Section 1 General

1.1.1 This Chapter specifies the method by which the total design loads for the optional Total Load Assessment, TLA, approach are derived. The TLA approach is given in Vol 1, Pt 7, Ch 3 Total Load Assessment, TLA, an overview of the TLA approach is given in Vol 1, Pt 7, Ch 3, 1 Introduction and illustrated in Figure 3.1.1 Overview of the Total Load Assessment, TLA Procedure

1.1.2 The total design loads derived in this Chapter are also to be used to form the basic load cases for the optional Structural Design Assessment, SDA, procedure, see Vol 1, Pt 7, Ch 1, 3.1 Structural Design Assessment notation – SDA.

1.1.3 The total design loads are derived by combining the local and global design loads, defined in Vol 1, Pt 5, Ch 3 Local Design Loads and Vol 1, Pt 5, Ch 4 Global Design Loads respectively, using load combination factors. These loads represent typical maximum values of combined loads that are simultaneously applied to the structure of a ship.

1.1.4 The total design loads given in this Chapter are applicable to all naval ships which are operating in the displacement mode.

1.1.5 The total design loads for ships that are operating in the planing or non-displacement modes will need to be specially considered. The loads given here are applicable for these ships whilst they are operating in the displacement mode, i.e. in severe sea states when planing is not possible.

1.2.1 The total design loads to be applied to each structural item are to include the following load and pressure components where applicable:

• global hull girder stress due to vertical bending, σ_hg in N/mm², derived in accordance with Vol 1, Pt 6, Ch 4 Hull Girder Strength;
• global hull girder shear stress loads, τ_hg in N/mm², derived in accordance with Vol 1, Pt 6, Ch 4 Hull Girder Strength;
• local pressure loads, P in kN/m², where P is the appropriate design pressure value for each component;
• local transverse, LT, or vertical support, LV, loads, in kN;
• mass inertial forces, in kN;
• local shear force loads, in kN.

1.2.2 In addition to the above loads, it may be necessary to consider the effects of the following on the structural components:

• bending of primary structure supported by major bulkheads;
• bending of primary structure supported by the side shell or longitudinal bulkheads;
• lateral bending moments and shear forces;
• global and local torsional moments.

1.2.3 Most of the above load components include a dynamically fluctuating component due to ship motions, e.g. side shell pressure due to wave and ship motion. These loads will not all be maximum simultaneously, due to their cyclic nature and the phase relationship between load values. Consequently it is not necessary to apply the maximum values of all these load components to the structure at the same time. Vol 1, Pt 7, Ch 2, 3 Design load combinations gives a method of combining these loads in order that representative total design loads may be applied to the structure.

1.2.4 The method of deriving the Total Design Loads for each structural component is given in Vol 1, Pt 7, Ch 2, 4 Design load systems for longitudinally effective components and Vol 1, Pt 7, Ch 2, 5 Design load systems for structural components or longitudinally ineffective material. However, it remains the responsibility of the designer to ensure that the loads applied are representative.

1.2.5 Details of all the loads applied to each structural component are to be supplied to Clasifications Register (hereinafter referred to as 'LR').

1.2.6 The major load components to be applied to, or reacted by, the structure are illustrated in Figure 2.1.1 Loads and stresses to be applied to the structure

1.3.1 The environmental conditions for the determination of the total design loads are to be based on the normal environmental design criteria specified in Vol 1, Pt 5, Ch 2, 2.3 Wave environment unless otherwise stated.

1.3.2 The standard values of wave height factor, f_Hs, and service area factor, f_s, given in Vol 1, Pt 5, Ch 3, 1.2 Environmental conditions 1.2.2 and Vol 1, Pt 5, Ch 2, 2.4 Service area factors, respectively, are to be used for the total design loads unless otherwise stated. These factors may be adjusted for damaged loading conditions, residual strength analysis, RSA, or for special operating conditions, e.g. a temporary draught condition for the recovery of amphibious vehicles in sheltered waters.

1.4.1 Alternative methods of establishing the total design loads will be specially considered, provided that they are based on established codes or standards acceptable to LR. In such cases, full details of the methods used are to be provided when plans are submitted for approval.

Figure 2.1.1 Loads and stresses to be applied to the structure

1.4.2 Throughout this Chapter, recommended values of effectiveness, ε, are given for each structural component. These effectiveness values specify the proportion of a particular load carried by a structural component as opposed to other supporting structure, see the text for more details. These efficiency values may be derived by direct calculation, similar ship analysis or other suitable techniques. The methods used and values derived are to be agreed with LR.