MATERIAL: GLASS

Although the origins of glassmaking go back nearly 5 thousand years, it was not until the 19th and 20th centuries that glass began to play a major role as a construction material. Today it is present mostly as a façade material

.

TABLE OF CONTENTS :

1. DEFINITION OF GLASS2. BRIEF HISTORY OF GLASS3. GLASS CONSTITUENTS4. CLEAR GLASS FORMULA 5. COLORED GLASS FORMULA 6. MANUFACTURED GLASS7. GLASS PROPERTIES 8. CHARACTERISTICS OF GLASS9. DENSITY OF GLASS10. TYPES OF GLASS 11. SPECIAL GLASS 12. TECHNICAL DIFFICULTIES AND THE LIMITATIONS OF GLASS13. DESIGN CONSIDERATIONS14. DEFECTS AND DETERIORATION IN GLASS ( CORROSION AND BREAKAGE)15. PROS AND CONS, RISKS AND POTENTIALS16. SPANS, WEIGHT AND DIMENSIONAL CHARACTERISTICS

DEFINITION OF GLASS:

o Glass is an amorphous substance having homogeneous texture.

o It is a hard, brittle, transparent or translucent material, super cooled liquid of infinite viscosity having no definite melting point obtained by fusing a mixture .

o It posses no definite crystalline structure .

o It is the most common material glazed into frames for doors, windows and curtain walls.

Brief history of Glass:o The history of the origin of glass can be categorized by periods according to the methods of the manufacturing process as follows: 1. The First Period: 1700 BC through 100 AD :Primitive method of making glass using molds.-Molding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern. A mold is a hollowed-out block that is filled with a liquid like plastic, glass, metal, or ceramic raw materials. The liquid hardens or sets inside the mold, adopting its shape.

2. The Second Period: 100 AD through 400-500 AD : Glassblowing technique discovered, and glass manufacture becomes a more practical process.Glassblowing involves the inflation of glass to hollow it out and create a vessel. It is possible to create a free-form object or to blow into a mold.

3. The Third Period: 4-500 AD ~ 1200 AD: Middle Ages, characterized by Byzantine glass.Also called stained glass: colored glass as a material or to works created from it.

4. The Fourth Period: 1200 AD ~ 1900 AD :Venetian glass, foundation for modern glass making is set.Venetian glass is a type of glass object made in Venice, Italy. It is world-renowned for being colorful, elaborate, and skillfully made.The glass is made from silica, which becomes liquid at high temperatures. As the glass passes from a liquid to a solid state, there is an interval when the glass is soft before it hardens completely. This is when the glass-master can shape the material.

5. The Fifth Period: 1900 AD ~ present: Glass objects used as everyday goods; large scale manufacturing.

Glass constituents: The raw materials used in manufacturing glass are sand, lime (chalks) and soda or potash which are fused over 1000° C. Oxides of iron, lead and borax are added to modify hardness, brilliance and color. The functions of the various ingredients are as follows.

1. Silica( sand) sio2: is used in the form of pure quartz, crushed sandstone and pulverized flint; should be free from iron contents for best quality glass. Since it melts at very high temperatures (1710° C) carbonates of sodium or potassium are added to lower down the fusing temperature to about 800° C. These also make liquid silica more viscous and workable.

2. Lime is used in the form of limestone, Also known as lime, calcium carbonate is found naturally as limestone, marble, or chalk. The soda makes the glass water-soluble, soft and not very durable. Therefore lime is added increasing the hardness and chemical durability and providing insolubility of the materials. Other materials and oxides can be added to increase properties (tinting, durability, etc.), produce different effects, colors, etc.

3. Soda ash (sodium carbonate Na2CO3): when its added it acts as an accelerator for the fusion of glass and an excess of it is harmful. Adding soda will lower the melting point to 1000°C making it more manageable.

6.CULLETS ( recycled glass) : are broken glasses added to act as a flux to prevent loss of alkali by vitalization during the process of forming glass and also to lower the fusion temperature. However, flux may reduce the resistance of glass to chemical attack.

4. POTASH :renders glass infusible and makes glass fire resistant.

5. LEAD OXIDE : imparts color and brightness. When 15–30% of it added to substitute lime it lowers the melting point, imparts good workability , while its transparency is lost with the glass becoming brittle and crystalline.

Potash:

IT is the common name for various mined and manufactured salts that contain potassium in water-soluble form. The name derives from "pot ash", which refers to plant ashes soaked in water in a pot, the primary means of manufacturing the product before the industrial era.

Clear Glass Formula

1. Former (sand) +

2. Flux (ash) +

3.Stabilizer (calcium carbonate) +

4. Heat (2100-2300F) =

Batch of Glass( 3 materials mixed and heated)

+

Metal Oxide (for

color)

-The previous formula creates clear glass.

-To make colored glass, metal oxides must be added to the batch. The following oxides produce the following colors:

• Copper = Turquoise

• Chrome = Green

• Cobalt = Blue

• Cadmium & Gold =• Ruby Red

Colored Glass Formula

GLASS MANUFACTURE:

o Glass is manufactured in the following steps:

1. MELTING 2. FORMING AND SHAPING 3. BLOWING 4. FLAT DRAWING 5. COMPRESSION

MOULDING 6. SPINNING 7. ANNEALING 8. FINISHING

From blown glass( vers souffler) to tinted glass:

• Free-blowing is the oldest glassblowing technique and what is essentially the same technique is still practiced today with tools very similar to those used 2000 years ago.

-The most important tool, the blowpipe.

• The production of flat glass, has passed through many technological advances.

• The principal techni ques up to the early 20th century are listed as follows: the crown glass technique; the cylinder blown sheet method; the machine drawn cylinder sheet method; and drawn sheet glass.

• All of the above mentioned techniques were substi tuted in the early 20th century for the drawn sheet process.

1. MELTING:

o The raw materials — lime, soda and sand — separately cleaned in definite proportion and mixed with water are fused in a continuous type (tank) furnace .

o The charge in the first stage melts, forming a bubbly, sticky mass, and as the temperature is raised (1100° C–1200° C) it turns to a more watery liquid and the bubbles rise to the surface.

o When all the carbon dioxide has escaped out of the molten mass, decolorizes such as MnO2 are added to do away with ferrous compounds and carbon. The coloring salts are added at this stage. Heating is continued till the molten mass is free from bubbles and glass balls.

o As the glass cools (800° C), it is ready to be drawn or floated to its desired thickness and size at the other end of the furnace as shown by a flow diagram in the picture below.

2.FORMING AND SHAPING:

The molten glass can be fabricated to desired shapes by any one of the following methods:o A. BLOWING: A 2 m long and 12 mm

diameter blow pipe is dipped in the molten glass and taken out. It is held vertically and is vigorously blown by the operator. The sticking molten glass takes the shape of a hollow ball. On cooling it is reheated and the blowing operation repeated a number of times till the desired articles are ready.

o B. FLAT DRAWING: The process of drawing the glass up into a sheet begins when an grille is lowered into the glass in the kiln. In a short time the liquid molten glass adheres to the bait, and as the bait is slowly lifted it draws a sheet of glass. The bait and the drawn sheet of glass are then drawn through rollers, the bait is cracked off and a continuous sheet of glass is drawn up. This sheet is then slowly cooled in a chamber and annealed for cutting into proper size. A machine for vertical drawing of glass Is shown in the picture below.

o C. COMPRESSION MOLDING: In this process molds are used to obtain the articles of desired shapes.

o E. SPINNING: A machine is used to spin the molten glass. The fibers so produced are very fine and are used for heat and sound insulation.

o D . ANNEALING : cooling glass at a slow controlled rate to counteract internal stresses. This is done in a kiln known as a Lehr.

o F. FINISHING :After annealing the glass articles are cleaned, ground, polished, cut and sand blasted.

A BRIEF DESCRIPTION OF THE GLASSMAKING PROCESS

ACTIVITY AT WHAT TEMPERATURE REQUIRES HOW MUCH

TIME?

Ingredients weighed and mixed

at room temperature approx. 30 minutes

Loaded into melting furnace approx. 2000 deg. F. approx. 5 minutes

Melting and refining takes place

approx. 2500 deg. F. 10-35 hours,

depending on type of glass and type of furnace

A group of men make glassware. They draw the glass from the furnace in

gobs ranging in size from 3 oz. to 90 oz. In some

factories the glass flows from the furnace into forming

machines on a lower level.

approx. 2000 deg. F. Men work 8 hour shifts

Each gob is formed into a basic shape by a man using air or mechanical force. In

factories making less complicated shapes

or higher quantities, this forming is performed by

machines.

approx. 2000 deg. F. 5 to 50 seconds

The basic shape is reheated and changed to the final

shape. 1800 deg. F. 20 to 60 seconds

The piece is put in an annealing lehr to strengthen the glass and to cool it off.

1000 deg. F. to room temperature

1 hour to 6 hours or longer

The piece is then inspected, packaged and shipped.

room temperature 1 day to weeks

The color controlling ingredients are mixed in with the main ingredients before melting. Some of the material used to create certain colors are:

MATERIALS COLOR PRODUCED

Uranium Yellow

Cobalt Blue

Sugar and Iron Amber

Neodymium Pink

Iron Green

Gold Red

Selenium and Cadmium Orange

Selenium and Manganese Crystal

Alumina and Fluorine White

COLOR COLORANT

Burmese Pure gold and Uranium Oxide

Custard Uranium Oxide

Amethyst Manganese Dioxide

Ruby Overlay Gold and Crystal Glass

Blue Satin Copper Oxide

PROPERTIES OF GLASS

oGlass has two important properties:

1.it does not have a definite melting point but softens gradually over a range of temperatures.

2. it does not cleave in a plane face like diamond or table salt.

-N.B: The explanation of both these properties lies in the fact that glass has no ordered structure, but is instead a super cooled liquid. A sheet of glass left to stand for a long time, perhaps one hundred years, will actually flow and change its dimensions slightly.

MECHANICAL PROPERTIES:

o STRONGHas great inherent strength. It is weakened only by surface imperfections, which give everyday

glass its fragile reputation. Special tempering can minimize surface flaws.o HARD

Surface resists scratches and abrasions.o ELASTIC

It gives under stress - up to a breaking point - but rebounds exactly to its original shape.

2-CHEMICAL PROPERTIES

CORROSION- RESISTANTIt is affected by few chemicals.

It resists most industrial and food acids.

3-THERMAL PROPERTIES

SHOCK- RESISTANTIt withstands intense heat or cold as well as sudden temperature changes.

HEAT - ABSORBENTRetains heat, rather than conducts it. It absorbs heat better than metal.

4-Optical Properties-

-Glass has the ability to refract, reflect and transmit light following geometrical optics, without scattering it, and it is used in the manufacture of lenses and windows. -Common glass has a refraction index around 1.5. According to Fresnel equations, the reflectivity of a sheet of glass is about 4% per surface (at normal incidence), and its transmissivity about 92%.

4-PHYSICAL Properties

Glass Is a Type of Solid Material : the molecule bonds are tighter compared to a liquid material. IT will not change its shape unless it being heated to a certain high temperature. Durable: due to the strong bonds between the molecules in it. Its strength and its durability mainly depend on its thickness.1 The thinner the sheets of the glass, the easier it is to break them. Static : Glass does not react with other materials and will not be a reactive to other materials and will not be decomposed by most acids. Absorbs Heat: Glass absorbs and transmits heat which means that if you heat a glass then the temperature of the contents inside of it will react.1 The heat applied will make the molecules in the glass to vibrate faster that pass thru one molecule to another.

Characteristics of Glass

1. Hard, amorphous solid

2. Transparent/ Translucent

3. Good electrical insulator

4. Primarily composed of silica with various amounts of elemental oxides

5. Brittle

6. Unaffected by air, water, acid or chemical reagents expect HF

7. No definite crystal structure means glass has high compressive strength.

8. Can absorb transmit and reflect light.

Density:

Type of Glass Density

window 2.46-2.49

headlight 2.47-2.63

pyrex 2.23-2.36

lead glass 2.9-5.9

porcelain 2.3-2.5

MOST COMMON TYPES OF GLASS:

1-Soda Lime glass2-Lead glass3-Fused glass4-Stained glass

TREATEMENT FOR SAFETY GLASS :

1. Annealed glass2. TEMPERED glass3. Toughened glass4. Laminated glass5. Wired glass6. Float glass7. Block glass

1. SODA LIME GLASS: While silica alone can be used to form glass, it has some

undesirable features, which make it unsuitable for use in making

glass containers.

Advantages

Inexpensive Raw Materials

Single Component

Low Expansion

Excellent Durability

Disadvantages

Hard to Fine*

Hard to Melt

Hard to Form

Used: in plate and window glass, glass containers, and electric

light bulbs

*Fining refers to the removal of the gas bubbles (seeds) from

molten glass. Expansion refers to the "Thermal Expansion

Coefficient", which is the relative change in volume per unit

change in temperature. Chemical durability is the resistance of

glass to be altered or harmed by solvents or products.

2. LEAD GLASS :

• As the name already indicates, lead glass has a high percentage of lead oxide (at least 20% of the batch).

• It has a relatively soft surface, making it especially suited for decorating using grinding, cutting, and engraving processes.

• This glass will not withstand high temperatures or sudden changes in temperature.

• Its refractive index gives a brilliance that may be exploited by cutting.

• It is somewhat more expensive than soda-lime glass and is favored for electrical applications because of its excellent electrical insulating properties.

• Uses: fine table ware and art objects

3. FUSED GLASS:• Fused glass is a term used to describe glass that has been fired (heat-processed) in a kiln at a range of high

temperatures from 593 °C to 816 °C.

• There are 3 main distinctions for temperature application and the resulting effect on the glass.

• Firing in the lower ranges of these temperatures 593–677 °C is called slumping. Firing in the middle ranges of these temperatures 677–732 °C is considered "tack fusing". Firing the glass at the higher spectrum of this range 732–816 °C is a "full fuse".

• All of these techniques can be applied to one glass work in separate firings to add depth, relief and shape.

USED FOR:to create Art glass, glass tiles, and jewelry, notably beads.

-The term stained glass can refer to colored glass as a material or to works made from it. Throughout its thousand-year history, the term has been applied almost exclusively to the windows of churches and other significant buildings.

-As a material stained glass is glass that has been colored by adding metallic salts during its manufacture. The colored glass is crafted into stained glass windows in which small pieces of glass are arranged to form patterns or pictures.

-The term stained glass is also applied to windows in which the colors have been painted onto the glass and then fused to the glass in a kiln.

-Usually used in the churches windows and as art work or as a design wall partiotion.

4. STAINED GLASS:

ANNEALED GLASS:

• Annealed glass is the basic flat glass product that is the first result of the float process. It is common glass that tends to break into large, jagged shards.

• It is used in some end products and often in double-glazed windows. • It is also the starting material used to produce more advanced products

through further processing such as laminating, toughening, coating, etc.

o Tempered Glass is annealed glass that is reheated and rapidly cooled, which strengthens the glass and causes it to break into pea-sized pellets if subject to impact.

Tempered GLASS:

• Vehicle manufacturers :used for the back and side windows.

• Commercial uses: include escalator and stairway barriers, sloped glazing, telephone booths, racquetball courts and solar panels.

• Household Uses: used to construct many household items, such as coffee carafes and baking dishes such as those manufactured by Pyrex . Tempered glass also is used in computer screens and oven windows.

Toughened Glass:

Cooling jets

Compression

Tension

Compression • It is stronger in bending than plain glass because bending stresses the outer layers in tension and these are initially in compression.

• For the same level of safety it is cheaper and lighter than laminated glass.

• If the material is broken the stress distribution becomes unbalanced and it shatters into small and relatively harmless fragments.

• It cannot be cut so it must be ordered to size. This has the advantage, however, that the stamp which is put on every sheet will always be there for checking. (note that laminated glass can be cut).

• There are restriction on dimensions of holes near the edge of a sheet.

o Properties of toughened glass:

• It has extremely broad applications in products for both buildings and, automobiles and transport, as well as in other areas. Car windshields and windows, glass portions of building facades, glass sliding doors and partitions in houses and offices, glass furniture such as table tops, and many other products typically use toughened glass. Products made from toughened glass often also incorporate other technologies, especially in the building and automotive and transport sectors.

Where it is used:

Laminated glass:

It consists of two or more plies permanently bonded together with one or more (PVB) interlayers using heat and pressure.

• The glass and interlayers can be a variety of colors and thicknesses.

• Laminated glass can be broken, but the fragments will tend to adhere to the plastic (PVB) interlayer and remain largely unbroken, reducing the risk of injury.

 

• Laminated glass is considered "safety glass" because it meets the requirements of the various Building Regulations and Standards.

• Heat strengthened and toughened glass can be incorporated into laminated glass units to further strengthen the impact resistance.Uses :Wind shield in automobiles and airplanes. Curtain walls, Ribbon Windows, Store Fronts, Punched or Architectural windows, Overhead Glazing, Handrails & Floors.

SIZES:up to 259x 508CM

LAMINATING PROCESS

• This is accomplished through a nip roll1 and autoclave2 process.

• In this process, the air is pushed out from between the glass and

the interlayer, sealing the components together.

 

• The pre-laminate is then put through an autoclave where heat

and pressure are applied, resulting in the finished laminate.

Advantages

• The outer layer can crack upon impact; however the plastic inner

layer would normally prevent the penetration of human limbs.

• It is more expensive than tempered glass, but it can be cut to

size.

• Generally it is less expensive than wired glass.

Demonstration of Laminated Glass Manufacture:

Wired Glass:-Wire mesh is inserted into plain glass during manufacturing. -Contrary to popular belief, the introduction of wired glass into annealed glass does not reinforce the glass for strength, it actually decreases it.  -Wired glass is weaker than plain glass because of the flaws inherent at the edges as each wire is cut.

-Glass that remains intact and restricts the expansion of fire.

Advantages: • It is Acceptable according to the

Building Code for applications in fire separations.

 • It can be cut to size and therefore

readily available when replacement glass is needed.

Places You Should Install Wire Glass:This glass is a smart addition in any area where a solid fire barrier and safety glass are beneficial. This includes public areas such as schools, public buildings, and businesses, and particularly in areas of these buildings that provide escape routes in case of fire.

Float Glass:

.

• The output of the float glass process is very high —around x5 m (g ft) can be produced per minute and 5oo,ooo sqm (5,38o,ooo sqft) per week and the quality of the glass is exceptional. Float glass currently accounts for 90% of glo bal glass production and is available in thicknesses from 2 to 25 mm .

• Most of the demand is for thicknesses ranging from 2 mm for picture framing to 6 mm (4/16 in) sheets for shel ves and tabletops. Standard

window glazing tends to be 3 or 4 mm float glass, the latter being the more common in double glazing units.

• In the float glass manufacturing process molten glass is poured from the glass kiln into a shallow bath containing molten tin. This molten glass floats on the tin and spreads freely over the surface under the in fluence of gravity to form a uniform sheet.

• The thickness of the sheet is determined by the speed with which the glass, still in the process of solidifying, is removed from the floating bed

GLASS BLOCKS• A hollow, translucent block of glass, often with molded patterns on either

or both faces, that affords diffused light when used in non-load-bearing walls or partitions

• It is used as interior wall partition .

Frameless Glass Block Wall Installation:

1-Ensure the opening is square and level, and the correct size. Ensuring that any fasteners do not protrude.

2-Run a generous bead of silicone adhesive across the center of the bottom of the frame and up the sides to the top of the first block level

3-Bed in the first glass block into the silicone adhesive starting from one end, Apply silicone to the exposed vertical side of the block , place  a vertical strip against the exposed silicone, repeat this process for the first layer.

4-Place a continuous bead of silicone along the weld of each glass block. Position the horizontal separation strip in the slots provided in the side frames and lock the glass blocks into place. Ensure that the first row of blocks is centered and level.

5-Continue these steps for each layer, until the final layer level is reached.

6- Line the top of the frame with a generous bead of silicone. Working towards the center from each side, install the blocks. No vertical separation strips are

required with the last layerApply sealant to all joints, using a wet sponge clean off excess sealant, to ensure a smooth neat finish.When all sealant is dry, buff and polish the glass

wall. 

SIZES (mm)190 x 190 x 80 (the most popular) 

190 x 94 x 80240 x 115 x 80 

300 x 300 x 100 240 x 240 x 80

What is the difference between (regular) annealed GLASS and tempered GLASS? -Raw materials are mixed together in a furnace that heats them to 2800

degrees F. As the materials melt and mix together, they float on a bath of molten tin. This is where the term “float glass "comes from.-As the glass comes out of the furnace is slowly cooled and travels down the line on rollers.-As it moves down the line the glass is checked for defects by a laser.-As the new glass comes to the end of the line is cut to size, and stacked on racks to be shipped.

Annealed Glass

•Advantages:– LOW Cost•Limitations:–Breaks in sharp pieces–Not as strong as Tempered Glass–Size limitationsSlide

• FLOAT PROCESS:• THIS Process IS introduced in 1959 by Pilkington Brothers• Float Glass Manufacturing Process video SEE VIDEO 2

The tempering process:1) First the glass is washed and then

heated.2) it must reach 1100°F (the softening

point for glass.) 3) The glass is then cooled with cold air.

Quenching with forced cold air sets up the tension and compression zones.

4) The tempered glass continues down the rollers to cool more and be packed for shipping. Glass to be tempered must be cut to size before the tempering step .

Glass expands when heated•Quenching “freezes” this expansion on the outside•Center cools more slowly, and contracts. Sets up tension and compression zones.

SPECIAL GLASSES

1. SECURITY GLASS2. SOLAR CONTROL GLASS3. INSULATING GLASS4. GLASS WITH MODIFIED OPTICAL CHARACTERISTICS5. FIRE RESISTANT GLASS6. CLIMATE CONTOLE GLASS 7. CAST GLASS 8. MOLDED GLASS

SPECIAL GLASS:1.Security glass:The most common use Of laminated glass is in secu rity panes, in which different thicknesses are combi ned to achieve a high impact resistance and danger limiting behavior in the case of failure, thanks to the binding effect of the plastic or resin layers. Security glass is used for ant(-theft screens, roof lights and large areas of glazing.

2. Solar control glass:Selective angular treatments or treatment with me tal oxide deposits are used to produced low emissivity (“low-e”) glass. These glasses transmit visible light but have a high reflection index for long wavelength infra-red rays, so emit much less heat to the exterior than normal glass.

3. Insulating glass :• Current solutions consist of creating a sealed cavity of 6 to 25

mm between two panes of glass. The insulating cavity acts as a thermal buffer and can be filled with dehydrated air to lower the mal conduction, or can be further improved by the incorporation of gels, gases such as argon or xenon, or films.

• Double glazing units have better thermal and acoustic insulation properties than single glazing

USES: provides thermal insulating for houses to remain cool in summer and warm in winter.

4. Glass with modified optical characteristics:

These are decorative glasses such as dichroic glass which decompose the light to create particular effects. They include glasses with ‘cold mirror” treatments, which reflect visible light but allow red waves to pass through or glazed glasses, often used in the field of corporate architecture.5.Fire resistant glass:

• Glass behaves poorly in fire because of its high thermal expansion coefficient and its fragility. Current solutions consist of introducing wire mesh into the glass (reinforced glass) to prevent it from falling from the sash although not from breaking.

• Another solution is to modify the chemical composition of the glass, an example being borosilicate glass which is widely used for kitchen utensils.

6.Climate control glass:

• Double glazing units with ventilated cavities often contain solar control blinds which transfer heat energy to the air within the cavity which circulates and is expelled to the exterior.

• A variant of this sys tern are the double façades in which single glazing is located in the exterior skin and a void is gene- rated between the two layers of the façade. Wind pressure on the inner skin is reduced, allowing ope ning windows even in very high buildings thus fa voring natural ventilation. Furthermore, heat losses through convection are significantly reduced.

7. Cast glass:

• Also known as “pressed glass”, it is used typically in kitchen or bathroom doors and windows to impede visibility without reducing light transmission. It is available in a wide range of colors.

 

• It is known as glass bricks, molded glass has been used throughout the 20th century as infill material in structural slabs, walls, vaults or domes, above when natural light is desired without transparen cy.

• The pieces are obtained by forcing molten glass into molds under pressure.

• The bricks are made by joining two half pieces to create an element with two faces and an air gap containing depressurized and dehydrated air.

• Today, the use of glass bricks is undergoing a revival, and pieces are available in a wide variety of colors, textures and finishes and with a range of translucency and transparency pro perties Due to the characteristics of the manufac turing process the product is available in a wide ran ge of sizes and formats, with special pieces.

 Textured glass, DecorFlu Design by OmniDecor

8. Molded glass:

GLASS BRICKS USED IN A WINDOW .

Technical difficulties and the limitations of glass:  • the use of glass does pose a number of pro blems: it has low thermal and acoustic insulation co efficients; can allow too much heat and light to

enter a building, causing overheating through the green house effect; optical distortions; its fragility; the di mensional limitations of the panes. o Solar radiation and the greenhouse effectThe most important property of glass is its trans parency, by which light and solar energy are able to pass through it with little dispersion. When infra-red waves pass through glass they heat the surfaces in their path causing them in their turn to irradiate infra-red waves but with longer wavelengths. Glass is opaque to these longer wavelength infra-red rays. causing heat energy to become trapped within the building. This effect, known as the greenhouse effect, can cause significant internal heat gains. o Thermal insulation:The poor thermal insulation properties of glass cause heat to be lost, a cold thermal sensation and can cause condensation, The first of these effects is the result of three processes: heat is lost from insi de the room through the surface of the glass which is at a lower temperature than the rest of the room; heat passes through the glass which is a good ther mal conductor; heat is lost from the outer surface of the glass through convection, evaporation and radiation to the sky. 

EXAMPLE :Le Corbusier made an attempt at alleviating these difficulties with his MUR NEUTRALISANT, a precursor to double glazing. Modern double glazing units work by having cavities with very low thermal conductivity, while the second pane of glass reduces the heat lost through conduction.

o Acoustic insulation:

While cavities of up to 20 mm improve the thermal properties of the glazing, they have no effect on the acoustic insulation properties of the glazing unit for which gaps must be at least 100 mm in width. At this width however, significant convection currents can arise within the cavity. A solution to both problems is for the glazing unit to have a large, me chemically ventilated cavity which contains within it panes of laminated glass of different thicknesses and even at varying inclinations. 

o Visual aspects

Reflectivity and the greenish tint in glass (particu larly notable in very thick pieces) are some of its most notable visual characteristics, as well as the optical distortion visible in large panes. These properties are difficult to eliminate as their origin is in the very composition of the glass or its polished surface finish. 

o Mechanical resistance:

• Glass is highly resistant to compression but is fragile and, above all, unpredictable.• Its thermal expansion is significant, so although it does have load-bearing ca pacity, it should always be allowed to expand freely. On reaching its critical

tension it breaks suddenly, which together with a low thermal conductivity and a high thermal expansion coefficient, means that it responds badly to sudden temperature changes. it is highly sus ceptible to fracture under thermal shock when subject to sudden temperature changes greater than or equal to ± 25 °C. Both of these weaknesses are particularly important in designing structural glazing façades.

 • The ever more ambitious use of glass in construction has led to the development of solutions to many of these problems. The different solutions have involved

changing the composition of the glass, adding spe cial layers or surface treatments to the panes, adding elements between the glass panes, the inclusion of active or passive solar control systems and combina tions of the above.

 

DESIGN CONSIDERATION:

• it is important that the glazing chosen is sufficiently strong and thick to receive the loads it will bear, and that its deformability even in exceptional circums tances will not compromise its function.

• Differential expansion within the glass can cause it to crack, above all if it is not well insulated or if the glazing or a thermally unbroken frame is in di rect contact with masonry.

• If the center of the pane warms up faster than the edges the central portion will expand more, rapidly creating internal tensions within it.

• If, furthermore, there are imperfections in the edges of the pane or a slight chip or hole, the glass could break.

• The probability the glass breaking under thermal stress increases if a partial shadow is cast on the glass from adjacent objects, particularly if the sha ded area comprises 25 % or less of the pane and in cludes 25 % or more of its perimeter.

o CORROSION:CAN LEAD TO LOSS GLASS TRANSPARENCY AND SHINE AND REDUCTION IN ITS THICKNESS.

CAUSES OF CORROSION:

o MANUFACTURING PROCESS: THIS CAN BE THE ROOT CAUSE OF THE GLASS AND RELATED TO ITS HOMOGENITY

o LENGTH OF EXPOXURE OF DETERIORATION AGENTSo ENVIRONMANTEL CONDITIONS: HUMIDITY, CONDENSATION,

TEMPRATURE CHANGES, POLLUTION…o CONSERVATION INTERVATIONS : MECHANICAL AND CHEMICAL

TREATEMENTo ATTACK FROM MICROPRGANISMS: FUNGI, BACTERA..o VIBRATIONS: PRODUCED BY ROAD, AIR TRAFFIC AND SEISMIC

TREMORS.

BREAKAGE OF GLASS:

• BREAKAGE MAY BE OCCASIONAD BY MECHANICAL OR THERMAL CAUSES OR COMBINATION OF THE TWO.

• IMPACT BREAKAGE: NUMBER OF CRACKS RELATING PROPORTIONALLY to the force of impact

• CONTACT BREAKAGE: direct contact between glass and masonry• FAILURE DUE TO SETTING BLOCK ERRORS• FAILURE DUE TO THE INSUFFICIENT THICKNESS• BREAKAGE CAUSED BY INSUFFICIENT EDGE CLEARANCE • BREAKAGE CAUSED BY POOR FIXING• UNEVEN SHADING: colored or reflective glasses are very sensitive to shadows

projected upon them .• THERMAL SHOCK AGGRAVATED BY FIXING CONDITIONS: reflective glazing

become so hot while edge are protected by pockets .• CURTAINS AND SHADING : using dark curtains will impede the cooling of the glass• THERMAL DIFFERENTIALS GENERATED BY LIGHTING OR HEATING

APPLIANCES.• OBJECT LEANT AGAINST THE GLASS., may disrupt the transmission of heat to the

inner face.

Advantages of using glass in construction include:1.It adds to the beautification of the facade of a building

2. It is useful for ornamental and decorative purposes both for interiors and exteriors of buildings

3. It performs the purposes of heat retention, lighting and energy saving

4. It conveys a sense of openness, harmony and accord

5. It is a versatile material that can be used for making transparent stairways, colored shelves and other design features like dividers and cubicles

Disadvantages of using glass in your home or office high rise:

1. It is costly and may increase construction costs.

2. Not advised for use in earthquake prone areas .

3. High maintenance costs .

4. Security concerns .  

GENERAL DIMENSIONS OF WINDOW GLASS:

• A standard 2.54 CM insulating glass unit, comprised of 2 lite of 0.6 thick glass and a 1.2 airspace weighs approximately 3 KG per square foot. Large insulating glass units are more likely to incur damage due to the additional weight causing difficulty during fabrication, handling, and glazing. The following table shows the calculated weight of a variety of standard Of 2.54 cm insulating glass units.

Large Insulating Glass Units – Design Considerations:

External Glazing :

Internal Glazing :

Frameless Glass used for showers:

Slope Glazing and Skylights:

• TYPES OF GLAZING MATERIALS USED FOR GLAZING MORE THAN 15 DEGREE OFF VERTICAL:

1. Laminated Glass2. Fully Tempered Glass3. Heat-Strengthened Glass4. Wired Glass5. Approved Plastics