MAPUA UNIVERSITY
SCHOOL OF ARCHITECTURE, INDUSTRIAL DESIGN, AND THE BUILT ENVIRONMENT
TENSILE STRUCTURE
AR164P – AR3
FALCIS, SHARMAINE G.
SALAVER, MIKAELA LOUISEE
TIANCHON, DAN JERICHO
TOBIS, IRA BEN
12.11.17
A tensile structure is a construction of elements, carrying only tension and no compression
or bending. Tensile structures are the most common type of thin-shell structures. Being
economically feasible, a tensile membrane structure is often used as a roof, because they can
stretch over large distances looking attractive. Most tensile structures are supported by some form
of compression or bending elements, such as masts (as in the Millennium Dome), compression
rings or beams. Tensile structures have been used since long in tents allowing it to withstand loads.
Steady technological progress has increased the popularity of fabric-roofed structures. The low
weight of the materials makes construction easier and cheaper than standard designs, especially,
when vast open spaces are to be covered. Its lightweight nature, translucent and reflective
properties, and environmental adaptability could also be taken advantage of, in building
construction. Russian engineer Vladimir Shukhov was one of the firsts, to develop practical
calculations of stresses and deformations of tensile structures, shells and membranes.
Covering the area of 27,000 sq m, Shukhov designed eight tensile structures and thin-
shell structures’ exhibition pavilions for the Nizhny Novgorod Fair, in 1896. In the 1950s,
architects and engineers began to take a renewed interest in using tension, as the
primary method of transferring loads in structures. Two main figures, namely, Frei Otto
and Horst Berger of Germany were responsible for the advancement in this investigation
of tensile structures. The concept was later championed by German architect-engineer
Frei Otto, who first used the idea in the construction of West German Pavilion at Expo 67,
in Montreal. Later, Otto used the idea for the roof of the Olympic Stadium of the 1972
Summer Olympics, in Munich. Some of the current well-known structures, utilizing
tension fabric include the largest cable-supported roof in the world are the London
Millennium Dome and the Haj Terminal in Jeddah, designed in parts by Berger. Currently,
it is one of the largest tensile structures in the world.
Concept Design and Criteria for Shape Finding
The concept design is the most important stage of the design process. A bad concept will
reverberate throughout the design, manufacture and installation process to impair the appearance
and performance of the final product. A number of factors need to be taken into consideration:
a) Geometric constraints of the site and adjacent buildings
b) Sun-shading levels required and Sun angles
c) Air-flow and ventilation of the space
d) Light transmission requirements for the space below
e) Availability and positions of anchorage points
f) Need for continuous-sealed perimeter anchorages
g) Aesthetic considerations and compatibility with adjacent elements
h) Achievement of adequate curvature to minimize fabric stresses and movements
i) Drainage of rainwater and avoid ponding
j) Suitable fabric slopes, to ensure adequate self-cleansing
k) Nature of supporting structure and tensile elements
Different Types of Tensile Structures
A two-dimensional tension fabric membrane can take planar tensile forces, but it cannot take
significant forces perpendicular to this plane. Therefore, in addition to being pre-stressed, tension
fabric must take a certain three-dimensional shape, in order to remain stable. These shapes were
discovered by Otto and Berger during their investigation of natural forms, such as soap bubbles.
There are two types of general shapes: Anticlastic and Synclastic Shapes.
1) Anticlastic Shapes are created by having the radii of the principal curvatures on opposite
sides of the tension fabric surface. As a result, when loaded at a particular point, tension
will increase on one curve of the membrane and leave the opposite curve. Thereby,
preserving equilibrium and keeping the structure stable. In order to keep anticlastic shapes,
some kind of structural frame or support is necessary in the form of cables or steel beams.
Some examples of anticlastic shapes are saddle, cone and wave forms.
2) Synclastic Shapes are characterized by having the radii of the principal curvatures on the
same side of the fabric (Fig. 2). In order to counteract external forces, pressure from the
within is necessary. This is why synclastic shapes are associated with air-inflated
structures. The difference of pressure created by air pumped into the building is able to
counteract the external forces, in the form of wind or snow .
Methods used for Concept Design
a) Wireframe Computer Models – The simple computer models are the starting point, for
investigating various fabric forms and developing the concept design into a practical form, to
ensure the design criteria are satisfied.
b) Fully-rendered Computer Models – Models of the final design of the fabric structure can
be added to the model of the whole building. They are considered very useful for the final
presentations to clients.
Anchors, Foundations and Supporting Structures
The provision of adequate anchorages and supporting structures must be addressed at the
earliest stages of the design process. Failure, to address these issues early on, could result in the
tensile structures being impossible to include, once the design and construction has progressed
beyond a certain stage. Even small canopy structures impose significant forces on the sub-
structures. Large structures will require special design features, to be able to resist the tensile
forces. Tensile fabric structures impose forces, which have significant horizontal and vertically
upward components. These are not the types of forces, which buildings are normally designed for.
If special provision has not been made for these forces, it is crucial that the tensile structure be
designed, taking these into account.
Fabric Options – PVC and PTFE
There are three main types of tension fabric used in architectural applications today: PVC-
coated Polyester, Silicon-coated Fiberglass, and Teflon-coated Fiberglass. PVC-coated polyester
is not only the cheapest and easiest to manage of the three, but also it has the shortest life span.
Teflon and silicon-coated fiberglass are more durable and are more expensive. However, the basic
structure of the material is similar, for all the three. Usually made out of polyester or fiberglass,
the bottom layer of the tension fabric is a base fabric. This fabric is created with fibers weaved in
and out of each other, which run perpendicular or in the warp and welt directions. The base fabric
is extremely important, because it dictates a number of the final fabric properties, including stress
and strain properties. They are relatively translucent and reflective, in addition to the incredible
strength of the base fabrics. For example, Teflon-coated fiberglass has a reflectivity of 70%.
Factors Influencing Fabric Performance
Observation of fabric structures in different situations in various parts of the world,
show a particular environment in which the fabric is situated. It has a very significant
effect on its performance. The main factors influencing the fabric performance are as
follows:
a) Geographic latitude and the temperature of the fabric
b) UV radiation level reaching the fabric
c) Humidity level
d) Pollution level, as well as, the type of pollutants
e) Dust level
f) Frequency and nature of cleaning operations
g) Deposition of vegetable matters (leaves, etc.) onto the fabric
h) Staining resulting from rainwater run-off, over other building materials
i) Exposure to direct rainfall, to assist in dirt and dust removal
PVC / Polyester Fabric: Properties and Characteristics
PVC / Polyester fabric consists of a woven polyester base cloth, which is coated with
PVC and another top coating. They can be classified into 2 basic categories, depending on the
type of protective top-coating:
a) Acrylic Lacquer
b) PVDF / Acrylic Lacquer Alloy Coatings in varying proportions
These top coatings have a large influence on the performance and appearance of the
fabric. They, not only provide the fabric with some of its UV resistance, but also, vastly improve
its self-cleaning characteristics. In general, fabrics with acrylic coatings have not performed well
over long term, in tropical countries. Most of the examples appear to attract and retain significant
amounts of dirt and dust after relatively short times, in service. On sites with high UV levels, the
acrylic coatings break down fairly quick and the deterioration in appearance can occur within a
few years, after installation. The fabrics with PVDF / acrylic alloy coatings are the most
commonly used. They have been in service for about 25 years. The PVDF / acrylic coating is
heat-fused onto the base fabric as part of the manufacturing process. The top surface of the fabric
has a smooth slippery feel, so it is very effective in repelling dirt and resisting mould growth.
With the anticipated life being directly proportional to the amount of PVDF in the top coating,
useful lives of 15-25 years are achieved with these fabrics.
PTFE / Fibreglass Fabric: Properties and Characteristics
The first outdoor PTFE / fibreglass structure was erected in California, almost 40 years
ago. It is still performing well in service. Therefore, it is likely that structures, which are made
with today’s PTFE / fibreglass fabrics, will achieve useful lives in excess of 50 years. PTFE /
fibreglass fabric is very effective in repelling dirt. Structures, which have been inspected after
years in service, have been found with perfectly clean surfaces. Even though, they have never had
cleaning maintenance. Three of the new stadiums, built for the Soccer World Cup in South Africa
in 2010 had PTFE / fibreglass roofs. The main disadvantage of PTFE fabric is its high cost – the
overall cost of structures, using this fabric is almost twice of the PVC structures.
Light and Heat Transmission
One of the main advantages of fabric is its translucent properties – on an average,
architectural fabrics transmit about 13% of the light falling on the top surface. This results in a
very pleasant light and airy feel to the space below. It can also result in significant cost savings on
lighting. Fabric is also very effective in reducing the transmission of radiant heat from the Sun. It
is a material, which has been significantly underutilised in the climatic conditions, prevailing in
South Africa. However, global warming is likely to result in increased usage of tensile fabric
structures in future.
Lighting of Fabric
Lighting is very effective in emphasising the aesthetic appearance of fabric structures and
should always be included, whenever possible. Both back-lighting and front-lighting can be used,
depending on the effect that is desired.
Fabric and Fire
PVC has fire retardant properties and achieves a class 2 fire rating. It means, the fabric is
self-extinguishing and does not produce drips of molten fabric. The fire rating is accepted by most
approval authorities for use, generally as a roof enclosure. PVC has an added advantage in a fire
situation. The fabric seams will separate at about 100ºC, thereby, allowing a very early venting of
toxic fumes and smoke. This is a major advantage in saving lives of people who, may get trapped
in the building.
Cleaning Fabric
Fabric is easy to clean. It can be done using soft brushes, light duty, non-acidic detergents
and copious rinsing water. Personnel can access the fabric by means of ropes and use soft-soled
shoes, to walk on the fabric.
REFERENCES:
[1] www.en.wikipedia.org/wiki/Tensile_structure
[2] Red Sky Shelters. “The History of Tensile Architecture.” Red Sky Shelters.
www.redskyshelters.com/tensilehistory.html.
[3] “Millennium Dome”, Midas User.
www.midasuser.com/info/land/read.asp?index_id=4&pg=1&so=1&sk.
[4] Intents. “About Membranes” Technical. Intents. http://www.intents.be/default2.asp.
[5] N. Browne. “CPD.” Fabric Architecture and Signature Structures.
www.fabricarchitecture.co.uk/cpd.htm.
[6] Seaman Corporation. “Utilization of Vinyl Coated Polyester Fabrics for Architectural
Applications.” Seaman Corporation. www.architecturalfabrics.com/whitepaper.html.
[7] U. Gandhi. Design and Construction of Tension Membrane Structures.
http://homepages.cae.wisc.edu/~ukgandhi/documents/tensile%20structures_paper.pdf.
[8] www.tensionstructures.co.za/tensile-fabric-structures/
[9] www.architen.com/2012/05/famous-examples-of-tensile-structures/
[10] www.tensinet.com/database/viewProject/3859.html
