Designing Fabric Structures
Architectural fabrics can be manufactured to vary in translucency from one to 95 percent and, in thermal resistance, from that of a single pane of glass to that of a conventionally insulated structure, while still maintaining adequate daylighting. A fabric roof can be a source of interior light at night if artificial light is directed onto its highly reflective surface.
The performance of today's architectural fabrics depends on the weaving pattern, choice of substrate, and coating. Each composite has unique properties and characteristics that suit it to different applications. Most materials presented have a minimum of stretch and shrinkage in a wide range of temperature and humidity conditions, and coatings prevent mildew, staining, and streaking.
Choice of a material calls for understanding of its light reflectivity and light transmission. Reflectivity is the amount of light the surface of the material reflects. Transmission is the amount of light that penetrates the material. Most fabrics allow some amount of light transmission, but some materials come with a blackout scrim between layers and allow no light to penetrate, so light and heat from the sun can be controlled.
All the materials come in some shade of white; some are also available in a limited range of colors, depending on supply and demand. The proper selection of membrane material will be based on the proposed size, form, function, and desired longevity of the structure, and the economics of the project.
Membranes can be fabricated in a number of ways based on the material chosen and the orientation of the seams. All aspects of a fabric structure should be derived from the same computer model or full-scale mockup. Computer-generated patterns are the most widely accepted template for fabrication. Smaller structures, such as awnings, are patterned directly off a full-scale mockup.
Seams determine the appearance of joined panels. The seams can be sewn, glued, electronically welded, or heat-sealed. Seam styles can be parallel or radial to a mast. Butt seams are joints produced by placing two adjacent pieces directly beside one another and covering the joint with a strip of material. Lap seams are joints made by overlapping the edges of the material.
Reinforcements — multiple layers of material applied to specific areas of a membrane to strengthen it where concentrated tension loads exist — are also a part of the fabrication process and differ from project to project.
Architect Samuel J. Armijos lives in New Jersey.
This article is excerpted from Fabric Architecture by Samuel J. Armijos, copyright © 2008, with permission of the publisher, W.W. Norton & Company, Inc.
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