Section 7 Application of scantling requirements to other structure

7.1 Symbols

7.1.1 The symbols used in this Chapter are defined as follows:

σ_yd

specified minimum yield stress of the material, in N/mm²

τ_yd

N/mm²

stiffener spacing, in mm

primary support member spacing, in metres

point load for the design load set being considered, in kN

design pressure for the design load set being considered, in kN/m².

7.2 General

7.2.1 Application.

The requirements of this Section apply to plating, local and primary support members where the basic structural configurations or strength models assumed in Pt 10, Ch 3, 2 Cargo tank region to Pt 10, Ch 3, 5 Aft end are not appropriate. These are general-purpose strength requirements to cover various load assumptions and end support conditions.
The requirements for local and primary support members are to be specially considered when the member is:
1. part of a grillage structure;
2. subject to large relative deflection between end supports;
3. where the load model or end support condition is not given in Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3.
The application of alternative or more advanced calculation methods will be specially considered.

7.3 Scantling requirements

7.3.1 General.

The design load sets to be applied to the structural requirements for the local and primary support members are given in Pt 10, Ch 3, 2.6 Bulkheads 2.6.7, as applicable for the particular structure under consideration. The static and dynamic load components are to be combined in accordance with Pt 10, Ch 2, 6.1 Symbols 6.1.1 and the requirements given in Pt 10, Ch 2 Loads and Load Combinations.

7.3.2 Plating and local support members.

For plating subjected to lateral pressure, the net thickness, t_net , is to be taken as the greatest value for all applicable design load sets, and given by:

t_net

where

α_p	=	correction factor for the panel aspect ratio
α_p	=

l_p

length of plate panel, to be taken as the spacing of primary support members, S, unless carlings are fitted, in metres

C_a

permissible bending stress coefficient for the design load set being considered, as given in Pt 10, Ch 3, 2.3 Hull envelope plating 2.3.2, Pt 10, Ch 3, 3.11 Scantling requirements 3.11.2 or Pt 10, Ch 3, 4.7 Tank bulkheads 4.7.1, as applicable for the individual member being considered.

For stiffeners subjected to lateral pressure, point loads, or some combination thereof, the net section modulus requirement, Z_net , is to be taken as the greatest value for all applicable design load sets, and given by:

Z_net

cm³, for lateral pressure loads

Z_net

cm³, for point loads

Z_net

cm³, for a combination of loads

where

l_bdg

effective bending span, in metres

f_bdg	=	bending moment factor for continuous stiffeners and where end connections are fitted consistent with idealisation of the stiffener as having fixed ends:
	=	12 for horizontal stiffeners
	=	10 for vertical stiffeners for other configurations the bending moment factor may be taken as in Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3

C_s

permissible bending stress coefficient for the design load set being considered as given in Pt 10, Ch 3, 2.4 Hull envelope framing 2.4.2, Pt 10, Ch 3, 3.11 Scantling requirements 3.11.2 or Pt 10, Ch 3, 4.7 Tank bulkheads 4.7.1, as applicable for the individual member being considered

indices for load component i

indices for load component j.

For stiffeners subjected to lateral pressure, point loads, or some combination thereof, the net web thickness, t_w-net , based on shear area requirements is to be taken as the greatest value for all applicable design load sets, and given by:

t_w-net

mm, for lateral pressure loads

t_w-net

mm, for point loads

t_w-net

mm, for a combination of loads

where

f_shr	=	shear force factor for continuous stiffeners with end connections consistent with the idealisation of the stiffener as having fixed ends:
	=	0,5 for horizontal stiffeners
	=	0,7 for vertical stiffeners for other configurations the shear force factor may be taken as in Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3

l_shr

effective shear span, in metres

d_shr

effective shear depth, in mm

C_t

permissible shear stress coefficient for design load set, as given in Pt 10, Ch 3, 2.4 Hull envelope framing 2.4.2 or Pt 10, Ch 3, 3.11 Scantling requirements 3.11.2, for the individual member being considered

indices for load component i

indices for load component j.

7.3.3 Primary support members.

The requirements in Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3 are applicable where the primary support member is idealised as a simple beam. More advanced calculation methods may be required to ensure that nominal stress levels for all primary support members are less than the permissible stresses and stress coefficients given in Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3 and Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3, when subjected to the applicable design load sets. See also 7.1.1.4.
The section modulus and web thickness of the local support members apply to the areas clear of the end brackets. The section modulus and cross-sectional shear areas of the primary support member are to be applied as required in the notes of Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3.
For primary support members intersecting with or in way of curved hull sections, the effectiveness of end brackets is to include an allowance for the curvature of the hull.

For primary support members, the net section modulus requirement, Z_net50 , is to be taken as the greatest value for all applicable design load sets, and given by:

Z_net50

cm³, for lateral pressure loads

Z_net50

cm³, for point loads

Z_net50

cm³, for a combination of loads

where

l_bdg

effective bending span, in metres

f_bdg

bending moment factor, as given in Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3

C_s-pr

permissible bending stress coefficient as given in Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3 for design load set given in , for the individual member being considered

indices for load component i

indices for load component j.

Table 3.7.1 Permissible stress coefficients, Cs-pr for primary support members

Acceptance criteria set	Permissible bending stress coefficient, Cs-pr	Permissible shear stress coefficient, Ct-pr
AC1	0,70	0,70
AC2	0,85	0,85
AC3	0,9	0,9

Table 3.7.2 Values of fbdg and fshr

Load and boundary conditions

Bending moment and shear force factor (based on load at mid span where load varies)

Application

Load model

Position, see Note 1

Support

Field

Support

f_bdg1

f_shr1

f_bdg2

f_bdg3

f_shr3

12,0

0,50

24,0

12,0

0,50

Built-in at both ends

Uniform pressure distribution

—

0,38

14,2

—

8,0

0,63

Built-in at one end plus simply supported one end

Uniform pressure distribution

—

0,50

8,0

—

0,50

Simply supported, (both ends are free to rotate)

Uniform pressure distribution

15,0

0,30

23,3

—

10,0

0,70

Built-in at both ends

Linearly varying pressure distribution

—

0,20

16,8

—

7,5

0,80

Built-in at one end plus simply supported one end

Linearly varying pressure distribution

—

2,0

1,0

Cantilevered beam

Uniform pressure distribution

8,0

0,5

8,0

—

8,0

0,5

Built-in at both ends

Single point load in the centre of the span

—

Built-in at both ends

Single point load, with load anywhere in the span

—

0,5

—

0,5

Simply supported

Single point load in the centre of the span

—

Simply supported

Single point load, load anywhere along the span

Symbols

effective span, l_bdg and l_shr , as applicable

l_bdg

effective span in bending, for local or primary support members, in metres

l_shr

effective span in shear, for local or primary support members, in metres

NOTES

1. The bending moment factor, f_bdg , for the support positions is applicable for a distance of 0,2l_bdg from the end of the effective bending span for both local and primary support members.

2. The shear force factor, f_shr , for the support positions is applicable for a distance of 0,2l_shr from the end of the effective shear span for both local and primary support members.

3. Application of f_bdg and f_shr for local support members:

(a) the section modulus requirement of local support members is to be determined using the lowest value of f_bdg1 , f_bdg2 and f_bdg3 ;

(b) the shear area requirement of local support members is to be determined using the greatest value of f_shr1 and f_shr3 .

4. Application of f_bdg and f_shr for primary support members:

(a) the section modulus requirement within 0,2l_bdg from the end of the effective span is generally to be determined using the applicable f_bdg1 and f_bdg3 ; however, f_bdg is not to be taken greater than 12;

(b) the section modulus of mid span area is to be determined using f_bdg = 24, or f_bdg2 from the Table if lesser;

(c) the shear area requirement of end connections within 0,2l_shr from the end of the effective span is to be determined using f_shr = 0,5 or the applicable f_shr1 or f_shr3 , whichever is greater;

(d) for models A to F, the value of f_shr may be gradually reduced outside of 0,2l_shr towards 0,5f_shr at mid span, where f_shr is the greater value of f_shr1 and f_shr3 .

For primary support members, the net shear area of the web, A_shr-net50 , is to be taken as the greatest value for all applicable design load sets, and given by:

A_shr-net50

cm², for lateral pressure loads

A_shr-net50

cm², for point loads

A_shr-net50

cm², for a combination of loads

where

l_shr

effective shear span, in metres

f_shr

shear force factor, as given in Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3

C_t-pr

permissible shear stress coefficient as given in Pt 10, Ch 3, 7.3 Scantling requirements 7.3.3 for design load set given in Pt 10, Ch 3, 2.6 Bulkheads 2.6.7, for the individual member being considered

indices for load component i

indices for load component j.