Section 7 Welding and structural details

7.1 Application

7.1.1 Requirements are given in this Section for the following:

Welding-connection details, defined practices and sequence, consumables and equipment, procedures, workmanship and inspection.
End connection scantlings and constructional details for longitudinals, beams, frames and bulkhead stiffeners.
Primary member proportions, stiffening and construction details.

7.2 Welding – general

7.2.1 The plans to be submitted for approval are to indicate clearly details of the welded connections of main structural members, including the type and size of welds. This requirement includes welded connections to steel castings. The information to be submitted should include the following:

Whether weld sizes given are throat thicknesses or leg lengths.
Grades and thicknesses of materials to be welded.
Location, types of joints and angles of abutting members.
Reference to welding procedures to be used.
Sequence of welding of assemblies and joining up of assemblies.

7.2.2 Unless otherwise indicated, all welding is to be in accordance with the requirements of Ch 13 Requirements for Welded Construction of the Rules for the Manufacture, Testing and Certification of Materials, July 2022.

7.3 Welding – fillet welds

7.3.1 The throat thickness of fillet welds is to be determined from:

Throat thickness

t_p x weld factor x

where

d	=	the distance between start positions of successive weld fillet, in mm
s	=	the length, in mm, of correctly proportioned weld fillet, clear of end craters, and is to be not less than 75 mm
t_p	=	plate thickness, on which weld fillet size is based, in mm

Weld factors are given in Table 4.7.1 Weld factors, Table 4.7.3 Connections of primary structure and Table 4.7.4 Secondary member end connection welds.

7.3.2 Where double continuous fillet welding is proposed, the throat thickness is to be determined taking equal to 1,0.

7.3.3 The leg length of the weld is to be not less than times the specified throat thickness.

7.3.4 The plate thickness, t_p, to be used in the above calculation is generally to be that of the thinner of the two parts being joined. Where the difference in thickness is considerable, the size of fillet will be considered.

7.3.5 Where the thickness of the abutting member of the connection (e.g. the web of a stiffener) is greater than 15 mm and exceeds the thickness of the table member (e.g. plating), the welding is to be double continuous and the throat thickness of the weld is to be not less than the greatest of the following:

0,21 times thickness of the table member. The table member thickness used need not exceed 25 mm.
0,21 (0,27 in tanks) times half the thickness of the abutting member.
As required by Table 4.7.2 Throat thickness limits.

7.3.6 Except as permitted by Pt 3, Ch 4, 7.3 Welding – fillet welds 7.3.5, the throat thickness of the weld is not to be outside the limits specified in Table 4.7.2 Throat thickness limits.

7.3.7 Double continuous fillet welding is to be adopted in the following locations, and may be used elsewhere if desired:

Boundaries of weathertight decks and erections, including hatch coamings, companionways and other openings.
Boundaries of tanks and watertight compartments.
All lap welds in tanks.
Primary and secondary members to plating in way of end connections, and end brackets to plating in the case of lap connections.
Where Pt 3, Ch 4, 7.3 Welding – fillet welds 7.3.5 applies.
All water ballast tanks.
Other connections or attachments, where considered necessary, and in particular the attachment of minor fittings to higher tensile steel plating.

Figure 4.7.1 Weld dimensions and types

7.3.8 Where intermittent welding is used, the welding is to be made double continuous in way of brackets, lugs and scallops and at the orthogonal connections with other members.

7.3.9 As an alternative to intermittent welding, single-sided welding may be used. Only mechanised single-sided welding is acceptable although manual single-sided welding may be used at non-critical locations, e.g. deck house stiffeners. Where single-sided welding is used, the welding is to be made double continuous in way of brackets, lugs and scallops and at the orthogonal connections with other members.

7.3.10 Where structural members pass through the boundary of a tank, and leakage into the adjacent space could be hazardous or undesirable, full penetration welding is to be adopted for the members for at least 150 mm on each side of the boundary. Alternatively, a small scallop of suitable shape may be cut in the member close to the boundary outside the compartment, and carefully welded all round.

Table 4.7.1 Weld factors

Item			Weld factor	Remarks
(1)	General application:			except as required below:
	Watertight plate boundaries		0,34
	Non-tight plate boundaries		0,13
	Longitudinals, frames, beams and other secondary members to shell, deck or bulkhead plating		0,10
			0,13	in tanks
			0,21	in way of end connections
	Panel stiffeners, etc.		0,10
	Overlap welds generally		0,27
	Longitudinals of the flat-bar type to plating			see Note 2
(2)	Bottom construction in way of tanks:
	Non-tight centre girder:	to keel	0,27
		to bottom	0,21	no scallops
			0,21	in way of 0,2 times span at ends
	Non-tight boundaries of floors, girders and brackets		0,27	in way of brackets at lower end of main frame
	Watertight bottom girders		0,34
	Connection of girder to inner bottom in way of longitudinal bulkheads supported on inner bottom		0,44
	Connection of floors to inner bottom in way of plane bulkheads, bulkhead stools or corrugated and double plate bulkheads supported on inner bottom. The supporting floors are to be continuously welded to the inner bottom		0,44	Weld material compatible with floor material
(3)	Hull framing:
	Webs of web frames:	to shell	0,16
		to face plate	0,13
	Tank side brackets to shell and inner bottom		0,34
(4)	Decks and supporting structure:
	Strength deck plating to shell			As shown in Table 4.7.5 Weld connection of strength deck plating to sheerstrake but alternative proposals will be considered
	Webs of cantilevers to deck and to shell in way of root bracket		0,44
	Webs of cantilevers to face plate		0,21
	Pillars:	fabricated	0,10
		end connections	0,34	see Note 1
		end connections (tubular)	full penetration
	Girder web connections and brackets in way of pillar heads and heels			continuous
(5)	Bulkheads and tank construction:
	Plane, double plate and corrugated watertight bulkhead boundary at bottom, bilge, inner bottom, deck and connection to shelf plate, where fitted		0,44	weld size to be based on thickness of bulkhead plating weld material to be compatible with bulkhead plating material
	Shelf plate connection to stool		0,44	weld size to be based on thickness of bulkhead plating weld material to be compatible with bulkhead plating material
	Plane, double plate and corrugated bulkhead boundaries in way of deep tanks:
	- Boundary at bottom, bilge, inner bottom and deck		0,44
	- Connection of stool and bulkhead to lower stool shelf plating		full penetration
	- Connection of stool and bulkhead plating to upper stool shelf plate		0,44
	- Connection of bulkhead plating to hopper and topside tanks		0,44
	- Connection of bulkhead plating to side shell		0,34
	Secondary members where acting as pillars		0,13
	Non-watertight pillar bulkhead boundaries		0,13
	Perforated flats and wash bulkhead boundaries		0,10
(6)	Structure in pump room:
	Centre girder to keel and inner bottom		0,27
	Floors to centre girder in way of machinery seating		0,27
	Floors and girders to shell and inner bottom		0,21
	Machinery seating to supporting structure		0,21
	Transverse and longitudinal framing to shell		0,13
(7)	Miscellaneous fittings and equipment:
	Rings for manhole type covers, to deck or bulkhead		0,34
	Primary and secondary stiffening of tank covers		0,13
	Ventilator, air pipe, etc. coamings to deck and fittings		0,21
	Scuppers and discharges, to deck		0,44
	Deck machinery seats to deck		0,21	generally
	Mooring equipment seats		0,21	generally, but increased or full penetration welding may be required
	Guard rails, stanchions, etc. to deck		0,34
Note 1. Where pillars are fitted inside tanks or under watertight flats, the end connection is to be such that the tensile stress in the weld does not exceed 108 N/mm². Note 2. The throat thickness of the weld is to be determined by Pt 3, Ch 4, 7.3 Welding – fillet welds 7.3.5. For longitudinals within D/4 of the strength deck and with a thickness less than 100 mm, the throat thickness need not exceed 5,5 mm.

7.4 Welding of primary structure

7.4.1 Weld factors for the connections of primary structure are given in Table 4.7.3 Connections of primary structure.

7.4.2 The weld connection to shell, deck or bulkhead is to take account of the material lost in the notch where longitudinals or stiffeners pass through the member. Where the width of notch exceeds 15 per cent of the stiffener spacing, the weld factor is to be multiplied by:

7.4.3 Where direct calculation procedures have been adopted, the weld factors for the 0,2 x overall length at the ends of the members will be considered in relation to the calculated loads.

7.4.4 The throat thickness limits given in Table 4.7.2 Throat thickness limits are to be complied with.

Table 4.7.2 Throat thickness limits

Item		Throat thickness, in mm
		Minimum	Maximum
(1)	Double continuous welding	0,21t_p	0,44t_p
(2)	Intermittent welding	0,27t_p	0,44t_p or 4,5
(3)	All welds, overriding minimum
(a)	Plate thickness t_p ≤ 7,5 mm
	Hand or automatic welding	3,0	-
	Automatic deep penetration welding	3,0	-
(b)	Plate thickness t_p > 7,5 mm
	Hand or automatic welding	3,25	-
	Automatic deep penetration welding	3,0	-
Note 1. In all cases, the limiting value is to be taken as the greatest of the applicable values given above. Note 2. Where t_p exceeds 25 mm, the limiting values can be calculated using a notional thickness equal to 0,4(t_p + 25) mm, but is not to be taken as less than 25 mm. Note 3. The maximum throat thicknesses shown are intended only as a design limit for the approval of fillet welded joints. Any welding in excess of these limits is to be to the Surveyor's satisfaction.

Table 4.7.3 Connections of primary structure

Primary member face area, in cm²			Weld factor
Exceeding	Not exceeding	Position see Note 1	In tanks		In dry spaces
			To face plate	To plating	To face plate	To plating
	30,0	At ends	0,21	0,27	0,21	0,21
		Remainder	0,10	0,16	0,10	0,13
30,0	65,0	At ends	0,21	0,34	0,21	0,21
		Remainder	0,13	0,27	0,13	0,16
65,0	95,0	At ends	0,34	0,44 see Note 2	0,21	0,27
		Remainder	0,27	0,34	0,16	0,21
95,0	130,0	At ends	0,34	0,44 see Note 2	0,27	0,34
		Remainder	0,27	0,34	0,21	0,27
130,0		At ends	0,44	0,44 see Note 2	0,34	0,44 see Note 2
		Remainder	0,34	0,34	0,27	0,34
Note 1. The weld factors ‘at ends' are to be applied for 0,2 times the overall length of the member from each end, but at least beyond the toes of the member end brackets. On vertical webs the increased welding may be omitted at the top but is to extend at least 0,3 times the overall length from the bottom. Note 2. Where the web plate thickness is increased locally, the weld size may be based on the thickness clear of the increase but is to be not less than 0,34 times the increased thickness.

Table 4.7.4 Secondary member end connection welds

Connection

Weld area, A_w, in cm²

Weld factor

(1) Stiffener welded direct to plating

0,25A_s or 6,5 cm² whichever is the greater

0,34

(2) Bracketless connection of stiffeners or stiffener lapped to bracket or bracket lapped to stiffener:

0,27

(a) In dry space

0,34

(b) In tank

0,34

(3) Bracket welded to face of stiffener and bracket connection to plating

0,34

(4) Stiffener to plating for 0,1 times span at ends, or in way of end bracket if that be greater

0,34

Symbols

A_s	=	cross-sectional area of the stiffener, in cm²
A_w	=	the area of the weld, in cm², and is calculated as total length of weld, in cm, times throat thickness, in cm
Z	=	the section modulus, in cm², of the stiffener on which the scantlings of the bracket are based, see Pt 3, Ch 4, 7.8 Secondary member end connections

Note For maximum and minimum weld fillet sizes, see Table 4.7.2 Throat thickness limits.

Table 4.7.5 Weld connection of strength deck plating to sheerstrake

Item	Deck stringer plate thickness, mm	Weld type
1	t ≤ 15	Double continuous fillet weld with a weld factor of 0,44
2	15 < t ≤ 20	Single vee preparation to provide included angle of 50° with root in conjunction with a continuous fillet weld having a weld factor of 0,39; or Double vee preparation to provide included angles of 50° with root
3	t > 20	Double vee preparation to provide included angles of 50° with root but not to exceed 10 mm

Note 1. Welding procedure, including joint preparation, is to be specified. Procedure is to be qualified and approved for individual Builders. Note 2. See also Pt 3, Ch 4, 7.3 Welding – fillet welds 7.3.10. Note 3. For thickness t in excess of 20 mm the deck stringer plate can be bevelled to achieve a reduced thickness at the weld connection. The length of the bevel is in general to be based on a taper not exceeding 1 in 3 and the reduced thickness is in general to be not less than 0,65 times the thickness of the deck stringer plate or 20 mm, whichever is the greater. Note 4. Alternative connections will be considered.

7.5 Welding of primary and secondary end connections

7.5.1 Welding of end connections of primary members is to be such that the area of welding is not less than the cross-sectional area of the member, and the weld factor is to be not less than 0,34 in tanks or 0,27 elsewhere.

7.5.2 The welding of secondary member end connections is to be not less than as required by Table 4.7.4 Secondary member end connection welds. Where two requirements are given, the greater is to be complied with.

7.5.3 The area of weld, A_w, is to be applied to each arm of the bracket or lapped connection.

7.5.4 Where a longitudinal strength member is cut at a primary support and the continuity of strength is provided by brackets, the area of weld is to be not less than the cross-sectional area of the member.

7.5.5 Where the secondary member passes through, and is supported by, the web of a primary member, the weld connection is to comply with the requirements of Pt 3, Ch 4, 7.11 Arrangements at intersections of continuous secondary and primary members

7.5.6 The throat thickness limits given in Table 4.7.2 Throat thickness limits are to be complied with.

7.6 Welding equipment, consumables and procedure

7.6.1 Welding plant and equipment are to be in accordance with the requirements specified in Ch 13, 1.8 Welding equipment and welding consumables of the Rules for the Manufacture, Testing and Certification of Materials, July 2022.

7.6.2 Welding consumables and associated equipment are to be in accordance with the requirements specified in Ch 13, 1.8 Welding equipment and welding consumables of the Rules for the Manufacture, Testing and Certification of Materials, July 2022.

7.6.3 Welding procedures are to be established for the welding of all joints in accordance with the requirements specified in Ch 13, 1.9 Welding procedure and welder qualifications of the Rules for the Manufacture, Testing and Certification of Materials, July 2022.

7.6.4 All welding procedures are to be tested and qualified in accordance with the requirements of Ch 12 Welding Qualifications of the Rules for the Manufacture, Testing and Certification of Materials, July 2022 and are to be approved by the Surveyor prior to construction.

7.6.5 Welders and welding operators are to be proficient in the type of work to be undertaken and are to be qualified in accordance with the requirements specified in Ch 12 Welding Qualifications of the Rules for the Manufacture, Testing and Certification of Materials, July 2022.

7.6.6 A sufficient number of skilled supervisors is to be provided to ensure an effective and systematic control at all stages of welding operations.

7.7 Inspection of welds

7.7.1 Effective arrangements are to be provided by the Shipbuilder for the inspection of finished welds to ensure that all welding has been satisfactorily completed.

7.7.2 All finished welds are to be subjected to non-destructive examination (NDE) by personnel designated by the Builder in accordance with the requirements specified in Ch 13, 2.12 Non-destructive examination of steel welds of the Rules for the Manufacture, Testing and Certification of Materials, July 2022.

7.7.3 In addition to the requirements of Pt 3, Ch 4, 7.7 Inspection of welds 7.7.2, a number of checkpoints are to be examined by volumetric examination as detailed in Pt 3, Ch 4, 7.7 Inspection of welds 7.7.4 to Pt 3, Ch 4, 7.7 Inspection of welds 7.7.9.

7.7.4 Typical locations and number of checkpoints to be taken are shown in Table 4.7.6 Checkpoint locations.

7.7.5 Checkpoints are not to be identified on the ship’s structural components prior to the welding taking place.

7.7.6 For ultrasonic examination the length of each checkpoint is to be 0,5 m and for radiographic examination the length is to be a minimum of 0,3 m. At weld intersections, examination is to be in both weld directions.

7.7.7 The Builder is to provide the Surveyor with all the NDE reports of the checkpoints. These reports are to be available for the Surveyor to review within a short time after inspection, normally considered to be within 10 working days of the examination being carried out. Where welds are repaired, the NDE report is to include details of examination of both the defective weld and of the re-weld.

7.7.8 Where the Surveyor notes that a checkpoint has been repaired without record of the original defect, the Shipyard is to carry out additional examinations on additional lengths of weld. These lengths are to be adjacent to and on both sides of the defective checkpoint. These additional examinations are to be carried out in the presence of the Surveyor and reported in accordance with Pt 3, Ch 4, 7.7 Inspection of welds 7.7.7.

7.7.9 Where checkpoints are found to contain continuous or semi-continuous defects, additional lengths of weld adjacent to and on both sides of the defective length are to be subject to further volumetric examination. The NDE reports are to be submitted in accordance with Pt 3, Ch 4, 7.7 Inspection of welds 7.7.7.

Table 4.7.6 Checkpoint locations

Item	Location	Checkpoints
Intersections of butts and seams of fabrication and section welds	Throughout
	(a) hull envelope, shell envelope and deck structure plating:
	at highly stressed areas, see Note 1 remainder	all
	at highly stressed areas, see Note 1 remainder	1 in 2
	(b) longitudinal and transverse bulkheads	1 in 2
	(c) inner bottom plating:	1 in 2
Butt welds in plating	Throughout	1 m in 25 m, see Notes 2 and 3
Seam welds in plating	Throughout	1 m in 100 m
Butt welds in longitudinals	Hull envelope within 0,4L amidships	1 in 10 welds, see Note 4
Butt welds in longitudinals	Hull envelope outside 0,4L amidships	1 in 20 welds
Bilge keel butt welds	Within 0,4L amidships	all
Bilge keel butt welds	Remainder	1 in 3
Structural items when made with full penetration welding as follows:	Throughout
connection of stool and bulkhead to lower stool shelf plating		1 m in 20 m
vertical corrugations to an inner bottom		1 m in 20 m
hopper knuckles		1 m in 10 m
sheerstrake to deck stringer		1 m in 20 m
hatchways coaming to deck	Hatchway ends within 0,4L amidships	all
	Hatchway ends outside 0,4L amidships	1 in 2
	Remainder	1 in 40 m
Note 1. Typically those at sheerstrake, deck stringer, keel strake and turn of bilge. Note 2. Checkpoints in butt welds and seam welds are in addition to those at intersections. Note 3. Welds at inserts used to close openings in hull envelope plating are to be checked by NDE. Note 4. Particular attention is to be given to repair rates in butt welds in longitudinals. Additional welds are to be tested if defects such as lack of fusion or incomplete penetration are observed in more than 10 per cent of the welds examined.

7.8 Secondary member end connections

7.8.1 Secondary members, i.e. longitudinals, beams, frames and bulkhead stiffeners forming part of the hull structure, are generally to be connected at their ends in accordance with the requirements of this sub-Section. Where it is desired to adopt bracketless connections, the proposed arrangements will be individually considered.

7.8.2 Where end connections are fitted in accordance with these requirements, they can be taken into account in determining the effective span of the member.

7.8.3 Where the section modulus of the secondary member on which the bracket is based (Pt 3, Ch 4, 7.8 Secondary member end connections 7.8.5 and Pt 3, Ch 4, 7.8 Secondary member end connections 7.8.6) exceeds 2000 cm³, the scantlings of the connection will be considered.

7.8.4 The symbols used in this sub-Section are defined as follows:

a, b	=	the actual lengths of the two arms of the bracket, in mm, measured from the plating to the toe of the bracket
b_f	=	the breadth of the flange, in mm
t	=	the thickness of the bracket, in mm
Z	=	the section modulus of the secondary member, in cm³.

7.8.5 Where a longitudinal strength member is cut at a primary support and the continuity of strength is provided by brackets, the scantlings of the brackets are to be such that their section modulus and effective cross-sectional area are not less than those of the member. Care is to be taken to ensure correct alignment of the brackets on each side of the primary member.

7.8.6 In other cases the scantlings of the bracket are to be based on the modulus as follows:

Bracket connecting stiffener to primary member: modulus of the stiffener.
Bracket at the head of a main transverse frame where frame terminates: modulus of the frame.
Elsewhere: the lesser modulus of the members being connected by the bracket.

7.8.7 Typical arrangements of stiffener end brackets are shown diagrammatically in Figure 4.7.2 Diagrammatic arrangements of stiffener end brackets.

7.8.8 The lengths, a and b, of the arms of end brackets are to be measured from the plating to the toe of the bracket and are to be such that:

a + b ≥ 2,0l
a ≥ 0,8l
b ≥ 0,8l

where

but in no case is l to be taken as less than twice the web depth of the stiffener on which the bracket scantlings are to be based.

7.8.9 The length of arm of tank side and hopper side brackets is to be not less than 20 per cent greater than that required above.

7.8.10 The thickness of the bracket is to be not less than as required by Table 4.7.7 Thickness of brackets.

7.8.11 The free edge of the bracket is to be stiffened where any of the following apply:

The section modulus, Z, exceeds 2000 cm³.
The length of free edge exceeds 50t mm.
The bracket is fitted at the lower end of main transverse side framing.

7.8.12 Where a flange is fitted, its breadth is to be not less than:

but not less than 50 mm

7.8.13 Where the edge is stiffened by a welded face flat, the cross-sectional area of the face flat is to be not less than:

0,009b_tt cm² for offset edge stiffening.
0,014b_tt cm² for symmetrically placed stiffening.

Figure 4.7.2 Diagrammatic arrangements of stiffener end brackets

Table 4.7.7 Thickness of brackets

Bracket	Thickness, in mm	Limits
Bracket	Thickness, in mm	Minimum	Maximum
With edge stiffened:
(a) in dry spaces		6,5	12,5
(b) in tanks		7,5	13,5
Unstiffened brackets
(a) in dry spaces		7,5	-
(b) in tanks		8,5	-

7.8.14 Where the stiffening member is lapped on to the bracket, the length of overlap is to be adequate to provide for the required area of welding. In general, the length of overlap should be not less than or the depth of stiffener, whichever is the greater.

7.8.15 Where the free edge of the bracket is hollowed out, it is to be stiffened or increased in size to ensure that the modulus of the bracket through the throat is not less than that of the required straight edged bracket.

7.8.16 The arrangement of the connection between the stiffener and the bracket is to be such that at no point in the connection is the modulus reduced to less than that of the stiffener with associated plating.

7.8.17 The design of end connections and their supporting structure is to be such as to provide adequate resistance to rotation and displacement of the joint.

7.8.18 For arrangements where end brackets are not perpendicular to the adjacent plating the strength of the brackets, in terms of lateral stability, may need to be specially considered.

7.9 Construction details for primary members

7.9.1 The requirements for section modulus and inertia (if applicable) of primary members are given in Pt 3, Ch 4, 4 Hull envelope framing. This Section includes the requirements for proportions, stiffening and construction details for primary members in dry spaces and in tanks.

7.9.2 The requirements of this sub-Section can be modified where direct calculation procedures are adopted to analyse the stress distribution in the primary structure.

7.9.3 The symbols used in this sub-Section are defined as follows:

d_w	=	depth of member web, in mm
k	=	higher tensile steel factor, see Pt 3, Ch 2, 1.2 Steel
t_w	=	thickness of member web, in mm
A_f	=	area of member face plate or flange, in cm²
S_w	=	spacing of stiffeners on member web, or depth of unstiffened web, in mm.

7.9.4 Primary members are to be so arranged as to ensure effective continuity of strength, and abrupt changes of depth or section are to be avoided. Where members abut on both sides of a bulkhead, or on other members, arrangements are to be made to ensure that they are in alignment. Primary members in tanks are to form a continuous line of support and wherever possible, a complete ring system.

7.9.5 The members are to have adequate lateral stability and web stiffening and the structure is to be arranged to minimise hard spots and other sources of stress concentration. Openings are to have well rounded corners and smooth edges and are to be located having regard to the stress distribution and buckling strength of the panel.

7.9.6 Primary members are to be provided with adequate end fixity by end brackets or equivalent structure. The design of end connections and their supporting structure is to be such as to provide adequate resistance to rotation and displacement of the joint and effective distribution of the load from the member.

7.9.7 Where the primary member is supported by structure which provides only a low degree of restraint against rotation, the member is generally to be extended for at least two frame spaces, or equivalent, beyond the point of support before being tapered.

7.9.8 Where primary members are subject to concentrated loads, particularly if these are out of line with the member web, additional strengthening could be required.

7.9.9 The geometric properties of the members are to be calculated in association with an effective width of attached plating determined in accordance with Pt 3, Ch 3, 2.1 Geometric properties of section.

7.9.10 The minimum thickness or area of material in each component part of the primary member is given in Table 4.7.8 Minimum thickness of primary members.

7.9.11 Primary members constructed of higher tensile steel are to comply with Table 4.7.8 Minimum thickness of primary members.

7.9.12 Primary members are to be supported by tripping brackets. The tripping brackets supporting asymmetrical sections are to be spaced no more than two secondary frames apart. The tripping brackets supporting symmetrical sections are to be spaced no more than four secondary frames apart.

7.9.13 Tripping brackets are also to be fitted at the toes of end brackets and in way of heavy or concentrated loads such as the heels of pillars.

Table 4.7.8 Minimum thickness of primary members

Item	Requirement
(1) Member web plate, see Note	t_w = 0,01S_w but not less than 7 mm in dry spaces and 8 mm in tanks
(2) Member face plate
(3) Deck plating forming the upper flange of underdeck girders	and 10 per cent greater for hatch side girders. Width of plate is to be not less than 700 mm
Note For primary members having a web depth exceeding 1500 mm, the arrangement of stiffeners will be individually considered, and stiffening parallel to the member face plate could be required.

7.9.14 Where the ratio of unsupported width of face plate (or flange) to its thickness exceeds 16:1, the tripping brackets are to be connected to the face plate and on members of symmetrical section the brackets are to be fitted on both sides of the web.

7.9.15 Intermediate secondary members can be welded directly to the web or connected by lugs.

7.9.16 Where the depth of web of a longitudinal girder at the strength deck within 0,4L amidships exceeds additional longitudinal web stiffeners are to be fitted at a spacing not exceeding the value given in (a) or (b) as appropriate, with a maximum of for higher tensile steel members. In cases where this spacing is exceeded, the web thickness is, in general, to be suitably increased.

7.9.17 The arm length of unstiffened end brackets is not to exceed 100t_w. Stiffeners parallel to the bracket face plate are to be fitted where necessary to ensure that this limit is not exceeded.

7.9.18 Web stiffeners can be flat bars of thickness t_w and depth 0,1d_w, or 50 mm, whichever is the greater. Alternative sections of equivalent moment of inertia can be adopted.

7.9.19 Where openings are cut in the web, the depth of opening is not to exceed 25 per cent of the web depth, and the opening is to be so located that the edges are not less than 40 per cent of the web depth from the face plate. The length of opening is not to exceed the web depth or 60 per cent of the secondary member spacing, whichever is the greater, and the ends of the openings are to be equidistant from the corners of cut-outs for secondary members. Where larger openings are proposed, the arrangements and compensation required will be considered.

7.9.20 Openings are to have smooth edges and well-rounded corners.

7.9.21 Cut-outs for the passage of secondary members are to be designed to minimise the creation of stress concentrations. The breadth of cut-out is to be kept as small as practicable and the top edge is to be rounded, or the corner radii made as large as practicable. The extent of direct connection of the web plating, or the scantlings of lugs or collars, is to be sufficient for the load to be transmitted from the secondary member.

7.9.22 End connections of primary members are generally to comply with the requirements for secondary member end connections, taking Z as the section modulus of the primary member.

7.9.23 The thickness of the bracket is to be not less than that of the primary member web. The free edge of the bracket is to be stiffened.

7.9.24 Where a deck girder or transverse is connected to a vertical member on the shell or bulkhead, the scantlings of the latter could be required to be increased to provide adequate stiffness to resist rotation of the joint.

7.9.25 Where a member is continued over a point of support, such as a pillar or pillar bulkhead stiffener, the design of the end connection is to be such as to ensure the effective distribution of the load into the support. Proposals to fit brackets of reduced scantlings, or alternative arrangements, will be considered.

7.9.26 Connections between primary members forming a ring system are to minimise stress concentrations at the junctions. Integral brackets are generally to be radiused or well-rounded at their toes. The arm length of the bracket, measured from the face of the member, is to be not less than the depth of the smaller member forming the connection.

7.10 Continuity and alignment

7.10.1 The arrangement of material is to be such as will ensure structural continuity. Abrupt changes of shape or section, sharp corners and points of stress concentration are to be avoided.

7.10.2 Where members abut on both sides of a bulkhead or similar structure, care is to be taken to ensure good alignment.

7.10.3 Pillars and pillar bulkheads are to be fitted in the same vertical line wherever possible, and elsewhere arrangements are to be made to transmit the out of line forces satisfactorily. The load at head and heel of pillars is to be effectively distributed and arrangements are to be made to ensure the adequacy and lateral stability of the supporting members.

7.10.4 Continuity is to be maintained where primary members intersect and where the members are of the same depth, a suitable gusset plate is to be fitted.

7.10.5 End connections of structural members are to provide adequate end fixity and effective distribution of the load into the supporting structure.

7.10.6 The toes of brackets etc. should not land on unstiffened panels of plating. Special care should be taken to avoid notch effects at the toes of brackets, by making the toe concave or otherwise tapering it off.

7.10.7 Where primary and/or secondary members are constructed of higher tensile steel, particular attention is to be paid to the design of the end bracket toes in order to minimise stress concentrations. Sniped face plates which are welded onto the edge of primary member brackets are to be carried well around the radiused bracket toe and are to incorporate a taper not exceeding 1 in 3. Where sniped face plates are welded adjacent to the edge of primary member brackets, an adequate cross-sectional area is to be provided through the bracket toe at the end of the snipe. In general, this area measured perpendicular to the face plate, is to be not less than 60 per cent of the full cross-sectional area of the face plate, see Figure 4.7.3 Bracket toe construction.

Figure 4.7.3 Bracket toe construction

7.11 Arrangements at intersections of continuous secondary and primary members

7.11.1 Cut-outs for the passage of secondary members through the web of primary members, and the related collaring arrangements, are to be designed to minimise stress concentrations around the perimeter of the opening and in the attached hull envelope or bulkhead plating. The critical shear buckling stress of the panel in which the cut-out is made is to be investigated. Cut-outs for longitudinals will be required to have double lugs in areas of high stress, e.g. in way of cross tie ends.

7.11.2 Cut-outs are to have smooth edges, and the corner radii are to be as large as practicable, with a minimum of 20 per cent of the breadth of the cut-out or 25 mm, whichever is the greater. It is recommended that the web plate connection to the hull envelope or bulkhead should end in a smooth tapered ‘soft toe’. Recommended shapes of cut-out are shown in Figure 4.7.5 Cut-outs and connections, but consideration will be given to other shapes on the basis of maintaining equivalent strength and minimising stress concentration. Consideration is to be given to the provision of adequate drainage and unimpeded flow of air and water when designing the cut-outs and connection details.

7.11.3 Asymmetrical secondary members are to be connected on the heel side to the primary member web plate. Additional connection by lugs on the opposite side could be required.

7.11.4 Symmetrical secondary members are to be connected by lugs on one or both sides, as necessary.

7.11.5 The cross-sectional areas of the connections are to be determined from the proportion of load transmitted through each component in association with its appropriate permissible stress.

7.11.6 The total load P, in kN, transmitted to the primary member is to be derived in accordance with Table 4.7.9 Total load transmitted to connection of secondary members.

7.11.7 This load is to be apportioned between the connections as follows:

Transmitted through the collar arrangement:

where A_l is derived in accordance with Pt 3, Ch 4, 7.11 Arrangements at intersections of continuous secondary and primary members 7.11.8 and is not to be taken as greater than 0,25.

The collar load factor, C_f, is to be derived as follows:

Symmetrical secondary members

C_f = 1,85	for A_f ≤ 18
C_f = 1,85 - 0,0341(A_f -18)	for 18 < A_f ≤ 40
C_f = 1,1 - 0,01 (A_f - 40)	for A_f > 40

Asymmetrical secondary members

where

A_f	=	the area, in cm², of the primary member web stiffener in way of the connection including backing bracket, where fitted (see Pt 3, Ch 4, 7.11 Arrangements at intersections of continuous secondary and primary members 7.11.10)
b_l	=	the length of lug or direct connection, in mm, as shown in Figure 4.7.5 Cut-outs and connections. Where the lug or direct connections differ in length, a mean value of b_l is to be used.

Transmitted through the primary member web stiffener:

Where the web stiffener is not connected to the secondary member, P₁, is to be taken equal to P.

Table 4.7.9 Total load transmitted to connection of secondary members

Head, h₁, in metres

Total load, P in kN, transmitted to connection

Side and bottom shell longitudinals

(a) In general

P = 10,06(S_w - s₁/2) s₁ h₁ kN

h₁ = load height, in metres, derived in accordance with the following provisions, but to be taken as not less than the greater of

or 1,20 m.

(a) With mid-point of span at base line, h₁ = 0,8D₂

(b) With mid-point of span at a distance 0,6D₂ above base line, h₁ = f D₂ B_f

(c) With mid-point of span intermediate between (a) and (b). The value of h₁ is to be obtained by linear interpolation between values from (a) and (b).

(d) With mid-point of span higher than 0,6D₂ above base line. The value of h₁ is to be obtained by linear interpolation between the value from (b) and zero at the level of the deck edge amidships.

Secondary stiffening members of transverse and longitudinal bulkheads

h₁ = distance from the mid-point of span to top of tank but need not exceed 0,8D₂

Symbols

B_f	=	bow fullness factor, to be taken as 1
f	=	load height factor at level 0,6D, see Table 4.7.10 Load height factor, f
h₁	=	load height, in metres, see also Figure 4.7.4 Load height diagram for framing members
S_w	=	spacing of primary members, in metres
s₁	=	spacing of secondary members, in metres
D₂	=	D in metres, but need not be taken greater than 1,6T
L₁	=	L but need not be taken as greater than 190 m

Table 4.7.10 Load height factor, f

	Ship depth, D, in metres
	≤17,5	20	22,5	25	27,5	30
(1) At and abaft of 0,2L from the forward perpendicular	0,6	0,6	0,582	0,556	0,535	0,517
(2) Forward of 0,15L from the forward perpendicular	0,7	0,685	0,685	0,628	0,6	0,577
Note Intermediate values to be obtained by linear interpolation

Figure 4.7.4 Load height diagram for framing members

7.11.8 The effective cross-sectional area A₁ of the collar arrangements is to be taken as the sum of cross-sectional areas of the components of the connection as follows:

Direct connection:
Lug connection:

where

f₁	=	1,0 for symmetrical secondary member connections
f₁	=
t_w	=	thickness of primary member web, in mm
t_l	=	thickness, in mm, of lug connection, and is to be taken not greater than the thickness of the adjacent primary member web plate
W	=	overall width of the cut-out, in mm
W_l	=	width for cut-out asymmetrical to secondary member web, in mm See Figure 4.7.5 Cut-outs and connections

7.11.9 The values of A_f and A₁ are to be such that the stresses given in Table 4.7.11 Permissible stresses are not exceeded.

7.11.10 Where a bracket is fitted to the primary member web plate in addition to a connected stiffener, it is to be arranged on the opposite side to, and in alignment with the stiffener. The arm length of the bracket is to be not less than the depth of the stiffener, and its cross-sectional area through the throat of the bracket is to be included in the calculation of A_f.

7.11.11 In general where the primary member stiffener is connected to the secondary member, it is to be aligned with the web of the secondary member, except where the face plate of the latter is offset and abutted to the web, in which case the stiffener connection is to be lapped. Lapped connections of primary member stiffeners to mild steel bulb plate or rolled angle secondary members may also be permitted. Where such lapped connections are fitted, particular care is to be taken to ensure that the primary member stiffener wrap around weld connection is free from undercut and notches, see also Pt 3, Ch 4, 7.7 Inspection of welds.

7.11.12 Fabricated longitudinals having the face plate welded to the underside of the web, leaving the edge of the web exposed, are not recommended for side shell and longitudinal bulkhead longitudinals. Where it is proposed to fit such sections, a symmetrical arrangement of connection to transverse members is to be incorporated. This can be achieved by fitting backing brackets on the opposite side of the transverse web or bulkhead. The primary member stiffener and backing brackets are to be lapped to the longitudinal web, see Pt 3, Ch 4, 7.11 Arrangements at intersections of continuous secondary and primary members 7.11.11.

7.11.13 Collar arrangements are to satisfy the requirements of Pt 3, Ch 4, 7.11 Arrangements at intersections of continuous secondary and primary members 7.11.1 to Pt 3, Ch 4, 7.11 Arrangements at intersections of continuous secondary and primary members 7.11.12 inclusive. In addition, the weld area of the connections is to be not less than the following:

Connection of primary member stiffener to the secondary member:
A_w = 0,25A_f or 6,5 cm² whichever is the greater, corresponding to a weld factor of 0,34 for the throat thickness
Connection of secondary member to the web of the primary member:
A_w = corresponding to a weld factor of 0,34 in tanks or 0,27 in dry spaces for the throat thickness

where

A_w	=	weld area, in cm², and is calculated as total length of weld, in cm, multiplied by throat thickness, in cm
A_f	=	cross-sectional area of the primary member web stiffener, in cm², in way of connection
Z	=	the section modulus, in cm³, of the secondary member.

Figure 4.7.5 Cut-outs and connections

Table 4.7.11 Permissible stresses

Item		Direct stress, in N/mm² (see Notes 1 and 2)	Shear stress, in N/mm² (see Notes 1 and 2)
Primary member web plate stiffener within distance a of end, see Figure 4.7.5 Cut-outs and connections.		157	-
Welding of primary member web plate stiffener to secondary member	Butted	117,7 (double continuous fillet)	-
	Butted	157 (automatic deep penetration)	-
	Lapped	-	98,1 See Note 2
Lug or collar plate and weld	Single	-	98,1
Lug or collar plate and weld	Double
Note 1. The welding requirements of Pt 3, Ch 4, 7.1 Application to Pt 3, Ch 4, 7.7 Inspection of welds and Pt 3, Ch 4, 7.11 Arrangements at intersections of continuous secondary and primary members 7.11.13 are also to be complied with. Note 2. Where longitudinals are of higher tensile steel having a yield stress of 315 N/mm² or more, these stresses are to be divided by the factor 1,2 for application to side longitudinals above 0,3D² from the base line. For definition of D₂ see Table 4.7.9 Total load transmitted to connection of secondary members.

7.11.14 Where the stiffeners of the double bottom floors, and the hopper primary members are unconnected to the secondary members and offset from them (see Figure 4.7.6 Arrangement with offset stiffener), the collar arrangement is to satisfy the requirements of Pt 3, Ch 4, 7.11 Arrangements at intersections of continuous secondary and primary members 7.11.1 to Pt 3, Ch 4, 7.11 Arrangements at intersections of continuous secondary and primary members 7.11.13 inclusive. In addition, the fillet welds attaching the lugs to the secondary members are to be based on a weld factor of 0,44 for the throat thickness. To facilitate access for welding the offset stiffeners are to be located 50 mm from the slot edge furthest from the web of the secondary member. The ends of the offset stiffeners are to be suitably tapered and softened.

7.11.15 Alternative arrangements will be considered on the basis of their ability to transmit load with equivalent effectiveness. Details of the calculations made and testing procedures are to be submitted.

Figure 4.7.6 Arrangement with offset stiffener

7.12 Openings

7.12.1 Manholes, lightening holes and other cut-outs are to be avoided in way of concentrated loads and areas of high shear. In particular, manholes and similar openings are not to be cut in vertical or horizontal diaphragm plates in narrow cofferdams or double plate bulkheads within one-third of their length from either end, nor in floors or double bottom girders close to their span ends, or below the heels of pillars, unless the stresses in the plating and the panel buckling characteristics have been calculated and found satisfactory.

7.12.2 Manholes, lightening holes and other openings are to be suitably framed and stiffened where necessary.

7.12.3 Air and drain holes, notches and scallops are to be kept at least 200 mm clear of the toes of end brackets and other areas of high stress. Openings are to be well rounded with smooth edges. Details of scalloped construction are shown in Figure 4.7.1 Weld dimensions and types. Closely spaced scallops are not permitted in higher tensile steel members. Widely spaced air or drain holes may be accepted, provided that they are of elliptical shape, or equivalent, to minimise stress concentration and are, in general, cut clear of the weld connection.

7.13 Sheerstrake

7.13.1 Where an angled gunwale is fitted, the top edge of the sheerstrake is to be kept free of all notches and isolated welded fittings.

7.13.2 Where a rounded gunwale is adopted, the welding of fairlead stools and other fittings to this plate is to be kept to the minimum, and the design of the fittings is to be such as to minimise stress concentration.

7.13.3 Arrangements are to ensure a smooth transition from rounded gunwale to angled gunwale towards the ends of the ship.

7.14 Fittings and attachments

7.14.1 The quality of welding and general workmanship of fittings and attachments are to be equivalent to that of the main hull structure. Visual examination of all welds is to be supplemented by non-destructive testing as considered necessary by the Surveyor.

7.14.2 Gutterway bars at the upper deck are to be so arranged that the effect of main hull stresses on them is minimised.

7.14.3 Minor attachments, such as pipe clips, staging lugs and supports, are generally to be kept clear of toes of end brackets, corners of openings and similar areas of high stress. Where connected to asymmetrical stiffeners, the attachments may be in line with the web providing the fillet weld leg length is clear of the offset face plate or flange edge. Where this cannot be achieved the attachments are to be connected to the web, and in the case of flanged stiffeners they are to be kept at least 25 mm clear of the flange edge. On symmetrical stiffeners, they may be connected to the web or to the centreline of the face plate in line with the web.

7.14.4 Where necessary in the construction of the ship, lifting lugs can be welded to the hull plating but they are not to be slotted through. Where they are subsequently removed, this is to be done by flame or mechanical cutting close to the plate surface, and the remaining material and welding ground off. After removal the area is to be carefully examined to ensure freedom from cracks or other defects in the plate surface.