Fabric structure

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.

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.
• Free Form Tensile fabric allows one to use free form in building construction as it is flexible material.

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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.

There can be multiple advantages to fabric structures over traditional buildings in certain scenarios. In some cases, no lighting is required as the fabric used is generally translucent, which makes it an energy efficient solution. 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:

• Shading coefficients
• General solar, optical, and thermal performance data
• Acoustical data
• Dimensional stability
• Colorfastness
• Cleanability
• Seam strength and stability
• General handling ability, including abrasion resistance, foldability, etc.

Fabric roof in Tulsa, Oklahoma: