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Continuing
Education
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Use
the following learning objectives to focus your study while reading
this month’s ARCHITECTURAL RECORD / AIA Continuing Education article.
Learning
Objective:
After
reading this article, you will be able to:
1.
Explain the advantages of using fabrics in a building's design.
2.
Describe which elements of a
building may be of fabric
3.
Identify the fibers and coating
used for structural fabrics.
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Fabric in
architecture captures the imagination. It conjures romantic images:
tent canvas staked out in a forest or luxuriously draped curtains
making shade for desert nomads. The sculptural shapes an architect
can achieve with fabric-from taut, firm roof peaks to pillowy
curves-cannot be accomplished with any other material. And the
atmosphere inside a fabric structure is unlike that of a conventional
building: The diffuse daylight, the acoustics, the shape of the
walls or ceilings, even the way the air moves through the space
are all different.
Todd Dalland,
FAIA, and Nicholas Goldsmith, FAIA, of FTL Happold Design and
Engineering Studio in New York City, are as entranced with tensile-fabric
structures today as they were when they were first introduced
to them in college; in 1971, Dalland made a kind of pilgrimage,
hitchhiking from Cornell University to New York City to see Frei
Otto's tensile structure in the courtyard of the Museum of Modern
Art. Goldsmith later worked with Otto in Germany.
While some
firms incorporate fabric in their design work, FTL Happold specializes
in it. They design and engineer all types of fabric structures,
from air-supported domes to tensile-membrane roofs. FTL Happold
has even developed its own software for structural designs (as
have a few other engineering firms and some of the fabricators,
including Birdair in Amherst, N.Y.).
In addition
to designing the structures, FTL Happold also gets about half
its business from consulting with other architects who want to
use fabric in their designs. Together with the British-based engineering
firm Buro Happold, which is in partnership with FTL, the integrated
staff provides the engineering, specifies the cutting patterns,
or helps the architect develop the design. "We're trying to show
other architects that working with fabric is not that hard, once
you try it," Dalland says. But engineering a tensile-membrane
structure is challenging, even though computer modeling helps
in understanding the stresses and loads and in visualizing the
finished product.
Fabric is
more widely used overseas than in the United States, especially
in Europe, Japan, Mexico, and South America, says Bruce Wright,
editor of Fabric Architecture, a publication of the Industrial
Fabrics Association International in St. Paul, Minn. That's because
there is a greater use of canopies and awnings in these countries
to limit heat gain. Since air conditioning is often considered
a luxury outside the United States, tensile-membrane roofs are
popular because they allow daylight while providing shade.
Cut from
different cloths
Structural
fabric may be used as the entire shell of a building, or as the
roof or the cladding. In a smaller role, it may serve as a shading
system, skylight, or entrance canopy. There are mesh fabrics (used
for shading structures), clear fabrics, liners that improve the
aesthetics and performance of outer fabrics, and a range of exterior
fabrics for permanent structures. All of these fall into two main
types of cloth: polyester and fiberglass. The coatings applied
affect the fabric's performance. Considered most durable among
these is DuPont Teflon polytetrafluoroethylene (PTFE) and a newer
variation of this called TEDLAR. All of these help prevent ultraviolet
degradation of the base fabric while adding strength and water-
and dirt-resistance.
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Case
Study
Project:
The Columbus Center, Baltimore Architect:
Zeidler Roberts Partnership, Toronto
Engineer: Peter Sheffield and Associates
Fabricator: Birdair, Amherst, N.Y.
Standing
next to the iconic aquarium in Baltimore's Inner Harbor,
the Columbus Center, a biotechnology laboratory and exhibition
space, is a landmark in its own right, thanks to the graceful
fabric roof and entry canopy that swoops across the facade,
shading the vast expanse of glass there from the sun. The
PTFE-coated fiberglass membrane attracts people "like a
circus tent," says Eb Zeidler, faia, of Zeidler Roberts.
"It just looks like an attraction, like something interesting
must be going on inside." At night, the fabric is lit from
within, making the structure glow like a lantern beside
the harbor.
The
architects, who have done many fabric structures, consider
the material a good, inexpensive way to create organic forms.
"Using metal and glass to accomplish the same shapes would
be too expensive and look too stiff," Zeidler says. "Fabric
is a wonderful material in that it is affordable and unique."
A two-layer
membrane was selected for the Columbus Center because of
its insulation value-primarily to keep the air conditioning
inside the space during Baltimore's hot, humid summers.
The reflective properties of the fabric and the lack of
artificial lighting also help keep it cool inside.
The
structural membrane is supported by 10-inch-wide steel posts.
Four small skylights are inserted into the fabric so that
the light in the spaces below is variable. The steel frames
of the skylights also serve as clamps for the fabric. All
of this was preassembled on the ground and hydraulically
hoisted into place.
One
of the goals of the center is to attract children and young
people who might not otherwise learn about biotechnology.
But private research is also conducted there, giving the
building a kind of dual personality. The fabric, installed
on the exhibition side, clearly signals that something good
is waiting inside for the young students. W.T.
Photo
by Michael Dersin, Alain Jaramillo
Steel
post supports and skylights are visible over an interior
walkway.
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The type of
fabric that's used depends on the building type. Permanent structures
typically use Teflon-coated fiberglass because of its longevity.
Manufacturers say the material will last 50 years, but independent
design professionals who have worked with it predict a more conservative
30 years. Owing to the material's relative newness (the first
Teflon-coated fiberglass roof was installed 25 years ago and is
still going strong), actual records of its longevity are not available.
Its installed cost is about $60 per square foot.
Deployable
structures are typically PVC-coated polyester, though the material
is also commonly used on permanent buildings. Teflon-coated fiberglass
is not meant to be packed and unpacked, Dalland says. "You set
it up once and it stays." But polyester is more flexible. The
fabric has an installed cost of about $40 per square foot. Its
fabric replacement cycle is about 15 years by most estimates but,
again, actual figures vary. When used on deployable structures
its life span may be shortened due to the rigors of setting it
up and taking it down.
Polyethylene
fabric, developed in 1994, consists of a woven polyethylene scrim
that is also coated on both sides with polyethylene films. The
material has a high weight-to-strength ratio, says Jay Alberts,
business development manager for Intertape Polymer Group, a manufacturer
in Bradenton, Fla. This material has a great deal of potential,
Dalland says. "Its biggest advantage is its low cost and its greenness,"
he continues. "It's the only fabric that is 100 percent recyclable,
and it costs about half as much as PVC-coated polyester. Manufacturers
already recycle the scraps and can recycle entire roofs."
PVC-coated
polyester is also being recycled, though not to the extent possible
with polyethylene (which is a mono-material). An experimental
but promising new process called Vinyloop, developed by two European
textile manufacturers, separates the polyester fiber from the
PVC compound found in postconsumer vinyl products. Teflon-coated
fiberglass typically comes only in white, but pvc-coated polyester
fabrics come in many colors. Fabric weights, measured in pounds
per square yard, range from 4 ounces to 48 ounces, depending on
wind- and snow-loading criteria.
How it
performs
Tensile fabric
offers many performance advantages, but the biggest is probably
its strength-to-weight ratio. "It enables you to cover large areas
with little material. That makes it easy to install and lessens
the amount of energy used in the building process," Dalland says.
"It can also mean a lighter building structure, because fabric
as a cladding material is much lighter than glass or stone." The
lightweight fabric also interacts more readily with natural forces
than a material that's more rigid, which is one reason that the
interior of a tensile-membrane structure feels so different from
that of a conventional building. "You don't feel so isolated from
the outdoors," Dalland adds.
Structural
fabric must perform up to the same codes, standards, and loading
criteria as other structural materials. It must meet fire-performance
standards; the base fabrics must be noncombustible or flame-retardant.
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Case
study
Project:
Palm Springs Regional Airport
Architect: Gensler, Santa Monica, Calif.
Fabricator: Birdair, Amherst, N.Y.
Palm Springs, synonymous with the great outdoors, felt its
airport should signal this association. Like Fentress Bradburn
and Associates' Denver International Airport, the peaked
structure at the Palm Springs terminal is meant to symbolize
the surrounding mountains, beckoning visitors. "We wanted
the airport to feel like a resort," says Andrew Cohen, aia,
project director for Gensler. "The gateway to every city
should be memorable in some way. The fabric makes this a
landmark."
The
PTFE-coated fiberglass membrane protects and shades the
airport's open-air concessions and seating areas. There
is even a putting green on site, since Palm Springs is a
golfers' mecca.
"We
realized that, with the tensile material for shade, we didn't
need to close off and air condition these spaces. The fabric
provides a luminous, natural light while keeping temperatures
25 to 30 degrees cooler during the day," Cohen adds. The
waiting rooms are sealed and air conditioned, but there
is no fabric membrane over these areas.
The
architects had done some fabric structures, but this was
their largest to date. The 39,000-square-foot structure
was installed over a 10-week period. The fabric is supported
by tension rings and cables; the cables, in turn, are supported
by steel masts. Turnbuckles are used to tension the cable.
The system provides large spans but is extremely lightweight.
The
energy savings as a result of use of the fabric were "incredible,"
Cohen says. That's because of the lack of air conditioning
and artificial lighting. Single layers of fabric were used
throughout the project. W.T.
Photo
by RMA Photography
Canopies
at the Palm Springs Regional Airport are made of PTFE-coated
fiberglass fabric. They are hung from the cables attached
to a tension ring. |
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"Sprinkler
installation for fabric roofs, when necessary, requires special
attention in order to integrate the sprinkler drops and head locations
formally and functionally with the fabric shapes and openings,"
says Goldsmith. "Variances for performance-based fire-resistance
analysis can be obtained in appropriate situations," says Douglas
Radcliffe, vice president of sales and marketing for Birdair.
For stability,
the fabric in tensile structures must curve equally in opposing
directions-known mathematically as a hyperbolic paraboloid. The
fabric is usually oriented so that the fibers run parallel to
these curves. As a result, stresses are balanced. Fabric is somewhat
elastic, but, properly designed, it won't sag or creep.
Translucency
is another principal advantage of fabric. Daylight, filtered through
the woven yarns, is soft and even, eliminating the need for supplemental
lighting. That can mean significant cost savings for energy, particularly
for shopping malls, convention centers, and places where lighting
needs are high. After dark, the fabric lets light out, creating
a structure that glows in the night. Light transmittance varies
according to the type of fabric and coatings and the number of
layers, colors, and, of course, the position of the building in
relation to the path of the sun and other structures.
The material's
performance is not as impressive when it comes to R-values. A
single layer has an R-value of about 1. This is improved with
double or even triple layers, which add air spaces that help insulate.
And low E films can be laminated onto the fabric layers. But when
the total energy package is examined, it may be that fabric will
save money.
That's because
natural lighting, which virtually eliminates the need for electric
lights, lowers energy costs and avoids heat gain from the lamps.
The highly reflective surface of fabric also lowers the amount
of heat gain from solar radiation, especially compared to conventional
roofs.
This dovetails
with the relatively new approach toward building services design
at FTL Happold, where only the portions of rooms that are occupied
by people are heated or cooled, and only during the times they
are occupied, but that's another story.
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Case
study
Project:
Burj Al Arab Hotel, Dubai
Architect: W.S. Atkins & Partners, London
Fabric: Dyneon, Oakdale, Minn.
Fabricator: Skyspan Europe, Germany
This
is the kind of project architects dream of: a luxurious,
spare-no-expense hotel and conference center on a man-made
island in Dubai. Opened less than a year ago, the hotel
features a brilliant white fiberglass and PTFE-coated vertical
cloth membrane that's meant to resemble the billowing sail
of a traditional Arabic sailing ship.
The
161,000-square-foot, two-layer screen covers the open side
of the V-shaped steel-and-glass building, creating an atrium
lobby. A more standard choice for this area would have been
glass, but in the extreme desert conditions, this would
have introduced heat and glare. The fabric provides a soft,
milky light and lessens heat gain. At night, it is used
as a gigantic projection screen onto which the faces of
high-ranking guests are shown [May 2000, page 321].
The
vertical installation may mark the first time that tensile
fabric was used as part of the facade, says Michael Wolf,
project manager for Skyspan. The application was more difficult
to engineer than a typical horizontally applied tensile
membrane. The fabricators, who also did the engineering,
created a fabric model and used it for structural analysis
and for cutting patterns.
Photo
Courtesy of Skyspan
 |
| The
coated Teflon fabric skin of the Burj Al Arab Hotel
in Dubai is divided into 12 parts. |
The
650-foot-tall screen is divided into 12 fields averaging
7800 square feet each. Installing a single membrane for
the whole area would have placed too much stress on the
fabric.
The
fields are each supported by steel arches and pairs of steel
rods that are also tied to the structure. The fabric was
clamped to the arches at ground level, then the entire assembly
was lifted into place and unfurled. The screen stops about
45 feet above the ground to allow for the steel-and-glass
entry facade.
The
desert heat and light will take a toll on the fabric's longevity,
though the fabricators estimate that it will hold up for
up to 50 years. The smaller individual fields, however,
are more easily replaced than the entire assembly. W.T.
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Structural
components and installation
Tensile-membrane
structures are supported by masts, arches, or external trusses.
The masts give fabric roofs their iconic peaks, which are typically
steel, but may be aluminum if the structure is relocatable. Mast-supported
structures are less expensive than the other two, but the spans
are shorter and there are more interior columns. Arches allow
larger spans but require greater structural gymnastics. External
trusses allow a wide-open space but, once again, require more
costly engineering and materials.
Working with
fabric requires some of a dressmaker's skills and sensibilities.
At FTL Happold, models are handsewn using white panty hose and
are supported with brass tubes, polyester threads, and Crazyglue.
On the building itself, darts, seams, and other details are common.
These are calculated and drawn by FTL Happold with special software
and executed by the fabricators.
The bolts
of cloth for actual construction come in varying widths, from
about 6 to 14 feet. During design, much thought is given to creating
a pattern that minimizes waste during the cutting process. The
fabric may be cut with lasers, using CAD drawing files for guidance.
Or it may be cut by hand, using templates and cutting equipment
borrowed from the fashion industry. Fabric seams achieve full
design loading, and vary in width from 1 to 3 inches wide, depending
on fabric type and on wind and snow loading; they are made by
RF (radio-frequency welding), or heat welding.
As well as
being predesigned and pre-engineered, the entire tensile structure
and its supporting structures are prefabricated off-site in factories.
The fabric is assembled at the plant, put on a roll, and transported
to the site, where it is unfurled into place.
Contractors,
usually ironworkers, work with sheets that are as large as possible
but can still be handled. Wind is a problem, according to Birdair's
Radcliffe. "If winds are above 20 miles per hour, we won't install.
It's like wrestling with a 10,000-square-foot kite." During installation,
the fabric is tethered with a guideline.
The only
work done on-site is the foundations. Masts are connected to these
via pins; some play is necessary to allow the mast to move slightly
to accommodate loads. The assembly is stayed in several directions
with cables. Replacing the fabric on a permanent structure, when
it is worn, is a significant undertaking that should be considered
during design. Generally the portion of the building adjacent
to the tensile structure will have to be closed during the replacement
time.
Try it,
you'll like it
Fabric is
not for everyone; nor is it for every building type. But as Dalland
says, "A space with a fabric roof or wall invariably becomes the
premium space within a building. Yet, despite these advantages,
most architects have never touched a fabric structure." He adds,
"I bet most secretly want to."
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Proper
design, engineering, material selection, and fabrication
all work together to ensure a sound tensile-fabric structure.
Since the industry is constantly changing with many new
players, architects should check out a variety of fabric
suppliers and structure fabricators to determine which company
works best for them. The list below is not definitive; often
suppliers will double as fabricators and vice versa. For
more information, visit the Industrial Fabrics Association
International's Web site at www.ifai.com.
Rita F. Catinella
Fabric
suppliers
Anchor
Industries Inc.
Evansville, Ind. 800/255-5552. www.anchorinc.com
Chemfab
Corp.
Salt Lake City. 801/262-3654.
www.chemfabcorp.com
Cover-All
Building Systems
Saskatoon, Canada.
800/615-4777.
www.coverall.net
Ferrari
S.A.
Cedex, France.
33/04-7497-6649.
Hansen
Weatherport Corp.
Olathe, Colo. 970/323-5932.
www.weatherport.com
Intertape
Polymer Group
Montreal. 800/565-2000.
www.intertapepolymer.com
Losberger
US LLC
Mooresville, Ind. 800/964-8368.
www.losberger.com
Mehler
Coating Fabrics Inc.
Charlotte, N.C. 704/527-7188.
Seaman
Corporation
Wooster, Ohio. 800/927-8578.
www.seamancorp.com
Snyder
Manufacturing Inc.
Dover, Ohio. 330/262-1111.
www.SnyderMan.com
Taconic
Petersburg, N.Y. 518/658-3202.
www.4taconic.com
Taiyo
Kogyo Corporation
Tokyo. 81/03-3719-37.
Universal
Fabric Structures
Quakertown, Pa. 800/634-8368.
www.ufsinc.com
Weatherhaven
Burnaby B.C. Canada. 604/451-8900.
www.weatherhaven.com
Structural
fabricators
Advanced
Structures Inc.
Marina Del Rey, Calif. 310/301-1984.
www.asidesign.com
Birdair
Inc.
Amherst, N.Y. 800/622-2246
www.birdair.com
Canvas
Specialty
Los Angeles. 800/423-4082.
www.can-spec.com
J&J
Carter Limited
Bagingstoke Hampshire, U.K. 44/01256 8114.
www.jjcarter.com
Landrell
Fabric Engineering
Monmouthshire, U.K.
44/01291 6277
www.landrell.com
Permafab
Pty Ltd.
Sydney, Australia. 61/02
9858 36.
Rainier
Industries, Ltd.
Seattle. 800/869-7162.
www.rainierindustries.com
Rubb
Buildings Inc.
Sanford, Maine. 800/289-7822.
www.rubb.com
Skyspan
(UK) Ltd.
Wiltshire, U. K. 44/ 01722 331599.
www.skyspan.com
Sullivan
& Brampton
San Leandro, Calif. 800/257-5900.
www.sullivanandbrampton.com
Tensile
Designs International
Kansas City, Mo. 800/58-SHADE.
www.tensiledesigns.com
Tentnology
Surrey, B.C. Canada.
800/663-8858.
www.tentnology.com
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Continuing Education