Section
6 Hull shear strength
6.1 Symbols
6.1.1 The symbols used in this Section are defined as follows:
|
qv |
= |
unit shear flow per mm along the cross-section under
consideration, in N/mm, see
Pt 3, Ch 4, 6.2 General 6.2.2 and Pt 3, Ch 4, 6.2 General 6.2.3 |
|
QS |
= |
design hull still water shear force, in kN, to be taken as
negative or positive according to the convention given in Pt 3, Ch 4, 6.4 Design still water shear force 6.4.2 |
 |
= |
permissible hull still water shear force, in kN, see
Pt 3, Ch 4, 6.5 Permissible still water shear force |
|
QW |
= |
design hull wave shear force, in kN, to be taken as
negative or positive according to the convention given in Pt 3, Ch 4, 6.4 Design still water shear force 6.4.2 |
|
τ |
= |
permissible combined shear stress (still water plus wave),
in N/mm2, see
Pt 3, Ch 4, 6.6 Permissible shear stress |
|
τA |
= |
design shear stress, in N/mm2, as given in Pt 3, Ch 4, 6.7 Design shear stress 6.7.1 |
6.2 General
6.2.1 For ships with length L greater than 65 m, the shear forces on the hull
structure are to be investigated.
6.2.2 Shear flow calculation procedures are generally to be in accordance with
LR's ShipRight Procedure Additional Calculation Procedures for Longitudinal
Strength.
6.2.3 Where shear flow calculation procedures, other than those available
within ShipRight are employed, the requirements of Pt 3, Ch 1, 3 Equivalents are to be complied with.
6.2.4 For passenger ships, the assessment of permissible still water shear forces is to
take into consideration the effectiveness of the continuous superstructures and the
sizes and arrangements of window and door openings.
6.2.5 Where longitudinal bulkheads are perforated by cut-outs, the assessment of
permissible still water shear forces is to take into consideration the loss of
material.
6.2.6 For ships where the side shell, side casings, superstructure or longitudinal
bulkheads contain large openings or large numbers of windows or openings,
consideration is to be given to assessing the permissible still water shear forces
using direct calculation techniques.
6.3 Design wave shear force
6.3.1 The design wave shear force, Qw, at any position along
the ship is given by:
where
|
Qwo |
= |
0,3C1LB(Cb+0,7)
kN |
C1 is given in Table 4.5.1 Wave bending moment factor and is
to be taken not less than 0,6.
K1 is to be taken as follows, see also
Figure 4.6.1 Shear force factor K1 :
- Positive shear force
|
K1 |
= |
0 at aft end of L |
| = |
 between 0,2L and
0,3L from aft |
| = |
0,7 between 0,4L and 0,6L from
aft |
| = |
1,0 between 0,7L and 0,85L from
aft |
| = |
0 at forward end of L |
- Negative shear force
|
K1 |
= |
0 at aft end of L |
| = |
-0,92 between 0,2L and 0,3L from aft |
| = |
-0,7 between 0,4L and 0,6L from
aft |
| = |
 between 0,7L and
0,85L from aft |
| = |
0 at forward end of L |
Intermediate values to be determined by linear
interpolation.
|
K2
|
= |
1,0 for unrestricted sea-going service
conditions |
| = |
0,8 for short voyages |
| = |
0,5 for operation in sheltered water. |
6.4 Design still water shear force
6.4.1 The design still water shear force, Qs, at each
transverse section along the hull is to be taken as the maximum positive and
negative value found from the longitudinal strength calculations for each of the
loading conditions given in Pt 3, Ch 4, 5.3 Design still water bending moments 5.3.3 and is to satisfy the following relationship:
6.4.2 Still water shear forces are to be calculated at each section along the ship length.
For these calculations, downward loads are to be taken as positive values and are to
be integrated in a forward direction from the aft end of L. The shear force
is positive when the algebraic sum of all vertical forces aft of the section is
positive.
Figure 4.6.1 Shear force factor K1
6.4.3 For hull configurations where there are no longitudinal bulkheads (not including the
inner hull) and where loading conditions feature either:
- cargo loading with specified or alternative cargo holds (or cargo tanks)
empty; or
- ballasting of cargo hold(s);
the actual shear forces obtained from the longitudinal strength calculations are to
be corrected for the effect of local forces at the transverse bulkheads. The
calculation of these local forces is to be submitted for approval or, alternatively,
the proportion of the double bottom load carried by the transverse bulkhead can be
arrived at by using the following bulkhead factor F:
|
F |
= |
 |
where
|
α |
= |
 |
|
IF |
= |
span of floors measured to the intersection of the hopper or ship’s
side, and inner bottom, in metres |
|
SH |
= |
length of hold measured between bulkhead stools, where fitted, at the
level of the inner bottom on the centreline, in metres |
6.4.5 The corrected shear forces, Q'A and
Q'B, at bulkheads A and B with respect to hold AB are then
obtained from:
|
Q'A |
= |
QA + 0,5F(QB −
QA) kN |
|
Q'B |
= |
QB − 0,5F(QB −
QA) kN |
6.5 Permissible still water shear force
6.5.1 Still water shear forces are to be determined for all vertical structural
elements which contribute to the shear strength capability of the ship. The
permissible hull still water shear force is given by the minimum value obtained
from:
where
|
t |
= |
the plate thickness of the structural member at the vertical
level and section under consideration, in mm
m is
given in Pt 3, Ch 4, 6.5 Permissible still water shear force 6.5.2
qv is the shear flow in the structural
member at the vertical level and section under consideration, calculated
in accordance with the ShipRight Procedure Additional calculation
procedures.
|
6.5.2 To account for the effects of non-uniform loading in the transverse direction,
m is to be taken as follows:
|
m |
= |
0,9 for loading conditions where the cargo region between
two consecutive bulkheads, see
Figure 4.6.3 Examples of uneven transverse loading, within 0,2LT, is unevenly loaded
in the transverse direction. Where there are two longitudinal bulkheads,
the symmetric loading condition where the centre region has a different
filling height to the port and starboard regions is considered to be
uneven loading in the transverse direction. |
|
m |
= |
1,0 otherwise |
where
- LT is the cargo hold length, in metres.
Figure 4.6.3 Examples of uneven transverse loading
6.5.3 For hull configurations where loading conditions are such that hull girder torsion is
induced, direct calculations are to be undertaken if considered necessary.
6.5.4 The calculation of shear forces immediately beyond the ends of the longitudinal
bulkheads will be considered in relation to the arrangement of structure in these
regions.
6.6 Permissible shear stress
6.6.1 The permissible combined shear stress (still water plus wave) is to be
taken as:
6.7 Design shear stress
6.7.1 The design shear stress for use in Pt 3, Ch 4, 7.4 Design stress is
to be taken as:
where
Figure 4.6.4 Tapered plates
|