Glass in Architecture

INNOVATIVE TECHNOLOGY IN THE FIELD OF GLASS ARCHITECTURE THESIS REPORT

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CONTENT

PREAMBLE----------------------------------------------------------02

ACKNOWLEDGMENT--------------------------------------------03

INTRODUCTION---------------------------------------------------04

JUSTIFICATION----------------------------------------------------05

SCOPE AND LIMITATION OF WORK------------------------06

AIMS AND OBJECTIVES----------------------------------------06

THE PROJECT DETAILS----------------------------------------07

A.1. SUSPENDED PARTICLE DEVICE (SPD) SMARTGLASS-----------------08

A.2 PRINTING ON GLASS --------------------------------------------------------------- 12

A.3 AREAS FOR INNOVATION, CHALLENGES AND OPPORTUNITIES---14

A.4 ARCHITECTURAL GLASS FOR EARTHQUAKE-RESISTANT BUILDINGS----------------------------------------23 A.5 A BRIGHT FUTURE FOR GLASS-CERAMICS---------------------------------25 A.6 PROCESSING OF LARGE GLASS SIZES, TYPES AND SHAPES----28

A.7 ROLE OF GLASS IN GREEN ARCHITECTURE------------------------------ 29

LITERATURE STUDY--------------------------------------------31

CONCLUSION------------------------------------------------------32

BIBLIOGRAPHY----------------------------------------------------33


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PREAMBLE

Glass is a fascinating material and its versatility makes it an indispensable

product for architecture and for other industries and its importance will further

increase in the future. It is difficult today to imagine a world of architecture

without glass. Envision the built environment of any other major urban city of

the world, and imagine all of the glass instantly disappeared; the naked

skeletons of towers poking into the sky surrounded by perforated buildings

and exposed storefronts. Or rather, imagine all else gone and envision the

glass landscape uninterrupted by steel or concrete; it is remarkable the

magnitude of glass material that comprises the urban construct.

The use of glass in architecture has grown steadily since its first application

as window glass, dating back to approximately the 1st century AD. Its

properties of color, translucency, and transparency are so uncommon that

mystical properties were often associated with it by the various cultures using

it. Early glass making processes were closely guarded secrets by the ruling

governments. Glass was traded as a prized material among kings and

emperors of the lands. The wealthy classes long ago developed an appetite

for glass that has pushed producers to make larger and better quality

products over the centuries and continuing to this day. Over the years, the

taste for glass spread throughout the population as glass in window

applications became a commodity item in the late 18th and into the 19th

centuries. Today, most people value floor-to-ceiling glass if they can get it, at

least a window if they cannot.

I hope this report will be of some help for Students, Architects, Engineers and

others who would want to bring about a change and advancement in the

construction technology.


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ACKNOWLEDGMENT

I would like to express my sincere gratitude towards the Head of the

Architectural Department, Dr. D.J.Biswas for his valuable advice and

guidance. I would also like to thank the other faculty members of the

Architectural Department.

Finally, I would like to thank all my fellow student colleagues of B Arch VIII

Semester for helping me complete this report..


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INTRODUCTION

Glass is arguably the most remarkable material ever discovered by man.

Glass has been produced and used by mankind for thousands of years, and

its use as a building facade has developed significantly with technological

advancements in production and the evolution of architectural design.

It was during the Medieval Era that glass was first widely used as a decorative

feature, and not just a means of letting light in. The architectural trend of

Gothic churches encouraged the use of stain-glassed windows to illustrate

biblical scenes, and set a future trend for the transparency and luminosity of

glass. It was not until the industrial revolution however that there were

substantial advancements in producing large sheet glass, as well as the

introduction of new construction materials to hold larger glass facades in

place. These developments opened up numerous possibilities of using glass

in construction and it was during this time that architects experimented with

the design of glass conservatories, and entire walls of glass. A famous

example in such glass projects is The Crystal Palace, built in 1851, and

consisting of 300,000 sheets of glass.

Architects use of glass during the 20th century evolved and flourished with the

dominant idea of transparency and dematerialization, in which architects

created „honest‟ buildings that accentuated the quality of light and space.

Architect and glass enthusiast Scheerbart expressed his opinion on the

importance of glass in architecture;

“If we want our culture to rise to a high level, we are obliged for better or for

worse, to change our architecture. And this only becomes possible if we take

away the „closed‟ character from the rooms in which we live. We can only do

that by introducing glass architecture, which lets in the light of the sun, the

moon, the stars, not merely through a few windows, but through every

possible wall, which can be made entirely of glass.”


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Glass has fascinated people ever since its discovery more than 4000 years

ago. Since then it has become a ubiquitous material in buildings and its use

has evolved rapidly over the last 30 years. There has been a noticeable shift

from traditional small window infill panels, to large area structural glass and

solar energy products. These novel applications are the result of a quick

succession of technological innovations in heat treatment processes, bending

techniques, laminating materials and high strength connections that are

underpinned by an improved understanding of the fundamental mechanical

and physical properties of glass.

Worldwide production of glass has for the last few years increased at 5%

annually, while glass for renewable solar energy applications is increasing at

15% per annum. In addition glass has a major impact on the comfort and well-

being of building occupants, mainly through the transmission of natural light

and the reduction of glare.

The safety of building occupants and pedestrians is also significantly affected

by glass. For example, up to 80% of human injuries from city centre blast

events are glass related.

JUSTIFICATION

The recent innovations in Glass manufacture and engineering create

unprecedented opportunities to design and construct robust, efficient and

delightful structures, but in doing so architects and engineers are faced with

equally onerous challenges. The major barrier to progress is the

fragmentation of knowledge which is exacerbated by the notoriously secretive

Glass industry. Structural engineering-led research on Glass is increasing but

still well below the research levels in other mainstream construction materials.

Furthermore, the university curricula does not include anything more than a

basic introduction to Glass.

I decided to take up this research topic in order to gain some detailed

knowledge on the technological advancement of Glass and its application in

the field of Architecture.


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SCOPE AND LIMITATION OF WORK

The scope of using Glass in the field of Architecture is very vast. The recent

advancement in the construction technology has made Glass as one of the

major building material worldwide.

In this thesis report, due to the vastness of the topic, I would like to cover only

a few selected aspects of Glass.

AIMS AND OBJECTIVES

The aim of this report is to perform a detailed study on the following topics:

The suspended particle device (SPD) smart glass

Printing on glass

Areas for innovation, challenges and opportunities

Architectural glass for earthquake-resistant buildings

A bright future for glass-ceramics

Processing of large glass sizes, types and shapes

Role of glass in green architecture


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THE PROJECT DETAILS

A.1. SUSPENDED PARTICLE DEVICE (SPD) SMARTGLASS

Driven for the need for better insulated zero-carbon buildings, a new

generation of actively controlled components, are starting to replace

conventional materials. These smart devices are able to respond to seasonal

variations in temperature and solar radiation. Such advancements in „smart‟

windows will stimulate the continued use of glass as a building facade and

also reduce the energy loads associated with achieving a comfortable internal

environment. SPD glass uses suspended particle device technology which

gives an electronic control of light and heat transmission by altering the „tint‟ of

the window. When switched on the glass turns clear and allows for around

45% visible light transmission, and when no current is applied the glass holds

a blue tint and allows less than 1% visible light transmission. In all states of

transparency the glass rejects over 99% of UV light transmission.

SPD glass transmission properties can also control the heat flow into a room

by rejecting solar heat gain.

A.1.1 Background into Switchable Technology

Research over the past decade has lead to the development of numerous

smart adaptive materials to regulate light and energy flows through glass

facades. These smart technologies primarily employ the following behaviours;

thermotropic, gasotropic, and electrotropic.

Thermotropic: This is a passive technology which responds to environmental

changes in temperature and can be used to control the infrared emissivity and

transmittance of glass, similar to thermochromic glass as well. Thermotropic

materials also have the ability to change the thermal conductivity of the glass

as well as transmittance values, which holds more energy saving potential.

However the thermotropic material will only change from transmissive to

reflective at a certain temperature, which needs to be set within the human

comfort range for it to have realistic architectural applications.


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A general disadvantage of passive control systems are also that the

performance is only optimized according to one factor (solar heat gain), and

cannot be manually overrun to take into account other variables such as the

visual light levels.

Gasotropic: The change in optical properties of gasotropic materials is

caused by the chemical reaction between a special layer coated on the glass,

and a gas fed into the cavity between the two glass panes. Advantages of

gasotropic glass is that it is able to retain high transmission properties in the

clear, „un-reacted‟ state, and it also experience a fast switching ability, taking

20 seconds to change from clear to coloured, and less than a minute to switch

back. Problems however arise with the complexity of the gas injection system

and the build-up of water when hydrogen atoms are added for the chemical

process. At this point gasotropic and gasochromic glazing is still not

commercially viable but is a technology still being heavily researched in order

to achieve marketability in the future.

Electrotropic: Within electrically activated smart glass systems there are

three main devices; Liquid crystal technology, electrochromic devices, and

suspended particle devices.

LC Technology: Liquid crystal glazing is made up of two sheets of glass

surrounding a liquid crystal film. With the application of an electric field, the

orientation of these liquid crystal chains can be altered and therefore the

optical transmission of the glass also. When no voltage is applied the

molecules are randomly scattered and visual light is diffused in multiple

directions, giving a translucent „opal white‟ effect. When a voltage is

applied the molecules align with the electric field and light can pass

through unobstructed. LC power consumption is low in general – less than

5 W/m2 and the transition from opaque to clear is immediate. However LC

technology is not able to reduce the amount of radiation transmission from

the sun very effectively. LC glass affects the way light is transferred but

does not alter the quantity of radiation, and thus heat flow through glass,

making it unsatisfactory for energy saving purposes. The use of LC glass

is currently popular for internal architectural designs, such as privacy

partitions, though due to many limitations does not have a foreseeable

future as an external building façade.


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Electrochromic: Electrochromic devices are currently probably the most

popular and complex of switchable glazing technology. The devices

consist of a thin solid electrochromic film which is sandwiched between

two layers of glass. On passing a low voltage across the thin coating the

electrochromic layer is activated and changes colour from clear to dark. It

is with this change in colour that the glass controls its optical transmission

properties. Electrochromic glass is able to control solar radiation by

absorbing the heat in its darkened state, though this can lead to heating of

the glass. An advantage of electrochromic glazing is that the low voltage

need only be applied until the desired colouration has been achieved and

then the device will exhibit colour memory and maintain radiation

transmission for up to 48hrs.

The electric current can be either activated manually or by active sensors that

respond to the external light. Darkening the glass will reduce solar

transmission, and when there is little sunlight the glass can brighten, reducing

the need for artificial lighting. Required time for colour switching is slower than

other technologies though and can take up to 30 minutes for a window size of

about 2.4 m2. Durability in electrochromic glazing is a current issue with

having to cope with large number of switching cycles to survive a reasonable

life-time of 10- 15 years.

SPD technology: SPD is a film based technology, with a uniform response

throughout the film. The film contains rod-like particles suspended in

billions of liquid droplets distributed across the film. When the film has no

applied voltage the particles are in random positions and block light

transmission, appearing as a dark blue tint. When a voltage is then

applied, the particles align and light is allowed to go through. The change

in tint is instant and a user advantage to this technology is that the voltage

can be varied to give a different level of tint and therefore the transmission

properties can be changed to suit any particular external environment.

SPD windows hold energy saving potential for the device uses solid

radiation-absorbing particles in the liquid suspension. Precise optical

properties depend on the thickness of the suspension film as well as the

concentration of particles within.


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Solar radiation and visible light transmittance is reduced with the

application of a voltage, which in turn reduces the heat flow into the

internal environment. SPD windows allow clear sight through the glass

even while fully switched on and in a state of minimum transmission, which

holds a visual advantage over other glazing technologies that turn the

glass „cloudy‟. The current downside of this technology is the cost. As it‟s a

very recent development, it is still in the early stages of demand, with the

patent owner controlling prices. With sufficient marketing and its energy

saving advantages made known then cost will come down as unit demand

increases.

Diagram of SPD technology

Source: www.smartglassinternational.com

This investigation into the performance of SPD glazing has shown that this

switchable smart technology has significant advantages over the use of

regular clear float glazing. It was identified before experimental

measurements that SPD glass had a lower visible light transmission, and a

similar solar heat transmission to other smart switchable glazing, such as

thermotropic, gasotropic and electrochromic.

These other technologies were

discussed briefly and disadvantages

that limited their potential noted;

disadvantages which SPD

technology does not experience.

Different tint of SPD windows

Source: www.smartglassinternational.com


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COMPARATIVE ANALYSIS OF GLAZING TECHNOLOGIES

Using data carried out in previous research into switchable glazing

technologies, a quantitative comparison can be made between the optical

characteristics of the different glass devices. Table 1 below shows the various

transmission and reflectance values of the four main switchable technologies.


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Main advantages of SPD windows;

• Accurate lighting control, while maintaining an optical view through the

window. Even with the bluish tint, it is still possible to see through the glass.

Figure.above shows the variation of window colour in the ON/OFF state

• The high durability and long life expected for smart glass technology. Testing

has occurred for over 100,000 cycles without an degeneration of performance

• Reduced glare in working environments that will cause uncomfortable

conditions, disruption to computer operation, and possible eye strain

• A wide working temperature from -30°C to +90°C so suitable for glass

façades in numerous climates. The temperature of glass in very sunny

locations can reach extremely high levels so this upper bound is very critical.

• Energy saving due to the reduced cooling and lighting costs. SPD windows

are able to reduce the solar heat gain into an office and therefore create a

more stable and cooler internal environment. The ability to control light levels

also removes the need to have blinds and therefore the use of artificial lighting

throughout the day.

A.2 PRINTING ON GLASS

The recent few years have been a time of reformation in the glass printing

industry. In addition to conventional screen printing and roller coating

technologies, digital printing technologies have invaded the market, and the

range of available machines has widened considerably.

Durst Rho 700 Printer

Source: Glasstec 2010


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Screen printing has dominated the glass printing industry due to its excellent

repeatability and low unit costs when printing big batches. It was adapted in

the industry ages ago. The approach of digital printing technology is to

complement the gaps in production that other printing technologies can‟t fulfill.

This refers to production with high set up costs and small batch sizes, which

could barely be printed cost-effectively. Additionally, one benefit of different

digital printing technology is the creativity option when preparing models,

while in screen printing the screen already sets some limitations for creativity.

Multicolor printing can be become rather expensive, because of complicated

operations management when balancing between printing, drying and set-up,

not to mention the price of multiple screens.

The system that is based on electro-photography process, works similar to a

photocopier. In this system, ceramic frit is converted into a toner to allow an

electrostatic transfer. It is handy when printing illustrative pictures that do not

need to have too thick ink layers, which is obviously limited when substrates

(ink and glass) are joined during the coloring process. There is also a

limitation regarding the size of the glass.

In Exterior/Interior Architecture, as a result of architectural concepts which are

applied to possibly just a single building, one of the main problems is the

extremely high cost of producing such huge screens, together with film

preparation and stenciling, For instance, 50 exemplars represent an extremely

large quantity and, quite often, they print less than ten exemplars!

What is then the relation between screen printing and digital printing? At the

moment, Screen printing is and will be indispensable when printing very large

quantities of the same design with one color. The Final unit costs will be low

and the overall set-up-time short. If a glass processor needs to print small or

limited quantities or multi-color printings, digital printing technology comes in.

Perhaps one day - in the not too distant future - the ink jet for all glass

applications will offer the advantages already being used today in the

advertising market.

Increasingly, it seems that digital printing, rather than becoming a competitor,

is now regarded as a complementary technology that enables screen printers

to offer their customers the best possible service at a reasonable price.


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A.3 AREAS FOR INNOVATION, CHALLENGES AND OPPORTUNITIES

Dematerialisation - The quest for the all-glass structure which has changed

the use of glass from a cladding material to load bearing elements.

Robustness - The need for robust glass elements and structures and the

ways in which glass can sustain heightened threats and extreme events.

Blob architecture – The ability (or inability) of glass to cope with geometrical

complexity and „freeform‟ surfaces.

The transparency, durability, uniformity and ease of maintenance make glass

a desirable material, but there has been a recent divergence in approach

between the glass used in building envelopes and the glass used in

installations that do not have any environmental performance requirement to

fulfill (e.g. staircases, internal walls and floors etc.).

In the case of glass intended for building envelopes, the trend for maximum

transparency seemed to reach a climax in the all glass façades of the1990‟s.

A.3.1 Dematerialised façades are still very desirable due to:

• The aspirational qualities of glass clad buildings.

• Daylight penetration and the resulting sense of well being for building

occupants.

• The high durability and low maintenance of glass.

• The uniformity and quality of finish.

• The improved letability of large percentage glazing buildings probably due to

the fact that buildings are often let when vacant i.e. when full height glazing

looks best.

These benefits must however be balanced with the building physics

requirements of improving the energy efficiency of buildings such as reducing

the amount of unwanted heat gains and losses through the building envelope

and improving comfort for building occupants by for example reducing glare.

From an environmental performance perspective, there is very little use for

the all glass façade. The notable exceptions are nested thermal spaces, semi-

protected / transition spaces and screens from wind and rain in temperate

marine climates where thermal mass and insulation are less important.


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As a result there have been some

noticeable retreats forms the fully

transparent façade.

In glass installations that are not

constrained by environmental

performance requirements the quest

for full transparency, lightness and

the all-glass structure persists.

Glass wall used as rain / windscreen in Central Station Berlin

Source: Steel Construction Institute, RWTH Aachen.

The industry has been edging closer to this with the recent advances in:

• The characterization of the mechanical properties of glass, in particular the

ability to predict the strength and variability of glass.

• The improved quality of laminated glass that leads to less delamination and

better long term performance and appearance.

• The development of high performance mechanical connections that seek to

reduce the stress concentrations while improving the post-fracture

performance of glass.

• The development of stiff adhesives and interlayers such as the Sentry Glass

Plus interlayer by DuPont, that enables glass plates to be laminated and

lapped together in a similar way to Glulam timber.

• The development of glass-to-metal bonded fixings that eliminate the need for

drilling holes in glass and reduce the stress concentrations around the joint.

Glass bridge constructed

from cold bent glass

plates laminated with

Sentry Glass Plus

Interlayer.

Source: Seele


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These innovations have enabled glass to be used as load bearing elements

where the glass contributes to the load bearing capacity of the structure, but

despite these advances there are several challenges and barriers to further

developments, namely:

• The reduction or elimination of metallic elements from glass is a novel

development and often requires expensive prototype testing on a project-by-

project basis.

• The large glass panels that are now possible are often limited by

transportation, access and replacement considerations.

• Most design guidelines do not distinguish between key load bearing glass

elements and secondary glass elements.

• The large sizes and prominence of the glass elements means that quality of

fabrication and low tolerances come to the fore. Although the quality of

lamination has improved there are only a handful of manufacturers and

installers who can laminate and install glass to the low tolerance levels and

high quality often required in glass structures.

• Bonding bits of metal to glass reduces the need and expense of bolting

through glass but the fixing is still visible and causes stress concentrations in

glass such that it often governs

design (e.g. glass thickness, number of plies, interlayer type etc.).

A.3.2 SECURITY GLAZING

As a means of keeping people and property safe, security glazing is used

in a variety of building types, and can offer a range of protection features.

Because these features vary from intrusion and bullet resistance to bomb

blast and hurricane resistance, security glazing is a catchall phrase that can

define a multitude of solutions.

From a product development standpoint, security-glazing options have

expanded over the years to include laminated glazing materials, applied films,

and blast curtains and shades.

In order to specify the appropriate security glazing solution, it is necessary to

make assumptions about the level of performance required to resist the

anticipated threat.


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Nowadays, test methods and specifications have been developed to address

many threat scenarios, and software programs can speed up the process of

selecting the proper type and thickness of security glazing.

Flying glass is a major source of injury and/or death in an explosive attack.

To prevent injury and loss of life during an explosive event, the window

system design is balanced.

Security glazing enables a building to be both attractive and functional

without jeopardizing the safety of occupants. Security glazing products fit into

categories of performance that range from low level security, such as

storefronts requiring smash and grab protection, to high levels of security,

requiring both forced entry and ballistics protection. The proper choice of

security glazing is dependent on understanding the desired level of

performance.

LightWise Architectural Systems Blast-Resistant

Glass Block Panels consist of glass block framed

by a 2-piece aluminum channel. Standard channel

is mill finished, anodized clear or bronze.

Source: Pittsburgh Corning Corporartion

A.3.3 THE ROBUSTNESS OF GLASS STRUCTURES

Glass is inherently brittle, and annealed (float) glass has a relatively low

tensile strength and breaks into large sharp shards that constitute a major risk

of injury. Annealed glass can be treated or combined with other materials to

produce a „safety glass‟ product that has some ability to reduce the likelihood

of injuries. Heat treating the glass to produce fully tempered (toughened)

glass increases the tensile strength of glass and modifies the fracture patterns

to small rounded dice. This is undoubtedly an improvement, but it is often not

considered safe enough, as the mass of falling glass (albeit in rounded dice)

is substantial and may cause injury. The prevalent form of safety glass is

laminated glass, which generally consists of two or more layers of glass

(annealed, heat treated or chemically strengthened) with a visco-elastic

polyvinyl butyral (PVB) interlayer.


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When laminated glass is broken, the interlayer tends to hold the glass

fragments in place thus reducing the likelihood of injury from falling or

propelled shards. However, the use of PVB laminated glass does not in itself

guarantee an adequate post-breakage performance of the glass element and

there have been several reports of laminated glass sagging like a „wet towel‟

and tearing away from the supports, particularly when fully toughened glass

plates are used in the laminated unit. On a system level, it is essential that

redundancy through alternative load paths is available to ensure that the

failure of one glass element does not cause disproportionate collapse of the

remaining parts of the structure.

Laminated glass composed of two sheets Laminated glass composed of two sheets

of fully toughened glass illustrating the of annealed glass illustrating the

low post-breakage capacity. superior post-breakage capacity.

In general it is inappropriate to classify a glass product as „safety glass‟

because the degree of safety is specific to the boundary conditions, the

anticipated actions on the structure and the critical nature of the element in

question. As a result a glass structure may be deemed safe if it ensures

adequate strength and stability for normal actions and in addition it provides

safe failure or adequate residual post-fracture capacity thereby minimising the

risk of human injury.

The relatively high level of threats of extreme loading on glass structures

ranging from malicious attacks (bomb blast and impact) to natural events

(high wind pressures and flying debris) and fire means that it is essential to

consider the performance of glass under extreme loads and in particular its

post-fracture performance. The glazing industry has responded to the post-

fracture limitations of glass and the increasing severity of normal and

exceptional loading conditions by developing a wide range of new products.


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The principal innovations in this area are:

• The stronger and stiffer interlayers such as DuPont‟s Sentry Glass Plus

interlayer which often provides an enhanced post-breakage resistance.

• The improved knowledge of interlayer behaviour under short and long term

conditions.

• The development of heat strengthened glass and chemically strengthened

glass. Heat strengthened glass has a design tensile strength of approximately

59MPa (compared to the short term design strength of annealed glass of

18.5MPa and the design tensile strength of fully toughened glass of

approximately 100MPa), and fails in large pieces thereby providing a superior

post-fracture resistance than that of fully toughened glass.

• The development of edge retention and enhanced connections that provide

a fail-safe system.

• The adoption of design approaches that ensure that there are alternative

load paths in the glass structure.

There are several challenges in ensuring adequate post breakage resistance

of glass structures, namely:

• Determining security requirements and risks for a glass structure and the

associated task of quantifying the magnitude and characteristics of the

extreme loads are non-trivial tasks. A particular difficulty in this regard is

simulating and validating the characteristics of a blast load as it travels

through the street canyons of a city centre.

• Despite the improved understanding of the strength of glass and the

properties of the interlayer, the causes of failure and resulting fracture

patterns which governs post-breakage behaviour are still elusive.

Prototype testing is therefore specified as a matter of course to validate

calculations of novel structures. This requires use of existing test standards,

but often requires adapting tests to suit the application such as adjusting pass

/ fail criteria or changing impact forces.

• There is no formal method for applying the fundamental „fail-safe‟ concepts

in glass design. This may lead to overly conservative structures or result in

unsafe glass structures.


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A.3.4 PRODUCING GEOMETRICALLY COMPLEX GLASS STRUCTURES

We are currently in a late style of architecture which seems to be

characterised by several emerging styles competing for international

dominance. One of these is Blob Architecture in which buildings and

particularly their envelopes have an organic free form shape.

Blob architecture relies heavily on the recent developments in digital

technology, namely:

• The recent developments in CAD technology, in particular the adoption of

nonuniform rational B-spline (NURBS) in CAD software for representing free

from surfaces.

• The use of computer aided manufacturing in the construction industry

specifically the use of programming tools for converting three dimensional

CAD models into CNC code for driving machine tools in the workshop.

• The development of powerful finite element analysis software that can

analyse free from continua and the development of powerful graphical pre-

and post-processors in engineering analysis software.

Wireframe CAD model of Centre de

Communication Citroen, Paris

Source: Steel Construction Institute, RWTH Aachen.

Glass is produced in flat sheets on the float line and it does not naturally lend

itself to the curved surfaces of Blob Architecture. This is one area of

application where more flexible and easily formed materials such as ETFE

seem to have an advantage. Despite this shortcoming there have been

several developments which have made the use of glass on free form

buildings possible, albeit at a significant capital cost.


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Triangulated shell structure at

BMW world, Munich.

Cold bent glass at Peek & Cloppenburg store,

Cologne, Germany

Curved geometries pose two major problems for glass. One of which is the

curvature of the glass which may be overcome by discretising the free from

surface into a mesh of planar triangular elements. The other difficulty is the

variation in panel sizes that are often required to build up a curved surface.

This may be mitigated by panelising the curved surface to generate the least

possible number of different sized panels.

A triangular mesh is not always aesthetically acceptable. In such cases it is

necessary to adopt the more expensive option of producing curved sheets of

glass. The traditional technique is by sag bending whereby the flat glass is

placed over a mould and heated to approximately 600°C, allowing the glass to

soften sufficiently to take the shape of the mould. The glass is then cooled

slowly to avoid any residual stress. Sag bending is a reasonably cost effective

process for producing curved vehicle windscreens as the mould can be

reused several times, but it becomes prohibitively expensive for bending a

single piece of glass for a building. There are also other problems associated

with the sag bending process, namely:

• The high temperatures required for sag bending damages the soft coatings

on glass.


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• Sag bent glass that is subsequently laminated may cause problems of

misaligned holes and uneven interlayer thickness.

• Double curvature glass cannot be heat treated.

A recent major innovation in this area has been the development of cold bent

glass where the glass is bent at ambient temperature thereby inducing flexural

stresses in the glass. There are two variations to cold bent glass. The first is

by forcing monolithic glass into a shape and securing it into the bent position

by mechanical fixings. The second is to force two or more layered glass

panels into a curved shape and hold them in position while laminating them in

an autoclave.

When the glass is laminated the curvature is retained by virtue of the

longitudinal shear stiffness of the interlayer. Cold bent glass is cheaper to

produce than sag bent glass but the maximum curvature of cold bent glass is

limited by the tensile strength of the glass. Insulated glazing units (IGU‟s) the

curvature is often limited by the maximum shear strain along the edge seal.

Cold bent glass also has the advantage of providing a curved surface with

very few optical distortions, but caution should be exercised when using hot

and cold bent glass next to each other as the finished appearance may vary.

There are several limitations and high costs associated with double curvature

glass elements. A technique currently being researched aims to redress some

of these difficulties by discretising a double curvature surfaces into a series of

single curvature strips.

It is likely that the demand for curved glass panels will increase in the future.

The extent of which depends on whether Blob Architecture will develop into

fully fledged architectural style that is adopted internationally. The main

challenge for producing curved glass elements is to understand the

permutations and combinations of the manufacturing and installation

processes and the constraints on what is possible. This understanding is not

limited to glass but also extends to the interfaces between glass and the other

elements of the building which become more complex with freeform shapes.

Cold bent glass is a very recent and exciting development, but it is unclear

whether there is a full understanding of the long term performance as the

interlayer creeps under long term longitudinal shear strain. This technique is

however very promising and has yet to be fully exploited in practice.


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A.4 ARCHITECTURAL GLASS FOR EARTHQUAKE-RESISTANT

BUILDINGS Recent attention has focused on the design of architectural glazing systems to

resist windborne debris impacts. Despite this activity in the wind engineering

field, building codes contain only minimal information regarding the seismic

design of architectural glazing systems.

This void in building envelope design practice is disturbing when one

considers the potential life safety hazards of falling glass during a severe

earthquake. In a less severe earthquake (or in regions farther away from the

epicenter of a severe earthquake), life safety considerations can be eclipsed

by the high costs associated with loss of building security, disruptions to

building operations that can occur when glass breaks (and building envelopes

are breached), and damage to building interiors during post-earthquake

storms. Such costs, when accumulated over a widespread region, can be

enormous. The insurance industry can attest to this.

Glass failure patterns were recorded during each storefront and mid-rise test.

Annealed monolithic glass tended to fracture into sizeable shards, which then

fell from the curtain wall frame.

Heat-strengthened monolithic glass generally broke into smaller shards than

annealed monolithic glass, with the average shard size being inversely

proportional to the magnitude of surface compressive prestress in the glass.

Fully tempered monolithic glass shattered into much smaller, cube-shaped

fragments. Annealed monolithic glass with unanchored 0.1 mm (4 mil) PET

film also fractured into large shards, much like annealed monolithic glass

without film, but the shards adhered to the film.

However, when the weight of the glass shards became excessive, the entire

shard/film conglomeration sometimes fell from the glazing pocket as a unit.

In contrast, annealed and heat-strengthened laminated glass units

experienced fracture on each glass ply separately, which permitted these

laminated glass units to retain sufficient rigidity to remain in the glazing pocket

after one glass ply (or even both) had fractured due to glass-toaluminum

contacts. Annealed and heat strengthened laminated glass units exhibited

very high resistance to glass fallout during the dynamic racking tests.


24

Typical failure patterns in various architectural glass types after in-plane

dynamic racking tests. Source: Richard A. Behr on Architectural glass for

earthquake-resistant buildings.

Observations and conclusions derived from only a limited number of

laboratory tests cannot produce generic guidelines for designing and

specifying seismic-resistant architectural glazing systems. Test data and

laboratory observations can, however, provide designers and specifiers with

meaningful insights regarding factors that can affect the safety and

serviceability of architectural glass subjected to seismic loading conditions.

From the dual perspectives of (1) protecting life safety and (2) maintaining

building envelope integrity and serviceability, annealed or heat strengthened

laminated glass units are wise choices for either new or retrofit building

envelope systems. Not only do these laminated glass units help protect

building occupants and pedestrians from falling glass during a severe

earthquake, but they also help maintain building envelope integrity after

earthquake-induced building motions that could cause other glass types to fall

from their glazed openings. By helping maintain building envelope integrity,

laminated glass units can help keep a building secure and weathertight in the

prolonged periods of cleanup and rebuilding following a major earthquake.


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A.5 A BRIGHT FUTURE FOR GLASS-CERAMICS

Glass-ceramics were discovered – somewhat accidently – in 1953.

Since then, many exciting papers have been published and patents granted

related to glass-ceramics by research institutes, universities and companies

worldwide. Glass-ceramics (also known as vitrocerams, pyrocerams,

vitrocerâmicos, vitroceramiques and sittals) are produced by controlled

crystallization of certain glasses – generally induced by nucleating additives.

This is in contrast with spontaneous surface crystallization, which is normally

not wanted in glass manufacturing. They always contain a residual glassy

phase and one or more embedded crystalline phases. The crystallinity varies

between 0.5 and 99.5 percent, most frequently between 30 and 70 percent.

Controlled ceramization yields an array of materials with interesting,

sometimes unusual, combinations of properties.

Several authors, have developed many glass-ceramics made from a wide

variety of waste materials, such incinerator ashes, blast furnaces slags, steel

slags and sugar-cane ashes. Their composition and predominant crystal

phases vary widely. These low-cost, dark colored (because of the high level of

transition elements in wastes) materials are generally strong, hard and

chemically resistant. Their intended use is for abrasion and chemically

resistant parts or floor and wall tile used in chemical, mechanical and other

heavy-duty industries or construction.

A high-end-use construction and architecture glass-ceramic is Neopariés,

which was pioneered by Nippon Electric Glass about 20 years ago and

continues to be used. Neopariés is a pore-free, partially crystallized material

with a soft rich appearance similar to marble and granite.

However, it has none of the maintenance problems of natural stone and is an

attractive material for exterior and interior building walls and table tops.

Because of the growing concern about sustainability and exhausting reserves

of natural stones, the use of glass-ceramics as a construction material

deserves much attention.


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A.5.1 HEAT-RESISTANT GLASS-CERAMIC FOR HIGH EFFICIENCY

HEATING APPLIANCES

Neoceram is a transparent low-expansion glass-ceramic with a number of

outstanding features that include high resistance to thermal shock, high

mechanical strength, and excellent electrical characteristics. With an almost

zero thermal expansion coefficient, the applications for Neoceram continue to

grow. Trusted for over 30 years, Neoceram now features a smoother, texture-

free surface with less visible color. This next generation of Neoceram was

developed specifically to address the larger glass areas that are becoming

common in contemporary hearth designs.

FEATURES

• Withstands continuous temperatures to 1292°F • Thermal shock resistant

• Impact strength • Superior heat resistance (nearly three times that of

tempered glass) • Improved surface quality and color • Available in 3 mm and

5 mm thickness • Good mechanical reliability • Available in a wide variety of

shapes and sizes including bent and curved configurations • Sheet sizes up to

42" x 78" • Available with mirrored and colored options (ceramic frit)


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A.5.2 GLASS-CERAMICS POSSESS MANY FAVORABLE FEATURES:

• Composition: 1052 compositions can, in principle, be vitrified by combining

and varying by 1 mole percent of all the 80 “friendly” elements of the

periodical table, which could then be crystallized to form a glass-ceramic.44

• Forming: Articles of any shape can, in principle, be made by rolling, casting,

pressing, blowing, drawing or by any other glass-processing method that

already exists or may be invented.

• Thermal treatment: Crystallization is induced on the cooling path, in one step

or multiple steps.

• Microstructure: Articles can be engineered from nanograins, micrograins or

macrograins; low or high crystallinity; zero, low or high porosity; one or

multiple crystal phases; random or aligned crystals; and surface-induced or

internal crystallization.

• Thermal properties: Thermal expansion can be controlled – negative, zero or

highly positive; stability can range from about 400°C to 1,450°C; and low

thermal conductivity is common.

• Mechanical properties: Articles have much higher strength and toughness

than glasses, but the limits are far from being reached, possibility to be further

strengthened by fiber addition, chemical and thermal methods. They are hard,

some are machinable.

• Chemical properties: Articles are resorbable or highly durable.

• Biological properties: Articles are biocompatible (inert) or bioactive.

• Electrical and magnetic properties: Articles have low or high dielectric

constant and loss, high breakdown voltage, ionic conducting or insulating,

superconducting, piezoelectric and ferromagnetic properties.

• Optical properties: Articles are translucent or opaque, opalescent,

fluorescent, and colored and photo-induction nucleations are possible.

An impressive variety of glassceramics has been developed during the past

six decades. Yet, many others with unusual and unforeseen properties and

applications are likely to be discovered in the future.


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A.6 PROCESSING OF LARGE GLASS SIZES, TYPES AND SHAPES

The latest changes and modifications in the architecture, architectural design

and construction methods set new challenges in to the glazing structures. The

large glass sizes, LOW-E coatings including the so called super LOW-E‟s

need to be tempered to meet the design of the latest architectural solutions

and applications. The new technological methods in glass tempering are

summarized along with the physical limitations in engineering and processing.

The growing use of glass brings entirely new challenges and requirements to

the safety glass market. It is natural that the main use is related in to the

tempered glass, which is dominating the safety glass market.

In the near future the most important conclusion and driving forces from the

development point of view are

• energy control (LOW-E)

• large windows with maximum

day lighting and ”miniframes”

• smart windows and glazing

with integrated solar panels

• increasing safety and security

Example of the today‟s glazing; Source: www.glassfiles.com

The use of low emissivity glass has helped preserve the energy efficiency of

window structures and it has thus sustained the trend in office and other

commercial construction applications which moves towards larger glass

surfaces and better day lighting properties. This results in to the high thermal

stress in to the window construction, which can be seen normally as a glass

breakage. The solution to avoid thermal breakage in large window structures

is tempering process, which increases the thermal resistance more than two

times when compared in to the float glass.

The designers and architects have found the large windows and shapes as a

natural part of their design tool. Part of this process has been the need to

bring natural day light in to the buildings. The large glass surfaces are the

most natural way to provide it. Less frames will support the idea of the

architects in designing the artistically glorious result.

http://www.glassfiles.com/


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A.7 ROLE OF GLASS IN GREEN ARCHITECTURE

Green building design criteria emphasizes the energy-efficient performance of

fenestration materials and maximum use of natural daylight. Given this

background, Glass is an indispensable material for green building. It has a

wide range of functional benefits. Its transparency allows day-lighting of the

interiors and integrates the interiors with the exteriors. Studies have proven

time and again that this substantially improves the productivity and health of

the occupants of the building.

Glass is completely recyclable and non-toxic in nature. It satisfies all the

ecological parameters of being the most sought after “green” building material

in Green Buildings. Moreover it harmonizes a structure with its environment.

Glass has varied “Green” benefits of which, some of them are:

Day-lighting - The use of glass brings in lot of light that helps in giving a

high amount of natural day lighting instead of depending solely on artificial

lighting thus reducing considerably electricity consumption.

Blending interiors with exteriors (Views) - Glass facades give a spectacular

view of the outside world from the cozy interiors.

Recyclability - Glass being recyclable satisfies the important parameter of

being a “Green” building material.

Achieving energy efficiency - High performance glass helps in controlling

the solar and thermal heat in the interiors and helps to maintain the

temperature at its minimum best and in turn helps to tone down the air-

conditioning expenses.

Innovative application - Being very flexible building material glass helps to

satisfy and capture an architect's utmost imagination in its shape and form.

Controls noise: Double glazed glass facades help in achieving a high

degree of acoustic comfort by keeping away noise penetrating from the

exteriors to the interiors thus ensuring a calmer atmosphere inside.

Self Cleaning: The future belongs to self-cleaning glass which keeps itself

clean on its own and brings out an ever sparkling effect.


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The Leadership in Energy and Environmental Design (LEED) Green Building

Rating System, developed by the U.S. Green Building Council (USGBC),

provides a suite of standards for environmentally sustainable construction.

The LEED rating system for Green buildings has six major areas of which four

have the potential to be tapped through appropriate usage of High

Performance Glass in design:

Sustainable sites

Water efficiency

Energy and atmosphere

Materials and resources High Performance

Indoor environmental quality Glass Impact

Innovation and design


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LITERATURE STUDY

WIPRO TECHNOLOGIES, GURGAON

Wipro Technologies Gurgaon Development Centre is the greenest building in

India and second greenest building in the world. The building has received 57

points and is Platinum rated.

Wipro Technologies, Gurgaon is designed by the eminent architectural firm,

M/s Vidhur Bharadwaj & Associates from Delhi.

Demographics

Plot size: 1.12 Acre

Building floor space: 175,000 sqft (incl of basement)

Benefit from proper use of glass:

Glass had contributed the following valuable points on LEED Rating:

1. More than 90% of the occupants in Wipro Technologies building, get

daylight and views of the outside which gave the building 2 points in Indoor

Environment Quality.

2. As per green building norm of Material & Resources:

a.20% of the total material should be locally manufactured.

In the case of Wipro Technologies: building the glass was procured locally.

This gives 1 point on the rating scale.

b.Glass has 15% recycle content plus it is 100% recyclable.

Recycle content has 2 points and Wipro got both.

3. By reducing energy requirement of the building by 50% on the base case,

Wipro could get 10 points.

Wipro Technologies reduces 51% energy on the base case. They opted for

high performance glass which reduced the energy requirement by 5.6%.

Summing up, in the case of Wirpo Technologies, glass contributed 2 clear

points and 13 combined points.


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CONCLUSION

Recent developments in societal needs and technology are creating

unprecedented challenges and opportunities in the use of glass in buildings

ranging from complex geometry to occupant safety and lightness /

transparency to energy efficient in buildings.

There is little doubt that the recent and future innovations in glass engineering

will improve the performance and will continue to extend the domain of what is

possible. The challenge for design engineers and architects is to select and

adopt these technologies not as fashionable add-ons, but at an early design

stage when decisions have the largest impact on the final design thereby

leading to optimised performance-based buildings.


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BIBLIOGRAPHY

Haldimann, M., Luible, A., and Overend M. “Structural use of glass, Structural

Engineering” International Association of Structural Engineers, 2008.

Hodkin, F.W., and A. Cousen. “A Textbook of Glass Technology” New York:

D. Van Nostrand Company.

Shelby, James E.” Introduction to Glass Science and Technology” Cambridge:

Royal Society of Chemistry, 1997

Watts, A. “Modern construction facades, Springer-Veriag/Wien, New York,

2005

ARTICLES & WEB REFERENCES:

Davidson, Adam. “Glass Ceiling.” Metropolis Magazine. 9 Feb. 2007

http://www.metropolismag.com/html/content_0200/gla.htm

Dutton, Hugh. “Structural Glass Architecture Opens up Possibilities.” Jun.

2001. National Glass Association. 9 Feb. 2007

http://www.glass.org/affprof/r_structural.htm

Glass to Glass System Specifications. Novum Structures. 25 Apr. 2007

www.novumstructures.com/novum/resources/specifications/download.htm

Innovative Structural Glass, Inc. 2007. 9 Feb. 2007

http://www.structuralglass.com/index2.html

Stairs, bridges and floors showcase the structural strength of laminated glass.

DuPont Laminated Glass News. 9 Feb. 2007

http://www.dupont.com/safetyglass/en/productServices/glasplus/2401.html

www.glassfiles.com

www.smartglassinternational.com

http://www.metropolismag.com/html/content_0200/gla.htm

http://www.glass.org/affprof/r_structural.htm

http://www.structuralglass.com/index2.html

http://www.dupont.com/safetyglass/en/productServices/glasplus/2401.html

http://www.glassfiles.com/

http://www.smartglassinternational.com/

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