Section 2 Rule structural concept

2.1.1 The Rules are based on the concept that the structural and watertight integrity and general safe operation of the ship will not be compromised by static and dynamic loads experienced during normal operating conditions.

2.1.2 For derivation of scantlings of stiffeners, beams, girders, etc. the formulae in the Rules are normally based on elastic or plastic theory using simple beam models supported at one or more points and with varying degrees of fixity at the ends, associated with an appropriate concentrated or distributed load. Alternative methods will be considered.

2.2.1 Scantlings are generally based on the strength required to withstand loads imposed by the sea, payload, ballast, fuel and other operational loads. However, the Rules assume that the nature and stowage of the payload, ballast, etc. are such as to avoid excessive structural stresses, and deformation.

2.2.2 The design loads and pressures given in Vol 1, Pt 5 Environmental Loads are to be used with scantling formulae or direct calculation methods to derive scantlings based on maximum allowable stress or other suitable strength criteria.

2.2.3 Hull structural vibration resulting from cyclic loadings arising from the sea and other sources are to be such that the normal operation and structural integrity of the ship are not impaired.

2.2.4 Static loads are based on standard conditions defined in Vol 1, Pt 5 Environmental Loads, or determined from loading conditions submitted by the Builder.

2.2.5 Dynamic loadings are examined for both the local and global structures. These loadings are based upon the designer’s stated operational and environmental conditions or the Rule minimum criteria, whichever is the greater.

2.2.6 Wave induced loads are considered both in the static condition, i.e. hydrostatic and pitching pressures, and in the dynamic mode, i.e. impact, slamming and hogging and sagging wave loading conditions.

2.2.7 Hull girder strength will in general require to be investigated dependent upon the length, configuration, proportions, proposed scenarios, etc. of the ship.

2.2.8 Structure in way of Replenishment at Sea, RAS, positions, cranes, heavy lift route points, weapon handling, etc. are to be designed in accordance with Vol 1, Pt 4, Ch 1, 5 Military design requirements. The equipment is to be designed in accordance with a specified standard(s), see Vol 1, Pt 1, Ch 2, 1 Conditions for Classification.

2.2.9 Scantling requirements in respect of miscellaneous items of structure such as local foundations, base plates, insert plates, bollards, etc. are not specifically indicated within these Rules. However, the acceptance of such items will be specially considered on the basis of experience, good practice and direct calculation where appropriate.

2.3.1 For the purpose of clarifying the nomenclature of items of structure referred to throughout the Rules, the following definitions are given:

• Secondary members are stiffeners supporting shell, deck or bulkhead plating, e.g. side/bottom/deck longitudinals, frames and beams, and transverse/ longitudinal bulkhead stiffeners.
• Primary members are those members supporting secondary members and will be the predominant members in grillage systems, e.g:
  • Bottom structure – floors, bottom and inner bottom transverse and girders.
  • Deck structure – deck transverses and girders.
  • Side structure – side transverses and side stringers.
  • Bulkheads – vertical webs and bulkhead stringers.

Deep web frames are members supporting primary members between bulkheads or decks, where additional support is necessary.

2.3.2 The fore end region structure is considered to include all structure forward of 0,7L _R.

2.3.3 The aft end region structure is considered to include all structure aft of 0,3L _R.

2.3.4 Critical structure is structure where the loss of a single element, such as a pillar, or section of deck or bulkhead between primary members, could lead to a collapse of the hull girder or a main deck.