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Tensile awnings, by design

March 16th, 2015 / By: / Awnings & Shades

Designing and fabricating tensile awnings calls for a special skill set.

Craig Flanagan, long-time owner of Shade to Order P/L, Gateshead, NSW, Australia, knows a thing or two about producing tensile awnings and canopies. He has some recommendations for those interested in the market.

“In a small factory the fabricator is the sales person, designer, manufacturer and installer. They may contract one or more of these out to a specialist, but let us assume they are completing all tasks except for engineering.

“Selling a tensile structure involves having a good knowledge of fabric types and finishes on the fabric surface. The sales person really needs an understanding of the design processes, the manufacturing process and installation.”

The designer needs a good understanding of the proposed structure, adds Flanagan. “What shape will it be? Freeform, conical, barrel vault or a combination of two or more structures? Catenary cable edges, structural beam edges, columns or attachments? And the designer must have some idea of the fabric that is to be used. They have to try to balance all this with the client’s wishes.

“The designer must have a good understanding of computer-aided design (CAD) and have access to a specialist tensile fabric program that will design, analyze and pattern the fabric skin. Fabric compensations are completed after patterning, and this is important on all but the smallest of tensile structures. Most of these computer programs analyze the whole structure, including footings, columns and attachments.

“The manufacturer will generally have a computer-controlled plotter or cutter to plot the seams, numbers, edge turnovers on the fabric and finally cut the panel out. The computer lets the designer nest the panels for efficient use of fabric on the roll, reducing waste. The manufacturer will be armed with a computer-generated plan for each panel of the structure, and then set about joining these together to form the completed skin. Depending on the fabric used, the panels are put together by a high-frequency weld, heat and pressure seal (hot air weld) or sometimes glue.

“The manufacturer also needs a good understanding of the process when finishing the edges of a tensile structure. Large catenary cable-edge curvatures can be challenging to complete and can be made easier by correct fabric orientation by the designer. Cable edges need to be perfectly fair; the slightest bump will transfer compression wrinkles into the fabric. Conical structures radially patterned require some thought with regard to panel orientation. It’s important to try as much as possible to match adjacent panel thread lines.

“The installer should be a qualified rigger or have an understanding of installing tensile structures. There can be enormous loads on the connection points; and tensioning the fabric skin complete with wire catenary cables, corner plates and link attachment points, or out to rafters and beams, can be challenging. There may be further adjustments needed around the edges with catenary cables or beam attachments.”

According to Flanagan, tensile structures can vary from incredible translucency to total block out, depending on fabric choice. Translucent fabrics can reduce interior lighting costs, have low maintenance costs and installation can be measured in days or weeks, not the months associated with conventional building materials.

Bruce N. Wright, AIA, a licensed architect, is a media consultant to architects, engineers and designers, and writes frequently about fabric-based design.

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