Section 5 Re-assessment of side shell frames and brackets

5.1.1 These requirements define steel renewal criteria or other measures to be taken for the webs and flanges of side shell frames and brackets as in Ch 2, 5.2 Renewal or other measures. Reinforcing measures of side frames are also defined in Ch 2, 5.2 Renewal or other measures 5.2.3.

5.1.2 Where ships are reinforced to comply with an ice class notation the intermediate frames are not to be included when considering compliance with this Section.

5.1.3 If an ice class notation is requested to be withdrawn, the additional ice strengthening structure, with the exception of tripping brackets, see Ch 2, 5.2 Renewal or other measures 5.2.3 and Ch 2, 5.5 Reinforcing measures, is not considered to contribute to compliance with this Section.

5.1.4 Finite element or other numerical analysis or direct calculation procedures cannot be used as an alternative to compliance with the requirements of this Section, except in cases of unusual side structure arrangements or framing to which the requirements of this Section cannot be directly applied. In such cases, the analysis criteria and the strength check criteria are to be in accordance with LR’s Procedures.

5.1.5 For the purposes of this Section the term “as new”, when referring to coating condition, is defined as without breakdown or rusting.

5.2.1 The following symbols and definitions are applicable to this Section:

5.2.2 The webs of side shell frames and brackets are to be renewed when the measured thickness, t _M, is equal to or less than the greatest of the values for t _REN defined below:

1. t _COAT-t _C

2. 0,75t_AB

3. t _REN,d/t applicable to zones A and B only, see Figure 2.5.3 Lower part of side frames

4. t _REN,S, where required by Ch 2, 5.2 Renewal or other measures 5.2.4.

5.2.3 The thickness criteria based on _d/t ratio is given by the following equation subject to the conditions given in Ch 2, 5.2 Renewal or other measures 5.2.3 and Ch 2, 5.2 Renewal or other measures 5.2.3 below:

• 65k ^0,5 for symmetrically flanged frames
• 55k ^0,5 for asymmetrically flanged frames and for the lower brackets, see below
• 87k ^0,5 for symmetrically flanged frames
• 73k ^0,5 for asymmetrically flanged frames

In no instance is t _REN,d/t for lower integral brackets to be taken as less than t _REN,d/t for the frames they support.

1. Lower brackets

   Lower brackets are to be flanged or a face plate is to be fitted, see Ch 2, 5.3 Criteria for frames and brackets. In calculating the web depth of the lower brackets, the following will apply:

   • The web depth of lower bracket may be measured from the intersection of the sloped bulkhead of the hopper tank and the side shell plate,perpendicularly to the face plate of the lower bracket, see Figure 2.5.1 Tripping brackets.
   • Where stiffeners are fitted on the lower bracket plate, the web depth may be taken as the distance between the side shell and the stiffener, between the stiffeners or between the outermost stiffener and the face plate of the brackets, whichever is the greatest.

2. Tripping bracket alternative

   When t _M is less than t _REN,d/t at Section (b), see Figure 2.5.2 Sections (a) and (b), of the side frames, tripping brackets in accordance with Ch 2, 5.5 Reinforcing measures may be fitted as an alternative to the requirements for the web depth to thickness ratio of side frames, in which case t _REN,d/t may be disregarded in the determination of t _REN in accordance with Ch 2, 5.2 Renewal or other measures 5.2.2. The value of t _M is to be based on Zone B, see Figure 2.5.3 Lower part of side frames.

3. Immediately abaft collision bulkhead

   For the side frames, including the lower bracket, located immediately abaft the collision bulkhead, whose scantlings are increased in order that their moment of inertia is such to avoid undesirable flexibility of the side shell, when their web as built thickness t _AB is greater than 1,65t _REN,S the thickness t _REN,d/t may be taken as the value t’ _REN,d/t obtained from the following equation:

   

   where

   t _REN,S is obtained from Ch 2, 5.12 Shear strength check.

5.2.4 Where t _M in the lower part of the side frames, as defined in Figure 2.5.3 Lower part of side frames, is equal to or less than t _COAT, t _REN,S is to be determined in accordance with Ch 2, 5.12 Shear strength check.

5.2.5 Where steel renewal is required, the renewed webs are to be of a thickness not less than t _AB,1,2t _COAT or 1,2t _REN, whichever is the greatest.

5.2.6 When t _REN< t _M ≤t _COAT, measures are to be taken, consisting of all the following:

1. sandblasting, or equivalent, and coating, see Ch 2, 5.4 Thickness measurements, steel renewal, sand-blasting and coating 5.4.1; and

2. fitting tripping brackets, see Ch 2, 5.5 Reinforcing measures, when the above condition occurs for any of the side frame Zones A, B, C and D, shown in Figure 2.5.3 Lower part of side frames. Tripping brackets not connected to flanges are to have soft toes, and the distance between the bracket toe and the frame flange is to be not greater than 50 mm, see Figure 2.5.4 Tripping brackets; and

3. maintaining the coating in “as new” condition at Special and Intermediate Surveys.

The above measures may be waived if the structural members show no thickness diminution with respect to the “as built” thickness and coating is in “as new” condition. When the measured frame webs thickness t _M is such that t _REN < t _M ≤ t _COAT and the coating is in GOOD condition, sand blasting and coating as required in Ch 2, 5.2 Renewal or other measures 5.2.6 above may be waived even if not found in “as-new” condition, as defined above, provided that tripping brackets are fitted and the coating damaged in way of the tripping bracket welding is repaired.

5.3.1 Where lower end brackets were not fitted with flanges, flanges are to be fitted so as to meet the bending strength requirements of 5.13. The full width of the bracket flange is to extend up beyond the point at which the frame flange reaches full width. Adequate back-up structure in the hopper is to be ensured, and the bracket is to be aligned with the back-up structure.

5.3.2 Where the length or depth of the lower bracket does not meet the requirements in Pt 4, Ch 7, 6.2 Transverse stiffening of the Rules for Ships, a bending strength check in accordance with Ch 2, 5.13 Bending strength check is to be carried out and renewals or reinforcements of frames and/or brackets effected as required therein. The bending check need not be carried out in the case that the bracket geometry is modified so as to comply with the requirements of Pt 4, Ch 7, 6.2 Transverse stiffening.

5.4.1 For the purpose of steel renewal, sand-blasting and coating, four Zones A, B, C and D are defined as shown in Figure 2.5.3 Lower part of side frames. When renewal is to be carried out, surface preparation and coating are required for the renewed structures as given in Pt 4, Ch 7, 2.2 Protection of steelwork 2.2.2 of the Rules for Ships. Representative thickness measurements are to be taken for each zone and are to be assessed against the criteria in Ch 2, 5.2 Renewal or other measures. When Zone B is made up of different plate thicknesses, the lesser thickness is to be used for the application of the requirements in this Section:

• In case of integral brackets, when the criteria in Ch 2, 5.2 Renewal or other measures are not satisfied for zone A or B, steel renewal, sandblasting and coating, as applicable, are to be done for both zones A and B.
• In case of separate brackets, when the criteria in Ch 2, 5.2 Renewal or other measures are not satisfied for zone A or B, steel renewal, sandblasting and coating are to be done for each one of these zones, as applicable.
• When steel renewal is required for zone C according to Ch 2, 5.2 Renewal or other measures it is to be done both zones B and C. When sand-blasting and coating, is required for zone C according to Ch 2, 5.2 Renewal or other measures it is to be done for zones B, C and D.
• When steel renewal is required for zone D according to Ch 2, 5.2 Renewal or other measures it needs only to be done for this zone. When sand-blasting and coating, is required for zone D according to Ch 2, 5.2 Renewal or other measures, it is to be done for both zones C and D.

Special consideration may be given to zones previously renewed or recoated, if found in “as new” condition. When adopted, on the basis of the renewal thickness criteria in Ch 2, 5.2 Renewal or other measures, in general coating is to be applied in compliance with the requirements of Pt 4, Ch 7, 2.2 Protection of steelwork of the Rules for Ships, as applicable. Where, according to the requirements in Ch 2, 5.2 Renewal or other measures, a limited number of side frames and brackets are shown to require coating over part of their length, the following criteria apply:

1. The part to be coated includes:

   • the web and the face plate of the side frames and brackets; and
   • the hold surface of side shell, hopper tank and topside tank plating, as applicable, over a width not less than 100 mm from the web of the side frame.

2. Epoxy coating or equivalent is to be applied.

   In all cases, all the surfaces to be coated are to be sand blasted prior to coating application.

5.4.2 When flanges of frames or brackets are to be renewed according to these requirements, the outstanding breadth to thickness ratio is to comply with the requirements Pt 4, Ch 7, 6.2 Transverse stiffening 6.2.3 of the Rules for Ships.

5.5.1 Reinforcing measures constitute tripping brackets, located at the lower part and at the midspan of side frames, see Figure 2.5.4 Tripping brackets. Tripping brackets may be located at every two frames, but lower and midspan brackets are to be fitted in line between alternate pairs of frames.

5.5.2 The thickness of the tripping brackets is to be not less than the as-built thickness of the side frame webs to which they are connected.

5.5.3 Double continuous welding is to be adopted for the connections of tripping brackets to the side shell frames and shell plating.

5.5.4 Where side frames and side shell are made of higher tensile steel, mild steel tripping brackets may be accepted, provided the electrodes used for welding are those required for the higher tensile steel, and the thickness of the tripping brackets is equal to the frame web thickness, regardless of the frame web material.

5.6.1 In case of steel renewal the welded connections are to comply with Pt 4, Ch 7, 6.2 Transverse stiffening 6.2.11.

5.7.1 If pitting intensity is higher than 15 per cent in area, see Figure 2.5.5 Pitting intensity diagrams (from 5 per cent to 25 per cent intensity), then a thickness measurement is to be taken to check pitting corrosion.

5.7.2 The minimum acceptable remaining thickness in pits or grooves is equal to:

• 75 per cent of the as built thickness, for pitting or grooving in the frame and brackets, webs and flanges
• 70 per cent of the as built thickness, for pitting or grooving in the side shell, hopper tank and topside tank plating attached to the side frame, over a width up to 30 mm from each side of it.

5.8.1 When all frames in one or more holds are required to be renewed by these requirements, compliance with the requirements of Pt 4, Ch 7, 6.2 Transverse stiffening of the Rules for Ships may be accepted in lieu, provided that:

• It is applied to all the frames of the hold(s)
• The coating requirements for the side frames of ‘new ships’ are complied with
• The section modulus of side frames is calculated according to Pt 4, Ch 7, 6.2 Transverse stiffening of the Rules for Ships.

5.9.1 In general, loads are to be calculated and strength checks are to be carried out for the aft, middle and forward frames of each hold. The scantlings required for frames in intermediate positions are to be obtained by linear interpolation between the results obtained for the above frames.

5.9.2 When scantlings of side frames vary within a hold, the required scantlings are also to be calculated for the mid frame of each group of frames having the same scantlings. The scantlings required for frames in intermediate positions are to be obtained by linear interpolation between the results obtained for the calculated frames.

5.10.1 The following loading conditions are to be considered:

• Homogeneous heavy cargo (density greater than 1,78 t/m³);
• Homogeneous light cargo (density less than 1,78 t/m³);
• Non homogeneous heavy cargo, if allowed;
• Multi port loading/unloading conditions need not be considered.

5.10.2 The forces P _fr,a and P _fr,b, in kN, to be considered for the strength checks at sections (a) and (b) of side frames, see Figure 2.5.2 Sections (a) and (b); (in the case of separate lower brackets, section (b) is at the top of the lower bracket), are given by:

5.10.3 The wave pressures, p ₁ and p ₂ are as defined below:

1. Wave pressure p ₁

   • The wave pressure p ₁, in kN/m², at and below the waterline is given by:
   
   • The wave pressure p ₁, in kN/m², above the water line is given by:
   

2. Wave pressure p ₂

   • The wave pressure p ₂, in kN/m², at and below the waterline is given by:
   
   • The wave pressure p ₂, in kN/m², above the water line is given by:
   
   Where

   p 1wl	=	p 1 wave sea pressure at the waterline
   p 2wl	=	p 2 wave sea pressure at the waterline
   L	=	Rule length, as defined in Pt 3, Ch 1, 6.1 Principal particulars 6.1.1 of the Rules for Ships
   B	=	greatest moulded breadth, in metres
   C b	=	block coefficient, as defined in Pt 3, Ch 1, 6.1 Principal particulars 6.1.6, of the Rules for Ships but not to be taken less than 0,6
   T	=	Draught, in metres as defined in Pt 3, Ch 1, 6.1 Principal particulars 6.1.5 of the Rules for Ships
   C	=	coefficient
   	=
   	=	10,75 for 300m < L
   C r	=
   k	=	1,2 for ships without bilge keel
   	=	1,0 for ships with bilge keel
   k r	=	roll radius of gyration
   k r	=	0,39B for ships with even distribution of mass in transverse section (e.g. alternate heavy cargo loading or homogeneous light cargo loading)
   	=	0,25B for ships with uneven distribution of mass in transverse section (e.g. homogeneous heavy cargo distribution)
   GM	=	0,12B if the actual value of GM is not available
   z	=	vertical distance, in m, from the baseline to the load point
   k s	=
   	=	C b between 0,2L and 0,6L from aft end of L
   	=

   Between the above specified points, k _s is to be interpolated linearly

   k f

   =

   0,8C

5.11.1 The allowable normal and shear stresses σ_a and τ_a, in N/mm², in the side shell frames and brackets are given by:

5.12.1 Where t_M in the lower part of side frames, as defined in Figure 2.5.3 Lower part of side frames, is equal to or less than t_COAT, a shear strength check is to be carried out in accordance with Ch 2, 5.12 Shear strength check 5.12.2.

5.12.2 The thickness t_REN,S, in mm, is the greater of the thicknesses t_REN,Sa and t_REN,Sb obtained from the shear strength check at sections (a) and (b) (see Ch 2, 5.10 Load Model and Figure 2.5.2 Sections (a) and (b)). They are given by the following, but need not be taken in excess of 0,75t_S12:

• at section (a):

• at section (b):

5.13.1 Where the lower bracket length or depth does not meet the requirements in Pt 4, Ch 7, 6 Shell envelope framing of the Rules for Ships, the actual section modulus, in cm³, of the brackets and side frames at sections (a) and (b) is to be not less than:

at section (a):

at section (b)

5.13.2 The actual section modulus of the brackets and side frames is to be calculated about an axis parallel to the attached plate, based on the measured thicknesses. For pre-calculations, alternative thickness values may be used, provided they are not less than:

• t_REN, for the web thickness
• the minimum thickness allowed by the renewal criteria for flange and attached plating.

The attached plate breadth is equal to the frame spacing, measured along the shell at midspan of h.

5.13.3 If the actual section moduli at sections (a) and (b) are less than the values Z_a and Z_b, the frames and brackets are to be renewed or reinforced in order to obtain actual section moduli not less than 1,2Z_a and 1,2Z_b, respectively. In such a case, renewal or reinforcements of the flanges is to be extended over the lower part of side frames, as defined in Figure 2.5.3 Lower part of side frames.