Section
8 Deck structures
8.1 General
8.1.1 Except
as otherwise specified within this Section, the scantlings and arrangements
for deck structures are to be determined in accordance with the procedures
described in, or as required by Pt 8, Ch 3, 8 Deck Structures for
mono-hull craft, using the pressures from Pt 5 Design and Load Criteria appropriate to multi-hull craft.
8.1.3 Special
attention is to be given to the connections of primary transverse
beams to hull side web frames in order to provide adequate load distribution
and avoid stress concentrations.
8.1.4 Primary
stiffening members are to be continuous and substantially bracketed
at their end connections to maintain continuity of structural strength.
8.1.5 Secondary
stiffening members are to be effectively continuous and bracketed
at their end connections as appropriate.
8.1.6 Design
loads to be applied for cross-deck scantling calculations are transverse
vertical bending moment and shear force, twin hull torsional connecting
moment, external pressure load and appropriate internal loads as defined
in Pt 5 Design and Load Criteria.
8.2 Arrangements
8.3 Symbols and definitions
8.4 Cross-deck laminate
8.4.1 The bending
moment assumed to be carried by the cross-deck laminate is to be not
less than that determined by Pt 8, Ch 3, 1.9 Plate and sandwich laminates 1.9.1,
using the design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for
non-displacement or displacement type craft as appropriate. This bending
moment is to be applied to laminates of both single skin and sandwich
construction in the determination of the panel scantling required
by Pt 8, Ch 4, 8.4 Cross-deck laminate 8.4.2 and Pt 8, Ch 4, 8.4 Cross-deck laminate 8.4.4 respectively.
8.4.3 In no case
is the minimum thickness of single skin laminate to be taken as less
than 4 mm.
8.4.4 An estimate
of the stiffness, E
 , thickness of single skin laminate for outer and inner
skins of the strength/weather deck sandwich panels and
the thickness of core material is to be determined from Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.2 and Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.9 respectively. The tensile
and compressive stresses are to be determined for each ply of reinforcement
in the proposed laminate using Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.7 and Pt 8, Ch 3, 1.14 Mechanical properties sandwich laminates 1.14.8. The
allowable tensile and compressive stress limits indicated in Table 7.3.1 Limiting stress criteria for local
loading in Chapter 7 are to be
complied with.
8.4.5 The amount
of reinforcement in laminates that form the skins of a sandwich laminate
is to comply with the requirements of Pt 8, Ch 4, 2.1 General 2.1.2.
8.4.8 It is recommended
that working areas of the weather deck have an anti-slip surface.
8.4.9 Where decks
are sheathed with wood or other materials, details of the method of
attachment are to be submitted, see also
Pt 8, Ch 3, 2.9 Sheathing.
8.5 Cross-deck stiffening
8.5.1 The Rule
requirements for bending moment, shear force, shear stress and deflection
for the cross-deck primary stiffeners are to be determined from the
general equations given in Pt 8, Ch 3, 1.15 Stiffeners general,
using the design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for
non-displacement or displacement type craft as appropriate, and the
coefficients φM, φS and φδ as indicated in Table 3.1.10 Shear force, bending moment and
deflection coefficients in
Chapter 3 for the load model (a).
8.5.2 The Rule
requirements for bending moment, shear force, shear stress and deflection
for the cross-deck secondary stiffeners are to be determined from
the general equations given in Pt 8, Ch 3, 1.15 Stiffeners general,
using the design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for
non-displacement or displacement type craft as appropriate, and the
coefficients φM, φS and φδ as indicated in Table 3.1.10 Shear force, bending moment and
deflection coefficients in
Chapter 3 for the load model (b). Special consideration will be given
to the application of other load models subject to the structural
arrangement and degree of end fixity provided.
8.5.5 For cases
where there may be excessive rotations or deflections at supports
or where the lateral pressure distribution is non-uniform, the above
scantlings may have to be increased appropriately.
8.5.7 Where the
floating frame system is used, the effect of the plating attached
to the stiffening members is to be ignored when calculating the required
section stiffness, E
 , of the primary stiffening members, i.e. the full stiffness, E
 , is to be provided by the primary stiffening members only.
8.6 Novel features
8.6.1 Where the
cross-deck structure is of unusual design, form or proportions, the
scantlings are to be determined by direct calculation, see
Pt 8, Ch 3, 2.7 Novel features.
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