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Introduction on use of glass in modern buildings

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Contemporary architecture has an increasing demand for transparent building elements such as facades or roof structures, predominantly as steel and glass constructions. While materials such as steel, stainless steel or aluminium have been well studied in the past, relatively little is known about glass, its properties, connections and design in modern building applications. This article gives an overview about glazing applications from a façade and structural engineering point of view, with built examples and recent research activities.
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ICOM
Laboratoire de la construction métallique (ICOM)
INSTITUT DE STRUCTURES
FACULTÉ ENVIRONNEMENT NATUREL, ARCHITECTURAL ET CONSTRUIT
ÉCOLE POLYTECHNIQUE FÉDÉRALE DE LAUSANNE
Rapport 462
January 2003
INTRODUCTION ON USE OF GLASS
IN MODERN BUILDINGS
Wilfried LAUFS, Whitby Bird & Partners, London
Andreas LUIBLE
Ecole polytechnique fédérale de Lausanne (EPFL)
Laboratoire de la construction métallique (ICOM)
CH - 1015 Lausanne
Tél. : + 41-21-693 24 25
Fax : + 41-21-693 28 68
INTRODUCTION ON USE OF GLASS
IN MODERN BUILDINGS
Wilfried LAUFS, Whitby Bird & Partners, London
Andreas LUIBLE
Rapport N° ICOM 462
Copyright © Janvier 2003 by EPFL - ICOM Lausanne
Tous les droits de reproduction, même partielle (photocopie, microcopie),
de mise en programmes d'ordinateur et de traduction sont réservés.
Introduction on use of glass in modern buildings 3
January 2003 ICOM 462
TABLE OF CONTENTS
1 INTRODUCTION .................................................................................................................................7
2 GLASS PRODUCTS .............................................................................................................................8
2.1 SHAPE .............................................................................................................................................8
2.2 STRENGTH-REFINED GLASS .........................................................................................................9
2.3 LAMINATED GLASS .....................................................................................................................10
2.3.1 Principal................................................................................................................................10
2.3.2 PVB-Interlayer ......................................................................................................................10
2.3.3 Resin interlayer .....................................................................................................................10
2.3.4 Other Laminated Products ....................................................................................................11
2.3.5 Overhead glazing ..................................................................................................................11
2.4 DOUBLE GLAZED UNITS .............................................................................................................12
2.5 FIRE RESISTANT GLAZING..........................................................................................................12
2.6 GLASS APPEARANCE/COATINGS ...............................................................................................13
2.6.1 Low iron glass .......................................................................................................................13
2.6.2 Coating techniques ................................................................................................................14
hard coatings......................................................................................................................................14
soft coating ........................................................................................................................................14
2.6.3 Aesthetic coatings..................................................................................................................14
2.6.4 Solar control coatings ...........................................................................................................15
2.6.5 Heat insulating coatings...............................................................................................................16
2.7 AVAILABLE PANEL SIZES ...........................................................................................................16
3 MATERIAL PROPERTIES...............................................................................................................17
3.1 PHYSICAL CHARACTERISTIC VALUES ......................................................................................17
3.2 GLASS STRENGTH........................................................................................................................17
3.2.1 General..................................................................................................................................17
3.2.2 Annealed glass.......................................................................................................................17
3.2.3 Fully toughened glass............................................................................................................17
3.2.4 Heat-strengthened glass........................................................................................................19
3.2.6 Laminated safety glass ..........................................................................................................19
4 GLASS CONNECTIONS ...................................................................................................................20
4.1 GENERAL......................................................................................................................................20
4.2 LINEAR SUPPORT.........................................................................................................................20
4.3 LOCAL EDGE CLAMP...................................................................................................................20
4.4 POINT SUPPORT ...........................................................................................................................21
4.5 STRUCTURAL SILICONE SEALANT.............................................................................................22
4.6 GLUED CONNECTIONS ................................................................................................................23
4.7 LOCALISED LOAD INTRODUCTION ...........................................................................................23
5 ENGINEERING DESIGN ..................................................................................................................24
5.1 RELEVANT LOAD CASES.............................................................................................................24
5.2 IMPACT RESISTANT GLAZING ....................................................................................................24
5.3 CONSTRUCTION PRINCIPLES .....................................................................................................25
5.4 GLASS PANEL MODELING ..........................................................................................................26
5.5 ULS................................................................................................................................................26
4 Wilfried Laufs and Andreas Luible
January 2003 ICOM 462
5.6 SLS ................................................................................................................................................27
5.7 TOLERANCES ...............................................................................................................................28
6 CURRENT STRUCTURAL STABILITY RESEARCH ACTIVITIES......................................... 29
7 SUMMARY AND FUTURE TRENDS..............................................................................................30
REFERENCES ............................................................................................................................................31
Introduction on use of glass in modern buildings 5
January 2003 ICOM 462
ABSTRACT
Contemporary architecture has an increasing demand for transparent building elements such as
facades or roof structures, predominantly as steel and glass constructions. While materials such as
steel, stainless steel or aluminium have been well studied in the past, relatively little is known about
glass, its properties, connections and design in modern building applications. This article gives an
overview about glazing applications from a façade and structural engineering point of view, with
built examples and recent research activities.
RÉSUMÉ
L'architecture contemporaine fait appel de plus en plus à des éléments de construction transparents
pour la réalisation des façades et des toitures de bâtiment, plus particulièrement à des éléments
constitués de verre et de métal. Les matériaux métalliques tels que l'acier, l'acier inoxydable ou les
alliages d'aluminium ont été largement étudiés par le passé, alors que le verre est encore un
matériau de construction relativement mal connu quant à ses propriétés, ses moyens d'assemblage
et son dimensionnement propres au domaine des bâtiments modernes. Ce rapport donne un aperçu
de l'application du verre en tant qu'élément structural de façade et de toiture, des exemples de
réalisation de bâtiments ainsi qu'un résumé des recherches en cours dans ce domaine.
ZUSAMMENFASSUNG
Die Architektur der Gegenwart zeigt eine zunehmende Nachfrage nach transparenten Bauelementen
wie etwa Fassaden oder Dachstrukturen, die im wesentlichen Stahl- Glas- Konstruktionen sind.
Während die Materialien Stahl, Edelstahl oder Aluminium in der Vergangenheit bereits gut
erforscht wurden, ist über den Werkstoff Glas, seine Eigenschaften, Verbindungstechniken und
Bemessung in moderner Bauanwendung noch relativ wenig bekannt. Der folgende Artikel gibt
daher einen Überblick über Glasanwendungen im Fassadenbau aus Sicht des Konstruktiven
Ingenieurbaus, einschließlich einiger gebauter Beispiele und gegenwärtiger Forschungsaktivitäten.
6 Wilfried Laufs and Andreas Luible
January 2003 ICOM 462
Introduction on use of glass in modern buildings 7
January 2003 ICOM 462
1 INTRODUCTION
Glass may be defined as an “inorganic melt product, which solidifies without crystallization”. Soda-lime-
silica glass is said to be a “frozen liquid”. That is a visco-elastic material which is solid at room
temperature, but liquid at temperatures above its transition zone (above ~580 °C). Due to the lack of a
lattice structure, light may pass through the material without being blocked, which leads to the qualities of
transparency and translucency of glass in buildings. At the same time, however, glass is a brittle material. A
single sheet of glass once broken offers minimal redundancy, which is why load-carrying glass elements
should be designed from an engineering point of view in order to avoid spontaneous failure.
Traditionally glass has only been used as single panes in conjunction with a load-carrying frame, but today
glazing may be locally fixed by means of point-supports, or even used as a primary structural member, as
glass fins (Figure 1), beams or columns. The use of glass in structural engineering needs further
investigation of the causes and effects of its brittleness, to be able to account for the glass material
characteristics in safety assessments and in structural detailing. When consequences of drastic failure are
expected, additional measures have to be taken to compensate for the fact that glass gives no pre-warning of
material failure. These aspects are considered in the following sections.
Figure 1 - Example of an “oscillating glass façade” with point-supported and locally clamped glass fins,
supported by horizontal cables [1]
8 Wilfried Laufs and Andreas Luible
January 2003 ICOM 462
2 GLASS PRODUCTS
2.1 SHAPE
Different types of glazing are standardized in EN 572. The most common manufacturing process is the float
glass process, where flat glass of thicknesses 3,4,5,6,8,10,12,15, 19 and 25mm is produced. The hot glass
melt is poured onto a zinc bath, slowly cooled down and cut for further processing. The initial glass size
dimension is about 6.0m x 3.2m (maximum). Different glass edge qualities are available, see Figure 2.
While a cut edge might be sufficient for traditional window applications, higher quality edge treatments are
required as soon as the panel edges are subject to bending or local load transfer. This is because the
grinding wheel application reduces the risk of micro-or macro-cracks on the glass edge surface. Also
rounded joints or beveled edges are possible for aesthetic reasons.
cut edge or
(matt finish)
arrised edge
ground edge, arrised or not
(smooth finish)
polished edge, arrised or not
(highest quality)
glass thickness t,
available in 3,4,5,6,
8,10,12,15,19 mm)
flat glass
curved glass
R
channel glass
glass tube
R
glass brick
Figure 2 - Basic edge qualities and available glass product shapes
In order give the glass surface a special pattern, the hot glass melt may also be poured out and pressed
between two rollers, which is the process for manufacturing ornamented glass (Figure 3). It is formed by a
reversal of the pattern on the roller, cooled down to room temperature. Patterned glass is only available in
certain thicknesses and should be checked with manufacturers data. It offers a variety of architectural
appearance, but is not as clear and flat as float glass.
Figure 3 - Example of patterned glass surface (ornamented glass)
Introduction on use of glass in modern buildings 9
January 2003 ICOM 462
The sides of the hot glass may also be further bent by means of additional rollers on either side to form C-or
U-channel sections up to approximately 6.0m length. Circular glass tubes are also available, with wall
thicknesses of about t= 0.7 to 10.0 mm and diameters ~ Ø = 3 to 325 mm. Translucent glass bricks (EN
1051) may be manufactured as standard ranges or according to project needs. Curved glass might be made
with the help of special ceramic moulds, where initially flat float glass is placed onto them horizontally and
slowly reheated. When warm enough, the glass panel then sags into or over the shape of the mould by
means of its self-weight. Possible radii vary from about R= 300 mm to , but depend on the type and
thickness of glass. Bends can be created in one or two planes. Various irregular curved shapes might be
manufactured, depending on the shape of mould (Figure 4).
Figure 4 - Curved glazing revolving door (left); partially bent façade glazing to form transition zone
between a straight façade with a cone area (center and right) [1]
2.2 STRENGTH-REFINED GLASS
Glass products may be divided into three different basic types with regard to their strengths and fracture
patterns according to Figure 5. Annealed glass often does not give sufficient strength for modern
applications. Fully toughened glass with high strength does not stay in position in the event of fracture
because of its fine fragments once broken. For that reason, heat-strengthened glass was developed to give
both high allowable strength values as well as a large breakage pattern in case of failure.
During the tempering process, basic annealed glass is heated up to >600°C in a furnace and then rapidly
cooled, using air nozzles from both sides down to room temperature. High temperature gradients between
the colder surfaces and the inside of the glazing panel temporarily occur. Together with interaction of the
viscous material properties of glass, an invisible, internal 3D pre-stress is induced, where all panel surfaces
are put in compression, held in equilibrium by inner tension. Tempered glass must be cut to size, edge
treated and hole drilled before being subjected to toughening, because attempts to work the glass after
toughening will usually cause the glass to shatter [2].
10 Wilfried Laufs and Andreas Luible
January 2003 ICOM 462
annealed laminated
safety glass
heat- strengthened
laminated safety glass
toughened laminated
safety glass (with PVB)
rising tensile bending strength
better residual safety after breakage
45 N/mm²
70 N/mm²
120 N/mm²
Figure 5 - Standard glazing types with their corresponding breakage patterns (laminated with PVB) and
5%-fractile characteristic tensile bending stress values (with 95% probability level)
2.3 LAMINATED GLASS
2.3.1 Principal
Laminated (safety) glass consists of two or more annealed or tempered or heat-strengthened glass panes
which are joined by a transparent intermediate layer of plastic, in general one or more foils of Poly-Vinyl-
Butyral (PVB-foil) with a basic thickness of t= 0.39 mm or cast resin in between the sheets. When the panes
are destroyed the broken glass pieces stick to the foil, and large deflections and energy absorption are
possible before the foil fails. The main application fields are for overhead glass, wind screens, bullet proof
glass, glass beams and glass columns. Laminated glass is standardised in EN ISO 12543.
2.3.2 PVB-Interlayer
The manufacturing process involves washing, pre-positioning, pre-heating and an autoclave in which the
glass panels with the PVB interlayers in between are superimposed onto each other and then laminated
under incremented pressure (~12 bar) and temperature (~140°C). This process locally may lead to a certain
offset of adjacent glass edges. Durability against weathering (water/UV) is generally sufficient, but exposed
horizontal edges of laminated glass could be weather-sealed with PVB-compatible silicone, if required.
PVB density is 1070 kg/m3, its poisson’s ratio close to 0.5 and its thermal expansion coefficient might be
taken to be 8 x 10-5 1/K. The PVB-foil should have a minimum rupture strength 20 N/mm2 and a PVB
minimum rupture strain (elongation) 300 % to offer sufficient strength and ductility.
2.3.3 Resin interlayer
Another lamination method involves cast resin, where two glass panels are closely positioned next to each
other vertically and the defined remaining gap (i.e. 2 mm) is filled with an injection of liquid cast resin,
which cures with time under UV (“cast-in-place”). Therefore, very large panel sizes may be realized, as no
additional autoclave etc. is required. Cast resin density is 1700 kg/m3, its poisson’s ratio about 0.45 and its
thermal expansion coefficient might be taken to be 4 x 10-5 1/K. Young’s modulus E varies from product to
Introduction on use of glass in modern buildings 11
January 2003 ICOM 462
product and is around 10 N/mm2 for cast resin. Compared with PVB, resin offers better acoustic insulation,
but once a laminated glass is broken, there is less residual safety available, see Figure 6. It is not
recommended to be used for overhead glazing, unless 1:1 testing is performed with sufficient results.
toughened laminated
glass (with cast resin)
overhead-
situation
Figure 6 - Typical insufficient breakage pattern of a laminated toughened glass with cast resin
2.3.4 Other Laminated Products
Glass may be laminated to other materials such as stone (i.e. glass/resin/marble) or opaque insulated panels
as well. New interlayers with higher strength than PVB, such as polycarbonate, have also been introduced
on the market more recently to make use of a higher shear interaction of the interlayer as well as an
improved post-failure behaviour of laminated safety glass. Increasingly, also photovoltaic elements are
embedded within glazing elements in high-transparency resin to transform solar energy into electricity. The
cells are connected to each other within the module and hence generate a direct electrical current. Mono-
crystalline solar cells (colour: black, silver, blue) may convert up to 16% of solar energy into electricity,
each cell with a size of about 100 x 100 mm. Multi-crystalline solar cells (colour: pale blue, grey shades,
bronze silver) comprise crystals oriented in different directions, converting about 14% of solar energy.
More recent developments use thin film layer technologies, where the PV consist of very thin layers of
cadmium-sulfide and cadmium telluride, which are electro-deposited on the glass (i.e. a laser-scribing
procedure forming the individual solar cells). Even though energy efficiency is lower than for crystalline
solar cells, production costs are less expensive, such that thin film technology might be more economical.
All intercell electrical connections (metallic conductive paths) are internal to the module, which forms a
monolithic structure. Between the layers and metallic conductive path there is an EVA interlayer (Ethylene
Vinyl Acetate). The total thickness between the two outer glass panels is approximately 0.80 [mm], where
the thin film itself only makes up 1.5 to 3.0 µm. No additional diode is necessary for “hot spots” due to
possible short circuits or local overheating, because no “reverse flow” is possible within this system. At the
glass panel edges, a danger of water penetration is precluded, as the thin film interlayer stops short and is
covered by the EVA. The interlayer is a transparent thermoplastic, amorphous elastomer, which remains
flexible at low temperatures and resists cracking. EVA density is similar to PVB, its poisson’s ratio 0.4 to
0.5, its Young’s modulus around 60 N/mm2 and its thermal expansion coefficient might be taken to be 9 x
10-5 1/K. The EVA-foil offers a minimum rupture strength 10 N/mm2 and an EVA minimum rupture
strain (elongation) 500 % for sufficient strength and ductility.
2.3.5 Overhead glazing
Overhead glazing may be defined as all glass that people pass below, including glass canopies, glass roofs
and glass facades under which people can pass. In some countries it is defined as all glazing inclined 10º
to the vertical. For safety reasons, the glazing shall be laminated, consisting of either two or more annealed
or preferably of two or more heat-strengthened panels or a combination of heat-strengthened and fully
toughened glass panels. This is to assure that in the case of glass breakage no dangerous glass fragments
12 Wilfried Laufs and Andreas Luible
January 2003 ICOM 462
can fall down, because they are bonded to the PVB or other interlayer for a sufficiently long time. As the
broken glass behaviour depends on its size, type, thickness and support conditions of the glazing, a full size
test has to be carried out for the most critical cases. The test is passed, if a broken panel with all individual
panels broken may remain in position for at least 24h (to be agreed with local authority in detail). This is to
assure sufficient time to close the area underneath the broken glass so it can be replaced safely. In practice,
this information is gained by 1:1-testing (Figure 7).
60
45
8 8152
200
2940
19015501000
1300
115 1151070
laminated safety glass
8 heat-strengthened
1.52 PVB interlayer
8 heat- strengthened
[mm]
detail
detail
Figure 7 - Example of an overhead-glazing test to determine residual safety after breakage (destruction of
both panes under additional loading UDL = 0.5 kN/m2, removed here) [2]
2.4 DOUBLE GLAZED UNITS
Double glazed units (EN 1279) consist of two or more glass panels enclosing a cavity space of about 12 to
16mm width (filled with air or rare gas), created by an aluminium spacer along the glass edges, such that
insulation properties compared to single glazing are considerably increased. In order to eliminate the
thermal bridge effect of the standard spacer, new spacers made of less thermally conductive materials i.e.
low thermal conductivity plastics or fibre-glass reinforced materials have been recently developed. To
prevent the cavity from condensation, a hygroscopic dehydrating medium is placed within the spacer
(desiccant). Normally the primary seal along the spacers is achieved by means of a thin butyral layer, which
is further weather-sealed and protected on the outside (secondary seal). If the outside air pressure differs
from the initially induced inner cavity pressure, an additional load case is induced [3].
2.5 FIRE RESISTANT GLAZING
Special modern glazing products allow for a fire protection of up to 120 minutes. The transparent glazing is
protective by becoming opaque when subjected to heat above ~120°C. This is achieved with the help of
special transparent gels or intumescent (swelling) interlayers carrying chemically bound water, i.e. such as
alkali-silicates, which are transparent at room temperatures, but foaming above a certain temperature, such
that heat waves are blocked and spread of fire is avoided (Figure 8). It might be distinguished between fire
protective systems that shall only stop smoke and flames from spreading through the glazing or additionally
also block heat radiation through the glass, where no flames on the side opposite the fire are allowed to
develop; the surface facing away from the fire shall stay below 140K (area-averaged increase above room
temperature) and locally not heat up more than 180K (local maximum); these temperature levels are
intended to ensure that any combustible material in contact with the unexposed face will not ignite.
Introduction on use of glass in modern buildings 13
January 2003 ICOM 462
The glazing might break, but shall stay in position after breakage without falling down. 1:1 testing of a fire-
protective glazing with its particular framing system as one unit has to be performed and certificated by
independent testing authorities. Glasses with low thermal expansion coefficients such as borosilicate glass
experience lower tensile stresses caused by temperature gradients within the panel and hence might
withstand smoke and flames up to 30 minutes without additional interlayers.
533
[mm]
i.e. Poly-
Sulfide
interlayer
5555
detail
detail
fire:
- up to 1000°C
- flames
- smoke
- heat radiation
clamping frame with sufficient rebate
depths and pressure to avoid slump
frame not
shown
fire insulating
glass unit, i.e.
90 minutes
resistance
toughened
toughened
annealed
annealed
interlayer
interlayer
Figure 8 - Build-up of a fire protective glazing, resistant against heat radiation, spread of flames and
smoke for at least 90 minutes
2.6 GLASS APPEARANCE/COATINGS
2.6.1 Low iron glass
Within the glass melt for normal annealed glass, the presence of a small amount of iron oxide (~0.05 to
0.1% FeO and Fe2O3) causes a slightly greenish appearance, because its complementary color magenta is
blocked to some extend. To achieve a very clear, almost “white” glass, a special glass melt with hardly any
iron oxide is used to produce low-iron glass, which is more expensive than regular float glass, but
increasingly popular due to aesthetic reasons, namely its colorless appearance and good light transmittance,
see Figure 9. It might be further manufactured in the same way as regular float glass.
clear white glass ("low iron")
standard float glass
direct energy transmission in %
wavelength λ in nm
visible
light
500 1000 1500 2000 2500
UV
light
Infra- red
light
0
100
80
60
40
20 (glass thickness t= 4mm)
Figure 9 - Wave lengths transmission of regular float glass and low-iron glass in comparison
14 Wilfried Laufs and Andreas Luible
January 2003 ICOM 462
2.6.2 Coating techniques
Different coating types might be distinguished in architectural glazing as follows [4][5]:
hard coatings
The coating materials are fired into the glass surface while it is under very high temperatures. For this
reason the so-called on-line coating process is integrated in the float process or in the annealing lehr. The
applied coating materials are metallic oxides that fuse by pyrolysis into the glass surface at 600-650°C. The
advantage is their hardness so that the coated surface can be glazed also to exterior sides of the glass unit.
On-line coatings show good economics in fabrication, but have the disadvantage of having to be integrated
in the float process and therefore they are not as flexible as off-line coatings. Only a maximum number of
two layers can be applied at once. Dip coating is another method to apply hard coatings on glass surfaces. In
this process the glass is dipped into the coating solution and then heated up to 650 °C to create a hard
transparent oxide coating.
soft coating
There are different application methods such as dip coating, chemical or physical vapour deposition to
apply soft coatings onto glass surfaces. Currently, the DC-magnetron sputtering process is the most
common technique. In this process the glass is placed in a vacuum chamber that contains the cathode target
and a sputter gas. A negative charge is applied to the cathode, and a glowing plasma ignites in the vacuum
chamber. The target is now bombarded by ions of the sputter gas which rip off atoms from it and deposit
them on the glass surface. The coating is carried out in several vacuum chambers with a certain number of
different cathodes targets. It is possible to apply up to 15 different target materials to be sputtered onto the
glazing and therefore to vary the coating composition as well. Typical coating materials for a low-e coating
are tin oxide and silver. The total coating thickness is only about 0.01 to 0.1 µm. The magnetron sputtering
is a very precise, flexible and modern technique that enables very constant coating quality. It makes it even
possible to reproduce exactly the same coating with the same technical properties after many years and the
color adjustment is very simple.
The disadvantage of soft coatings is their susceptibility to aggressive air pollution and mechanical damage.
This makes it necessary to protect the soft coating with a protective layer or assemble them into double
glazing units, with the coating on face 2 (for optimum solar control performance) or face 3 (heat insulation,
low-e). The magnetron sputtering coating of curved glass is not yet fully developed. In this case the glass
units have to be made of laminated glass with a special plastic interlayer to monitor the transmission and
reflection. Very recently, a high rate reactive mid frequency magnetron sputtering is used for glass coatings
more often. Advantages of the so-called MF-magnetron sputtering are harder coatings, higher sputtering
rates (up to 3-9 more compared to DC-sputtering) and lower costs.
2.6.3 Aesthetic coatings
Most commonly, colored aesthetic glazing patterns are produced using an enameled frit technique, where a
ceramic color is sprayed onto the glass surface through a screen (with embossing the negative pattern) and
then burned into the glazing surface during toughening. It is possible to further laminate surfaces with
ceramic frit pattern with PVB or resin, but its tensile bending strength is somewhat reduced by about 25%.
Introduction on use of glass in modern buildings 15
January 2003 ICOM 462
Figure 10 - Enameled finish, white ceramic frit on face 2, laminated safety glass (left); surface treatment
with a partially acid etching pattern, t= 10 mm (right)
A rough surface might be generated using a sandblasting technique, where the glazing surface is roughened
and hence an engraved, translucent pattern is created. An abrasive is blasted under pressure onto the surface
of the glass. With acid etching (either with liquid acid baths or acid pastes/screens) very durable patterns
with warranties up to 10 years can be produced (Figure 10), where the surface durability is only affected by
dirt which can be cleaned, but not by means of any chemical reactions as for ceramic frit, when used on
face 1 in direct contact to weathering. Acid etching relies on the fact that glass is subject to attack by some
acids (i.e. hydrofluoric acid), such that a consistent translucent obscuring surface of different depths may be
created.
2.6.4 Solar control coatings
Solar sky radiation that reaches the earth consists of 3% short-wave ultra-violet rays (UV), 42% visible
light (wavelengths from ~380 nm to 780 nm) and 55% long-wave infra-red radiation (IR). As the energy is
particularly high for infra-red light above the visible wavelengths, the strategy for solar protective glazing is
to block as much light in that range as possible, but without reducing visible light transmission too much,
see Figure 11. Solar coatings reflect and absorb a large amount of energy, such that the total energy
transmission of the glazing is significantly reduced. When solar glazing alone is not sufficient, alternative
shading strategies such as external moveable blinds may have to be considered additionally.
1500
wavelength λ in nm
0500 1000 2000 2500
visible
light
total sky energy spectrum
normative graph
according to EN 410
solar control glazing
transmitting visible
light, but blocking
infra- red energy
infra- red
light
absorbtion A
reflection R
transmission T
total energy
transmission
100 %
T + R + A
= 100 %
soft solar
coating
outside inside
100
solar control double glazing
face 2
Figure 11 - Principle function of a solar control coated glazing panel
16 Wilfried Laufs and Andreas Luible
January 2003 ICOM 462
2.6.5 Heat insulating coatings
Heat insulating coatings have the objective to reduce the high emission coefficient of glass for thermal
radiation from ε = 0.89 down to ~0.05. These coatings are therefore called low-e coatings and can either be
a hard or a soft coating. They are predominantly transparent over the visible wavelength, but reflective in
the long-wave infra-red range. It is possible to reduce the infra-red radiation down to 20 % with a light
transmittance greater than 0.70. In temperate climates where a high thermal insulation with simultaneous
solar control is required, it is possible to combine the functions of heat insulating coatings with solar
control coatings within one single coating. For a regular double glazed unit with no further coatings, about
1/3 of heat exchange is due to conduction and convection, while 2/3 is due to heat radiation. With a low-e
coating on face 3 the radiation heat loss is significantly reduced (Figure 12).
cavity (filled with air,
argon or crypton)
spacer (aluminium,
plastic or other material)
desiccant
primary seal: butyral
secondary seal: silicone
warm side of insulated
glazing with heat transfer
towards cold side
t2t112 to 16 [mm]
conduction
+
convection
+
radiation
=
total
heat transfer
glass
panel
low- e
coating
outside inside
insulating low-e double glazing
energy reflection
face 3
Figure 12 - Principle build-up and heat transfer mechanisms of a double glazed insulating unit with low-e
coating
2.7 AVAILABLE PANEL SIZES
For orientation, Table 1 shows some useful values with regard to available glass panel sizes, depending on
type and refinement.
Table 1 - Available glass panel sizes (check with manufacturer’s data in more detail)
Glass product/refinement panel size [mm] x [mm] Comment
Single basic annealed float glass 6000 x 3210
Restricted by float plant
(maximum band width)
Single basic patterned glass 4500 x 2040 Thicknesses 4 to 10 mm
Basic insulated glass 6000 x 2700
Toughened glass
6000 x 2700 or 7000 x 1670
or 4500 x 2150
Restricted by temper furnace
Laminated safety glass (PVB)
7000 x 1800 or 4000 x 2000
or 3800 x 2400
Restricted by autoclave size
Laminated glass (resin) 6000 x 3210 Limited by injection facility
Introduction on use of glass in modern buildings 17
January 2003 ICOM 462
3 MATERIAL PROPERTIES
3.1 PHYSICAL CHARACTERISTIC VALUES
Some relevant physical values of glass panels are given in Table 2.
Table 2 - Design-relevant physical data for glass panels used in buildings
Glass property Value Unit
Density σ 2500 kg/m3
Young’s modulus of elasticity E 70000 N/mm2
Poisson’s ratio (transverse contraction) µ 0.23 -
Thermal expansion coefficient β 9 x 10-6 1/K
Thermal conductivity λ 1.0 W/(mK)
Emissivity ε 0.89 -
3.2 GLASS STRENGTH
3.2.1 General
Glass is very strong under compression (up to 500 N/mm2), but rather weak in tension. Traditionally, the
concept of “allowable stresses” has been used, where a defined characteristic bending strength value is
defined for each type of glazing, which is then divided by a global safety factor. The bending strength might
be determined by a four-point-bending test or a coaxial double ring test (EN 1288), where short term
bending stresses are determined and then statistically evaluated (i.e. 5% fractile values for 95% probability
level).
3.2.2 Annealed glass
Due to the brittle material behavior of glass, strength of annealed glass is not a constant, but influenced by
its micro- and macro-cracks at the surfaces and hence fracture mechanics is applicable. Under bending, the
glass resistance (tensile strength) depends on various factors: the area under tension and its surface
condition, load duration and distribution of stresses, the stress rate and environmental conditions.
3.2.3 Fully toughened glass
Toughened glass (EN 12150) has a higher breakage resistance than annealed glass, but once broken it bursts
into small pieces. Such a spontaneous failure may also occur due to small nickel sulfide inclusions (NiS),
which expand their volume within the glass even up to about 2 years after production. A so-called
destructive heat-soak test (i.e. according to DIN 18516, part 4) should therefore be performed before
delivery to determine those inclusions within the toughened glass.
Fully toughened glass panels exhibit high values of bending strength, composed of the frozen-in
compressive surface stress in addition to the tensile strength of the annealed float glass, that is effective
after decompression by loading. As the compressive surface stress is not influenced by surface defects, the
tensile strength of a single pane safety glass may be approximately considered to be independent of the
surface condition, the size of the surface, the distribution of stresses, the stress-rate and the environmental
18 Wilfried Laufs and Andreas Luible
January 2003 ICOM 462
conditions, if the tensile strength of the annealed glass is neglected. Toughened glass might withstand local
temperature differences of up to 150K, i.e. due to local heat. As the pre-stress is not equally distributed over
the surface of a toughened glass panel, the safety verifications should be performed according to a zonation
[6] that takes the design situation for pre-stress into account (Figure 13).
R, radius
axis
compression
tension
compression
Zone 1: central area
Zone 2: panel edge
Zone 3: panel corner
Zone 4: bore hole
glass panel with
bore holes
t, glass
thickness
Zone 4:
~1.5 t
Zone 2:
~1.5 t
Zone 3:
~3.0 t
Zone 1
pre-stress
3D field
pre-stress
3D field
pre-stress
3D field
plan
Figure 13 - Zonation of a toughened glass panel with regard to different pre-stress distributions,
compressive areas marked
Edges or the areas around holes should be treated differently from the central area of a glass panel. As an
example, the principal pre-stress distribution for a bore hole with a cone is given in Figure 14. The
reliability of pre-stress can be checked by quality control measures that include optical measurements. It
might be distinguished between out of plane or in-plane loading [7].
3
tangential membrane
pre- stress , 3D
x
3
x
= 0
3
xr
R
=
bore hole axis
radial pre-
stress r
12
(thickness
pre- stress)
3
transition
to Zone 1
well- known
2D parabolic-
like pre- stress
in Zone 1
overview
all surface pre- stress perpen-
dicular to any surface = 0
Figure 14 - Principle of thermal pre-stress distribution near a bore hole with a cone (Zone 4)
Introduction on use of glass in modern buildings 19
January 2003 ICOM 462
3.2.4 Heat-strengthened glass
In many cases there are reasons to reduce the surface pre-stress level in the toughening process to about -55
to -35 MPa for heat-strengthened glass (EN 1863) instead of -140 to -90 MPa for fully toughened glass
(zone 1). The fragmentation is similar to that of annealed glass; that keeps the panes in position after
cracking when they are framed or laminated and hence the residual safety is sufficient. Heat-strengthened
glass is manufactured in a similar way than fully toughened glass, but no spontaneous failures do to NiS-
inclusions have been observed in the past, such that no heat-soak test is necessary. Heat-strengthened glass
might withstand local temperature differences of up to 100K, compared to annealed float glass of up to
40K. The safety assessment for heat-strengthened glass is performed in the same way as for tempered glass
taking lower pre-stress values into account. Particular quality control is necessary to avoid a too high or too
small level of compressive pre-stress, i. e. non-destructive optical measurements.
3.2.6 Laminated safety glass
In general, at least for long-term actions, the composite action by the foil is not taken into account in design.
Therefore, for a laminated safety glass, e.g. with a total thickness of 20.78 mm, that is composed of two
single glass panes, only the sum of the strength and stiffness of the single 10 mm panes may be considered
in order to allow for creep effects at elevated temperatures and for longer load duration. However, recent
tests with laminated safety glass have given evidence that for short-term loading, such as from wind gust or
impact the composite action is significant. Depending on load duration and temperature, the shear modulus
G of the foil may be taken according to Table 3. For shorter spans differences of stress distribution might be
even more significant.
Table 3 - Influence of PVB interlayer shear modulus G on mid-span deflection and bending stresses in a
laminated safety glass with asymmetrical composition (10mm/1.52mm PVB/6 mm)
Load duration [s] unknown long short < 180 s very short < 10 s
Temperature [°C] unknown ~22 ~22 ~22
Comment
Safe side always:
“no shear
interaction”
i.e. self- weight i.e. wind gust
loads
i.e. impact loads,
almost „full
shear
interaction“
Effective PVB shear
modulus G [N/mm2] 0 0.01 1 4
mid-deflection fmax [mm] 148.7 138.3 44.4 36.9
1 kN/m2
L = 3000 mm
1,52
610
bending stress in the
glass layers [N/mm2]
-55.5
55.5
-33.3
33.3
-52.7
50.7
-29.5
32.0
-24.6
4.2
7.8
23.7
-22.5
6.7
4.7
23.0
20 Wilfried Laufs and Andreas Luible
January 2003 ICOM 462
4 GLASS CONNECTIONS
4.1 GENERAL
In general, a direct steel–glass contact should be avoided with the help of separating intermediate materials.
Normally self-weight is taken by plastic setting blocks or by epdm/silicone layers with hardness 60 to 80
Shore A, separating the glazing from the frame. For the loading perpendicular to the panel, different fixing
possibilities exist, see Figure 15 [8]. These are described in the following in more detail.
linearly supported
(i.e. pressure caps)
local edge supports
(clamps)
local point supports
(point fixings)
strucutral silicone sealant
(SSG support, i.e. 2- sides)
~10 to 20
min t = 6
~20 to 40
~50 to 80
>20
support pad
and drainage
separating layer,
i.e. neoprene
hinge i.e.
DC 993
[mm]
carrier
frame
Figure 15 - Overview of common glazing support possibilities
4.2 LINEAR SUPPORT
Linearly supported glazing is usually framed, where its self-weight is transferred through support pads
either side at the horizontal bottom glass edge (Figure 15). The frame size is larger than the glass pane, such
that production tolerances as well as temperature movements can be taken without any in-plane constraint.
Wind pressure and suction is taken by the frame system (i.e. pressure caps) and transferred to the main
structure.
4.3 LOCAL EDGE CLAMP
In order to minimise the visual impact of linearly supporting frames or pressure cap profiles, panel edges
may be fixed only locally by means of clamps that are fixed to the sub-structure, where there is a frame-like
structure only on the inside of the glazing (Figure 16). In addition to the visual impact it may also be
beneficial for overhead glazing where certain rainwater ways are required.
Introduction on use of glass in modern buildings 21
January 2003 ICOM 462
2600
20001000 1000
4000
1150150 1501150
[mm]
separating layer,
epdm material
20
12
toughened
clamp detail
80
self- weight
Figure16 - Example of a locally clamped triple façade outer glazing panel, t= 12mm toughened glass
4.4 POINT SUPPORT
Normally point-supported structures are driven by aesthetic requirements to minimize the visual impact of
the glass panel support. One of the key problems of structural detailing is to solve the connection problem
in such a way that unforeseen peak stresses and extreme stress concentrations as well as a direct steel-glass-
contact are avoided. This is achieved by plastic interface elements such as bushings or pads or injected resin
that avoids direct glass-metal-contact and acts as a buffer. To allow for proper assembly and to avoid
unfavourable in-plane constraints (i.e. due to temperature), the point-support pins should be tightened
carefully (i.e. torque screw moment < 30 Nm) and fixed into slot/wide holes of the sub-structure with
suitable low-friction interlayers (i.e. teflon) according to Figure 17. Annealed glass should always be
avoided here, because its insufficient strength around the holes may lead to breakage under loading.
allowance of movement of
pin within sub- structure:
self- weight
wind load
spider
glass
low-friction
material
fix slot
wide
slot
wide slot
hole
wide
pin
detail
detail
distribution of
loading:
section of point- support
with hinge and wide hole:
bushing
Figure 17 - Example of a point-supported glazing panel and its support conditions (sub-structure)
Numerical modelling should be performed in a way to find the maximum tensile stress on all glass surfaces,
especially near the connections with high stress concentrations. Point-supported glass structures might be
modelled numerically with the help of finite 3D-shell-elements. Suitable FEM-detailing for local stress
concentrations have to generate all holes or other geometric irregularities.
22 Wilfried Laufs and Andreas Luible
January 2003 ICOM 462
4.5 STRUCTURAL SILICONE SEALANT
For linearly supported glazing sometimes there is an aesthetic demand to achieve a flush façade surface.
Mainly for that reason, linear structural silicone sealant glazing supports have been developed (SSG), where
the glass panel edges are silicone-bonded to a sub-structure (“carrier frame”) which is then fixed to the
main building structure (Figure 18). There are specific quality procedure requirements for both factory-
applied as well as on site-applied SSG, see EOTA. Some relevant values are given in Table 4. It is
important to state that SSG might only be glued to special surfaces other than glass, such as anodized
aluminium or stainless steel profiles, but not to pure or painted mild steel or standard polyester powder
coated materials. SSG is UV-stable and compatible with PVB and resin interlayers. In some countries
building authorities ask for additional fail safes in case of failure of the silicone, which may lead to local
edge clamps around the glazing panes and therefore such requirements should be discussed during the
design process already.
Table 4 - Structural silicone sealant glazing properties
SSG property Value
Minimum recommended thickness t 6.0 mm
Allowable normal stress σ for dynamic loading such
as wind, includes global safety γ = 6
0.14 N/mm2
(perpendicular to glazing surface)
Allowable normal stress σ for static loading such as
self-weight, includes global safety γ = 6
0.015 N/mm2
(perpendicular to glazing surface)
Allowable shear stress τ for dynamic loading such as
wind, includes global safety γ = 6
0.07 N/mm2
(parallel to glazing surface)
Allowable shear stress τ for static loading such as
self-weight, includes global safety γ = 6
0.007 N/mm2
(parallel to glazing surface)
Figure 18 - Example of a structural silicone glazing façade, main sub-structure mullions before glazing
(left); finished façade (center) and anodized aluminium carrier-frame (right) [1]
Introduction on use of glass in modern buildings 23
January 2003 ICOM 462
4.6 GLUED CONNECTIONS
In glass furniture production, acrylate glues have been used for many years, but they generally carry only
minor loads and are only used internally (with minor temperature changes only, little environmental impact
such as UV-light). In order to develop a durable suitable glued connection for external structural use,
suitable glue compositions and required testing are still under development and in general not yet ready for
applications. From a structural point of view the aspects of any adhesive to be used as a permanent glazing
connection shall be examined by means of testing, calculations and further careful examinations with regard
to durability, strength, dynamic loading and ease of application.
4.7 LOCALISED LOAD INTRODUCTION
In new modern constructions where glass is often used as a structural element, localized load introductions
made of plastic or neoprene pads are no longer sufficient to resist high compressive stresses between the
glass edges and the intermediate material. In this case soft aluminum may be used instead. The advantage of
aluminum is a Young’s modulus almost identical with glass and a yield strength lower than the compressive
strength of glass. Preliminary tests [9] with hard intermediate materials showed a good behavior and
capability of aluminum to introduce in-plane forces into the glass panels. The tests also showed the high
compressive strength of glass that caused even plastic deformation of the steel and aluminum plates (Figure
19). The edges of the glass panels have to be at least grounded with chamfers (arrised) to avoid a local
stress concentration and failure of the glass. A load introduction within a distance less than 2 times the glass
panel thickness away from the weaker corners of heat-strengthened and fully toughened glass should be
avoided. Due to the lower residual stresses around the corners their load capacity is relatively low compared
to the rest of the glass edge.
F
5
10
glass
panel
testing
material
[mm]
local edge
compression
Figure 19 - Plastic deformation by a grounded 10 mm glass edge with chamfer of: steel t = 30mm
(σmax = 580 N/mm2, left) and aluminum t = 30 mm (σmax = 540 N/mm2, center); section (right)
The lamination process normally leads to glass edges that are not absolutely flush with each other and
therefore a homogenous load introduction into both panels is no longer guaranteed. Hard materials
extending over the full width of the laminated glass should not be used to introduce forces in more than one
layer of laminated safety glass consisting of tempered glass layers, because toughened glass can not be
treated after toughening any more. In this case steel shoes should support laminated glass, where the space
between the steel shoe and the glass edge might be filled with a special injection mortar (i.e. epoxy resin) or
two-component glue to adjust the glass edges. Further research to develop high performance load
introductions and design methods for laminated safety glass will be necessary.
24 Wilfried Laufs and Andreas Luible
January 2003 ICOM 462
5 ENGINEERING DESIGN
5.1 RELEVANT LOAD CASES
Relevant load cases for façade or roof glazing are given in Table 5.
Table 5 - Summary of relevant load cases in structural glazing applications
Load case
Example/comment
Self-weight g i.e. 0.25 kN/m2 for 1m2 of t = 10 mm panel
Wind load w wind pressure/suction, see national codes
Snow load s snow/snow drift, see national codes
Temperature loading T i.e. summer: T = 30K;
i.e. winter: T = -20K
Local panel heating i.e. due to shadowing/solarisation T = +/-10 K
Climate loading c For insulated glass units only:
i.e. +/-16 kN/m2 isochore pressure
(then further calculations for pressure onto glazing [3])
Human impact
i.e. horizontal line load of 1.5 kN/m at railing height;
i.e. point load of 1.0 kN onto 100 x 100 mm2 area;
or more advanced dynamic calculation and 1:1 testing
man-load cleaning operation i.e. man load 1.5 kN onto 100 x 100 mm2 area of roof glazing
Movement of supporting sub-structure
s
Consider tolerances in all directions, possible blocking of local
supports etc.
Blast loading
For bomb blast resistant glazing only,
Perform advanced dynamic calculations and 1:1 testing
Accidental/after-failure behavior
(laminated glass units only)
Add self-weight of broken panels onto remaining panels
Perform 1:1 testing or refer to existing testing data
5.2 IMPACT RESISTANT GLAZING
Glazing balustrades, glass doors or wall elements might be designed to resist dynamic human impact. A
standard testing procedure according to prEN 12600 has been developed which uses a twin tyre around a
50kg pendulum, which is released from certain dropping heights in order to determine whether glass
breakage occurs and how a broken glass pattern may affect human health. However, this test method is
restricted to one single panel size with a four- sided linear support only. Therefore, great care shall be
taken, when results of this standard testing method are to be used for impact resistant glazing of different
sizes or support conditions, i.e. point-supported glazing might behave more critically than linearly
Introduction on use of glass in modern buildings 25
January 2003 ICOM 462
supported glazing. Also, smaller glazing sizes are not necessarily more secure under dynamic impact due to
their possibility to be “punched-out” of their supports as a whole (Figure 20). 1:1 testing with original glass
size and support stiffness is therefore strongly recommended. It is also advised that bottom-clamped glass
balustrades with no further handrails or posts in front of the glazing should not be made of a single
toughened sheet only. Detailed and practical advice might be gained from [10].
Figure 20 - Impact test EN 12600 (left), sufficient impact resistance of a curved laminated safety glazing
balustrade with additional handrail at the top (center), failure example of a rather small, locally clamped,
toughened glazing balustrade, punched-out as a whole (right) [2]
5.3 CONSTRUCTION PRINCIPLES
In order to avoid severe failure consequences in case of damage of a single glass element with load carrying
functions (i. e. car crash), global safety concepts have to be developed by the design engineer that include
redundancies. Those might be the protection of the load-bearing glass by additional glass panels with no
load-bearing function or the use of statically undetermined systems with the possibility of load-
redistribution or certain owner regulations like inspection intervals of the building. Vandalism or other
failure reasons of the glass should always be taken as important load cases to deal with in design. E.g. for
roofs, laminated glass should stay in position for at least 24 hours to have enough time to change the panels.
Also, a cleaning strategy should always be developed to reach all glazing everywhere for cleaning purposes
as well as glass replacement.
26 Wilfried Laufs and Andreas Luible
January 2003 ICOM 462
5.4 GLASS PANEL MODELING
For stress and deflection design, the finite element method is a powerful tool to determine design decisive
maximum tensile stresses and deformation patterns. 3D-isoparametric shell elements might be used and
connected to 3D volume-elements near point-supports or local load introduction points. An example of such
a FE-calculation is given in Figure 21.
Figure 21 - FE-mesh for a point-supported toughened glazing 1.5 x 3.0 m, (left); deflection (center) and
maximum tensile stress near the center holes (right); wind loading w= 1.0 kN/m2, t= 10mm
5.5 ULS
Until now only few design codes [11] [12] and safety concepts [3] [13] for glass in buildings are available.
As glass panels were used mainly as a filling material in windows, most of the design methods are restricted
for wind and climate loading only. Most of the existing design codes are still based on maximum allowable
tensile stresses of the glass panels that do not represent the brittle breakage behavior of glass sufficiently.
Glass is an ideal-elastic material until fracture occurs without any plastic deformation like common building
materials. The maximum tensile stress glass can resist is the sum of the thermal pre-stress and the maximum
tensile strength of glass. The maximum tensile strength of glass is unfortunately a high scattering value
dependent on:
- size of micro cracks and the damages occurring during lifetime on the glass surface
- environmental conditions (humidity, temperature)
- load distribution and load duration
Fracture mechanic models have been developed in the past to determine this value. For example the tensile
strength of annealed glass with a 0.1 mm large surface crack is 26 N/mm2 for a load duration of 1s and only
6 N/mm2 for a load duration of 30 years. A future safety concept for glass therefore has to take into account
the possible glass damages and the accumulated load duration during lifetime.
Existing and currently developed safety concepts [3][11][13] [14] for ultimate limit state design (ULS) are
based on the method of separate partial safety factors for load and resistance corresponding to the Eurocode
(EC) design philosophy. The three concepts compare a so-called effective stress, which is a weighted
average value of the distributed main stresses on the glass surface, with a maximum tensile resistance of the
glass. The tensile resistance contains the influence of size and quality of the glass surface, accumulated load
duration and environmental conditions. In [11], for example, the verification equation reads:
Introduction on use of glass in modern buildings 27
January 2003 ICOM 462
dgeff f,
σ
N
V
kgkb
am
kg
dg
ff
k
f
kf
γ
γγ
+= ,,,
mod,
σeff : effective stress
fg,d : design resistance
kmod : load duration influence
fg,k : characteristic glass strength
γM : partial safety factor for glass
ka : influence of the glass surface size
fb,k : characteristic glass strength of pre-stressed glass
γV : partial safety factor for pre-stress
γN : national coefficient
5.6 SLS
Verifications necessary for the serviceability limit state (SLS) concern glazing deflections, movement of the
glass elements within the structure and the structure itself as well as vibrations (normally uncritical). Only
some indications [15] concerning deflection limits currently exist for glass design (Table 6). An important
part in verification of a glass element also is its post-breakage behavior. Glass panels have to remain in
place for a certain time even if all glass layers are already broken (see chapter 2.3.5).
Table 6 - Allowable deflections according to [15]
type of glass type of linear supports Deflection limit Definitions
single glass f l/100
four sides f l/100 and f d
l: span in main load-
carrying direction
d: glass thickness *)
insulated glass unit
two or three sides
f l/100,
f d and
f 8 mm
l: length of free glass
edge
d: glass thickness *)
*) the nominal glass thickness of a laminated safety glass unit is 33
2
3
1ddd +=
The maximum allowable deflections of a structural glass element should be more severe than the values
given in Table 6. Deflection limits given for steel structures might be values of orientation for glass
elements as well here. Supports should be flexible enough to follow these deformations without creating
secondary bending moments. In façade construction deflection limits can be more restrictive because of
architectural aspects to avoid negative lens effects of the façade surface, for example. Relative
displacements between different glass panels should also be checked, because they can lead to high shear
stresses in the silicone sealant joints, glass-glass or glass-steel-contact might occur.
28 Wilfried Laufs and Andreas Luible
January 2003 ICOM 462
5.7 TOLERANCES
The structure should always be able to allow for tolerances in the glass production as well as tolerances of
the sub-structure. Movements of the glass in the direction of the panel should be made possible to avoid the
case of severe temperature load or other likely eventualities. Tolerances of glazing dimensions might be
calculated from the given allowable size deviations in the codes or specifications. More importantly,
tolerances of the sub-structure should be taken from calculations or specifications of the main building
structure. Taken together these allow for the design of required joint widths and local adjustment devices
such as slot holes or adjustable brackets for the supports of the glazing. Constraint-free assembly on site
should be achieved for all glazing types.
Introduction on use of glass in modern buildings 29
January 2003 ICOM 462
6 CURRENT STRUCTURAL STABILITY RESEARCH ACTIVITIES
Transparency in conjunction with allowable high compressive glazing stresses make the use of glass sheets
as primary load-carrying elements such as beams, columns and shear panels both attractive and possible.
Due to their high slenderness such load carrying elements tend to fail because of structural instability
(Figure 22). Therefore, one aspect of the research works in progress [16] consists of the experimental and
theoretical study of fundamental glass stability problems for single-layered as well as laminated safety
glass. This is leading to the development of a safety concept for structural glass design. The brittle, linear-
elastic behavior of the material means that glass lacks the properties of steel, which plastic deformability or
strain hardening effect has to be compensated for through the composite action of laminated safety glass,
subjected to compressive and bending stress due to the foil which creates a „ductile“ behaviour for
columns, on which tests were performed with initial imperfections.
Glass columns Vertical glass stiffeners Shear panels
column buckling lateral torsional
buckling
plate buckling
Figure 22 - Example for load-carrying glass elements subject to different stability problems
Existing design methods, such as the use of buckling curves for steel or timber structures cannot be directly
transferred to glass panels [17]. The influence of production tolerances, initial deformations due to the
tempering process, and the breaking stress in glass have to be investigated for glass in a different way. This
is not due to the material property, but depends on the residual stresses due the tempering process, the
degree of damage of the glass surface, the distribution of stresses on the glass surface, humidity and the
load history For the experimental study, column buckling tests on upright glass strips were performed. A
total of 60 displacement- and force-controlled tests were carried out (Figure 23).
0
10
20
30
40
50
60
50 100 150 200 250 300 350 400 450 500 550 600
λk,nom [-]
σ [N/mm2]
critic al buckling
stress (E uler)
test results
Figure 23 - Test set-up for laminated safety glass unit (2x 10 mm heat-strengthened), L x w = 800 x
200 mm (left); failure in Euler mode 2 (center) and derived buckling curve for glass (right)
30 Wilfried Laufs and Andreas Luible
January 2003 ICOM 462
To simulate the sandwich behavior of laminated safety glass a finite element model was constructed with
the PVB interlayer represented by linear visco-elastic solid elements. Initial deformation w0 was found to be
the most important influence on the load-carrying behavior, together with load eccentricity and breaking
tensile stress of the glass. A very good conformity between experimental and numerical results was
obtained [18].
7 SUMMARY AND FUTURE TRENDS
Clearly, glass in structural building applications has not yet reached its full potential. In the future, glass
panels might be used more regularly as a load-carrying element in conjunction with well-known materials.
Best practice experiences may be transformed into accessible codes and safety regulations. New glazing
materials such as integrated light sources within laminated glazing, testing results and improved coating
performances will offer new possibilities within the field of façade engineering.
Façade engineering has developed into an engineering discipline in its own right, where close attention can
be given to the glass material and its applications. It is a specialized service integrating engineering and
architectural skills, combining analysis, specification, the customizing of commercial systems, bespoke
design and detailing. As various interdisciplinary aspects play its part here, the European initiative COST
C13 “Glass and Interactive Building Envelopes” is currently collecting available relevant research results.
Introduction on use of glass in modern buildings 31
January 2003 ICOM 462
REFERENCES
[1] Steel-glass facades of DS8 building, Canary Wharf London, façade engineering by Whitby Bird &
Partners (WBP), England, 2002.
[2] ZiE-Report for overhead glazing, Trube und Kings, Institute of steel constructions, RWTH Aachen,
1998.
[3] Sedlacek, G., Blank, K., Laufs, W., Güsgen, J., Glas im Konstruktiven Ingenieurbau, Verlag
Ernst&Sohn, 1999.
[4] Glass Guide, Saint Gobain Glass UK, edition 2000.
[5] Glass in Building, edited by D. Button and B. Rye, Butterworth architecture, Pilkington Glass
Limited, 1993.
[6] Laufs, W., Sedlacek, G.: Stress distribution in thermally tempered glass panes near the edges,
corners and holes, Glass, Science and Technology, 01 and 02/1999.
[7] Laufs, W., Ein Bemessungskonzept zur Festigkeit thermisch vorgespannter Gläser, dissertation at
the Institute of steel construction, RWTH Aachen, Shaker Verlag, 2000.
[8] Laufs, W., Luible, A., Mohren, R., Etude préliminaire sur le verre comme élément de construction
dans le bâtiment, ICOM Rapport 403F + 403D, EPFL, Lausanne, 2001.
[9] Luible, A., Lasteinleitung in Glaskanten, ICOM Rapport 463, EPFL, Lausanne 2002.
[10] DIBt : Technische Regeln für die Verwendung von absturzsichernden Verglasungen, 03/2001, DIBt-
Mitteilungen (German national rule).
[11] DIN EN 13474-1, Glass in building - Design of glass panes - Part 1: General basis of design;
(Draft standard).
[12] Standard Practise for Determining Load Resistance of Glass in Buildings, ASTM Designation: E
1300-97, American Society for Testing Materials.
[13] Wörner, J.D., Schneider, J., Fink, A., Glasbau, Springer Verlag, 2001.
[14] Haldimann, M.: Safety of steel-glass structures, dissertation EPFL-ICOM, Lausanne, currently in
progress.
[15] DIBt : Technische Regeln für die Verwendung von linienförmig gelagerten Verglasungen, 12/1998,
DIBt-Mitteilungen (German national rule).
[16] Luible, A.: Stabilität von tragenden Glaselementen, dissertation EPFL-ICOM, Lausanne, currently
in progress.
[17] Laufs, W., Kasper, Th.: Biegedrillknickverhalten thermisch vorgespannter Gläser, Bautechnik, 05,
Berlin, 2001.
[18] Luible, A., Crisinel, M., Auf Biegen und Brechen, tec21, Zürich, N° 12, 2002.
... Laminated glass, see [1], is a composite material, which consists of a solid glass plates (float, toughened, tempered glass or their combination) and interlayers made of polymers (mostly the polyvinyl butyral, which will be also considered in the following text) or cast resins. The interlayer has primarily the safety function, it improves the post-breakage behaviour of the glass elements. ...
... describing purely elastic response, remind Equation (1). We see that in this limit the parameter ξ is equal to the modulus of elasticity E and the behaviour of the springpot corresponds to the behaviour of an elastic element. ...
Article
Fractional calculus, i.e. the theory of derivatives and integrals of non-integer order, can be efficiently used for the theoretical modelling of viscoelastic materials. Our research is focused on the polyvinyl butyral which is used as an interlayer for the laminated glass. Polyvinyl butyral can be classified as a viscoelastic material and the introduction of the fractional viscoelasticity seems to be appropriate tool for its description. This paper briefly introduces the springpot element and its connection into more complex theoretical models. We mainly consider the generalized Maxwell model in its standard and fractional form and show their application by fitting the data obtained by experimental analysis.
... Glass panels critical load carrying capacity was determined for of glass panels designed in different thickness [5]. In generally, however, bolted connections are used connection type in glazing system [6,7]. Bolted connections called as point supported concept [8] which usually require small metal components to be mechanically attached to holes in glass are commonly used a connection type in glazing systems. ...
... It is a significant aspect of structure and informs services design through its capacity to influence energy use. Whitby Bird & Partners Façade Engineering group supplies all the engineering and architectural skills needed for the design and installation of high value facades [5,6]. The above examples show how modern glazing might be used structurally in addition to its classical benefit of transparency and insulation. ...
Article
Full-text available
Title: Temperature values inside aluminium profiles of glazed partition walls under standard fire conditions. Abstract: This paper presents and discusses the results of temperature measurements inside the profiles of aluminium glazed partition walls during fire resistance tests. Partition walls are usually lightweight internal walls made of plasterboard or sandwich panels, but they can also be glazed walls, including those of aluminium construction, which are the subject of this article. Such structures play a key role in meeting the fire safety requirements of buildings. They separate an entire floor of a building into individual rooms and are therefore often required to meet an appropriate fire resistance class, which is verified experimentally. In typical fire resistance tests, attention is paid to what happens on the unheated surface of the specimen, whereas this article presents the results of measurements carried out inside the specimen. For this purpose, six fire resistance tests of aluminium glazed partition walls of different heights (from 3 to 6 m) were carried out over the years. The main objective of the tests was to verify the influence of the wall height on its fire resistance, and one of the parameters tested, extensively discussed in this article, was the temperature inside the mullion profiles. This article presents the results of an analysis of the temperature rise inside the profiles of aluminium glazed partition walls during fire resistance tests.
Chapter
The paper presents a study made on the stress–strain state of mullion-transom glass facade under the action of uniformly distributed load simulating wind impact. Structural systems with various parameters were modeled and analyzed in Finite Element software package. Obtained results were compared with experimental investigation performed on full-size fragments of facade system. Dependencies allowed to evaluate the influence of changing parameters on the results and select the calculation scheme which reveals the operation of facade system in a more accurate way. The filling’s contribution to overall stiffness was described. The methods for determination of the joint stiffness of the connection between adjacent transoms and for analytical calculation of inner efforts and deflections were developed.KeywordsGlassFacadeMullion-transomHingeMulti-span beam
Article
The actual class of fire resistance of glazed partitions can only be determined according to a test, which meets the normative requirements. The test standards in this field determine the minimum dimensions of the test specimens (2800 × 3000 mm, width × height, in the clear opening of the furnace), on which the test should be carried out. The testing of elements with the minimum dimensions allowed by the test standard, assess the fire resistance of components with slightly larger dimensions. This, however, does not solve the real problem, which is the use of glazed partitions with fire resistance, significantly exceeding the dimensions of the sample walls verified by the tests. The aim of the research described in this article was to verify the influence of the height of glazed partitions on their fire resistance. The results of six tests of partitions with different height (from 3 up to 6 m) and the same width (3 m), made on the basis of the same glazing and the same aluminium profiles have been compared. During the fire resistance tests, the performance criteria of integrity and insulation were verified. Additionally, the deflection of the partition was measured in specific places by means of laser and draw wire sensors. Based on the presented test results, it can be argued that the height of the partition does not have a significant impact on its insulation and integrity, provided that the size of the glass panes is not increased along with the wall height, that the structure of the element is symmetrical in relation to the central vertical axis and, most importantly, that the mullions are properly stiffened.
Chapter
Wood and wood-based materials are combustible materials. This does not mean, however, that in the event of a fire, the elements made of these materials pose a threat. Separate the flammability from the spread of fire and fire resistance. Contrary to appearances, doors made of wood and wood-based composites obtain good results in the field of fire resistance and constitute an effective barrier for the spread of fire to neighbouring fire zones.
Article
Full-text available
Currently, windows and glass facades are increasingly being used as a building envelope. These are elements that are functional and aesthetic, but there is a need to focus on their safety. Windows as a part of protection system are one of the most vulnerable assets, so they need to be addressed. The paper is focused on the experimental investigation of two types of windows that are commonly used in buildings. The subjects of the interests are wooden frame windows and PVC frame windows. In the experiment, burglar resistance was investigate, carried out by dynamic tests with different weights of steel balls dropped from various heights. Results of the experimental measurement pointed to the limit energy glass panels were broken. Windows with safety film were also tested. The measured results were further evaluated.
Article
Full-text available
This paper deals with design of compression members made of monolithic and laminated structural glass. Glass columns are analysed by numerical models using RFEM and ANSYS software with consideration of variable value of the interlayer shear modulus. Obtained elastic critical forces, stresses and deflections are compared with the values from the analytical calculation according to the second order theory.
Article
Full-text available
With temperature profiles during the thermal strengthening process determined in part I of this paper, the distribution of thermal stresses for the central area, near the edges and holes of the glass plates are calculated numerically with the help of a finite-element-simulation (THERVO PRO) which models the formation of temper stresses with time. Comparison with existing experimental data for the central area (zone 1) shows very good correspondence with numerical results. For zone 2 (edge), at about a distance d away from the edge, a somewhat reduced surface compression due to membrane stresses is observed. At zone 2 and zone 3 (corner) surface compression is found parallel to the edge surfaces, since due to equilibrium requirements there is no thermally induced stress perpendicular to the surfaces. In general, near the edge and corner stress distribution is three-dimensional as well as around zone 4 (hole). The hole with a cone has a certain difference compared with a cylindrical hole: it does not have a reduction of tangential surface compression at some distance from the hole on the cone side.
Book
Full-text available
Dissertation: http://www.shaker.eu/en/content/catalogue/index.asp?lang=en&ID=8&ISBN=978-3-8265-8044-4
Technische Regeln für die Verwendung von absturzsichernden Verglasungen
  • Dibt
DIBt : Technische Regeln für die Verwendung von absturzsichernden Verglasungen, 03/2001, DIBt- Mitteilungen (German national rule).
Safety of steel-glass structures, dissertation EPFL-ICOM, Lausanne
  • M Haldimann
Haldimann, M.: Safety of steel-glass structures, dissertation EPFL-ICOM, Lausanne, currently in progress.
Technische Regeln für die Verwendung von linienförmig gelagerten Verglasungen
  • Dibt
DIBt : Technische Regeln für die Verwendung von linienförmig gelagerten Verglasungen, 12/1998, DIBt-Mitteilungen (German national rule).
Report for overhead glazing, Trube und Kings, Institute of steel constructions
  • Zie
ZiE-Report for overhead glazing, Trube und Kings, Institute of steel constructions, RWTH Aachen, 1998.
Lasteinleitung in Glaskanten, ICOM Rapport 463, EPFL
  • A Luible
Luible, A., Lasteinleitung in Glaskanten, ICOM Rapport 463, EPFL, Lausanne 2002.