Civil Engineering Reference
In-Depth Information
fabric panels in the future. Limiting reasons that would keep a manufacturer from
immediately going to the CAM approach are the cost of purchasing equipment and
the cost of upgrading technically-trained staff to work with computer-generated
manufacturing data.
9.2.2 Wider Roll Goods
Since the publication of the first edition of this topic, roll goods wider than the
ordinary 60 inch wide rolls have become more generally available. These are often
desirable because of the lower cost of fabrication due to a reduction in the amount of
cutting, sealing, and other efficiencies that result.
In certain fabric types, Teflon-coated fiberglass, for instance, wide-width fabric has
been available for many years. Most PVC-coated polyester fabrics have generally
been manufactured in narrower roll widths, but now are sometimes available in
anywhere from 70 inch to 108 inch widths.
The trend toward the use of wider width fabric will probably continue. However, it is
worth noting that if the project involved is a small structure with severe surface
curvature, the shape required may not allow wide un-sealed fabric panels without
problems, both cosmetically and structurally. Wide un-sealed fabric panels are those
that, for the purposes of this discussion, cannot adequately model the surface and the
resulting stresses in the system. Wide un-sealed fabric panels in surfaces that have
severe curvature may be cosmetically problematic because wrinkling is likely to
occur. They may be structurally problematic in that the engineer is likely to lose
capability to accurately model the stress distribution in the system and overlook
potentially dangerous over-stresses (or under-stresses) in fabric/cables/connections.
See Section 9.1.2.
9.2.3 Availability of Patterning Software
More computer programs are now available that produce fabric patterns. These
represent a broad range of approaches. Some generate patterns that flow directly out
of an equilibrium shape that has been used to perform the stress analysis that controls
the structural design. Some others generate patterns that flow out of an equilibrium
shape that has been contrived from a notion of a certain ratio of warp pre-stress to fill
pre-stress - without, necessarily, any evidence of how such a shape would perform
under superimposed design loads. In other words, the shape produced may look well
- or not - but whether the structure behaves properly in service is unknown. Some
others generate patterns that are based on ratios of warp-to-fill surface curvature;
these are similar to the previous type in that they are not necessarily indicative of a
defined structural response due to the application of design loads.
Any patterning software is suspect that does not generate patterns from an
equilibrium shape that is the same shape that has been subjected to an analysis and
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