Glass in Architecture

INNOVATIVE TECHNOLOGY IN THE FIELD OF GLASS ARCHITECTURE

THESIS REPORT

CONTENT PREAMBLE----------------------------------------------------------02 ACKNOWLEDGMENT--------------------------------------------03 INTRODUCTION---------------------------------------------------04 JUSTIFICATION----------------------------------------------------05 SCOPE AND LIMITATION OF WORK---------------WORK------------------------06 --------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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THESIS REPORT

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 will be of some help help for Students, Architects, Engineers Engineers and others who would want to bring about a change and advancement in the construction technology.

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THESIS REPORT

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 will be of some help help for Students, Architects, Engineers Engineers and others who would want to bring about a change and advancement in the construction technology.

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THESIS REPORT

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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THESIS REPORT

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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THESIS REPORT

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 wellbeing 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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THESIS REPORT

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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THESIS REPORT

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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THESIS REPORT

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. 8




THESIS REPORT

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. 9


THESIS REPORT

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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THESIS REPORT

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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THESIS REPORT

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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THESIS REPORT

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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THESIS REPORT

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, semiprotected / transition spaces and screens from wind and rain in temperate marine climates where thermal mass and insulation are less important.

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THESIS REPORT

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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THESIS REPORT

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-byproject 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. 16


THESIS REPORT

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. 17


THESIS REPORT

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 of fully toughened glass illustrating the low post-breakage capacity.

Laminated glass composed of two sheets of annealed glass illustrating the 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 postfracture limitations of glass and the increasing severity of normal and exceptional loading conditions by developing a wide range of new products. 18


THESIS REPORT

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 ch emically 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 tha t 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. 19


THESIS REPORT

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 preand 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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THESIS REPORT

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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THESIS REPORT

• 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. 22


THESIS REPORT

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. 23


THESIS REPORT

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. 24


THESIS REPORT

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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THESIS REPORT

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, texturefree 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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THESIS REPORT

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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THESIS REPORT

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. 28


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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.

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Blending interiors with exteriors (Views) - Glass facades give a spectacular view of the outside world from the cozy interiors.

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Recyclability - Glass being recyclable satisfies the important parameter of being a “Green” building material.

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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 airconditioning expenses.

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Innovative application - Being very flexible building material glass helps to satisfy and capture an architect's utmost imagination in its shape and form.

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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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THESIS REPORT

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:

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Sustainable sites

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Water efficiency

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Energy and atmosphere

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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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Glass in Architecture

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