Section 5 Residual strength hull girder loads

5.1.1 The residual strength hull girder loads specified in this section are applicable to all displacement mono-hull naval ships for which the optional RSA1, RSA2 or RSA3, Residual Strength Assessment, notation is required. The design criteria detailed in this Section are to be used in conjunction with the residual strength assessment procedure given in Vol 1, Pt 6, Ch 4, 4 Residual Strength Assessment, RSA.

5.1.2 The residual strength hull girder loads are used to assess the capability of the ship’s global hull girder after suffering structural damage to meet specified global strength requirements. The effects of flooding, as a consequence of structural damage, on the static global bending moments and shear forces are also to be considered.

5.2.1 The environmental design criteria for residual strength analysis given in Vol 1, Pt 5, Ch 2, 3 Air environment are to be used to determine the residual strength hull girder loads.

5.2.2 The global loads for the residual strength hull girder strength assessment for unrestricted service operation, i.e. service area notation SA1, are typical maximum loads that are predicted in North Atlantic sea conditions that have a probability of exceedance of 20 per cent. The loads predicted for the ship in head seas at low forward speed are to be considered.

5.2.3 For other service area notations, the global loads for the hull girder residual strength assessment are typical maximum loads that are likely to be encountered within the restricted operational area in sea conditions that have a 20 per cent probability of being exceeded.

5.2.4 The designer/builder may stipulate the environmental conditions to be applied to the residual strength assessment. In which case the residual strength notation will be assessed against the required performance level.

5.2.5 The residual strength area reduction factor, K _fRS, is given by the following:

where
H _rw is given in Vol 1, Pt 5, Ch 2, 2.3 Wave environment 2.3.5.

5.3.1 The residual strength wave loads may be derived from the formula given below. The residual strength vertical bending moment specified here is applicable to all mono-hull ships.

5.3.2 The residual strength vertical wave bending moment, M _WRS, at any position along the ship is given by:

5.3.3 Alternatively the residual strength wave loads may be derived using direct calculation methods, model tests or similar taking into account the likely range of wave periods and the environmental conditions specified in Vol 1, Pt 5, Ch 4, 5.2 Environmental conditions

5.3.4 In deriving the residual strength wave bending moment, the longitudinal distribution is to be taken in accordance with the longitudinal distribution factor, D_f, see Vol 1, Pt 5, Ch 4, 3.3 Vertical wave bending moments 3.3.1. Where appropriate, the hogging and sagging correction factors, F _fH and F _fS may be used to derive the hogging and sagging bending moments from a direct calculation.

5.3.5 For conventional ships, it is not normally necessary to consider the effects of flooded compartments on the wave bending moments and shear forces.

5.3.6 For bottom damage assessment as a result of grounding, the residual strength vertical wave bending moment may be based on a M _W value derived using a service area factor, f _s, for a SA4 service area notation; provided that the ship will not be required to proceed beyond sheltered water. Similarly for other damage assessments which are restricted to sheltered water environments, provided that there is no requirement for operation outside sheltered water areas.

5.4.1 The residual strength vertical wave shear force, Q _WRS, at any position along the ship is given by:

5.4.2 Alternatively the method of derivation of residual strength wave shear forces is to be consistent with that used to derive the bending moments.

5.5.1 Direct calculation procedures may be used to derive the residual strength hull girder loads. LR’s calculation method of the residual strength hull girder loads involves derivation of the short term maximum probable responses.

5.5.2 The residual strength hull girder loads are to be based on the probable maximum values that are likely to be experienced during moderately severe sea conditions. The parameters of the seastate, i.e. significant wave height, wave period range and duration of storm, are given in Vol 1, Pt 5, Ch 2 Environmental Conditions.

5.6.1 The still water hogging and sagging shear force, Q _SRS, and bending moment, M _SRS, distributions in the damaged condition are to be calculated taking into account any flooding of the ship as a consequence of damage. If no flooding occurs then the still water values are to be taken from Vol 1, Pt 5, Ch 4, 2.3 Still water shear forces and Vol 1, Pt 5, Ch 4, 2.2 Still water bending moments respectively.

If no flooding occurs

or if flooding occurs

5.6.2 The loading conditions used to derive the undamaged still water shear force and bending moment curves are to be used for the assessment of the damaged still water bending moments together with the addition of flood water in damaged compartments.

5.7.1 The residual strength design vertical bending moment, M _RRS, and associated shear forces, Q _RRS, for all naval ships are to be determined as follows:

1. The residual strength design bending moment, M _RRS, is to be taken as (M _WRS + M _SRS), as defined in Vol 1, Pt 5, Ch 4, 5.3 Residual strength vertical wave bending moments and Vol 1, Pt 5, Ch 4, 5.6 Damaged still water shear forces and bending moments, taking into account the appropriate hogging and sagging conditions.

2. The residual strength design shear forces, Q _RRS, is to be taken as (Q _WRS + Q _SRS), as defined in Vol 1, Pt 5, Ch 4, 5.4 Residual strength vertical wave shear forces and Vol 1, Pt 5, Ch 4, 5.6 Damaged still water shear forces and bending moments, taking into account the appropriate hogging and sagging conditions.

5.7.2 Where it is required that the ship is to be capable of operating at high speed after damage, it may also be necessary to consider the effects of dynamic bending moments and shear forces.