Section 2 Design Principles

201. Design principles

1. Safety of the structure can be demonstrated by addressing the potential structural failure mode(s) when the unit is subjected to loads scenarios encountered during transit, operation and in harbour.

2. Structural requirements are based on a consistent set of loads that represent typical worst possible loading scenarios.

3. Unit is to be designed so as to have inherent redundancy. The unit’s structure works in a hier- archical manner and as such, failure of structural elements lower down in the hierarchy should not result in immediate consequential failure of elements higher up in the hierarchy.

4. Structural continuity is ensured. The hull, ture should have uniform ductility.

topside structures and topside interface to the hull struc-

202. Limit states

1. General

Table 3.1 Structural strength assessment

2. Limit states

(1) Serviceability limit state

Serviceability limit state, which concerns the normal use, includes:

(A) local damage which may reduce the working life of the structure or affect the efficiency or appearance of structural members

(B) unacceptable deformations which affect the efficient use and appearance of structural mem-

bers or the functioning of equipment.

(C) Motions or accelerations that can exceed the range of effective functionality of topside equipment

(2) Ultimate limit state

Ultimate limit state, which corresponds to the maximum load-carrying capacity, or in some cas- es, the maximum applicable strain or deformation, includes:

(A) attainment of the maximum resistance capacity of sections, members or connections by rup- ture or excessive deformations

(B) instability of the whole structure or part of it.

(3) Fatigue limit state

Fatigue limit state relate to the possibility of failure due to cyclic loads.

(4) Accidental limit state

Accidental limit state considers the flooding of any one cargo hold without progression of the flooding to the other compartments

3. Strength criteria

(1) Serviceability limit states

(A) For the yielding check of the hull girder, the stress corresponds to a load at ËŊG Ē proba- bility level.

(B) For the yielding check and buckling check of platings constituting a primary supporting

member, the stress corresponds to a load at

ËŊG Ē

probability level.

(C) For the yielding check of an ordinary stiffener, the stress corresponds probability level.

(2) Ultimate limit states

to a load at ËŊG Ē

(A) The ultimate strength of the hull girder is to withstand the maximum vertical longitudinal bending moment obtained by multiplying the partial safety factor and the vertical longi-

tudinal bending moment at

ËŊG Ē

probability level.

(B) The ultimate strength of the plating between ordinary stiffeners

members is to withstand the load at ËŊG Ē probability level.

and primary supporting

(C) The ultimate strength of the ordinary stiffener is to withstand the level.

(3) Fatigue limit state

load

at ËŊG Ē probability

The fatigue life of representative structural details such as connections of ordinary stiffeners and primary supporting members is obtained from reference pressures at ËŊG Ė.

(4) Accidental limit state

The accidental load condition, where a cargo tank is flooded, is to be assessed for longitudinal strength of the hull girder consistent with load cases used in damage stability calculations.

4. Strength check against impact loads

Structural strength shall be assessed against impact loads such as forward bottom slamming, bow impact, green water on deck and sloshing loads in cargo or ballast tanks.

5. Strength check against accidental damage

Consideration is to be given to accidental damage (e.g. collision, dropped objects, fire and ex- plosions, etc.) and examination sheets for reference is to be submitted to the Society.