1.1.1 All parts of the structure are to be designed to withstand the most
severe combination of overall and local loadings to which they may be subjected.
Permissible stresses for direct calculation methods are to comply with the
requirements of Pt 4, Ch 5 Primary Hull Strength.
1.1.2 The local effects of the loadings listed in Pt 4, Ch 3, 4 Structural design loads are to be considered and all parts of the
structure are to be examined individually as necessary, and the calculations
submitted. The minimum Rule scantlings of all structures are also to comply with the
requirements of this Chapter, as applicable. These requirements are based on a net
scantlings approach, see
Pt 4, Ch 3, 7 Corrosion additions where the corrosion addition for structural
elements is to be derived independently of the net scantling requirements, and is to
consider the service life, operating environment and the inspection regime of the
Owner/operator, as agreed with LR.
1.1.3 The design heads for local strength of column-stabilised, sea
bed-stabilised and self-elevating units are to be in accordance with Pt 4, Ch 6, 2 Design heads.
1.1.5 The scantlings of machinery seatings are to be specially considered. On
self-propelled units, full details of power, and RPM, etc. are to be submitted.
1.1.6 The connections to anchor points as defined in Pt 3, Ch 10, 10 Fairleads, bending shoes and stoppers and the structure in way
of fairleads, stoppers, winches, etc. (see
Pt 3, Ch 10, 10 Fairleads, bending shoes and stoppers and Pt 3, Ch 10, 11 Anchor winches and windlasses) forming part of anchoring or positional mooring
systems are to be designed for a working load equal to the breaking strength of the
mooring or anchoring lines main component it connects to. Permissible stresses are
to be in accordance with Table 5.2.1 Factors of safety for the
combined load cases – load case (d). Special
consideration will be given to grouped line redundant positional mooring systems.
Note a) Exposure of the support
structure to breaking loads is most likely to occur in an accidental scenario. Such
scenarios may overload the mooring line component closest to the anchor (attachment
or connection) point to Offshore Unit, short cutting any weaker component in the
mooring line.
Note b) The breaking strength referred
to here is the mean breaking strength plus two standard deviations (as new from test
data) of the component considered (e.g. steel wire rope, chain or fibre rope)
directly acting on or closest in the load path to the structure under consideration
and is generally not to be taken lower than 110 per cent of the nominal minimum
break strength of the component.
1.1.7 The mooring equipment between the unit and visiting vessels including
supply boats and shuttle tankers is to be designed for a working load equal to the
breaking strength of the mooring line. The supporting structure on the unit for
these moorings is to be designed for a working load equal to the breaking strength
of the mooring line. Permissible stresses are to be in accordance with
Table 5.2.1 Factors of safety for the
combined load cases – load case (d).
Note a) The breaking strength referred
to here is the mean breaking strength plus two standard deviations (as new from
test data) of the component considered (generally chain) directly acting on or
closest in the load path to the fairlead and stopper structures and is generally
not to be taken lower than 110 per cent of the nominal minimum break strength of
the component.
Note b) The
design of structural arrangements around fairlead and mooring line connection
area should consider the potential shock load from recoil in case of mooring
line failure under tension.
1.1.8 When the minimum breaking strength of the main mooring line component
directly connected to the structure, is governed by design aspects other than
strength criteria, such as fatigue, LR will give special consideration to the use of
the maximum breaking strength of the next component inline as long as the likelihood
of the mooring line component directly connected to the structure being subject to a
pull equal or greater than its maximum breaking strength can be disregarded on the
basis of the conclusions of a risk assessment.)
1.1.9 Towing brackets and supporting structure are to be designed for a working
load equal to the breaking strength of the towline in accordance with the
requirements of Pt 4, Ch 9 Anchoring and Towing Equipment.
1.1.11 The supporting structure to turret bearings on ship units is to comply
with Pt 10 Ship Units.
1.1.16 Where a pipe-laying system is installed, the structures and equipment mentioned in
Pt 3, Ch 17, 2.2 General 2.2.1 are
to be integrated into the unit's hull structure. The integration structure of the
hull is a classification item and its local permissible stresses are to comply with
Pt 4, Ch 5 Primary Hull Strength.