Civil Engineering Reference
In-Depth Information
Chapter 8
Non-Structural Performance Considerations
8.1 Tensioned Fabric Structure Applications
8.1.1 Introduction
Variability of form is a hallmark of tensile membrane construction, and membrane
shapes can be adapted to fit a wide range of building footprints. As a result of the
curvature requirements of the membrane, however, these structures typically have
fairly tall profiles in elevation, and cannot easily be adapted to the flat roof profile of
conventional construction. Near flat membrane profiles are only possible on small
structures or those with members that support the fabric at close intervals. In the
latter type of application, the membrane serves more as a cladding material than a
true structural element.
An attractive feature of tensile membrane structures is their enormous range of
spanning capability. Membranes have been used in a number of applications as an
alternative to translucent glazing, using pretensioned fabric without curvature over
spans up to 4 or 5 meters. Membranes supported on arches or other shaping elements
are common in skylight applications with spans of 20 meters or more.
Membranes have been used just as effectively in stadiums and other assembly
structures with spans of up to 250 meters. In these applications, the membrane is
typically restrained or supported by steel cabling in conjunction with air pressure or
rigid steel elements, so that its unsupported span is seldom greater than 20 meters.
(On spans greater than this limit, membrane stresses and deflections tend to become
excessive.) While air-supported and cable dome roofs can and have been sheathed in
materials other than fabric, the membrane provides a significant portion of the
strength and stiffness of these roofs, and is integral to their global behavior. Design
of these structures explicitly considers the properties of the fabric, and these roofs are
therefore appropriately considered true tensile membrane roofs rather than membrane
clad roofs.
It is useful to categorize the basic forms of membrane structure application in order to
delineate the particular issues or advantages associated with each. Membrane
structures may be categorized according to their relationship to other construction: as
membrane covers (membranes that serve as building roofs or complete enclosures),
attached membranes such as awnings), or internal membranes (such as decorative or
acoustic ceiling membranes).
8.1.2 Membrane Covers
The majority of membrane structures cover space and carry their own loads to grade.
Because they form an exterior shell, they are exposed to environmental loadings that
may include wind, snow, rain, and ice, and their design must provide membrane
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