Section
11 External glass balustrades
11.1 General
11.1.2 The requirements of this Section apply solely to external glass
balustrades. External glass balustrades are barriers constructed with glass that are
used on exposed decks.
11.1.3 External glass balustrades are not to be situated in areas deemed essential
for the operation of the ship. Such areas include but are not limited to mooring decks,
lifeboat decks, external muster stations and in the vicinity of davits. Where external
glass balustrades are not to be used, more traditional bulwarks or guard rails are to be
fitted in accordance with Pt 3, Ch 8. 5, guard rails and other means for the
protection of crew.
11.1.4 Glass is to be manufactured in accordance with a recognised National or International
Standard.
11.2 Design considerations
11.2.1 External glass balustrades are to be designed to resist the most unfavourable
anticipated loads within service, including weather loads or personnel loads, without
unacceptable deflection. Detailed plans and calculations are to be submitted clearly
indicating the position, arrangement and the anticipated loads for all external glass
balustrades.
11.2.2 Laminated toughened glass is to be used for the glazing of all external glass
balustrades. The use of chemically strengthened glass is generally limited to passenger
yachts but will be considered on a case-by-case basis on other ship types.
11.2.3 The minimum characteristic breaking strength of the glass corresponding to
a 90 per cent confidence level is to be as required by Table 2.11.1 Characteristic breaking
strength of glass.
Table 2.11.1 Characteristic breaking
strength of glass
| Glass type
|
Characteristic breaking strength
N/mm2
|
| Thermally strengthened
glass
|
120
|
| Chemically strengthened
glass
|
160
|
11.2.4 External glass balustrades are to be not less than 1,0 m in height.
11.2.6 In general, openings (e.g. the gaps between panels or the gap between the deck and the
bottom of a panel) should not be greater than 76 mm unless required for water freeing.
Openings for water freeing are not to be greater than 230 mm.
11.2.7 Consideration is to be given to minimising the possibility of surface deterioration of
the balustrade glass panels in service by means of suitable edge protection or
finishes.
11.3 Types of glass balustrade
11.3.1 The following types of glass balustrade are acceptable:
- free-standing glass balustrade;
- free-standing glass balustrade with top rail;
- barrier with infill panel.
11.3.2 A free-standing glass balustrade is clamped at the bottom of the glass
panel, see
Pt 4, Ch 2, 11.8 Connections, and free to rotate at the top.
11.3.3 A free-standing glass balustrade with a handrail is clamped at the bottom of
the glass panel, see
Pt 4, Ch 2, 11.8 Connections, and free to rotate at the top. The handrail is to
be designed such that it spans between panels of glass within the balustrade so that in
the event of the failure of one panel, the handrail will remain attached.
11.3.4 A barrier with an infill panel is a steel or aluminium framed structure
with a glass infill panel which is supported either with a continuous edge or by
isolated bolt fixings or clamps, see
Pt 4, Ch 2, 11.8 Connections.
11.4 Loads
11.4.1 The weather load, Pgb, in kN/m2, is given by:
Pgb = 9,81Hd
where Hd is as required by Table 2.10.2 Design pressure,
Hd, on windows. For passenger yachts, the weather loads can be determined in
accordance with the requirements of Pt 4, Ch 2, 10.4 Loads 10.4.1 of the Rules and Regulations for the Classification of Special Service Craft, July 2022.
11.4.2 The horizontal pressure (applied perpendicular to the balustrade) due to personnel loads
is to be taken as 1,5 kN/m for unpopulated areas (e.g. balconies) and 2,25 kN/m for
populated areas (e.g. areas where people could congregate). The load is to be applied to
the top of the balustrade.
11.4.3 A safety factor of 4,0 is to be applied to the personnel load.
11.4.4 A safety factor of 2,0 is to be applied to the weather load.
11.4.5 When calculating the applied bending moment, Mg, free-standing glass
balustrades are to be considered as cantilever beams of unit width and infill panels are
to be considered as simply supported beams of unit width.
11.4.6 The loads are to be considered as separate load cases.
11.5 Glass thickness
11.5.1 The required thickness of monolithic glass, treq, is given
by:
where
|
Zreq |
= |
is the required section modulus of the glass panel, in
mm3 |
11.5.2 The effective thickness of laminated glass, td, in mm,
for deflection is given by:
where
|
t1, t2,
tn |
= |
thickness of each ply, in mm |
|
d1, d2,
dn |
= |
distance between the middle of each ply and the middle of the
laminated glass pane, in mm |
11.5.3 The effective thickness of laminated glass, ts, in mm, for bending is
given by:
|
dmax |
= |
distance between the middle of the thickes ply and the middle of the laminated
glass pane, in mm |
11.5.4 The shear transfer coefficient is dependent on the interlayer, where a
shear transfer coefficient of 1 indicates that all the load is transferred between the
plies. Common shear transfer coefficients are given in Table 2.11.2 Shear transfer
coefficient; where an alternative interlayer is specified, the shear transfer
coefficient can be obtained by means of a four-point bending test in accordance with
EN-ISO 1288-3 or an equivalent recognised National or International Standard.
Table 2.11.2 Shear transfer
coefficient
| Load type
|
Family 1 (e.g.
PVB)
|
Family 2 (e.g.
Ionoplast)
|
| Weather
|
0,3
|
0,7
|
| Personnel -
normal
|
0,1
|
0,5
|
| Personnel -
crowds
|
0
|
0,3
|
|
Note Refer to EN 16613
Glass in building – Laminated glass and laminated safety glass –
Determination of interlayer viscoelastic properties
|
11.6 Assessment
11.6.1 The effective thickness of a laminated glass panel, see
Pt 4, Ch 2, 11.5 Glass thickness 11.5.2 and Pt 4, Ch 2, 11.5 Glass thickness 11.5.3, is to be greater than
or equal to the required thickness of a monolithic glass panel, see
Pt 4, Ch 2, 11.5 Glass thickness 11.5.1. Alternatively, the
strength of the glass balustrade can be assessed using Finite Element Analysis where the
loads and safety factor are to be as required by Pt 4, Ch 2, 11.4 Loads in association with the glass strength
given in Pt 4, Ch 2, 11.2 Design considerations 11.2.3 and the shear
transfer coefficient given in Pt 4, Ch 2, 11.5 Glass thickness 11.5.4.
11.7 Balustrade stanchions and top rail
11.7.1 Where fitted, balustrade stanchions are to have adequate strength to resist
the anticipated loads specified in Pt 4, Ch 2, 11.4 Loads .
11.7.2 Where fitted, the top rail is to be sufficiently stiff so as not to deflect
more than Lb/96 when subject to the personnel loads specified in Pt 4, Ch 2, 11.4 Loads , where Lb is the span of the top rail between
stanchions.
11.7.3 The top rail minimum section modulus is to be greater than:
where
|
qk |
= |
line load on top rail, in kN/m, determined based on the personnel
loads and associated safety factor given in Pt 4, Ch 2, 11.4 Loads |
|
Lb |
= |
the span of the top rail between stanchions, in mm |
|
fσ |
= |
bending stress coefficient, not to be taken as less than 0,6 |
|
σo |
= |
specified minimum yield stress, in N/mm2 |
11.8 Connections
11.8.1 The connections of external glass balustrades are to be designed in
accordance with a recognised National or International Standard in association with
the loads given in Pt 4, Ch 2, 11.4 Loads . Typical examples of connection
design are given in Table 2.11.3 Typical glass balustrade connections.
11.8.2 Where sealant is used in association with a clamping system, the minimum depth of the
clamp is to be 100 mm for free-standing glass balustrades and 50 mm for infill
panels (i.e. 50 mm for each clamp top and bottom).
11.8.3 The strength of connection designs is to be verified using a prototype
strength test, see
Pt 4, Ch 2, 11.9 Testing 11.9.4. Where a designer proposes
to change a design including, but not limited to, a change in clamp size, bolt size,
sealant type, overlaps, clearance and manufacturer, the prototype test is to be
repeated. Where testing is impractical or where the proposed connection design is
unusual, Finite Element Analysis is to be used to confirm the strength of the
connection.
Table 2.11.3 Typical glass balustrade connections
Figure 2.11.1 Bolt fixing
Figure 2.11.2 Clamp fixing
Figure 2.11.3 Continuous fixing clamp
Figure 2.11.4 Alternative clamping system
11.9 Testing
11.9.1 External glass balustrades are to be subjected to a prototype pendulum
test in accordance with EN 12600 Glass in building – Pendulum test – Impact test
method and classification for flat glass or an equivalent recognised
National or International Standard utilising a drop height of not less than 1,2
metres. The glass is not to fracture, no cracks are to form and the glass is to be
retained in its frame/retaining arrangement.
11.9.2 Free-standing glass balustrades are to be assessed for post-failure strength where
failure is to be induced in one glass ply and the impact test is to be repeated. The
remaining glass ply or plies are not to fracture, no cracks are to form and the
glass is to be retained in its frame/retaining arrangement.
11.9.3 Where it is proposed to use thermally strengthened glass, the failure mode of the
glass balustrade is to be assessed where failure is to be induced in one of the
plies. The glass is to fail in such a way that the glass fragments do not detach
from the balustrade.
11.9.4 External glass balustrades (including both glass and retaining arrangement) are
subject to a prototype strength test where the test pressure is taken as the design
pressure multiplied by the safety factor, see
Pt 4, Ch 2, 11.4 Loads . The glass is to be retained in its
frame/retaining arrangement and the frame/retaining arrangement is not to detach
from the deck.
|