Section 6 Stiffeners

601. General

1. Where the angle between the web of stiffeners and shell plating is less than 75 ° the section mod- ulus is to be suitably increased above the normal requirements and, where necessary, the tripping brackets should be fitted.

2. Unless specified otherwise, the section modulus of members required by the rules are those includ- ing steel platings with the effective breadth of 0.1 is not to exceed one-half of the spacing of member. is the length specified in the relevant chapter.

3. Equal angles should be avoided for full bending due to reduced effective free flange by torsional stresses, and tripping effects.

4. The thickness of web and flange is not to be less than the following values, defined in Table 3.3.8.

Table 3.3.8 Scantlings of Stiffeners

602. Longitudinals

1. The section modulus of bottom, side longitudinals, longitudinal beams and longitudinal stiffeners in longitudinal bulkhead is not to be less than that obtained from the following formula :

or

cm

However, the following extended formula may be used when necessary.

or

cm

: span of the stiffeners (m ), defined in Ch 3, 107.

spacing of stiffeners (m ).

: bending moment factor, defined in Table 3.3.12, for load and boundary conditions, not defined in Table 3.3.12 -values are directly from general elastic bending theory.

: material factor, defined in Table 3.3.2.

load or impact pressure, defined in Ch 2.

: 83

: allowable stress, defined in Table 3.3.9. Between specified regions the s-value may vary linearly.

2. The bottom longitudinals should preferably be continuous through transverse members. If they are to be cut at transverse members, continuous brackets connecting the ends of the longitudinals are to be fitted.

3. In case of a keel plating, the distance between the center girder and the first longitudinal should not exceed 400 mm .

Table 3.3.9 Allowable Stress of Longitudinals

603. Transverse frames

The section modulus of transverse frames is not to be less than the greater of following formula.

or

c

: the values in accordance of locations.

= 6.5, below freeboard deck and in forepeak to the deck above freeboard deck.

= 4.0, elsewhere.

a nd : defined in 602.

: basic spacing of stiffeners (m

604. Lower frames

1. The lower frames are frames located outside the peak tanks, connected to the floors by strong brackets.

2. The section modulus of lower frames is not to be less than the greater of following the formula.

or

c

c

: defined in 602.

: basic spacing of stiffeners (m ).

3. The sectional modulus for lower frame is not to be less than that for the above frame.

4. The requirement given in Par 2 is based on the mid-span moment and on the assumption that ef- fective brackets are fitted at the lower end. The length of brackets is not to be less than 0.1

( = span from top of bottom structure to upper span point). The section modulus of frame includ- ing bracket is not to be less than 2 times that of the section modulus (Par 2 and Par 3) at top of bottom structure.

5. When the length of the free edge of the bracket is more than 40 times that of the plating thick- ness, a flange is to be fitted, the width being at least 1/15 of the length of the free edge.

6. If bracket at top of floor is omitted, the section modulus of the lower frames is to be increased by 75 %. The frames are to have effective end connections.

605. Transverse beams

The sectional modulus of transverse beams is not to be less than that obtained from formula :

the following

cm

and : defined in

606. Bulkhead stiffeners other than longitudinals

1. The section modulus of bulkhead stiffeners other than longitudinals is not to be less tained from the following formula :

than that ob-

cm

and : defined in

basic spacing of stiffeners (m ).

: allowable stress, defined in Table 3.3.10.

bending moment factor, defined in Table 3.3.11, for load and boundary conditions, not defined in Table 3.3.11, m-values are directly from general elastic bending theory.

Table 3.3.10 Allowable Stresses of Bulkhead

Stiffeners ( )

Table 3.3.11 Bending Moment Factor ( )

2. The end attachment of the stiffeners is to comply with the following.

(1) For tank, cargo and collision bulkheads : Bracket to be fitted at both ends, defined in 612.

(2) Transverse watertight bulkheads : Brackets are normally to be fitted at both ends. Brackets may be omitted when the distance from top of bulkhead to lower end of span is less than 6.0 (m ).

607. End bulkheads of superstructure and deckhouse, and exposed sides in deckhouse

1. The section modulus of stiffeners is not to be less than that obtained from the following formula :

cm

and : defined in 602.

2. Front stiffeners are to be connected to deck at both ends with connection areas not less than that of the following formula. Side and after end stiffeners in the lowest tier of erections are to have end connections.

cm

and : defined in 602.

3. When the poop front bulkhead is forming part of the engine room casing, the stiffeners are to have bracketed end connections.

4. In long deckhouses, openings in the sides are to have well rounded corners. Horizontal stiffeners are to be fitted at the upper and lower edge of large openings for windows.

608. Machinery casings

The section modulus of stiffeners is not to be less than that obtained from the following formula :

cm

: length of stiffeners (m ), minimum 2.5 m .

: spacing of stiffener (m ).

609. Bulwark stiffening

1. A strong bulb section or similar is to be continuously welded to the upper edge of the bulwark.

2. Bulwark stays are to be spaced not more than 2 m apart, and are to be in line with transverse beams or local transverse stiffening. Alternatively the toe of stay may be supported by a longi- tudinal member. The deck beam is to be continuously welded to the deck in way of stay.

3. Bulwarks on forecastle decks are to have stays fitted at every frame where the flare is considerable.

4. Stays of increased strength are to be fitted at ends of bulwark openings. Openings in bulwarks should not be situated near the end of superstructures.

610. Weather deck hatch covers and shell doors

1. The section modulus of stiffeners is given in 602. However, the coefficient ( ) and allowable stress are defined as follows:

=

= 135

2. The moment of inertia is not to be less than that obtained from the following formula :

cm

611. Doors in watertight bulkheads

The section modulus of stiffeners is given in 602. The coefficient ( ) and allowable stress are de- fined as follows:

= 125 , =

612. End connections of stiffeners

1. Normally all types of stiffeners (longitudinals, beams, frames, bulkhead stiffeners) are to be con- nected at their ends, defined in Par 2. Sniped ends may be allowed.

2. The arm lengths formula (refer to

of brackets for stiffeners is not to be less than that obtained from the following

Fig 3.3.4).

mm

= 70, flanged brackets.

75, unflanged brackets.

: rule section modulus (cm ).

: thickness of brackets (mm ).

Fig 3.3.4 Stiffener Brackets

3. The arm length is in no case to be taken less than 2 times the depth of the stiffener and brackets to be flanged if free lengths exceed 40 .

4. Bracketless end connections may be applied to longitudinals and other stiffeners running con- tinuously through girders.

5. End connection of the bottom and strength deck longitudinals is applied as below :

(1) The longtudinals are normally to be continuous at transverse members within 0.5

amidship.

(2) The longtudinals may be cut at transverse members. In that case, continuous brackets connecting

6. the ends of the longitudinals are to be fitted.

Stiffeners with snipped ends may be allowed in compartments and tanks where dynamic loads are small and where vibrations are considered to be of limited importance, provided the thickness of

: stiffener span (m ).

stiffener spacing (m ).

: pressure on stiffener