety factor for yielding strength
checks: Np : Coefficient defined in Tab 2
0,25(t C1 + t C2 )
γK8 = NP ψY ψB = 1+
tB
Np : Coefficient defined in Tab 2