Portable Fabric structures
In architecture, fabric
structures are forms of constructed fibers that provide end
users a variety of aesthetic free-form building designs. Custom-made fabric structures
are engineered and fabricated to
meet worldwide structural, flame retardant, weather-resistant, and
natural force requirements. Fabric structures are considered a sub-category
of tensile structure.
A fabric structure's material
selection, proper design, engineering, fabrication, and installation are
integral components to ensuring a sound structure.
Uses of fabric structure buildings
Fabric buildings have
many uses around the world in all climate conditions. They can be used for
Soccer practice, football practice, basketball practice, baseball practice and
even tennis practice structures. In fact they can be used to have full
competitions in including seating for thousands of fans. Fabric buildings can
be used for airplane hangars, army bases, agricultural growing nurseries, portable
warehouses, farm animal shelters, churches, convention centers, boat storage
units, nightclubs, entertainment arenas, film studios and so many more uses
only limited by ones imagination
Fabric structure basics
Membrane
materials
Most fabric structures are composed of
actual fabric rather than meshes or films. Typically, the fabric is coated and
laminated with synthetic materials for increased strength, durability, and environmental resistance. Among the most widely
used materials are polyesters laminated or coated
with polyvinyl chloride (PVC), and
woven fiberglass coated with polytetrafluoroethylene (PTFE).[1]
Cotton
canvas
The traditional fabric for fabric
structures is light cotton twill, light canvas, or heavy
proofed canvas.
Polyesters
Strength, durability, cost, and stretch
make polyester material the most widely used in fabric structures. Polyesters
that are laminated or coated with PVC films are usually
the least expensive option for longer-term fabrications. Laminates generally
consist of vinyl films over woven or knitted polyester meshes (called scrims or substrates),
while vinyl-coated polyesters usually have a high-count, high-tensile base
fabric coated with a bondable substance that provides extra strength.
Precontraint fabric is made by placing the polyester fabric under tension both
before and during the coating process. This results in a weave that has
increased dimensional stability.
Vinyl-laminated
polyesters
A laminated fabric usually is composed of a
reinforcing polyester scrim pressed between two layers of unsupported PVC film.
For most fabric structure uses, however, it refers to two or more layers of
fabric or film joined by heat, pressure, and an adhesive to form a single
ply.
With an open-weave or mesh polyester scrim,
the exterior vinyl films bond to themselves through the openings in the fabric.
Heavier fabric scrims, however, are too tightly woven to allow the same
bonding. In this case, an adhesive is used to bond the exterior films to the
base fabric.
A good chemical bond is critical to both
prevention of delamination and development of seam strengths. The seam is
created when vinyl-coated fabrics are welded together. The adhesive enables the
seam to meet shear forces and load requirements for a structure at all
temperatures. The adhesive prevents wicking of moisture into the scrim’s
fibers, which also prevents fungal growth or freezing that could affect the
exterior coating's adhesion to the scrim. Adhesives are water-based to comply
with EPA regulations.
Open-weave scrims generally make the fabric
more economical, although this can also depend on the number and type of
features that you require in the vinyl. Almost any color, UV resistance vinyl coated polyester, and colorfastness may
be incorporated into the vinyl. However, the more features added, the higher
the cost of the fabric.
Vinyl-coated
polyester
Vinyl coated polyester is the most
frequently used material for flexible fabric structures. It is made up of a
polyester scrim, a bonding or adhesive agent, and exterior PVC coatings. The
scrim supports the coating (which is initially applied in liquid form) and
provides the tensile strength, elongation, tear strength, and dimensional
stability of the resulting fabric. Vinyl-coated polyester is manufactured in
large panels by heat-sealing an over-lap seam with either a radio-frequency
welder or a hot-air sealer. A proper seam will be able to carry the load
requirements for the structure. The seam area should be stronger than the
original coated fabric when testing for tensile strength.
The base fabric's tensile strength is
determined by the size (denier) and strength (tenacity)
of the yarns and the number of yarns per linear inch or meter. The larger the
yarn and the more yarns per inch, the greater the finished product's tensile
strength.
The adhesive agent acts as a chemical bond
between the polyester fibers and the exterior coating and also prevents wicking,
or fibers absorbing water, which could result in freeze-thaw damage in the
fabric.
The PVC coating liquid (vinyl Organisol or
Plastisol) contains chemicals to achieve the desired properties of color, water
and mildew resistance, and flame retardancy. Fabric can also be manufactured
that contains high levels of light transmission or can be made completely
opaque. After the coating has been applied to the scrim, the fabric is put
through a heating
chamber that
dries the liquid coating. PVC coatings are available in a range of colors,
although non-standard colors can be pricey. Colors may be subject to minimum
order runs that allow the coating machine to clear out traces of any previous
color.
Fiberglass
Woven fiberglass coated with PTFE (Teflon or silicone) is also a widely used
base material. Glass fibers are drawn into continuous filaments, which are then
bundled into yarns. The yarns are woven to form a substrate. The fiberglass
carries a high ultimate tensile strength, behaves elastically, and does not
suffer from significant stress relaxation or creep. The PTFE
coating is chemically
inert,
can withstand temperatures from 100 °F upwards to 450 °F+. It is also
immune to radiation and can be cleaned with water. PTFE fiberglass is
additionally Energy
Star and
Cool Roof Rating Council certified. During scientific tests of its solar
properties, it was discovered that PTFE fiberglass membranes reflect as much as
73 percent of the sun’s energy while holding just seven percent on its exterior
surface. Certain grades of PTFE fiberglass can absorb 14 percent of the sun’s
energy while allowing 13 percent of natural daylight and seven percent of
re-radiated energy (solar heat) to transmit through.[2]
Because of its energy efficiency, high melting
temperature and lack of creep, fiberglass-based fabrics have been the material
of choice for stadium domes and other permanent structures, particularly in the
United States. However, when properly constructed, polyester structures may be
equally durable.
Olefin
/ polyolefin
A number of polymers consisting mainly of
polyethylene, polypropylene or combinations of the two are available for fabric
structures.
PVDF
woven
PVDF woven fabric are available for fabric
structures.
ePTFE
woven
ePTFE woven fabric are available for fabric
structures..
Blackout
fabric
Blackout material, also known as blockout
material, is an opaque fabric. Blackout fabric consists of a laminate that
sandwiches an opaque layer between two white exterior layers. Heating and
lighting of a structure may be controlled because the fabric does not allow
light to permeate the top or walls. The opaque quality also prevents stains,
dirt, repairs, or slightly mismatched panels on the structure's exterior from
being noticed from the inside.
Topcoatings
Most fabrics used for fabric structures
have some form of topcoating applied to the exterior or coating to make
cleaning easier. Topcoating provides a hard surface on the outside of the
material, forming a barrier that aids in preventing dirt from sticking to the
material, while allowing the fabric to be cleaned with water. As the material
ages, the topcoating will eventually erode, exposing the fabric to dirt and
making it more difficult to clean. The thicker the topcoating, the longer it
will last. However, coatings that are too thick will embrittle and crack when
folded.
There are several commonly used
topcoatings:
·
PVF film lamination is made up of polyvinyl fluoride (commercially known
as Tedlar). It consists of a film layer laminated to the PVC fabric during the
manufacturing process. The result is a thicker fabric that can resist weather
and chemical agents better than competing fabrics. Its self-cleaning ability
repels such things as acid rain, graffiti, and bird droppings. Because of these
characteristics it can often be found in use in industrialized areas, desert regions, and
coastal zones. The thicker coating has a slow erosion rate, resulting in
a life
expectancy of
approximately 25 years depending upon environmental conditions. This topcoating
is flexible, which creates a strong and consistent bond to the PVC. PVF coated
fabrics may be manufactured in a variety of colors, but are also subject to
minimum manufacture runs. PVF coating also makes the fabric non-weldable. Seams
are not overlapped, but instead are butted with an extra
welded seam, then applied to the underside of the fabric that does not have a
topcoating.
·
Acrylic topcoating is the most economical
and widely available topcoating used. Its spray-on application provides a
glossy finish and a resistance to UV degradation. Because the coating is
thin, the material is both easy to fabricate and is reparable by high frequency
or hot air welding. Depending on environmental conditions, an acrylic
topcoating will give the fabric a life span of 10 years or more. Acrylic
topcoats are ideal for fabric structures, and can be found on products used as
tradeshow pavilions, temporary concert halls, and portable warehouses.
·
PVDF topcoating is composed of a mix of
fluorine, carbon, and hydrogen. The combination of the fluorine and carbon
provides superior resistance to UV degradation and chemical damage than that of
the acrylic topcoat. PVDF coated fabrics also maintain color longer than do
those coated with acrylic. PVDF fabrics resist algae and fungi, and also have
self-cleaning properties that make them easy to maintain. These coated fabrics
are flexible, resist cracking, are easily handled, and generally have a life
span of 15 to 20 years depending upon environmental conditions. PVDF is
chemically grafted to the PVC and polymers used, which reduces the color
choices. Because white is the only standard color, other color choices are
limited and must be specially manufactured. Because of the chemical properties
of the coating, it must be abraded off to expose the PVC before welding.
This, too, increases fabrication costs. On site repairs are also difficult, as
the membrane must be manually abraded before repair.
·
PVDF/PVC topcoating is essentially a
dilution of the PVDF topcoat that makes the finished fabric less expensive to
manufacture. The finished fabric may be welded without having to abrade the
material, which reduces costs. However, because the PVDF is diluted, longevity
and the ability to withstand environmental factors are reduced. This results in
a general life expectancy of 10 to 15 years. These materials are also available
in colors, but are subject to limited manufacturing runs.
·
Tio2 (Titanium Dioxide) Top coating
"Titan W": TITAN W is a surface finish whose formulation was prepared
by Naizil S.p.A. in collaboration with the Chemical Engineering Department of
Padua University.
TITAN W exploits the most innovative nanotechnology methods for the use
of particular particles in combination with fluoropolymers (PVDF) mixed with
acrylic resin. The effectiveness of TITAN W compared to coatings based on
acrylic lacquering and PVDF has been shown by numerous tests on deterioration
by atmospheric agents, both accelerated and outdoors (weathering test).
The result is a coating that gives the
fabric the following advantages:
·
Less yellowing and colour variation
·
Longer lasting physical properties
·
Better preservation of flexibility
·
Better self-cleaning properties
With these additional advantages, the
fabrics coated with TITAN W lacquering will offer better durability compared to
the existing coatings used. In addition to the above-mentioned characteristics,
fabrics with TITAN W lacquer are high frequency and hot air weldable.
Fabric properties
When discussing fabric properties for use
on a structure, there are several terms that are commonly used:
·
Tensile strength is a basic indicator of
relative strength. It is fundamental for architectural fabrics that function primarily
in tension.
·
Tear Strength is important in that if a
fabric ruptures in place, it generally will do so by tearing. This can occur
when a local stress concentration or local damage results
in the failure of one yarn, which thereby increases the stress on remaining
yarns.
·
Adhesion strength is a
measure of the strength of the bond between the base material and coating or
film laminate that protects it. It is useful for evaluating the strength of
welded joints for connecting strips of fabric into fabricated assembly.
·
Flame retardancy does not have the
same meaning as flameproofing. Fabric that contains a flame-retardant coating
can withstand even a very hot point source. However, it can still burn if a
large ignition source is present.
Structural properties
When deciding on a fabric it is imperative
to keep certain fabric properties in mind. These include stress versus strain
(unit load versus unit elongation), expected service life, the mechanisms of
joining the material together (welding, gluing, etc.), and the fabric’s
behavior in or around fire.
Stress versus strain data should be
obtained in both uniaxial and biaxial forms. This information characterizes the
fabric in terms of stiffness, elasticity, and plasticity. This is essential
information when determining the material's response under load in a
load-carrying application. Shear strength, shear strain, and Poisson's ratios, though difficult to
obtain, are fundamental when analyzing a fabric as a structural material.
Cost savings to fabric buildings
The benefits of fabric buildings are many -
no lighting is required as fabric is translucent, which makes it an energy
efficient solution.[3] Mobility: You can
move them, either on wheels or relocate them completely. Savings: They cost
about half of what a traditional structure costs.
Fabric properties: When discussing fabric
properties for use on a structure, there are several terms that are commonly
used:
Tensile strength is a basic indicator of
relative strength. It is fundamental for architectural fabrics that function
primarily in tension. Tear Strength is important in that if a fabric ruptures
in place, it generally will do so by tearing. This can occur when a local
stress concentration or local damage results in the failure of one yarn, which
thereby increases the stress on remaining yarns.
Adhesion strength is a measure of the
strength of the bond between the base material and coating or film laminate
that protects it. It is useful for evaluating the strength of welded joints for connecting strips
of fabric into fabricated assembly. Flame retardancy does not have the same
meaning as flameproofing. Fabric that contains a flame-retardant coating can
withstand even a very hot point source. However, it can still burn if a large
ignition source is present.
Of course, other properties must be
factored in when determining a material's suitability for a structure. To fully
understand a fabric's value and usefulness, consider the following:
·
General solar, optical, and thermal
performance data
·
Acoustical data
·
Dimensional stability
·
Cleanability
·
Seam strength and stability
·
General handling ability, including
abrasion resistance, foldability, etc.
Portable
Building Systems specializes in these portable fabric structures and buildings
and can customize a building for you whatever your needs are. We are
wholesalers for all of the top manufacturers including Irmarfer, BriteSpan,
ClearSpan and so many more. Whatever configuration or size you need our
engineers can make it happen. Our construction teams can meet your needs
worldwide including in Europe, North America, South and Central America, the
north and south poles or anywhere on the globe. Give us a call today to start
planning your next fabric structure building. Portable Building Systems, http://www.Portable-Building-Systems.com
or call today us at (954) 667-7597.
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