Civil Engineering Reference
In-Depth Information
combinations of annealed and toughened glasses. When lami-
nated glass is broken, the interlayer tends to prevent the frag-
ments of broken glass from falling out and may be therefore
considered a safety glazing material. There is a range of per-
formance tests that can be performed to assess the suitability of
laminated glass for a given application. These are described in
Chapter 18.
Curved glass
: Produced by either heating flat glass beyond
its softening point or by bending the glass at ambient tempera-
ture (cold-bending). The most popular heat bending process
is sag bending, wherein the glass is heated to around 700°C
at which point the softened glass relaxes onto a mould. Single
curvature sag-bent glass is limited to a radius of curvature of:
manufacturers and processors should be consulted for up-to-
date information.
14.9.7 Tolerances and defects
Float glass can normally be cut within ±2 mm and ±4 mm of
the specified length or squareness. The surface of a glass panel
is not perfectly flat and it normally contains some imperfec-
tions that are measured optically in annealed glass as specified
in BS EN572 (2004). In toughened glass the imperfections are
limited to roller wave distortion ≤ 1 mm and overall bow ≤ 5
mm; the two can occur simultaneously and are additive.
Spontaneous fracture has been a major concern with tem-
pered glass in the past. This is caused by nickel sulphide
inclusions in the glass, which tends to expand with time thus
leading to sudden fracture. This problem can be minimised
by using high quality material and by heat soaking the tem-
pered glass at 290°C for several hours as described in BS
EN14179 (2005).
100 mm for 6 mm thick glass
■
300 mm for 10 mm thick glass
■
750 mm for 12 mm thick glass
■
1000 mm for 15 mm thick glass
■
14.10 Conclusions
An understanding of the characteristics of structural materi-
als, including strength, stiffness, flexibility, durability and fire
resistance - as well as the potential problems and financial
considerations associated with their use - is essential for good
structural design and the realisation of robust structures that
are fit for purpose. This chapter illustrates that, by virtue of
their varying properties, frequently used structural materials
are appropriate for different uses and situations, and have dis-
tinct impacts and applications for structural design.
1500 mm for 19 mm thick glass
■
Double curvature bending is available from specialist glass
processors.
Other processes
: There are several other on- and off-line
processes that are not discussed here for brevity's sake. These
include several forms of coatings (normally nanometre thick
metallic oxide) that improve the light transmittance and the
thermal performance of the glass. Furthermore glass panels for
building applications are often assembled into insulating glaz-
ing units.
Glass
product
Maximum
panel size
(mm)
14.9.5 Product permutations
Multiple treatments and processes may be applied to the same
glass panel, for example, basic float glass may be clear, tinted
or coated, which in turn can then be heat treated and/or bent.
It can subsequently be printed, laminated and double glazed.
This gives rise to a very large number of product permutations
which have been increasing as new processes become avail-
able. There are, however, some permutations that are not pos-
sible, namely:
Comments
Monolithic
annealed
float glass
6000 × 3210
Glass width (3210 mm) governed
by width of float bath. Lengths
6000 mm available by special
order
Monolithic
toughened
glass
4500 × 2150 or
7000 × 1670 or
6000 × 2700
Size governed by toughening
furnace which varies from one
manufacturer to another.
Length-to-width aspect ratio is
generally limited to 1:10.
Deeply patterned or deeply worked glass cannot be heat treated.
■
Fully toughened glass cannot be subsequently surface worked
■
PVB
laminated
glass
3800 × 2400 or
4000 × 2000 or
7000 × 1800
Size limited by size of autoclave
which varies from one
manufacturer to another.
Super size laminated glass
measuring 2800 x 13000 mm
is available from some
manufacturers, but can be limited
by size of monolithic glass used to
built laminated unit.
or cut.
14.9.6 Glass sizes
Glass panel sizes are governed by the size of the equipment
used in their production. This tends to change regularly as
manufacturers and glass processors invest in larger plant.
Float glass forms the basis for all other glass products dis-
cussed in this manual. It is produced in thicknesses of 3, 4,
5, 6, 8, 10, 12, 15, 19 and 25 mm. These thicknesses can be
processed into other glass products as shown in
Table 14.5
,
which provides a summary of indicative panel sizes, but
Insulated
glazing units
6000 × 2700
Limited by size of monolithic glass
used to build up IGU
Table 14.5
Glass panel sizes
