Section 3 Design load combinations

3.1.1 The local and global loads given in Vol 1, Pt 5, Ch 3 Local Design Loads and Vol 1, Pt 5, Ch 4 Global Design Loads do not include any allowance for phase relationships between the various loadings. These loads are not all maximum at the same time and consequently it is not correct to apply all loads simultaneously to the structure. The purpose of this section is to define the phase relationships and hence allow typical maximum load combinations to be applied to the structure.

3.1.2 Special load case combinations may be required to reflect specific operational requirements of the vessel, e.g. sea state 6 operation with the stern well dock flooded for amphibious operations. The details of such operational modes together with any service limitations are to be recorded in the design disclosure document and the Operations Manual, Loading Manual or Stability Information Book.

3.1.3 Proposals for deriving the load combinations using direct calculation techniques are to be agreed with LR at the earliest opportunity.

3.2.1 The load combinations given in Table 2.3.1 Design load combination factors are the minimum to be considered for the assessment of the scantlings. Additional load combination cases may be required to demonstrate that the structure is adequate.

3.2.2 Each set of load combinations may need to be considered for individual loading conditions to account for differences in local loadings, e.g. different tank fillings, payload or other loadings. This may be performed using either:

1. an envelope approach with due consideration of full/ empty tanks, etc. or

2. individual load combination sets, in which case the actual still water bending moment and shear force distributions may be used together with the actual draught, trim and deadweight distribution.

For example, it will be necessary to consider two design cases to review the double bottom tanks, i.e. one with the double bottom tank full and one with the double bottom tank empty.

3.2.3 Load combination cases 1 to 4 are based on the premise that the maximum wave bending moment and shear forces are likely to be generated on a wave that has the same length as the ship.

3.2.4 Each load case combination consists of a set of w factors, some of these combination factors are longitudinally position dependent factors, e.g. the w _p term will produce maximum pressure amidships and low pressures at the ends for the maximum hogging BM case.

3.3.1 The design global hull girder vertical bending moment to be associated with the design load combination cases is as follows:

where

M _S and M _W are the sagging or hogging values of M _S and M _W at the longitudinal position under consideration. If w _g is positive then the hogging values of M _S and M _W are to be taken, otherwise w _g is negative and the sagging values of M _S and M _W are to be taken.

M _S and M _W are given in Vol 1, Pt 5, Ch 4, 2.2 Still water bending moments and Vol 1, Pt 7, Ch 2, 3.3 Design global loads – Intact conditions

w _g is given in Table 2.3.1 Design load combination factors.

3.3.2 The design global hull girder vertical shear force to be associated with the design load combination cases is as follows:

where

Q _S and Q _W are the sagging or hogging values of Q _S and Q _W at the longitudinal position under consideration. If w _g is positive then the hogging values of Q _S and Q _WH are to be taken, otherwise w _g is negative and the sagging values of Q _S and Q _WS are to be taken.

Q _S is given in Vol 1, Pt 5, Ch 4, 2.3 Still water shear forces

Q _WS and Q _WH are given in Vol 1, Pt 7, Ch 2, 3.7 Vertical wave shear forces

w _g is given in Table 2.3.1 Design load combination factors

3.4.1 The design global hull girder vertical bending moments to be associated with the design load combination cases for residual strength assessment or damaged conditions is to be taken as follows:

where.

M _SRS and M _WRS are the sagging or hogging values of M _SRS and M _WRS at the longitudinal position under consideration. If w _g is positive then the hogging values of M _SRS and M _WRS are to be taken, otherwise w _g is negative and the sagging values of M _SRS and M _WRS are to be taken.

M _SRS and M _WRS are given in Vol 1, Pt 5, Ch 4, 5.6 Damaged still water shear forces and bending moments

w _g is given in Table 2.3.1 Design load combination factors

3.4.2 The design global hull girder vertical shear force to be associated with the design load combination cases for residual strength assessment or damaged conditions is to be taken as follows:

where

Q _SRS and Q _WRS are the sagging or hogging values of Q _SRS and Q _WRS at the longitudinal position under consideration. If w _g is positive then the hogging values of Q _SRS and Q _WRS,H are to be taken, otherwise w _g is negative and the sagging values of Q _SRS and Q _WRS,S are to be taken.

Q _SRS is given in Vol 1, Pt 5, Ch 4, 5.6 Damaged still water shear forces and bending moments and Vol 1, Pt 5, Ch 4, 5.4 Residual strength vertical wave shear forces

w _g is given in Table 2.3.1 Design load combination factors

Q _WRS,S and Q _WRS,H are given in Vol 1, Pt 7, Ch 2, 3.7 Vertical wave shear forces 3.7.2

3.5.1 The inertial force load combination factor, w _f, to be associated with the design load combination cases is as follows:

where

w _fheave and w _fpitch are to be taken for the appropriate loading condition, see Table 2.3.1 Design load combination factors

a _heave and a _pitch are defined in Table 3.2.1 Ship motions

3.6.1 The side shell pressure, P _SS, to be applied to all external plating is to be derived as follows:

but

• P _SS ≥ 0

w _p is defined in Table 2.3.1 Design load combination factors

P _h and P _w are defined in Vol 1, Pt 5, Ch 3, 3.2 Combined hydrostatic and hydrodynamic pressure on the shell plating, Ps and Vol 1, Pt 5, Ch 3, 3.3 Hydrostatic pressure on the shell plating, Ph.

3.6.2 The weather deck pressure, P _WD, to be applied to all external plating is to be derived as follows:

but

P _WD ≥ 0

w _p is defined in Table 2.3.1 Design load combination factors

P _wd is defined in Vol 1, Pt 5, Ch 3, 3.5 Pressure on exposed and weather decks, Pwd

3.7.1 The wave shear force curves associated with the hogging and sagging bending moments required by the total load approach are to be taken as follows:

where

K _b is to be taken as follows:

where

K _b is to be taken as follows:

Intermediate values are to be determined by linear interpolation.

M _o, F _fH and F _fS are given in Vol 1, Pt 5, Ch 4, 3.3 Vertical wave bending moments

3.7.2 The wave shear force associated with the residual strength assessment load cases or damaged load cases is to be taken as follows:

where

where