Section 5 Acceptance criteria
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules for the Classification of Trimarans, July 2022 - Volume 4 Direct Calculation Procedure - Part 1 Direct Calculation Procedure - Chapter 2 Structural Strength Analysis and Verification - Section 5 Acceptance criteria

Section 5 Acceptance criteria

Parent topic: Chapter 2 Structural Strength Analysis and Verification

5.1 General

5.1.1 The global structure must comply with the acceptance criteria described in this Section.

5.2 Stress

5.2.1 The stress acceptance criteria given in Table 2.2.1 Stress acceptance criteria permissible stresses apply to all of the combined load cases described in Table 2.3.1 Load combinations, for all structure.

5.3 Buckling

5.3.1 A minimum factor against buckling, λ, of 1.1 is to be achieved for the cross-deck structure and cross-tank structure (bulkheads and web frames). All other structure is to have a minimum factor λ2 of 1.0. In addition, all structure is to comply with the buckling requirements described in the Complementary Rules.

5.3.2 Panel buckling calculations are to be based on the proposed thickness reduced by the standard thickness deduction for corrosion given in Table 2.5.1 Stress acceptance criteria.

Table 2.5.1 Stress acceptance criteria

Structural item Complementary Rule Set
Ship NSR/SSC
Boundaries and internal structure of tanks 1 0
Bottom shell and side shell not in way of tanks Other internal structures (except the boundaries of tanks) Exposed decks protected by sheathing or protective coatings 0 0

5.3.3 The combined interaction of bi-axial compressive stresses, shear stresses and ‘in plane’ bending stresses are to be included in the buckling calculation. In general, the average stresses acting within the plate panel are to be used for the buckling calculation.

5.3.4 The factors against buckling are to be derived using the computer program LR Buckle (ShipRight IS) or program Buckling of lat rectangular plate panels (ShipRight Direct Calculation program no. 10403) or equivalent.

5.3.5 In calculating the factors against buckling, the edge restraint factor may be taken into account in calculating the critical buckling stress of wide panels subjected to compressive loading on the long edge of the panel. The edge restraint factor is not to be used in the calculation of the critical buckling stress for compression applied on the short edges. The edge restraint factor is defined in the Complementary Rules as follows:

  1. Rules for Ships: ‘C’ defined in Pt 3, Ch 4, 7 Hull buckling strength.

  2. Rules for Special Service Craft: ‘C’ defined inPt 6, Ch 7, 4 Buckling control.

  3. Rules for Naval Ships: ‘C’ defined in Table 2.4.1 First mode of vibration constant Ki in Vol 1, Pt 6, Ch 2.

5.3.6 When the calculated elastic critical buckling stress exceeds 50 per cent of the specified minimum yield stress then the buckling stress is to be adjusted for the effects of plasticity using the Johnson-Ostenfeld correction formula, given below:

where
= σcrp, σyd and σcr are defined in Vol 4, Pt 1, Ch 3, 1 General.
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