Common Structural Rules - Common Structural Rules for Bulk Carriers and Oil Tankers, January 2019 - Part 1 General Hull Requirements - Chapter 3 Structural Design Principles - Section 6 Structural Detail Principles - 4 Primary Supporting Members (PSM)
4 Primary Supporting Members (PSM)
4.1 General
4.1.1 Primary supporting members web stiffeners, tripping brackets and end brackets are to comply with [4.2] to [4.4]. Where the structural arrangement is such that these requirements cannot be complied with, adequate alternative arrangement has to be demonstrated by the designer.
4.2 Web stiffening arrangement
4.2.1 Web stiffeners arranged on primary supporting members are to comply with the requirements to scantlings of such stiffeners are given in Ch 8, Sec 2, [4.2].
4.3 Tripping bracket arrangement
4.3.1 Tripping brackets (see Figure 4) are generally to be fitted:
- At positions along the member span such that it satisfies the criteria of Ch 8, Sec 2, [5.1] for tripping bracket spacing and flange slenderness.
- At the toe of end brackets.
- At ends of continuous curved face plates.
- In way of concentrated loads.
- Near the change of section.
4.3.2 Where the width of the symmetrical face plate is greater than 400 mm, backing brackets are to be fitted in way of the tripping brackets.
4.3.3 Where the face plate of the primary supporting member exceeds 180 mm on either side of the web, a tripping bracket is to support the face plate.
Figure 4 : Primary supporting member: Tripping bracket arrangement
4.3.4 Arm length
The arm length of tripping brackets is not to be less than the greater of the following values, in m:
d = 0.38 b
d = 0.85b
where:
b : Height, in m, of tripping brackets, shown in Figure 4.
st : Spacing, in m, of tripping brackets.
t : Net thickness, in mm, of tripping brackets.
4.4 End connections
4.4.1 General
Brackets or equivalent structure are to be provided at ends of primary supporting members.
End brackets are generally to be soft-toed.
Bracketless connections may be applied provided that there is adequate support of adjoining face plates.
4.4.2 Scantling of end brackets
In general, the arm lengths of brackets connecting PSMs, as shown in Figure 5 are not to be less than the web depth of the member, and need not be taken greater than 1.5 times the web depth.
Within the cargo hold region the thickness of the bracket is, in general, not to be less than that of the adjoining PSM web plate. Outside of the cargo hold region the thickness of the bracket is not to be less than that of the PSM web plate.
Scantlings of the end brackets are to be such that the section modulus of the PSM with end bracket, excluding face plate where it is sniped, is not to be less than that of the primary supporting member at mid-span.
The net cross sectional area, Af, in cm2, of face plates of brackets is not to be less than:
Af = 
btb
where:
b : Length of bracket edge, in m, see Figure 5. For brackets
that are curved, the length of the bracket edge may be taken as the length of the
tangent at the midpoint of the edge.
tb : Minimum net bracket thickness, in mm, as defined in [3.2.4].
Moreover, the net thickness of the face plate is to be not less than that of the bracket web.
4.4.3 Arrangement of end brackets
Where the length of free edge of bracket, 
b, is greater than 1.5 m, the web of the bracket is to be
stiffened as follows:
- The net sectional area, in cm2, of web stiffeners is to be
not less than 16.5
, where 
is the span, in m, of the stiffener.
- Tripping flat bars are to be fitted. Where the width of the symmetrical face plate is greater than 400 mm, additional backing brackets are to be fitted.
Figure 5 : Dimension of brackets
For a ring system where the end bracket is integral with the webs of the members and the face plate is carried continuously along the edges of the members and the bracket, the full area of the largest face plate is to be maintained close to the mid-point of the bracket and gradually tapered to the smaller face plates. Butts in face plates are to be kept well clear of the bracket toes.
Where a wide face plate abuts a narrower one, the taper is not to be greater than 1 to 4.
The toes of brackets are not to land on unstiffened plating. The toe height is not to be greater than the thickness of the bracket toe, but need not be less than 15 mm. In general, the end brackets of primary supporting members are to be soft-toed. Where primary supporting members are constructed of higher strength steel, particular attention is to be paid to the design of the end bracket toes in order to minimise stress concentrations.
Where a face plate is welded onto the edge or welded adjacent to the edge of the end bracket (see Figure 6), the face plate is to be sniped and tapered at an angle not greater than 30°.
Figure 6 : Bracket face plate adjacent to the edge
The details shown in this figure are only used to illustrate items described in the text and are not intended to represent design guidance or recommendations.
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