by Samuel J. Armijos
The first step in designing a fabric structure is to create a form with sufficient pre-stress, or tension, to prevent it from fluttering like a flag or sail. Lightweight structures with minimal surfaces optimally should have double curvature — a surface that possesses a high-point (positive) curvature along one principal axis and a low-point (negative) curvature along the other principal axis.
Anticlastic surface forms have double curvature in diametrically opposite directions, like a saddle, while synclastic surface forms have double curvature in the same direction, like a balloon. The degree of curvature depends upon the type and weave of the fabric as well as the type and direction of the loads.
The three basic forms associated with tensioned fabric structures are the hypar (hyperbolic paraboloid), the cone, and the barrel vault. The hypar, or simple saddle, is often a square or rectangular form in plan that in elevation is a series of high and low points. Mast- and point-supported structures are cone forms. Arch- and frame-supported structures, in which the membrane is supported by a compression member, are barrel vaults.
Determining Boundaries
The second step of the design process is to determine the boundaries of the tensioned fabric, which is referred to as the membrane. Boundaries include frames, walls, beams, columns, and anchor points. The fabric is either continuously clamped to frames, walls, or beams, or attached to columns and anchor points with membrane plates with adjustable tensioning hardware.
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This article is excerpted from Fabric Architecture by Samuel J. Armijos, copyright © 2008, with permission of the publisher, W.W. Norton & Company, Inc.
