3 Screening Procedure

3.1 Screening areas

3.1.1 The structural details subject to this screening procedure are checked in the following ship areas:

Within the full cargo hold region for the details given in [3.2.1],
Outside midship cargo hold region for the details given in [3.2.2].

Table 1 : Screening areas of transverse web frame in oil tanker



	Bracket toes
	Openings and manholes (shaded regions)
	Openings and manholes (unshaded regions)	Screening check to be performed for openings except if: h_o/h < 0.35 and g_o < 1.2, and each end of the opening forms a semi circle arc (i.e. radius of opening equal to b/2). This criterion does not apply to manholes which are to be evaluated by screening irrespective of size. h_o, h and g_o is defined in Ch 7, Sec 2, [2.4.9], b is the smallest of the length and breadth of the opening.

3.2 List of structural details

3.2.1 Cargo hold region

The following structural details and areas in the cargo hold region are to be evaluated by screening:

a) Openings which do not require modelling and manholes, see Ch 7, Sec 2, [2.4.9], in way of web of primary supporting members, such as transverse web frame as indicated in Table 1 and Table 2, horizontal stringers as indicated in Table 3, floors and longitudinal girders in double bottom.
b) Bracket toes on transverse web frame as indicated in Table 1 and Table 2, horizontal stringer and transverse plane bulkhead connected to double bottom or buttress structure specified in Table 3.
c) Heels of transverse bulkhead horizontal stringers specified in Table 3.
d) Connections of transverse lower stool to double bottom girders and longitudinal lower stool to double bottom floors as indicated in Figure 5.
e) Connection of lower hopper to transverse lower stool structure as indicated in Figure 5.
f) Connection of topside tank to inner side as indicated in Figure 6.
g) Connection of corrugation and upper supporting structure to upper stool as indicated in Figure 7.
h) Hatch corner area, such as the hatch coaming end bracket, the hatch corner and the hatch end beam connection as indicated in Figure 8.

Within each group of the structural details having the same geometry and the same relative location inside the cargo region, the screening verification can be performed for the detail for which the yield utilisation factor, λ_y, is maximum

Table 2 : Screening areas for transverse web frame in bulk carrier


	Bracket toes
	Openings and manholes (shaded regions)
	Openings and manholes (unshaded regions)	Screening check to be performed for openings except if: h_o/h < 0.35 and g_o < 1.2, and each end of the opening forms a semi circle arc (i.e. radius of opening equal to b/2). This criterion does not apply to manholes which are to be evaluated by screening irrespective of size. h_o, h and g_o is defined in Ch 7, Sec 2, [2.4.9], b is the smallest of the length and breadth of the opening.

Table 3 : Screening areas for horizontal stringer and transverse bulkhead to double bottom connections in oil tanker



	Bracket toes
	Openings and manholes (shaded regions)
	Openings and manholes (unshaded regions)	Screening check to be performed for openings except if: h_o/h < 0.35 and g_o < 1.2, and each end of the opening forms a semi circle arc (i.e. radius of opening equal to b/2). This criterion does not apply to manholes which are to be evaluated by screening irrespective of size. h_o, h and g_o is defined in Ch 7, Sec 2, [2.4.9], b is the smallest of the length and breadth of the opening.

Figure 5 : Screening areas at connections of lower stool to inner bottom and hopper tank

Figure 6 : Screening areas at connections of topside tank to inner side

Figure 7 : Screening areas at connection of corrugation and upper supporting structure to upper stool

Figure 8 : Screening areas at hatch corner in bulk carrier

3.2.2 Outside midship cargo hold region

The following structural details outside midship cargo hold region are to be evaluated by screening:

a) Hopper knuckle, as defined in [2.1.2] and [2.1.3],
b) Side frame end bracket, as defined in [2.1.3],
c) Large openings, as defined in [2.1.4],
d) Connections of corrugation to adjoining structure, as defined in [2.1.6],
e) Bracket at the heel of horizontal stringers in [2.1.7],

The connections of corrugation to adjoining structure and the bracket at the heel of horizontal stringers to be screened are to be similar in its geometry, its proportion and its relative location to the corresponding detail modelled in fine mesh in the midship cargo hold region.

When the connections of corrugation to adjoining structure and the bracket at the heel of horizontal stringers outside the midship cargo hold region are different from the corresponding detail modelled in fine mesh in the midship cargo hold region, a fine mesh analysis is to be performed for the detail located where the yield utilisation factor, λ_y, is maximum for structural details having the same geometry and the same relative location,

When it is deemed necessary, the Society may request a fine mesh analysis to be performed according to [1.1.3].

3.3 Screening criteria

3.3.1 Screening factors and permissible screening factors

The screening factors, λ_sc, and the permissible screening factors, λ_scperm, are given in Table 4 for the screening areas defined in [3.1].

Table 4 : Screening factors and permissible screening factors

Type of Details	Screening factors, λ_sc	Permissible screening factors, λ_scperm
Within the whole cargo hold region		S+D	S
Openingsfor which their geometry is not required to be represented in the cargo hold model in accordance with Ch 7, Sec 2, [2.4.9] in way of webs of primary supporting members, such as transverse web frame as indicated in Table 1 and Table 2,horizontal stringers as indicated in Table 3, floors and longitudinal girders in double bottom.	Table 5	1.70	1.36
Manholes (2)	λ_y	0.85 λ_yperm
Bracket toes on transverse web frames as indicated in Table 1 and Table 2, horizontal stringers and transverse plane bulkhead to double bottom connection or buttress structure specified in Table 3.	Table 6	1.50	1.20
Heels of transverse bulkhead horizontal stringers specified in Table 3.	Table 7	1.50	1.20
Connections of transverse lower stool to double bottom girders and longitudinal lower stool to double bottom floors as indicated in Figure 5. The connection of lower hopper to transverse lower stool structure as indicated in Figure 5. The connection of topside tank to inner side as indicated in Figure 6. The connection of corrugation and upper supporting structure to upper stool as indicated in Figure 7.	λ_y	0.75 λ_yperm
Hatch corner area.	λ_y	0.95 λ_yperm
Outside midship cargo hold region
Hopper knuckle	λ_y	0.65 λ_yperm
Side frame end bracket		0.85 λ_yperm
Large openings ⁽²⁾		0.85 λ_yperm
Connections of corrugation to adjoining structure and bracket at the heel of horizontal stringer	⁽¹⁾	1.50 f_f	1.20 f_f
where: λ_y : Coarse mesh yield utilisation factor, as defined in Ch 7, Sec 2, [5.2.4]. λ_yperm : Coarse mesh permissible yield utilisation factor, as defined in Ch 7, Sec 2, [5.2.4]. K_sc : Screening stress concentration factor, taken as: σ_FM : Von Mises fine mesh stress, in N/mm², for the considered detail calculated in the midship cargo hold region according to [2]. σ_CM : Von Mises coarse mesh stress, in N/mm², for the considered detail calculated in the midship cargo hold region according to Ch 7, Sec 2. σ_c : Von Mises coarse mesh stress, in N/mm², for the area in way of considered detail. f_f : Fatigue factor defined in [6.2.1]. (1) For each screened detail, σ_FM and σ_CM are to be taken from the corresponding elements in the same plane position. (2) The representative element which has maximum yield utilisation factor around the manhole and the large opening is to be verified against criterion.

Table 5 : Screening factor for openings in primary supporting members

λ_sc : Screening factor taken as

C_h : Coefficient taken as ⁽²⁾:

For opening in web of PSM.
For opening in web of main bracket and buttress (see figures below).
- C_h = 1.0

r : Radius of opening, in mm.

h₀ : Height of opening parallel to depth of web, in mm.

ℓ₀ : Length of opening parallel to girder web direction, in mm.

h : Height of web of girder in way of opening, in mm.

σ_x : Axial stress in element x-direction determined from cargo hold FE analysis according to the coordinate system shown, in N/mm².

σ_y : Axial stress in element y-direction determined from cargo hold FE analysis according to the coordinate system shown, in N/mm².

τ_xy : Element shear stress determined from cargo hold FE analysis ⁽¹⁾, in N/mm².

(1) The element shear stress is to be adjusted using the formula given in Ch 7, Sec 2, [5.2.6] prior to the evaluation of yield utilisation factor for verification against the screening criteria.

(2) Where the geometry of the opening is required to be modelled in accordance with Ch 7, Sec 2, [2.4.9], fine mesh FE analysis is to be carried out to determine the stress level and the screening criteria are not applicable.

Table 6 : Screening factor for bracket toes of primary supporting members

λ_sc : Screening factor taken as:

C_a : Coefficient taken as:

b₁, b₂ : Height of shell element in way of bracket toe in cargo hold FE model, in mm.

A_beam-n50: Sectional area of beam or rod element in cargo hold FE model representing the face plate of bracket, in mm².

σ_beam : Beam or rod element axial stress determined from cargo hold FE analysis, in N/mm².

σ_vm : Von Mises stress of shell element in way of bracket toe determined from cargo hold FE analysis, in N/mm².

t_n50 : Net thickness of shell element in way of bracket toe, in mm.

R_a : Leg length, in mm, not to be taken as greater than 1400 mm.

3.3.2 Screening criteria

Stresses in areas defined in [3.1], calculated for all applicable FE load combinations given in [5], are to be checked against the following screening criteria.

λ_sc ≤ λ_scperm

where:

λ_sc : Screening factor defined in [3.3.1]

λ_scperm : Permissible screening factor defined in [3.3.1]

Where the screening criteria are not met, fine mesh analysis of the corresponding structural detail is required and to be performed according to [1.1.3].

Table 7 : Screening factor for heels of transverse bulkhead horizontal stringers

λ_sc : Screening factor taken as:

For heels at side horizontal girder and transverse bulkhead horizontal stringer, at the locations 1, 2 and 3 in figure below.
For heel at longitudinal bulkhead horizontal stringer, at the location 4 in figure below.

σ_x : Axial stress in element x direction determined from cargo hold FE analysis in accordance with the coordinate system shown, in N/mm².

σ_vm : Von Mises stress of shell element in way of heel determined from cargo hold FE analysis, in N/mm².

Individual element in web to be verified against criteria.