Glass is one of the oldest man made materials whereas its use evolved from purely decorative to
architectural and structural. It has been used to enclose the space for two millennia and in this
period, it’s manufacturing and refining processes improved noticeably. While its structural
capacities was considered, particular treatments including annealing, tempering and heat-
treating was improved in order to enhance its structural characteristics. Although glass cannot
compete with steel in terms of strength or durability, but it’s the only transparent material with
the load-bearing capacity and high strength.
To accept glass not as a delicate material but as a structural material, we might ask ourselves
if we feel safe watching sharks through a thick glass panel in an aquarium or sail a glass boat in
the water, why not feel safe walking on a glass bridge.
Windows preceded the development of glass by several centuries; they were part of the
architectural aesthetics of buildings. “It was in Germany that the word ‘glesum’ meaning
‘transparent’ was first used, from which the word ‘glass’ came.” (Elkadi, 2006) The cylinder
method of making glass enabled the production of relatively large flat glass-panes. The
techniques for making stained-glass windows for cathedrals and churches were established in
Europe by the twelfth century. In the seventieth century, in the age of enlightenment and
Glass structures, from theory to practice
Taubman College of Architecture & Urban Planning, University of Michigan, Ann Arbor, MI, USA
ABSTRACT: In the last century and especially after the modern movement, the architects
emphasized more on the ‘lightness’ and ‘transparency’ of the buildings, pushing towards fully
glazed envelopes. Le Corbusier stated the glass envelope as the ‘minimum membrane’ between
indoors and outdoors. Today, architects are not satisfied by the natural illumination and
panorama views which is provided by the glass skins, but they are looking after something
more. They want to create the whole building, from the beams and the columns to the ceilings
and the roofs from glass. Their desire to use glass as a structural element has pushed the
architects and researchers towards conducting practical experiments on the structural capacity of
this material. Many all-glass prototypes and structures have been constructed in this regard.
Following the above mentioned desire, the main subject of this paper would be confined to
distinguishing of potentials and abilities of the glass structures. Thus after a quick review of the
historical procedure and the structural characteristics of the glass, glass structures are
categorized based on their primary establishing elements. Then the results on creation of
different architectural spaces and the built proposals are checked, concerning their form and
structural behavior. The objective of this study is to learn about experiences of the structural
glass masterpieces in the new age.
rationalism, clarity and quantity of light was favored by the use of clear glass rather than stained
The idea of glass architecture reaches back to 18th and 19th century greenhouses in England.
Crystal Palace (1852) was an important outcome of this horticultural movement. The
greenhouse proved ideal for experimenting with glass and iron. “After World War I and when
the modern architecture was born, Le Corbusier described his skyscrapers that raise immense
geometrical facades all of glass, and in term reflected the blue glory of the sky… immense but
radiant prisms”. (Elkadi, 2006) The developments in structural glazing took place after World
War II and high quality glass which was the product of new technologies became a key material
in the development of simple modern architecture. The development of the curtain wall in the
1950s and 1960s dictated a different image from that of pre-war architecture. “The production
of maximum office floor area, flexibility for office use, greater window area and lowest possible
costs were the main keywords.” (Elkadi, 2006) The idea of a suspended glass façade whereas
the glass was clamped and hung from a top edge was first used at the Maison de la Radio in
Paris in 1953. This attitude was followed in England with constructing the Willis Faber &
Dumas Building in 1975. Patterson in his book on structural glass states that the progenitor of
Structural Glass Façade or SGF technology may very well be this building by Foster Architects.
SGF is different from curtain walls in terms of supporting system. Aluminum extrusions are
generally used to construct a frame for the glass panels in the curtain walls, while in the SGF,
clear glass is often used without any framing element. The SGF came in to widespread use and
this trend continues today.
In recent years more aggressive application of glass as a structural material is seen. Many
research projects have been dedicated to the structural use of glass. Engineers are trying to
design load carrying glass elements by pushing the limits of glass strength to specify the
material in novel applications including floors, beams, walls, column and roofs.
3STRUCTURAL CHARACTERISTICS OF THE GLASS
Glass is a strong material in compression, but it is weak if the ‘surface cracks’ spread under
tensile loads. This brittle behavior of the glass makes it unsafe in structural design. Therefore,
the failure of the glass occurs at tensile stress levels long before it reaches to its strength
capacity. Any attempt to measure compressive stress generates tensile stresses, so an accurate
representation of actual allowable compressive stress is difficult to obtain.
In addition, Structures must warn before collapsing, to allow people taking protective actions.
“A good structure must warn by deformation, i.e. cracking noises or whatever signals that an
overload and fatal loss of integrity is imminent”. (Nijsse, 2001) To make glass safe, it must be
redundant (capable of carrying after failure of a major part) and not ductile. To add a ‘warning’
property, contemporary techniques have been developed including laminating and toughening of
Laminating or layering a glass is done by gluing panels of glass together. If a single crack
starts to grow in glass, there’s no mechanism to stop it and the crack will grow at a great speed
until it reaches to a free edge of the glass which ends up with the complete collapse of the
material. Therefore in laminated glass, if one panel is cracked or broken, it’s still glued to
another panel which is unbroken. In this case nothing falls down and the unbroken glass panel is
able to carry the dead load of the two panels. PVB and resin are two possible solutions to glue
layers of glass.
Toughening a glass is a process in which the glass is heated up about 600 degrees and then
cooled down quickly on the outer skin while the inside is still hot. After the process,
compression is created in the outside skin while a tensile stress is created inside. This makes the
existing cracks of a glass to be pushed closer and if it’s loaded, prevents the existing cracks to
open, grow and collapse.
The major challenge emerges when the construction components of this brittle material is
connected. “The connection must provide predictable and efficient load transfer to accommodate
the load path” states Patterson in his book on structural glass. Wurm has categorized connections
between glass elements, depending on the mechanism of force transfer, in to three categories:
‘mechanical interlock’, ‘force connections’ and ‘adhesive connection’. Bolted and bearing bolt
connections are considered as a mechanical interlock; a friction grip or contact connection is
considered as a force connection and finally using silicones and epoxy resins are some examples
of adhesive connections. In all cases, it’s important to have a uniform force transfer between
glass and connecting elements.
Due to the special treatments that can be applied to the glass, its resistance to mechanical and
thermal loads is improved considerably. By applying the appropriate factors of safety, glass can
be designed to work safe under the loads.
4STRUCTURAL GLASS ELEMENTS
The new technological methods that some of them were mentioned in the previous chapter,
enables engineers to integrate glass in load-bearing elements like beams, columns, roof and etc.
Thus their behavior in the structural context is explored in order to develop new applications
4.1 Glass beams
The concept of a glass beam was “in the air” in the 1980 states Nijsse. But who dare to put the
first glass beam in the building while clients have a tendency to avoid risky experiments
especially in the construction industry? Perhaps the introduction of a structural beam made of
glass is a good example of an accepted innovation. Wurm states that “depending on the number
and arrangements of supports, a glass beam can act as simply supported span, a continuous
beam or a cantilever”. A glass beam used in a glass floor is different from a glass beam which is
used only in a roof, as the floor is subject to foot traffic and needs to carry higher live loads in
addition to long-term loads. Also because of the extra ordinary slenderness of glass beam cross
sections, buckling is more likely to happen on them on other types of beams. Stronger and
stiffer interlayer materials could greatly improve buckling behavior of glass beams.
4.1.1 Case study: Courtyard roof of the International Chamber of Commerce, Munich
Perhaps the glass roof for the International Chamber of Commerce (IHK) in Munich which
was built in 2003 is a good example of a built-up glass beam technique in which smaller
component cross sections are combined in to a larger stiffer beam. (Figure 1) The architect of
this project is Betsch Architekten and the engineer is Ludwig Und Weiler GMBH. “Five main
beams are the primary load-bearing structure, each composed of thirteen individual glass fins
that spans roughly 14 meters, and the length of the secondary glass beams between the beam
axes is 2.2 meters.”(Wurm, 2007) The interlocking individual glass fins are 4.5 meters long and
they form a five-part cross section in the middle while a three-part cross section is formed at the
support end. The outer glass fins are heat strengthened glass while the inner fins consist of a
three-layer laminate glass. The depth of the segments is increased in the middle where the
bending moment increases.
Figure 1. Glass roof above interior courtyard at the IHK in Munich
4.1.2 Case study: Yurakucho station canopy
The Yurakucho station canopy in Tokyo is an example of a cantilevered glass structure which
was built in 1996 at the entrance of an underground railway station. The design is by Rafael
Vinoly architects with Dewhurst Macfarlane and Partners. The canopy is 10.6 meters long with
4.8 meters width. The height at the apex is 4.8 meters. According to Leitch, The canopy’s beams
were created by laminated glass and acrylic blades that decrease in number from four blades at
the base to one blade at the top. 40 milimeters diameter stainless steel pins attach the blades to
T-shaped brackets, making up the supports for the glass panels. The end result is a canopy roof
connected at the base by V-shaped stainless steel brackets which connect each cantilever to a
horizontal beam running the full width of the canopy.
Figure 2. Glass cantilever in Yurakucho station canopy
4.2 Glass Columns
Architects dislike columns, because they think they obscure views and interrupt space. Structural
engineers like columns because they think the more columns they design the less complex is
their structure! Maybe a glass column can be a solution to satisfy both sides. It has an ability to
create visual and sculptural feature without disrupting the openness of a space.
In general, a column may be difficult in terms of structural behavior. It may fail by crumbling,
buckling and breaking. If a column is made of glass, buckling will result in tensile stresses and
the miniature cracks will lead the whole structure to fail.
4.2.1 Case study: Saint-Germain-en-Laye Town Hall
One of the first glass columns was built in a glass patio of the French town hall, Saint-
Germain-en-Laye, near Paris in 1994. The new administrative office is covered with a700 m2
glazed roof supported by cruciform glass columns. (Figure 3) A large glass cone penetrates the
roof supported and surrounds a single living tree in the center of the courtyard. Each column is
capable of bearing a weight of 50 tons and is made from a load-bearing sheet of laminated glass
15 mm thick by 20 cm wide, held in a sandwich between two protective glass layers of the same
thickness. The structural layer of glass is recessed from the edges of the adjacent panels for
protection. The cross is constructed of one continuous glass panel to which two shorter pieces
are glued. According to Rob Nijsse, there was sufficient redundancy in the design that if one
column should fail, the steel roof system would be able to self-sustain until the damaged column
was replaces. This is probably due in part to the steel tension ring around the patio. (Nijsse,
Figure 3. Glass columns in French Town Hall
4.3 Glass floors and bridges
Walking on a glass floor is both a fascinating and scary experiment. Slipping on the glass floor
is an issue imposes an impact on the glass surface. According to Leitch, there exists a slip test
that involves sliding a sample of shoe rubber across a glass surface and measuring the amount of
energy that it absorbs. This test is supported to simulate the slipping action of the pedestrian
heel. The design of a glass floor depends on the type of traffic and the location of the bridge.
The glass must be kept safe from scratches or impacts that tend to increase the tensile forces.
4.3.1 Case study: National Glass Centre
The National Glass Centre in Sunderland, UK by Andrew Gollifer Associates, has a glass roof
that people can walk around and look down in to the centre below. (Figure 4) There is a total of
3250 square meters of glass on the roof and it can hold 4600 people on at any time. Each glass
panel on the roof is 6 cm thick. To ensure safety, laminated glass was used in a 4 lite of 8 mm
configuration for the 1.25 square meter panels. Each lite of glass was bonded by a 1.52 mm
thick layer of PVB foil. This was the first instance of heat-strengthened glass for flooring. “To
reduce slippage, ceramic granules were fired onto the top surface during the heat strengthening
process. About 40% of the glass surface was covered with the abrasive surface to improve
safety, yet maintain translucency. The dots created by the surface treatment also psychologically
served to reassure those who were reluctant to across the floor”. (Leith, 2005)
Figure 4. The glass bridge of the National Glass Center
4.4 Glass domes
A glass dome that provides a view without interruption through the sky is a dream. The 19th
century glasshouses mostly had domes made of steel and glass. Although the glass was
providing transparency to the interior space, the steel structure was the main supporting system
and the glass panes were usually providing stiffness for the whole structure. Designing the grid
geometry in terms of mesh size and geometry is an important factor in designing the glass dome
grid. Besides, glass can be used for structural elements that are in compression while steel can
be used for the structural elements in tension.
4.4.1 Case study: Stuttgart Glass Shell
Following the glasstec 2002, a research was undertaken by Lucio Blandini at the ILEK
institute of the University of Stuttgart, Germany. He had the idea that it might be possible to
build a frameless glass dome while using adhesives as the joint between the different glass
panes. The end result of his research was a built structure of a frameless glass dome with a
diameter of 8.5 meters and a rise of 1.76 meters. (Figure 5) According to Aanhaanen, this
minimal structure was built in three months using an advance movable scaffolding system. This
was needed to precisely position every glass pane before the adhesive was put in place. After the
connections were made, the scaffolding could be lowered all at once to make sure to start
loading the entire shell simultaneously. The structure proved itself in a snowy winter and it
remained strong although the adhesive is considered weaker in low temperatures.
Figure 5. The glass dome by Blandini in ILEK
Architects and engineers are inspired to use glass to create not only transparent spaces, but also
illusion and wonder. The combination of being protected from natural forces as well as
maintaining view to the outside, is a unique characteristic of the glass which merges exterior
and interior. The desire to use the structural capacity of the glass spreads among the architects
and engineers, and they started to push the limits in this regard.
Despite the high strength of the glass and the advances in the technology, it’s still susceptible
to concentrated loads and the development of local stresses. Its behavior in different
temperatures and under impact loads must be examined. Failure of a glass must always be
considered as a likely problem and essential extra cares must be taken in this regard. While
failure in every case might have dramatic affects, there’s a difference between failing a glass
column comparing to a glass roof. If a glass column fails, it tends to affect the whole structure,
imposing extra loads to the adjutant columns whereas in the case of a glass pane’s failure, it can
easily be replaced with another pane.
All in all, the advantages of using the glass structures in domes and roofs of the buildings far
outweigh the disadvantages. The glass skin maximizes the natural light which results in
increasing the humankind’s mood and productivity as well as connecting to the environment.
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