arc 542 membrane structure.docx

7/28/2019 ARC 542 MEMBRANE STRUCTURE.docx

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Abstract

Membrane structures are hugely popular in architectural design and are

increasing in their abundance within buildings. There is an increasing trend

concerning the use of membrane structures within architectural design. It is

important to recognize the reasoning behind the growth in popularity: why

are so many architects starting to use the design feature within their

designs? The features of the membrane structure have been provided; an

analysis of the strengths and weaknesses provides strength to the reasoning

behind its use. This study examines a variety of different factorsconcerning the membrane structures. It provides a detailed study of the use

of membrane structures within building design; additionally, all of the

different contributory factors have been referenced, such as the structural

components and mechanical usages. Much primary and secondary research

has been referenced to illustrate the breadth of the topic.

Membrane structures have been used in architecture for over 50 years;

therefore, there is a large back catalogue of research papers that focus on

them. The study follows a case study structure and uses 12 examples of

membrane structures within architecture. Each case study provides a real-

life example of how membrane structures have been successfully applied tomodern day architecture. Additionally, it examines the complexity behind

the construction of membrane structures and materials. It is important to

understand the structural components that make it so appealing to


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architects. The associated advantages and disadvantages of membrane

materials have been examined. Furthermore, the relationship between the

construction components and the integrated design has been mentioned. All

of these factors provide a strong understanding behind the use of membrane

structures, explaining how they can be used and why they are becoming so

popular.

IntroductionMembrane Structures

Membrane structures consist of thin membrane or fabric as a major

structural element. A membrane has no compression or bending stiffness,

therefore it has to be prestressed to act as a structural element. Major

applications of membrane structures occur mainly in large span lightweight

roof structures, temporary buildings such as tents and shelters. The

analysis, design and construction of such structures is a field that has

developed very considerably during the last 50 years.

Membrane structures are one form of architectural feature that arebecoming hugely popular within modern day engineering. They are

becoming majorly prominent in many designs. Although they have been

used in architecture for over 50 years, their use an aesthetic and ergonomic


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feature is becoming more apparent. Much of society is unaware of the

detailed specification behind the membrane structures. The complexity of

the construction process, involving all of its contributory materials, is

unknown to many people within the industry.

The history of membrane structure

A German designer by the name of Professor Frei Otto amazed architects

from around the world with his design of the Pavilion of the Federal Publicof Germany for the EXPO held in 1967 (Roy, 1967). At the time it was

standard to observe structures composed of steel and glass. Professor Freis

membrane structure was lightweight, slim and soft which provided

something new and fresh to the architectural field. His design was also very

different from any other designs at the time, as he used curved surface

areas which were made brighter due to the translucency of the membrane

material.

Membrane structures that closely resemble tent like structures came from

Germany. These were sturdy and reliable structures that quickly came to

form a vital aspect of modern day architecture which quickly spread across

the globe. Even in present times these structures are still regarded as veryreliable and still well suited to specific types of structures.


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In an essay he wrote in 1961, Professor Otto argued that buildings should

not be viewed or designed as fixed structures into which people can be

squeezed into. He further put forward his viewpoint that buildings should

grow along with us, and be renovated in such fashion. Otto stated that the

minimal structural material developed through extensive research was also

present in the natural environment, and that it was possible to utilize

properties present within organists to produce aspects of the membranes.

(Koch, 2004).

Otto reminded the world that although tents had been in existence for over

30,000 years and are considered as easy to construct, they are in fact

extremely difficult to structure correctly and that precise tent construction

is among the most difficult methods of construction.

Otto and his colleagues published an article in 1965 known as

Spannweiten, which detailed all of their findings in the research of

membranes structures from an architectural perspective. This paper

received attention from academics and experts in the field from across the

globe. Otto went on to work with other experts at the institute for

Lightweight structures where advancements in technology were made.These advancements were put into practice when the German Pavilion was

constructed for the 1967 Expo in Montreal (Roy, 1967). This building went

on to significantly shape the worlds knowledge of membrane structures


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and symbolized the latest advancements in this technology across the

globe.

The 1970 Expo was held in Japan. Rather than use structural forms

traditional to Japan, the architects decided to use membrane structures for

many of the constructions. Although the Expo showcased the reliable

potential of the membrane structures, they were not widely favored until

many years later (HeeKyun, 2005).

Numerous designs for membrane structures were put forward for The

USAs entry for the 1970 Expo. David Geigers design was accepted as it

was seen as more realistic as well as aesthetically pleasing to the eye. His

idea was to use a low profile air supported membrane for the structure of

the US Pavilion.

The US Pavilion was required to meet safety standards and therefore it was

designed so that in the event that the membrane structure did deflate, it

would not intrude on the spectators seating area or the field. This design

was hailed as further advancement in the development of membrane

structures that potentially allowed the development of air domes. Future airdome structures used the US Pavilion as a model for their designs.


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From 1970 it was the USA that led the way in terms of research and

investment into membrane structures. This paid dividends as Geiger Berger

associates made many new developments within the technology throughout

the 1970s. One such development was the use of PTFE coated glass fiber

membrane as a new membrane material. This material made it possible to

construct enduring, fixed membrane structures throughout the USA(Brown,

2001).

Famous early air dome structures in the USA were the Steve Lacy FieldHouse at

Milligan College which was built in 1974 and the Thomas E. Leavey

Activities Center at Santa Clara University which was built in 1976. These

were hailed throughout the USA as brilliant designs fit for purpose, and it

was these buildings which sparked a high demand throughout the USA for

air dome structures to be built(Mewes, 1993). Entertainment and stadiums

were hugely popular in the USA and they wanted these Domes to protect

them against all types of weather and to be capable of hosting a large

capacity of people. One example of these stadiums that successfully

utilized this technology was the Silver Dome of Pontiac city which was

constructed to be able to seat 80,000 spectators.

Before the construction of these air Domes, large scale spaces were

associated with negative characteristics such as shadowy and stuffy.


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However, this all changed with membrane structures which made it

possible for light to spread around the entire complex. Another great

advantage of the membrane structures are that they could be constructed

very economically, which is why they grew so rapidly throughout the USA

(Mewes, 1993). However, membrane structures used for air domes were

not without their problems. There were a significant number of structural

accidents, the costs associated with continual inflation was high and it was

complicated to control the inflation pressure. As such in the 1980s,

alternative viable structural techniques began to be investigated.

By the mid 1980s membrane structures were not just used to make spaces

bigger, but they had evolved to combine beauty with unique structural

forms. Buildings using this evolved technique included the Lindsay Park

sports center built in 1984 and the Chene Park Amphitheater built in 1990.

Additionally, membrane structure also began to be mixed with glass in

order to generate bright filled spaces (Kaltenbach, 2004). This technique

was particularly prevalent in shopping malls.

The air dome as the dominant structure in the USA was replaced towards

the end of the 1980s by the tensegrity dome which used an efficientsystem of cables and posts to securely cover large spaces. Examples of

buildings utilizing this new method at the time included the Redbird Arena

constructed in 1988, the thunder dome constructed in 1989 and the Georgia


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Balanced from a space frame acting as a compression ring, the membrane

structure of the Rome Olympic Stadium was a bright roof which utilized a

combination of a cable structure and a membrane structure. This was roof

was not only visually pleasing to the eye bit it also did not weigh very

much compared to structures that were used in the past. Other stadiums

such as the San Nicola

Stadium built in 1990 and the Gittlieb-Daimler stadium built in 1993 also

sought to use membrane structures to produce both beautiful and well lit

stadiums with their own blend of creativity (HeeKyun, 2005).

As developments were made in technology, PFTW coated glass fiber fabric

came to replace the PVC coated polyester fabric as the material of the

membrane structures in Europe (Kaltenbach, 2004).

There was too much replication of membrane structure designs according

to Frei Otto, and it was not until alternative framing techniques were

developed and that the structures were produced on a greater scale that

many individualist and creative form emerged.

Although Japan used membrane structures within the Expo that they hostedin 1970, there was not much demand for these types of structures in the

immediate years following this Expo. This was because Japan already had


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a uniquely aesthetically pleasing design style and because they were not

used to constructing suspension structures.

This situation changed quickly in the 1980s as design competitions were

hosted in Japan. A lot of the entrees in these competitions provided very

imaginative designs utilizing membrane structures and as such numerous

amazing structures utilizing this method began to be developed throughout

Japan. As this happened many architects began to realize how

advantageous membranes structures could be. Buildings were designed

with membrane structures which served to spread light to specific parts ofthe complex. Additionally, membrane structures allowed indoor crops to be

nurtured by the natural light which was filtered through, and as such the

position of the these plants were also factored into the blue prints of the

structures(HeeKyun, 2005).

Increasingly imitation of structures is become more prevalent around the

world. This was due in part to modern technology and the increased speed

of communication that this technology allows. When advancements in

design are found in one section of the globe, they quickly spread to other

parts.

Structure, Construction Method and Membrane Material


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A construction that directly utilizes the elements of membrane materials is

known as a membrane-structure building. Either a cable frame or a

skeleton frame can form the structure that sustains the membrane. It is

possible for a structure on a small scale to consist of the membrane itself as

the structural material. However, such a process is not possible on a larger

scale structure because the membrane is not strong enough. If used on a

large scale construction it is essential for the membrane to be strengthened

somehow or used in conjunction with a frame (Smith, 2001).

Membrane materials have enough strength to be directly linked to the main

frame unlike other roof materials. A membrane material has a natural

tendency to curve, and although it can endure tension, it cannot withstand

compression or bending. It is a complex task to make a curved surface

using tension, and the process of designing the membrane structures is

dependent on utilizing the tension in a precise fashion (Kaltenbach, 2004).

In the early days it was believed that membrane structures could only be

designed with mechanics in mind and that there was no room for creativity

in the design. However, it was later discovered that although the curved

surface is subject to specific mechanical requirements, there is much roomfor individualistic touches on the periphery of the surface area. Even so it is

important to note that the periphery must still be supported either with

cables or a frame.


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An architect, who is used to working on traditional structures, may find it

helpful to use a skeleton-frame membrane structure when constructing a

membrane structure. This is because the membrane is able to be extended

over steel, word or even a reinforced concrete frame in order to shape the

space (Herzog, 1996).

Balloons actually provided the inspiration for air inflated membrane

structures. Although F.W. Lancheser of England may have been first to putforward the idea for a field hospital, it was the Radar Dome built in the

USA in the year of 1946 that was actually the first time that this structure

had been created for a building on the ground. Following the success of this

dome, similar structures were replicated across the private sector in the

USA. As more of these structures were seen, international interest in these

structures significantly increased.

It is theorized that the use of membranes as structures were used over

30,000 years ago for the tents used by Nomadic tribes. Since these times,

the technology involved with membrane structures has been ever

increasing. These days, membrane structures are now as safe and durable astraditional buildings. This is due in part to the materials that form them.

Synthetic fibers and glass fibers are now utilized and coating materials

have enabled the structures to contain both water and fire resistant


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qualities. Advancements have been made and there are many advantages to

using membrane structures including their qualities of transparency, low

weight and their ability to be applied to frames for large scale spaces. For

instance, it is now possible to cover a large space that would not be

possible with traditional techniques with just one sheet of membrane

material (Kaltenbach, 2004).

However, it must be recognized that membrane materials are not simply

suited for all projects. If just one thin sheet is used then it will be difficultto adequately protect it from tearing as well as being difficult to provide

insulation for heat and sound

Advancements in the materials of the membrane structures have been

continually been made.

Significant advancements have included the industrialization of PVC in

1933, the development of PTFE in 1938, the industrialization of Polyester

fiber in 1947, and finally PTFE coated glass fiber fabric which was

developed in 1972(Mewes, 1993).

PTFE coated glass fiber fabric is considered a fixed long lasting building

material. It is incombustible, strong and durable, as well as having the

advantage of being self-cleaning. In contrast to previous membrane


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materials, PTFE coated glass fiber fabric is not designed to fold or to

detach from its support.

A critical advancement in the development of membrane structures has

been a material known as PTFE coated glass fiber fabric which is very

similar to stainless steel in terms of its durability. Its development as a

material increased the potential of membrane structures to be applied in a

many more circumstances.

However, when this material was first introduced and used in the

construction of permanent buildings in the 1970s, there were doubts in

some quarters regarding the enduring features of the material. In fact some

believed that over time the material would begin to crumble. However, as

of yet there is no sign as of fragmentation in any of the buildings in which

it was used. However, PTFE coated glass fiber fabric is not always favored.

Despite problems with its durability and the tendency for the material to

become easily dirty, there is a high demand for PVC coated fabric of

synthetic fibers as a membrane material due to its cheap rate of production

and the fact that it can be folded (Mewes, 1993).

Membrane structure design techniques are established on allowable unit

stress where the figure of 4.0 as a frequency is internally accepted as the

safety factor for a membrane material (Clough, 1995). Although this figure


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is not as safe as it could be, it is considered adequate as it takes into

consideration the potential decline in the strength of the membrane

material. This safety factor is very low and is possibly only accepted due to

the economical costs associated with this material. In the past damage has

occurred due to tearing in the membrane material. Such tears begun in

small specific areas of the material. In order to ensure adequate safety, the

design of the membranes must consider every detail (Berge, 2001).

Characteristics of Membrane Structures

1. Larger Span

In 1985 a tennis court with a height of 15m and 45.2m span was built in the

International Sports Expo in Japan. In the same year, The Calgary Stadium

was built in Canada, which is 36.5m in height, 112m in span and 11150 in

covered area. In 1988, the Tokyo Dome was built, which is 201m in span

and 56.19m in height. The Georgia Stadium built in Atlanta, US has a

major axis of 235m, has a minor axis of 186m and is 79.24m in total

height. Based on pertinent data, it is speculated that the larger the span of a

building, the better the application of membrane structure will embody itseconomy (Brown, 2001)

2. Beautiful design with fashion sense


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Membrane structures which break through the structural form of traditional

building, is easily manipulated into various types of shapes and is rich in

color. Therefore they are easily formed into night scenes with the

coordination of light. This brings modern beauty to people. What is more,

in combination with technological progress, membrane structures are

known for use in hi-tech modern buildings; the buildings in 21st century.

3. Reduce energy-consuming

Membrane material is relatively good in transmission of light. It has a light

transmittance of approximately 7% to 20%, thus full use can be made of

natural light. During the daytime, without any artificial lighting provided, it

can completely satisfy the needs of various athletic contests. In addition,

membrane material with a reflective index of light over 70% can form a

soft scattering of light in a room with sunlight in order to make people feel

comfortable and dreamlike.

4. Rapid construction speed

The tailoring of diaphragms, the manufacturing of steel cables, steel

structures etc. are finished in factories, and can be used in combination

with lower reinforced concrete structures or structural components. Only


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linkage, installment, positioning and stretch-drawing of steel cables, steel

structures and diaphragms are carried out on the construction site, thus the

installment of construction on site is relatively easy, quick and convenient.

5. Apparent economic benefits

Although, presently construction projects with a membrane structure

require an initial and once-off high investment, the daily maintenance cost

on this type ofstructure is negligible (hence the label free maintenancestructure). Thus, in the long-term, the economic benefits are quite

apparent. If this type of structure is applied to buildings with a super-large

span, more obvious advantages in price will be seen. The economic

advantages of membrane structure are positively proportional to the spatial

span of a building and the technical difficulties associated with

construction.

6. Safety and reliability

Membrane structures are light-weight and its earthquake resistance is

relatively good. Soft membrane structures can tolerate of a huge amount ofdisplacement and overall collapse of building is uncommon. In addition,

membrane material is generally a flame-retardant material. The fire hazard

is minimal.


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7. Easily made into a detachable structure, easy to transport, and can

be used for touring performances, exhibitions and etc.

For example, a music studio designed and made by a company in America,

covers an area of over 300m. However its dismantlement and re-installment

only takes six hours.

_

8. Broad scope of application

From the perspective of location, membrane structures are from Alaska to

Saudi Arabia. The scale of the structures range from small one-man tents

and garden pieces to large buildings that cover with thousands even

hundreds of thousands squared meters of area. Some have even imaged

conceived a small city make of membrane structures.

Basic Properties of Membrane Material of Building

1.Composition and Classification of Membrane Material

The development of membrane structures is closely related to research on

and the application of membrane structure. From early examples such as

PVC, PTFE to the later ones such as ETFE membrane material, the


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development and application of each new type of membrane material has

sharply impacted upon the development of membrane structures.

Contemporaneously, the application of construction membrane comprises

two categories of membrane; a coating fabric and a thermoplastic

compound.

2.Coating Fabric Membrane

Coating fabric membrane material is a type of composite material and isgenerally composed of a substrate, coating and surface course, shown in the

fig. 1. below. A substrate is weaved through various textile fibers which

determine the properties and structural mechanics of the membrane.

Coating and surface course can protect the substrate, and are designed to be

self-cleaning, protect against pollution, and durable. Examples of Common

coating fabric membrane materials include glass fiber membrane materials

made from Teflon coating (generally called PTFE membrane material) and

glass fiber membrane material made from PVC coating (generally called


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PVC membrane material).

Fig. 1. Compositions of Coating Fabric Membrane Material

PVC membrane material is cheap and is divided into several colors such as

white, red, blue and green. It is applied broadly. Soft membrane material

with good tensility is easy to make and to stretch, thus it is easily adaptable

to tailoring errors. However, its durability and self-cleaning properties are

poor. Its properties will change due to outward movement of the coating

mold-increasing agent and ultraviolet effects so that its surface gradually

turns yellow and sticky over time. Moreover, dust and dirt in air are

attached to membrane surfaces and stain the surface and thus reducing light

transmittance. Thus, its service life is decreased. In order to improve the

durability and self-cleaning of this type of membrane material, a PVF or

PVDF surface course can be added to the surface of coating.


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PTFE membrane material has good durability and does not turn yellow or

moldy in the atmospheric environment. Additionally, rainwater will flow

away after forming water drips on the surface as it has good self-cleaning

properties. However, PTFE membrane material is more expensive and is

stiffer. Thus, the folding &rolling of material during transportation and

construction can lower its strength, the convenience of construction of the

membrane material is poorer, and consequently refined calculations are

required during design and tailoring processes.

Substrates of membrane material are weaved into using glass fiber or

polyester fiber yarn. Glass fiber has a certain flexible capacity and a higher

elastic modulus and strength than polyester fiber, however it gradually

becomes smaller. Therefore it does not age well nor does it have a long

service life.

However, due to its brittleness, glass fiber should be processed precisely,

treated properly and carefully. It should be borne in mind that humid and

hot environments an impact on its mechanical property. Polyester fiber, on

the other hand, has a longer life, deformation and it is easy to install.

However, long-term tension and ultraviolet light will gradually result inruffles on the membrane surface. Perception and light transmittance are

both affected over time.


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Basic methods of weaving yarn into substrates of membrane material are

plain weave or panama weaves. Plain weave, also called as basket weave,

is a process that warps yarn tightly to be straight line while weft yarn

crosses upper and lower parts to bypass warp. Warp yarn is weaved

orthogonally at a right angle to weft yarn, shown in Fig. 2. Plain Weave has

several variations of method. For example, weft yarn can bypass a warp

yarn from below, then three warp yarns from top. When the knitting

tightness is relatively high, a substrate of plain weave with relatively high

tensile strength is easily treated directly by a liquid coating agent.However, more coating materials are needed when the thickness of the

substrate equals that of nearly three-layer fiber yarns. In contrast to plain

weave, several fiber yarns can be weaved one time, shown in Fig. 2a. As

shown in Fig. 2-2. And Fig. 2-3. Panama Weave weaves two or three yarns

at one time in the warp direction and the weft direction. When the same

fiber material yarns are adopted, membrane material made using the

Panama Weave can weave several yarns one time. Furthermore, its

mechanical properties are better than that weaved by single yarn in plain

weave.

a) Plain Weave b) Panama Weave


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Fig. 2a. Weaving Methods of Yarns in the Substrate of Fabric Membrane

Materials.

Common resin coating materials include PVC and PTFE. The earliest

application used was PVC which has relatively good flexibility and is easy

to process. However, it reacts poorly to ultraviolet light, thus chemical

changes are common following long-term exposure to sun. Furthermore, it

is a poor self-cleaning material. Therefore, membrane materials externally

coated with PVC are generally applied in temporary structures. However,PTFE is an inert material and thus does no react to exposure to ultraviolet

light. Furthermore, PTFE has a long life in terms of light transmission and

self-cleaning, fire-retardation. In addition, it is not flammable and its

opaque color (initially cream-colored) endures over a long period (25-

30years). Thus, it is commonly applied in permanent constructions.

3.Thermal Polymerization Compounds MembraneMaterials

Thermal Polymerization Compounds mainly refer to ethane-ETFE, and are

often applied in buildings with high light transmittance and rich models. Incomparison to coating fabric membrane materials, ETFE membrane

materials are lighter and thinner, and light transmittance reaches up to 95%,

and thickness is often smaller than 0.3mm (Kaltenbach, 2004). Although


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the strength of ETFE membrane material itself is high, its thickness leads to

common applications of the material in inflatable membrane structures.

These are structural entireties composed of several two-layer or three-layer

air mattress units with a span of usually not more than 5m.

4.Physical properties in building of building membrane properties

As a type of structural form with intensely artistic expressions, the higher

degree of physical building properties of membrane materials should alsosatisfy the needs of the membrane. Physical building properties include

several aspects such as weather resistance, optical property, acoustic

property, thermal property, and fire-resistance property. During the design

of membrane structures, the physical architectural properties of each type

of membrane material, in combination with the overall properties of

membrane structure should be fully understood. Proper materials should be

chosen to correspond to the designs in order to obtain optimal architectural,

economic and technical effects.

5.Weather resistance of membrane materials

Membrane material, as the covering system of building, is often directly

exposed to the external atmospheric environment. Thus it is affected by

natural phenomena such as daylight, temperature variation, rain wash and


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dust erosion. Thus, the appearance and color, brightness and strength of the

material all gradually deteriorate over time. The weather resistance of

membrane material is a comprehensive index that outlines its years of

service, its aging resistance, self-cleaning ability and intensity attenuation.

Coating materials such as PTFE and PVDF on the surface of membrane

material stem this process. Both are inert materials, thus their chemical

properties relating ultraviolet protection, aging resistance and corrosion

resistance are better than those of PVC coatings. In general, the serviceyear of a PVC membrane material with coated PVDF surface course is over

25 years while the service year of PVC membrane material with coated

PVDF surface course is 10 to 15 years. Therefore, membrane material can

be broadly used in permanent buildings (Kaltenbach, 2004).

At present, weather aging experiments are often undertaken to evaluate the

weather resistance of a membrane material. Generally speaking, tests

investigating the effect of natural climate aging and of artificial weathering

aging are conducted. Laboratory tests often adopt artificially accelerated

climate aging experiments, referred to as Xenon lamp aging experiment.

The light source of the xenon-arc lamp is adopted to continuouslyilluminate the membrane while temperature, humidity, radiant energy,

rainfall cycle and time are controlled to imitate and strengthen principal

environmental factors such as light, heat, oxygen, moisture and rainfall. In


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natural climate conditions the speed of aging of a sample and the

differences of a samples tensile strength underradiant energy over the

course of time is regarded as an indicator of weather resistance.

6.Optical property of membrane material

The optical properties of membrane material refer to of the effects of

membrane material on light of various different wave bands, including such

properties as reflection, transmission, absorption and scattering. Differentmembrane materials display large differences in reflection, absorption and

transmission of light in each wave band. In general, membrane material has

relatively good light transmission. Light transmittance of natural light of

fabric membrane material can reach 20%. However, in double-membrane

buildings, built in accordance with relatively high thermal heat-insulation

properties, light transmittance reaches 4% to 8%. However, the light

transmittance of ETFE can reach 95%, which exceeds that of clear glass

(Kaltenbach, 2004).

Inside membrane structure buildings transmission light produces uniformly

diffused light. The light has no shadow, no dazzle and no significantdirection, thus it is gentle and uniform. During daylight hours, it will satisfy

the light requirements of various indoor activities. Therefore, membrane

structures are especially applied to buildings that demand higher lighting


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specifications, such as sports facilities, exhibition halls and patios. In

addition, during the night, the surface of buildings with membrane

structures can give off a soft light, which can be advantageous in terms of

adverting and in increasing the ease with which buildings are identified.

When interior lighting is used, lamps should be kept at a proper distance

from membrane surface to prevent the heat given off by lamps from searing

the membrane surface.

7.Acoustic properties of membrane material

The acoustic properties of membrane material are similar to its optical

properties and include reflection (reverberation) and transmission loss

properties for the various frequencies of sound waves. Reverberation and

sound absorption properties comprehensively determine the quality of

audio and the soundproof properties of buildings with membrane

structures. Single-layer membrane material has poor acoustic properties

and can result in strong echoes and weak sound absorption. In addition its

soundproof volume is also lower than that of a general palisade structure.

With respect to the vibration of sound waves, membrane material fabrics

have very strong reflectivity which increases the noise level inside

buildings with membrane structures. Buildings with inner concave, in


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particular, such as air supported membrane structures or arch supported

membrane structures, the ceiling can collect the reflection of sound waves

to further impact upon the indoor acoustic environment. However, this

relatively poor sound insulation capacity determines that membrane

structures are not applied to building facilities that demand high noise

reduction.

In general, corresponding architectural measures need be taken to improve

the acoustic environment of buildings with membrane structure. Forexample, the addition of a light and poly-porous bottom cloth to the

membrane can effectively reduce reflection of sound wave and increase

attenuation of transmission of sound waves. Perhaps an acoustic screen

which is hung on the ceiling of membrane structure can increase the

absorption of sound waves. Changing the curved shape of ceiling so that

direction of reflection is changed will also have an impact. Furthermore,

specialized sound-absorption membrane lining can apparently lower

reverberation to increase sound absorption. This has produced good results

in the Georgia Dome and New Denver National Airport where such lining

has been applied. However, when choosing these technical solutions, we

must fully consider the impact of these methods on the performance of themembrane structure in relation to lighting, and fireproofing, for example.

8.Thermal properties of membrane materials


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The thermal insulation performance of buildings with membrane structures

is poor, and at present widely used membrane materials cannot limit the

impact of internal environment very well. The heat transfer coefficient of

single-layer membrane material is large, and refrigeration-consumption is

also high. Therefore, it is only applied to open buildings or in areas with

warmer climate.

When the thermal insulation property of a building is required to be high,

two-layer or multi-layer membrane structure can be adopted. In general,there should be a 25-30cm air buffer between two membranes.

Cold condensed dew inside the membrane surface is also a problem that

needs to be considered. When a membrane structure is applied to buildings

with larger sources of interior humidity such as swimming pool or a

botanical garden for example, damp air easily turns into dew on contact

with the internal surface of membrane. Therefore, measures such as indoor

ventilation, installation of a cold condensed water drain or air circulation

system should be taken.

9.Fireproofing performance of membrane material

Membrane has a good fireproofing performance. The substrate of

membrane material is itself non-inflammable or flame retardant. Glass fiber


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is non-combustible material while polyester fiber is non-flammable

material. When membrane material is applied in half-open buildings such

as the grandstand tent of stadium, the awning of public facilities and

architectural art sketches and in temporary structures fireproofing safety

need not be taken into consideration. However, when membrane material is

applied in a roof system of totally enclosed and permanent buildings, as the

fireproofing of a membrane material in terms of fire-proofing, smoke

volume, toxicity and structural collapse should be comprehensively

considered in order to judge its fire-proofing performance compared totraditional fire-resistant and fire-proofing methods. In enclosed buildings,

utilization of PVC membrane material simply cannot be denied.

After a fire is lit, PVC membrane material is burned through in the third

minute and twelfth second to form an open hole corresponding to the size

of contact surface of flame. Thanks to this hole, heat, smog and gas can be

automatically excluded. This open hole remains until the fire is

extinguished. Early occurrence of the hole results in the emission of heat &

smoke from the building and postpones the collapse of the steel structure,

which is beneficial for staff in public places as more time is given to

evacuate. In comparison, PTFE membrane material only crazes at the jointof membrane surface in the third minute and 35th second after fire is lit,

and finally comes off in chunks along the joint (Kaltenbach, 2004). It is

found from test analysis of interior membrane buildings that the volume of


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CO and CO2 from PTFE membrane material is at least over double that of

PVC membrane material. PTFE membrane material also produces the toxic

gas HF at a level that exceeds critical concentration while PVC membrane

material when burned through does not show evidence of HF. Therefore, it

is concluded that the fire-proofing performance of PTFE judged by

membrane material in accordance with certain standards does not conform

to the practical reaction of membrane structure under fire hazard; therefore

PVC membrane material is better (Kaltenbach, 2004).

Maintaining the stability of the framework of membrane structure in thecase of damage of membrane surface is one another noticeable issue

connected to the fireproofing of membrane structure. In a membrane

structure the membrane material is force-carrying material. Therefore,

regardless of whether the membrane material is burnt through or comes off,

it is always the first part to be damaged. When the membrane material loses

tension because it is damaged, the framework of membrane structure

should not collapse.

Study on the Mechanical Properties at the Joint

Node of the Membrane Structure

A. Basic Principles of Design for the Joint Nodes of

Membrane Structure


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The development of designs for membrane structure is the process in which

the overall design and a detailed design of membrane structure

simultaneously interactively influence each other and develop. The basic

function of the joint node of a membrane structure is to safely and reliably

connect each part of the membrane structure to make a whole. After 50

years of development, the current design of the joint nodes of membrane

structure need be beautifully designed, in addition to their basic functions

being realized (Motro, 1996).

B. Direct and brief force transmission paths can effectively transfer

internal force

Negative Gauss Hyperboloid produced by equalization of strain is a

necessary condition in which Tensional Membrane Structure keeps stable.

Brief design for the joint node can simply and specifically pass on complex

membrane surface and force is carried by angle points of the membrane to

other parts of the membrane structure so that there is a continuous

transmission of force flow in line with the analysis and design model.

C. Sufficient intensity, stability and durability

Intensity, stability and durability are basic mechanical properties that all

building structures must satisfy. With respect to membrane structure,


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sufficient node mechanical property an important factor that guarantees the

overall performance of the structure. In terms of the design of joint nodes,

we must consider the possible reduction of the joint node property that may

be caused by local stress concentrations and a weakening of the membrane

material at the joint point so that the mechanical property of the

membranes joint point can be evaluated accurately.

D. Necessary harmony of deformation

In comparison to traditional building structures, membrane structures can

produce large deformations under the impact of external loads. In each

phase of design of the membrane structure, the large deformation property

of the membrane structure must be considered. With respect to the design

of joint points, a certain amount of displacement and rotation must be

permitted in order to guarantee accurate positioning. Meanwhile, we must

also consider the operability on construction of pre-stretch-drawings of

membrane material and twice stretch-drawings.

E. Integrity of architectural appearance

The strong expressive force that membrane structures offer is one of its

principal advantages. Once its mechanical properties are met, the joint

point should be as exquisite and small as possible in order to be in line with


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the overall geometric modeling and architectural appearance of the

membrane structure. The impact of joint point on light transmission, gas

tightness, water tightness and water draining must also be considered.

F. Basic forms of membrane structure to link joint point

The specific forms of joint points of membrane structures are complex.

Moreover, according to the effects and connection of membrane unit, they

can be divided into three basic forms: membrane to membrane, membraneto rigid edge and membrane to soft edge.

G. Membrane to membrane joint point

The main functions of membrane-membrane joint points are to weave

various cutting units of a diaphragm into the whole diaphragm, with

necessary diaphragms added to reinforce it. Basic forms of membrane-

membrane joint points include heat seals, splints, bonding, sutures, belt and

combination mode. Presently, the first three of these forms of membrane-

membrane joint point s are most commonly used engineering project.

Common forms of thermal bonding membrane joint points include lapping,

single-side back sticking and double-side back sticking, shown in Fig. 3.


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Thermal bonding methods include high frequency heat seals, hot air heat

seals and the use of hot soldering irons. Thermal bonding membrane joint

points fuse through membrane coating and shear transfer force, and the

diaphragm a carries uniform and continuous force, thus its joint strength is

strongly related to heat seal form, heat seal method and lap width. For PVC

membrane material, considering the solder ability of PVC coating and

waterproofing requirements, the most commonly used thermal bonding

PVC membrane joint point at present is the single-sided back sticking form

shown in Fig. 3(b), where the covering diaphragm is located in the innerside of the membrane structure. For PTFE and

ETFE membrane material, overlap joints shown in Fig. 5.3(a) is a relatively

commonly used membrane to membrane joint point (Kaltenbach, 2004).

Fig. 3. Thermal Bonding Membrane Joint Point


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A splint membrane joint point is shown in Fig. 4. In the procedure one

screws the bolt tight, clamps two rigid splints and two diaphragms in the

middle tight, and passes on the internal force of the diaphragm from the

bolt-rope of the diaphragm and the rigid splint through friction and

extruding force. Determination of the length of the rigid splint depends on

the size of curvature of the membrane to membrane connecting line. Splint

membrane joint point is often applied in field installations of large

membrane units to avoid the inconvenience of processing plants. Moreover,the connection of single-side splint also fits that of the membrane unit and

the steel boundary components (Kaltenbach, 2004).

Fig. 4. Splint Membrane Joint Point


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Transfer force connecting splints mainly focus on the extruding force

between the bolt-rope and the splint. The clamp force and the individual

stiffness of the splint are large enough so that the bolt-rope and the splint of

the diaphragm can rely on the transfer force to avoid the phenomenon in

which the bolt-rope of diaphragm squeezes into splints. Splint connection

does not rely on the screw bolt and the shear of diaphragm to transfer force.

Therefore, the open size of the membrane should be 2-3cm larger than the

screw bolt so that tearing damage from shear stress between the diaphragm

and the screw bolt in the open hole can be avoided.

Bonding membrane joint points, whose two pieces of membrane units are

bonded together by a special glue water and adhesive, transfers the force

through the bonding of the membranes coating. This form of joint point is

in line with that of the thermal bonding membrane joint point, shown in

Fig. 5. However, bonding membrane joint point is time-consuming, costly

and its quality is not easy to ensure, therefore it is commonly applied in

such cases as field repair of the membrane structure and in the installation

of twice membrane.


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Fig. 5. Bonding Membrane Joint Point

H. Membrane-rigid boundary joint point

Membrane-rigid boundary joint point is applied in connection with the

supporting part between the membrane unit and the membrane structure,such as steel structures, aluminum alloy structures, concrete and timer

structures. In essence, the membrane unit directly connects with the metal

components through specialized metal adapting pieces. At present,

common membrane-rigid boundary joint point are pressing plate

connections, U-style clip connections and metal fastening connections. A

pressing plate connection is shown in Fig. 6. It is almost in line with a

pressing plate membrane-membrane joint point in structure and force-

transfer mechanism. The friction from the clamping of the pressing plate


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and the extruding force between the bolt-rope and the pressing plate passes

on the internal force of membrane to surrounding components.

(a) Membrane-wood structural rigid (b) Membrane-steel structural

rigid joint point joint point

Fig. 6. Pressing Plate Junctional Membrane-rigid Boundary Joint Point

The u-type clip connection method withdraws the edge of the membrane

through the pressing plate and the bolt-rope first, and then it is connected to

the surrounding components through the U-type clip arranged at

proportionate space, shown in Fig. 7. The internal force of the U-type clip

fits the adjustment of membrane boundary and twice the lead-in of

membrane stress.


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Fig. 7. U-type clip connecting membrane-rigid boundary joint point

I. Membrane-flexible boundary joint point

The membrane-flexible boundary joint point mainly refers to various jointpoints connected to flexible cable unit that includes membrane cover

connection, U-type clip, and belt, shown in Fig. 8.

The membrane cover connection refers to the cable body that passes

through the membrane cover formed by the membrane surface, and its

internal force is passed on to the membrane cover from the membrane unit,

then on to the cable unit. Meanwhile, joint points are continuous, and the

transfer of force is uniform. The membrane cover can be formed by a direct

reversal of the membrane material once through the thermal bonding


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method, and is also formed by the addition of a membrane cover. The joint

strength of the membrane cover connection mainly depends on the width of

the membrane cover created by a heat seal, which is similar to the thermal

bonding membrane-membrane joint point. In comparison, a U-type clip

connection fits the condition in which the diameter of a cable body is long

and when force-carrying is large, and its connection mode is similar to that

of a U-type clip with rigid boundary.

Fig. 8. Membrane-flexible boundary joint point


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Philosophy, engineering and material

A membrane-structure building is a building in which active use is made

of the characteristics of membrane materials. Membrane materialscommonly used nowadays are PVC coated polyester, PTFE coated glass

fiber fabrics and recently a third material: ETFE-foil.

Hence the name fabric structures or fabric architecture is sometimes

encountered in literature.

The structure supporting the membrane can be a skeleton frame or a cable

frame. If the membrane itself is used as a structural material, the structure

can only be small in scale because of the limited strength. In a large-scalestructure, the membrane must be reinforced in some way or combined with

a frame. A membrane naturally forms a curved surface and can resist

tension but not compression or bending. This is the reason why membrane

structures are often put under the heading of tensile structures.

Lightweight, thin and soft are some of the main characteristics of

membrane structures, mostly enveloping large spaces by curved shapes.

Another important characteristic of membrane building is the fact that the

inherent architectural language of membranes isinvariably

morphologically independent of the historical, geographical, architectural

andsocial context into which they are introduced. In this respect they can

represent a neutralintervention whilst still possessing their own strong

architectural identity. (Koch, 2004)

As mention earlier on Modern membrane structures were first developed

in Germany, where their basic properties, structural characteristics and

design methods were elucidated and their formal potential wassystematically investigated. These structures were first called tent

structures, but now the most common name is membrane structures.


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Form, structure and design

The concept

To obtain an understanding of a structural form tracing the flow of tensionand compression forces throughout its elements is essential. Bending

elements, or beams, are the most common structural elements for simple

structures. The simplest structural elements are those in which load is

carried by a single element, where the extremes are the suspended cable in

pure tension or an arch in pure compression.

These are both two-dimensional, but if these systems move into three

dimensions it gets more complicated. The simple (catenary) cable will then

become a bidirectional cable net (just as the arch becomes a bidirectionalgrid shell). This net may then be triangulated and finally developed into

woven and coated structural fabric. At each stage, load is carried in tension

alone.

Since for both structural concepts the material will be thin the generated

stresses can be referred to as membrane stresses. In this respect, both

systems can be referred to as membrane structures for their load-carrying

mechanism. In this thesis only membrane structures will be discussed

which also refer to their construction material/foil.

The ability of a membrane to carry load is increased by the introduction of

curvature to the surface. The amount of deflection under load is controlled

by both the degree of curvature and the amount of permanent stress, or pre-

stress, in the membrane. Two fundamental classes can be distinguished for

membrane shapes, those with negative and those with positive surface

curvature: anticlastic and synclastic respectively (fig. 9.) The first class are

the hyperbolic paraboloid (4-point sail), the simple saddle and the cone andthey all exhibit negative Gaussian curvature. The second class contain for

example domes where the curvature is the same in all directions and the

stabilisation should be realized by permanent internal inflation pressure.


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Fig. 9. Negative and positive surface curvature [1]

Two basic components can be distinguished in membrane structures: the

membrane itself and the support structure. The membrane may be

connected directly to the support structure or via edge-cables. The support

structure transmits the tension forces from the membrane to the ground.

When the supporting structure is rigid, both systems may be structurallyanalyzed separately. When a flexible boundary is applied this is not the

case.


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Primary structures

Membrane structures can have an analogy of skin and bone, with the

bones performing the primary and the skin the secondary load-bearing

functions. The primary structure meant here is the earlier mentionedsupport structure. Four basic primary structures can be distinguished with a

fifth membrane type structure. The simple Saddle, the arch-supported

structures, point or mast supports, the ridge-and-valley principle and the

fifth group the air-supported structures.

Arch-supported structures

Membrane saddle areas are created between the support lines along

the arch members when applied correctly. The arch functions as aLoad-bearing element subjected only to compression. The membrane is

then subjected to purely tension stresses.

Arch-supported structures are suited for large-scale structures, where big

spans should be reached and an appropriate geometry should be provided


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for the membrane (e.g. Hangar in Brand). Other constructions are suited as

well, namely spoked-wheel constructions, cable nets and mast structures

(e.g. Millennium Dome).

Mast supported structures

A minimal type of structure in this category can be achieved by a single

supporting mast with appropriate cable stay (and three other anchor points

may be on the ground). With this a cone structure can be created, which

can also be put in a row. Another separation within this type can be made

when no mast/support is wanted on the ground area. The flying mast is

introduced with a supporting structure above the membrane (figure 10).

Fig.10 Flying mast example [1]


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Ridge-and-valley support structuresThis principle is based on setting out cables with opposite curvatures next

to each other. The upper cable is called the ridge-cable and the lower thevalley-cable.

Air-supported structures

This type of structure is different because the supporting element of the

membrane is air. The system is based on air pressure between the ground

and the membrane (figure 11). Incorporating a support ring that is capable

of resisting horizontal loads, can create dome forms.

In these domes, again, a higher pressure is maintained in the entireinternal

space.

From time to time, helium-filled pneumatic structures in the form ofcushions are investigated, such as the Cargolifter (airship hangar). In

general, inflated structures are being used more and more as secondary

systems for smaller spans. Here, high-transparency foils

(ETFE) are used for many types of cushion.


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Another type resulted from this, the so-called air-supported linear elements

such as inflated arches or even beams.

Fig.11. Pneumatic dome example [1]

Retractable structures

Membrane structures especially designed for roofs are required to change

form. The most common way for membranes is to fold the skin and

packing it together. Distinction can be made between retractable structures

with a radial system, parallel sliding-folding structures, umbrella structuresand sliding roof elements.

Membrane Engineering

Many of the concepts for the form finding, analysis and design of

lightweight and long span structures originated from the observation of

structures in nature and from physical modeling techniques. The latter

principally through work at the Institute for LightweightStructures (IL), Stuttgart University directed by Frei Otto [3] (Appendix

4A). The engineering science was aided by SFB64 (1976-84), the first

special research group, directed by Leonhardt, Argyris, Linkwitz, Otto and

others at the University of Stuttgart [4, 5].


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SFB64 pulled together all the technology, design method and material

science that was necessary to successfully design and construct the

Olympic Stadium at Munich [6]. Argyris and Haug outlined the

background to the development of matrix based numerical methods for the

analysis of tension structures.Membrane engineering covers the numerical procedures for the form-

finding, load analysis and patterning of these stressed-membrane tensile,

non-linear structures. Any analysis must account for relatively large

displacements since membrane structures undergo significant surface

movement in order to carry load. Accurate fabrication information for the

membrane, cables and support structure must be provided to the contractor.

Physical and numerical modeling

Early developments in tensile architecture were based upon physical

models using soap films (for minimal surfaces), stretch fabric and wire,

done by Otto, Gaud, Happold, Arupet al. Very accurate physical models

were created to derive to cutting patterns. Physical models are still used

today (during conceptual design stages), but the principal design stages of

form finding, load analysis and patterning are done by the use of

computers.

The computer-based numerical modeling of structures is based upon the

finite element method. The geometry is presented by a series of points and

finite beams (or masts) between them, covered by fabric modelled by

triangular elements with each three connecting points. From this the

element stiffness matrices are assembled, but since membrane structures

have additional on-off non-linearitys (slacking cables and wrinkling

membrane as a result), determining the equilibrium state of membrane

structures needs form-finding capabilities that does not exist in standard

structural analysis systems.

Form-finding

Goal is to create a satisfactory long-term behaviour of a membrane

structure, done by creating either a uniform or smoothly varying


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distribution of stress within the warp and fill (or weft) directions of the

fibres. These fabric-weave directions, in the end, should ideally coincide

with the directions of the principal curvatures of the surface.

In practice an iterative process of form generation (finding) and load

analysis is undertaken, which is done by computer programs. It is farbeyond the scope of this assignment to discuss the exact process

undertaken by designer and his/her computer program.

Load analysis

After introducing the material properties above load analysis (self-weight,

snow, wind) can be started. Now the non-linear behaviour of the structure

under load is analyzed using the finite element model from earlier. As saidbefore, the final form of the structure will be developed through an iterative

cycle of form adjustments and load analysis (figure 12).

Fig.12.Load analysis of a saddle shaped roof [1]


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Cutting patterns

After the form finding and load analysis stage, it is needed to translate the

found form into realizable pieces (after the pattern orientation). These

pieces are so-called cutting patterns. The curved (and usually doublecurved) membrane cannot be build up from flat planes easily. It is done, by

the computer program, by the geometric unfolding of a set of sequential

triangular finite elements into a plane.

The way then to develop cutting patterns with computer programs is to

introduce deformation and compensation for the cutting patterns (figure

13). The use of geodesic seam trajectories helps to optimize the use of

material by providing a set of balanced patterns with equal material anglesand thus preventing banana-shaped patterns.

Fig 13 Cutting pattern generation and Compensation [1]

Details

The details, such as anchorage, are of importance for this thesis in such a

way that the extent, in which the sealing of the entire space is facilitated, is

relevant for the sound insulation as well as for room acoustics. But since

the main focus of this thesis will be on sound insulation, all connections


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should be carried out in such a way that no sounds leaks appear. For triple-

layer membrane detailing, please refer to figure 14.

Seams

The connection between the different pieces of membrane (cutting patterns)

is usually made by seams formed in a double overlap. Glueing is also

possible; however, the available methods often offer not enough weather

resistance. When the surface layers (coatings) are made from PVC, the

connection can also be made by welding. In the factory multiple cutting

patterns are connected using seams and these bigger pieces are then

connected on the construction site. These seams give different detailing.

For detailing, please refer to figure 14.

Anchorage to the ground

Most of the examples seen in this chapter are of open roofing and small

canopies. These membrane structures are not relevant to this thesis,

because sound energy will leave (or enter) the structure at the open gaps

around the membrane. What relevant is here, is the sound tight connection

with the ground. Please refer to figure 14 for detailing on this matter.

Four details for a normal triple-leaf membrane structure. 1) membrane itself(including seams)


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,2) connection between membrane and the supporting mast, 3) connection between

membrane roof and membrane wall, 4) connection between membrane and asupporting (neighboring) structure.

The material

The Latin word membrane means a parchment or skin [7, 8]. The

membrane has a tradition of thousands of years old, but only in the last

decades membrane construction plastics became important. A membrane is

a flexible building component that is stabilized only under tension. So its

mechanical tensile strength and elastic qualities are important for the

design. Up to the present about 90% of all membrane projects used one of

the three following kinds:

- PTFE (polytetrafluorethylene)-coated glass fibre,

- PVC (polyvinylchloride)-coated polyester fabric, and

- ETFE (ethylenetetrafluorethylene)-foil.

Reason for this is that they have successfully been used in the past and so

they are extensively tested and proved. ETFE-foil for instance is a

transparent and high-performance foil mainly used for pneumatic cushions.

Today for each of these materials different strengths can be produced andthe properties are expanded to the higher requirements in regard to energy,

low-emissivity, translucency, fire safety and sound absorption and

transmission.

One example of this new development is the membrane roof of the New

Bangkok International airport (figure15). More is described in the

preceding chapter. In the following sections most of the materials used in

practice will be discussed and categorized.


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Fig. 15 Bangkok International Airport roof system and model photo [1]

Material types, qualities and characteristics

Products used for membranes may be divided into two main groups [8]:

anisotropic and those at least an approximate of isotropic materials. The

latter have identical mechanical properties in both main directions and are

mainly thin thermoplastic skins, or more rarely metallic sheeting, in the

building industry. Anisotropic membranes can be seen as technicaltextiles or fabrics. These fabrics may then be divided into three main

groups according to their manufacturing: knitted, woven and non-woven

(fleece, layered fibres). Woven fabrics consist of threads, which each

consist of several hundred individual fibres. The fibres may be natural

(cotton, silk, hemp or flax), mineral, metallic or synthetic.

During the industrial production process of high-quality membrane

materials the yarn (long continuous length of interlocked fibres) used for

the fabric is twisted in the weaving mill, using bond types specific to the

product. The direction of the fibres along the long length of a roll ofmaterial is known as the warp direction, while the perpendicular direction

across the roll is the weft (or fills) direction. Two weaving techniques are

used for membrane structures: the basket weave (warp/weft thread is 1/1)

or the Panama weave (2/2 or 3/3). For uncoated fabrics this is the end

result.


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When coated products are wanted, after a series of further pre-treatments

the raw fabric is coated on both sides with for example PVC, PTFE or

silicone. When coated extremely careful and not overlapping the seams of

the coating and the base material, higher strengths then the material itself

can be reached. The coating protects the fabric; against for examplemoisture and UV light, and ensures an accordingly long life. Coatings

presently on the market are PTFE, ETFE, TFA/PFA, THV, FEB and

PVDF, but are better known through their trade names such as Teflon,

Hostaflon, Polyflon, Toyoflon or Tedlar.

For external use only foils made on a fluoropolymer basis can be applied

successfully made for example of ETFE. An extrusion process ensures high

quality, consistent material thickness and maximum transparency. These

are sometimes brought under the heading of fluoroplastic foils.One of the most important criteria for the variety of materials available

today is the protection against the elements. Three main groups can be

distinguished from the text above

[1]: water tight (closed or coated), water permeable (open or uncoated)

materials and foils. All groups can be used internally, but for the open

materials to be used externally they must be weatherproof; i.e. for

protection against the sun for example. Both groups are discussed here,

since both types of materials are used for multi-layered systems.

Closed / coated materials

Two main products, already seen above, can be distinguished: PVC-coated

polyesters and PTFE-coated glass fabrics (other groups are PVC-coated

glass fibre and silicone-coated glass fibre). The PVC-coated polyesters are

low flammable and can have different surface finishes, such as

fluoropolymer top-coat. This type is in particular resistant against crackingduring folding. Another surface top-coat is laminated Tedlar film, which

provides good protection against UV-light (figure 16-1). The PTFE-coated

glass fabrics have a long life expectancy, are incombustible and have a low

coefficient of adhesion which provides them with good self-cleaning

capabilities (figure 16-2.1 and 2.2).


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In the fluoropolymer coated glass fabrics, in contrast to PTFE-coated glass

fabric, material is offered which can be printed and PTFE-laminated glass

fabric is under development which is not coated but laminated on both

sides with transparent fluoropolymer film for better translucency (figure

16-3).A new development recently is the highly translucent material on a purely

PTFE basis, which after a special coating can be welded and is rainproof

(figure 16-4). Silicone-coated glass fabric is an inexpensive alternative for

PTFE-glass and its main characteristic is its resistance to soiling (figure 16-

5.1 and 5.2).

Three foils are normally used, namely ETFE foil, THV foil and PVC foil.

ETFE foil is mostly used as double layer system in pneumatic structures

(and cushions). Advantages are the low self weight, full recyclability, highlevel of UV translucency and a self-cleaning surface with different

printings (figure 16-6 and 7).

Open / uncoated materials

The first groups are the uncoated or impregnated narrow or broad mesh

fabrics. PTFE fabric (one of the fluoropolymer fabrics) still dominates this

group and is used for the more exclusive projects (figure 16-8). Cotton

fabrics and (woven) metal fabrics are not less behind the PTFE fabric. For

textile suspended ceilings PTFE-coated glass lattice fabric (figure 16-9) can

be used.

Another group are the monofil fabrics made of fluoroplastic which are

produced with or without coating. They have excellent weatherproof

qualities and allow pleasant diffused light and have a high resistance to

soiling (and are expensive) (figure 16-10).

Micro-perforated acoustic membranes can be produced in the form of

textiles and also as perforated transparent foils with very good acousticabsorbency values [1]. An example


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1 2.1

2.2 3

4 5.1


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5,2 6

7 8

9 10


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11 12

Fig. 16Different kind of membrane materials [1]

1 PVC-coated polyester

2.1 PTFE-coated glass fibre fabric2.2 PTFE-coated glass fibre fabric - light3 PTFE (fluoropolymer)-laminated glass fibre

4 PTFE fabric5.1 Silicone-coated glass fabric - light

5.2 Silicone-coated glass fabric6 ETFE-foil

7 ETFE-foil with printing

8 PTFE (fluoropolymer) fabric

9 PTFE-coated glass lattice fabric

10 Fluoropolymer monofil fabric11 Micro-perforated membrane(polycarbonate- or ETFE-foil)

12 Acoustic polyester fabric

is the micro-perforated foil made from polycarbonate- or ETFE-foil. These

have excellent absorption qualities, according to [1], and are used more and

more, so that the improvement of the acoustic environment is less

expensive afterwards (figure 16-11).

Then there is the groups of uncoated or impregnated narrow or broad

weave fabrics (e.g. incombustible glass fabrics) and can be produced in a

wide range of characteristics, optimizing lighting and acoustics. Another

example is the polyester fabrics groups which can be seen in figure 16-12.

Properties overview


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In table 1 all relevant properties (known so far) per material type are

summed up. Only properties relevant to the subject of this thesis are

presented. Since sustainability and durability are always an important issue

nowadays this is also mentioned. Whether or not the materials arerainproof, fire resistant, UV-light resistant, translucent, light reflective,

self-cleaning, resistant to chemicals or suitable for folding membranes are

left out of the table. These can be found in [1, 8].

Properties and qualities mentioned in the table are sustainability,

recyclability, durability, self weight, total thickness, Youngs modulus

(elasticity) and tensile strength.

Values for sound insulation and absorption are scarse and not complete,

which are therefore not mentioned in table1.Most of these properties are not well documented. Or just not known (yet).

The bending stiffness is so far unknown, it can only be said that it is very

low. For permeability (applies only to meshes in practice) the flow

resistance is sometimes mentioned and is of importance later on (Moulder

and Merrill said that when a membrane is coated, it is impermeable, thus

the airflow resistanceR is infinite).

Manufacturers and producers

Producers and manufacturers producing membrane materials do this under

a brand name usually. Brand names Mehlers Valmex or Ferraris

Prcontraint series. Fabric types are also better known for their brand

names, like Teflon, Kevlar, etc. Some of the most seen manufacturers are

Ferrari Industry, Mehler Tex-nologies (coated fabrics), Verseidag

Technologies (coating and composite technology) and Heytex.

Since most materials on the market are common types, described earlier,

differ in strength, thickness, UV-resistance, the ability to self-cleaning,colour, etc., only some are interesting for this thesis. Table1 is

supplemented by the values found at the manufacturers(Heytex, Verseidag,

Mehler and Ferrari).


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Table 1 Material properties Recyclability: ++ is excellent,+ is good, 0 is neutral

*Polyester fibre itself has a Youngs modulus of 7.5 kN/mm2 and Aramide fibres112kN/mm2.


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Other special materials

Thermal insulation materials play an important role in the building

industry. Recently transparent thermal insulation materials for multi-

layered systems are produced and used effectively (figure 17-2).Stainless steel mesh materials have acquired an importance since the 1980s

and can be produced in a lot of different ways (different wires, cables and

weaving methods) (figure 17-3).

Gas-tight membrane materials (as analogy to glass products) have been

used in the area of helium filled membrane constructions for airships and

experimental studies. It encompasses polyurethane-coated, low-

flammability and light polyester fabric. The loss of helium is minimized

but materials that are completely impervious to helium are not yetavailable. PVC-coated aramide fibre fabrics are made from one of the

strongest synthetic fibres (Aramide or aromatic polyamide) on the market

today (with a maximum failing strength of 24.500 N/5cm). These fabrics

will be chosen when strength is important and where elasticity and

translucency of less importance. Also from Aramide fibres comes the

Kevlar fabric (usually with a PVC coating) which is more and more used

(especially for experimental use) as Kevlar fibre Air Tubes. As mentioned

before, these high pressure air tubes can take on the support function of a

beam, an arch, or a grid becoming a type of frame structure. Teflon

(PTFE)-coated glass-fibre fabrics and a variety of special coatings were

specifically developed to provide fire resistance, self cleansing, durability

and can withstand a tremendous temperature difference. This came from

the space industry, just like Spectra vibers, which consists of Vectran, a

high performance thermoplastic yarn spun from liquid crystal polymers.

Tenara is a woven Teflon fabric probably best known from the dental floss

fibres. It has the drape and feel of fine silk, withstanding continuously

folding and unfolding without fatiguing the yarns and is manufactured byGoreTex.


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1 2

3Fig. 4.8Different kind of special membrane materials [1]

1 Fluoropolymer-coated low-e acoustic glass fabric

2 Membrane insulation material

3 Stainless steel mesh

Project examples

1.Case San Nicola StadiumBari, Italy, 1990


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In 1990, World Cup was held in Italy and the country has built eight

stadiums to accommodate the event. This is one out of the eight stadiums

for the event. By rearranging the spectators seats within the stadium using

310 crescent shaped concrete beams, an oval shaped is eventually formed.

It is split into different segments and one such segment consists of 26 largepetals located in the upper deck.

The building does not longer feels so heavy on the eyes as slits were in

placed between the petals.

This also demonstrates the circulation areas, accommodating all the entries

and exits doorways thus it meets the health and safety requirements.

Computer simulations were used beforehand in order to maintain the

aesthetic side of the stadium.


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A special glass coated with PTFE fibre roof, designed by Over Arup &

Partners were used in order to protect the spectators of the outdoor weather

conditions. There are two levels to this roof; the principal level consists of

box shaped beams built from the top.

The second level consists of supporting beams for floodlights and trussmade using steel and cables. This method of build has ensured tension

within the whole structure. Bristol University has assisted in the project by

using computer simulation to monitor the wind flow ofthe stadium. Arups

computer programs such as Fablon and General Structural Analysis

program were used to create the simulation.

This was vigorously tested to ensure the wind does not have an unwelcome

affect to the spectators.


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