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Designing fabric structures

September 1st, 2008 / By: / Structure Basics

Three quick steps to success.

Step one: Do your research

The best way to incorporate a fabric structure in a project or design a stand-alone fabric structure is to see what has already been done. Magazines such as Fabric Architecture, books on fabric structures and basic searches on the Internet using keywords like “fabric structures,” “fabric architecture,” “membrane structures,” and even “tents,” “awnings” and known fabricator’s names can be helpful. You will find examples of projects that have been done around the world to give you some ideas of shape, form and building type. Another place to look is Europe’s TensiNet group (www.tensinet.com). It has a wonderful Web site with links to other helpful databases and libraries. Spend some time with pen, paper and some stretch nylon. If you understand the basic concept of double curvature and the common forms of the cone, barrel and hyperbolic paraboloid (“hypar”), explore a few sketches before you go straight to CAD. Playing with stretch nylon and dowels or brass rods will help you understand the process of “form finding.” A common mistake designers make is to immediately go into Autocad®, SketchUp or other 3D-CAD program without totally understanding what forms work and what forms don’t. Taking time to understand the forms gets you half way there.

It’s important to research which material is best suited to your application. Materials range in price, width, translucency and lifespan, to name a few, and knowing what you can do with a certain fabric or why certain fabrics are used is extremely important. Fabric can be found by looking on the Industrial Fabrics Association International Web site (www.ifai.com) or typing in keywords such as “architectural fabrics.” Don’t be afraid to ask a supplier for a fabric sample. There is no substitute for seeing and feeling fabrics.

Step two: Create a wish list or set the criteria

“It’s basically steel, fabric and cables” is a common response from designers when it comes to discussing a fabric structure’s components. True, but it’s important to make a “wish list” with some certain decisions about size, shape and the specifications of your structure prior to talking to an engineer or fabricator. People in the construction industry like to discuss the size of projects in terms of square foot and primarily in plan area. Fabric structures are normally discussed in surface area because their form plays such a role in determining size, length and cost of components. For example, a flat “hypar-style” structure will have less surface area than a conical structure. If you cannot calculate the surface area, assume you will have at least 1.5 to 2 times as much membrane surface area as plan area due to its shape. Another key point is lifespan. Few other building materials are looked at from the stand-point of lifespan. Fabric structures have different life spans based on the material chosen and its major use. Some fabric structures are designed as temporary structures, with a life span of 5 to 10 years. There are fabrics for that life span. Some fabric structures are required for 10 to 20 years, and there are materials in that range as well. Permanent fabric structures require materials that are long lasting, with life spans of more than 30 years. All come with different costs, as do paint and cable specifications. Add foundations, water diverters and lighting to the wish list and you will soon find yourself with more than just “steel, fabric and cables.” Prioritize your list by choosing the most appropriate components for the application. Ask yourself these types of questions: What truly is the life span of my project? Are the finishes on the steel and cables exposed to a corrosive environment? What’s important to my client?

Step three: Set a realistic budget

“How much does it cost?” is the most asked question from both the client and the designer to the specialty contractor. Perception is the first thing that comes to the fabricator’s mind. The client’s perception and the designer’s perception of a fabric structure’s cost are always different from the fabricator’s. The main reason is that when fabricators see a project, they see beyond the size and shape of the fabric structure. They see the complexity of fabrication, the installation and labor, the material wastage, and the design, detailing and engineering required. A suggestion: Set a realistic budget. How do you do that? One way is to send a dimensioned sketch to get a relative order of magnitude (ROM). This will give you a price range to work with. You can then decide your next step. If you are getting a price range, play it safe and assume the higher price. Another way is to find a fabricator to work on a “design/build” basis, where the fabricator becomes a “partner” in the design process so you can discuss fabric, finishes and your wish list, before you nix the whole project for lack of funds. The result of this collaboration can be very cost effective.

Finally, you can consult with an engineering firm that specializes in membrane structures. The firm can do a complete analysis and produce a complete set of buildable documents from which a firm proposal can be made. There is usually a fee involved with this, but there is no substitute for experience and building from plans and specifications produced by a qualified engineer. Find the process that works best for you.

A seasoned veteran of fabric structures once told me, “Remember, companies don’t build fabric structures, people do.” Just like picking the most appropriate material for the application, choose a designer, engineer or fabricator who you feel comfortable working with and take the plunge.

I wish you much success!

Samuel J. Armijos, AIA, is an architect with FabriTec Structures and a frequent contributor to Fabric Architecture. His recent book is Fabric Architecture: Creative Resources for Shade, Signage, and Shelter (W.W. Norton, 2008).

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