analysis on glass structures, types and composition.pdf

GLASS AND GLAZING
SYSTEMS
KARAMJIT SINGH CHAHAL
Reader , Dept of Architecture
GND University, Amritsar

GLASS
 Main component - Soda lime silicate glass or silicon dioxide
(silicate)
 Other ingredients such as soda and lime are added to lower the
melting temperature of silicate and promote optical clarity of the
finished glass product.
 The colour and solar properties of clear glass can be altered in two
ways.
 Firstly, the glass can be tinted (coloured) by adding small
amounts of metallic oxides to the existing ingredients. For
example, the addition of iron oxide produces a green glass.
Bronze and grey are produced by the addition of selenium and
nickel oxide.
 Secondly, a thin metallic coating can be applied to the surface of
clear or tinted glass. This is known as coated or reflective glass.
COMPOSITION

CHEMICAL COMPOSITION
The magnitude of the proportions by mass of the principle
constituents of soda lime silicate clear float glass are as
follows:

TREE STRUCTURE FOR VARIOUS TYPES OF GLASS

ACCORDING TO FORMATION
1. SHEET GLASS - Prepared by passing molten glass between water
cooled liquid as it cools. The glass is cut to size at the top of the tower.
2. PLATE GLASS - It is similar to sheet glass except that it is ground and
polished before being cut. Cutting takes place after both the surfaces have
been ground and polished by fine sand and emery grains.
3. FLOAT GLASS - The float glass process is the most common method of
flat glass production in the world. This process basically involves melting
silicate (sand), lime and soda in a furnace and floating it onto a large bed of
molten tin, hence the name float glass. This mixture slowly solidifies over
the molten tin as it enters the annealing oven where it travels along rollers
under a controlled cooling process. From this point the glass emerges in
one continuous ribbon and is then cut and further processed to customers’
needs. Float glass is also known as soda lime silicate glass as these are
the major components used in manufacture.

3.1 CLEAR FLOAT - Clear float
glass is transparent, offering high
visible light transmittance (VLT).
Clear float can be processed into
heat strengthened, toughened,
laminated, curved glass and
Insulating Glass Units.
3.2 EXTRA CLEAR FLOAT(LOW IRON) –
Extra Clear low iron glasses contain approximately
one quarter of the iron content of standard clear float
glass, providing an extra clear glass that is crystal
clear in appearance.
Ultra clear float glass product with 75% less iron
content than standard float glass.
Manufactured in 3 - 19mm
Available in 4, 5, 6, 8, 10, 12mm
It can be used in rooflites and atrium glazing when
solar control is not a factor.

3.3 TINTED FLOAT - Tinted float is produced by adding metal oxides during
float glass production.
Apart from its function in an aesthetic sense, tinted float is primarily designed
to reduce solar heat gain, UV and glare inside a building.
Tinted float glass achieves its performance by absorbing solar energy and so
is sometimes referred to as heat absorbing glass.
Tinted float can be processed into heat strengthened, toughened, laminated,
curved glass and Insulating Glass Units.
Tinted glass products are sourced from quality float glass manufacturers
including Guardian, Glaverbel, Asahi and Pilkington.
The most common colours are grey, bronze, green and blue.

3.4 HIGH PERFORMANCE TINTED FLOAT -
High performance tinted float products that are
engineered to limit the traditional compromise
between high light transmission and low solar
gain.
These products have been designed for very
low light transmission for privacy or to assist
computer viewing.

4. ANNEALED FLOAT - Glass is reheated
to its annealing temperature for about 15
mins.
Then it is cooled gradually to room
temperature at a predetermined rate to
produce a glass that is stronger and more
uniform.
This strengthening of glass is required for
performance against wind (surface
strengthening) and thermal expansion
(edge strengthening).
When broken, it shatters into
large sharp pieces.
The property of pure elasticity
with brittleness means that the
glass cannot be permanently
deformed by load as is the
case for most solids such as
metals and plastics, and that it
fails without warning as shown
on a stress-strain curve.

ACCORDING TO CHEMICAL COMPOSITION
1. SODA LIME GLASS - Consists of sand, soda-ash and Lime. Addition of
small amount of magnesium reduces its tendency to crystallize. It has a low
resistance to thermal shock. This has a low softening temperature (600°C).
2. BORO SILICATE GLASS: In this type some of the sodium ions in the soft
glass are replaced by boron in the form of boric acid or borax, to reduce
thermal coefficient of expansion that is responsible for breakage due to
sudden heating or cooling of glass. It is widely employed for cooking
utensils, laboratory glassware, and chemical process equipment.
3. LEAD GLASS -The fine-quality table glass known as crystal is made from
potassium-silicate formulas that include lead oxide. Lead glass is heavy and
has an enhanced capacity to refract light, which makes it suitable for lenses
and prisms, as well as for imitation jewels. Because lead absorbs high-
energy radiation, lead glasses are used in shields to protect personnel in
nuclear installations.
4. OPTICAL GLASS: The refractive index of the glass is adjusted by change in
chemical composition of the glass. Molten glass is cooled gradually in this
process.
5. PHOTOSENSITIVE GLASS: It is formed by incorporating tiny crystals of
chlorides of copper, silver or gold into molten glass. Brief exposure to
sunlight produces a temporarily darkened glass as the chloride is
decomposed to form metal and chlorine.

ACCORDING TO FUNCTIONS PERFORMED
1. SAFETY GLASS - These are specially manufactured to avoid
flying fragments and vandalism. It is of the following types:
 WIRED GLASS -
Wired glass has 13mm square
electrically welded steel wire mesh
sandwiched in its centre during the
manufacturing process. It is commonly
used in fire rated windows and doors to
the maximum sizes. It is a Grade B
safety glass.

 TOUGHENED GLASS -
Toughened glass is also known
as tempered glass.
 It is produced by first cutting
and processing sheets of
glass, which are then loaded
into a furnace, that has a bed
of oscillating rollers.
The glass is heated to a plastic state at around 650ºC, and then by
computer control, the glass is moved into the quench area where it is
rapidly cooled by a series of high pressure air nozzles.
This rapid cooling or quenching induces high compression stress in
the glass surface, while the centre remains in tension. Although the
physical characteristics remain unchanged, the additional stresses
created within the glass increases its thermal and mechanical strength

ADVANTAGES OF TOUGHED GLASS
 Safety - It fractures into small particles, significantly reducing the
risk of injury; Grade A safety glass
 Strength - High mechanical strength and is 4 to 5 times stronger
than annealed glass of the same thickness due to the stresses
induced during toughening. It also has high thermal strength, when
compared to annealed glass, can withstand a temperature
differential of 250ºC, and is stable in temperatures ranging from -
70ºC to 300ºC.
 Mechanical Fixing - High mechanical strength and can therefore be
used with mechanical fixings, such as patch, spider, hinge, point and
countersunk fixing.
 Security - Much harder to break than annealed float or laminated
glass. If broken it will not provide security, however the noise due to
breakage is often a deterrent.
 Sound and Solar control same as annealed float glass
 Applications - Frameless Glass Doors and Entries, Structural Glass
Walls, Glass Canopies, Internal Partitions, Low Level Glazing

 LAMINATED GLASS - Laminated glass consists of two or more
sheets of glass permanently bonded together by a plastic or resin
interlayer. Laminated glass offers superior safety. Although it will
break on impact, the fragments are held by the interlayer.
The layered nature of laminated glass means that it blocks more
noise and UV light than single glass. It can also be made with Low E
glass and used in Insulating Glass Units for increased
environmental benefits.

BENEFITS AND APPLICATION
 SAFETY & PROTECTION - When subjected to impact, the bond
between the glass and interlayer adhere any broken fragments,
keeping the glass intact and resisting penetration.
 This important breakage characteristic significantly reduces the
likelihood of serious injury, qualifying laminated glass as a Grade
A safety glass
 In addition, the glass will not fall out if used in sloped or overhead
glazing applications providing environmental protection.
 SECURITY - Laminated glass offers greater protection for people and
property by providing an effective barrier from attack. Although the glass
will break if hit with a hammer, brick or similar object, the interlayer can
resist penetration, ensuring any attempt to enter a premises will be slow
and noisy.

 FADING CONTROL - PVB laminated glass products absorb the
sun’s UV radiation while allowing important visible light to pass
through. It therefore helps protect curtains, furnishings and carpets
from fading caused by the damaging effects of short-wave ultra-
violet radiation.
 SOUND CONTROL - Laminated glass is very effective in reducing
the transmission of noise through glazing. This is achieved through
the sound dampening properties of the interlayer, which will vary
with the type and thickness of the interlayer.
 CLIMATE CONTROL - Laminated glass can have a tinted interlayer
or be made with tinted or reflective glass to reduce glare and heat
gain in a building.

COLOUR AND LIGHT - Laminated glass can be made with a wide
range of coloured PVB interlayer to provide special lighting effects.
These colours can be combined with tinted and/or printed glass to
provide special effects.
PICTURES AND IMAGES - New techniques allow PVB interlayers to
be printed with coloured pictures or images before laminating to
create special effects
VISIBLE DISTORTION - Due to the controlled nature of the
laminating process, façades glazed with annealed laminated glass
avoid the risk of visible distortions that are sometimes created by the
heat treatment processes, providing significantly sharper visual
transmission and reflections.

 In addition to this they are resistant to attack by bullets blast ,
cyclones
SURFACE POSITIONS

 HEAT STRENGTHED GLASS - Heat strengthened glass is about
twice as strong as annealed float glass and is used generally as a
protection against thermal breakage and breakage fallout. It is not a
safety glass.

THERMAL BREAKAGE
In annealed glass the risk of thermal breakage is greatest and in applications
where the thermal stresses is of concern, heat strengthed or toughed glass is
used.
The risk of thermal breakage is also influenced by the condition of the glass
edge. For applications where thermal breakage is a concern, heat treated glass
should be specified.

The crack in thermally broken glass is initially perpendicular to the edge
and glass face for 20-50mm and then branches out into one or more
directions. The number of branches or secondary cracks is dependent
on the amount of stress in the glass.

GLAZING SYSTEM
SYSTEM is defined as
Instrumentality that combines
interrelated interacting parts
designed to work as a coherent
entity
COMPONENTS
OF GLAZING SYSTEM
GLASS
STRUCTURAL
FRAMEWORK
SEALANT
In a glazing system the above mentioned three elements perform together
under any circumstances.
It is their composite performance that determines the performance of the
system as a whole as regards different performance characteristics.

 SLOPED OVERHEAD GLAZING
 Sloped Glazing is glazing which is sloped more than 15° from the
vertical. When sloped glazing is used over populated areas, an A
Grade Safety Glass is required to be used and has to withstand a
greater range of loadings than vertical glazing.
 Sloped Glass Loads
 Any overhead glazing system must be designed to meet the
stress and deflection resulting from windloads. These can be
either positive load from wind, or negative when the wind acts
in suction. Unlike vertical glazing, loads caused by snow,
maintenance and water and the dead load (the self weight of
the glass as a permanent load) need to be considered
DESIGN OPTIONS

PERFORMANCE CHRACTERISTICS
 The sloped orientation of overhead glazing can result in increased heat gain
and solar intensity thus increasing the levels of thermal stress particularly
with solar control glass. The level of heat loss can also be higher making
the installation of insulating glass units desirable.
 For adequate water runoff over sealant joints and flashings the pitch should
not be less than 5°C.Condensation is likely to drip from sloped glazing at
angles of 30° or less.
For sloped overhead glazing utilising
insulating glass units, at least one pane
must be Grade A safety glass, always the
underside glass.
Where laminated glass is the lower pane
annealed can be the upper pane. Where
toughened is used as the lower pane,
safety glass should also be used for the
upper pane.

 FULL HEIGHT GLASS FINS -
Glass fins are used to achieve
the ‘all glass’ clarity required by
designers while meeting the
structural requirements of the
glazing system.
 A glass fin replaces a frame or
mullion and must be assessed
as to size and thickness and
securely fixed or supported at
the head and sill.
 The fins must be adhered to
the façade glass with silicone
sealant to cope with positive
and negative loads.

CRITICAL SILICON JOINT - The amount of silicone used to bond the
fin is known as the ‘bite’. The depth of the joint is known as the glue
line and is normally 6mm.
Clear silicone is commonly used but the absence of a bond breaker
can inhibit the quality of the joint. Black silicone allows the use of a
bond breaker, hides any minor bubbles and gives a better long term
joint particularly with tinted and reflective glasses.

SILICONE STRUCTURAL GLAZING
 Silicone Structural Glazing (SSG) is a method of attaching a glass panel to
a metal frame using a structural silicone adhesive sealant. The sealant
contact dimension (bite) and thickness are designed to provide a method of
structural support to glass, an airtight and weather-tight seal and a flexible
connection that absorbs differential movements between dissimilar
materials from wind, thermal or seismic loading.
 The joints are not intended to absorb live load movements due to floor
loadings.
 This method of glass attachment provides a smooth exterior glass facade
on a building either as a 2 sided, 3 sided or 4 sided system.
2 Sided Structural Glazing involves adhering the glass or cladding to
aluminium on opposite sides, either vertically or horizontally, with the other
two edges held captive with an aluminium bead or cover strip. Generally
an on-site application

GENERAL PRINCIPLES FOR SELCTION OF GLASS AND
GLAZING SYSTEMS
 The ability of the framing to support and retain the glass
under dead weight, wind and seismic loads.
 The allowance of adequate edge cover and clearances.
 Edge clearance is critical as the glass should not
become load bearing.
 The correct blocking and drainage.
 The provision of an effective weather-tight seal.
 The use of compatible glazing materials.
 The use of durable glazing materials.
 The ability to easily re-glaze the system.

FRAMING SYSTEMS
 The framing system must structurally
support the glass under static and
dynamic loads and provide openings
within specified limits for squareness,
corner offset and bow.
 Typical limits are:
 Square: 3mm max difference in
diagonal length.
 Bow: 1.6mm in any 1.2m length of
framing.
 Corner Offset: 0.8mm at each corner
DEFLECTION
The deflection of the glass framing
members under design load should not
exceed Span ÷ 175 or 19mm, whichever
is less.
The deflection of horizontal members due
to the weight of the glass should be
limited to 3mm or 25% of the design edge
clearance, whichever is less.

GLAZING SYSTEMS
 DRY GLAZING SYSTEMS
 Dry glazing is the installation of glass using extruded gaskets in PVC,
EPDM or Santoprene to one or both sides of the glass to provide a
compressed weather seal. No sealants or putties are present in this
system and the windows are designed to be self-draining.
 Installation of gaskets commences from the corner of a frame and they
are inserted under pressure to form a tight compressed weather seal.
Gaskets should be cut over-size to allow for shrinkage and to assist with
installation they can be lubricated and softened by immersion in hot
soapy water
 It is recommended that Santoprene gaskets be used in buildings over 3
stories and/or in high exposure conditions.

 WET GLAZING SYSTEMS - Wet glazing is the installation of glass using
elastomeric sealants and butyl tapes to bed the glass and seal it at either face to the
framing. Silicone and MS sealants are the most commonly used but polyurethane
and polysulphide sealants are also used.
 It is important to use the correct product for the application to ensure adhesion to the
substrate as some sealants adhere better than others to materials such as paints,
wood, anodised and powder coated surfaces. In addition some sealants such as
polyurethane are not UV stable
 SILICONES - All silicone sealants are UV resistant and have excellent adhesion to
glass. They act as adhesives and sealants for both interior and exterior use and are
not generally paintable. There are two basic types, Neutral Cure and Acid Cure and a
range of strengths known as the modulus
 ELASTOMERIC SEALANTS - A number of elastomeric sealants are available such
as MS sealants, polysulphides, polyurethanes, acrylics and butyls in either one-pot or
two-pot products. When selecting a sealant for a glazing situation it is important to
consider the properties of the sealant and its compatibility with the glass type and
other construction sealants which may be present.

PUTTY GLAZING
 Putty glazing is the traditional
method for glazing timber and
steel windows. It is largely being
replaced by more modern
techniques and/or higher
technology sealants
 E.g - Woodsash putty, Steel
sash putty

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