Re: spectacular and serene

[Patrick Salsbury <salsbury at sculptors dot com>]

On Tue, Jan 16, 2001 at 10:38:59AM -0600, Charles J Knight wrote:
> > my initial thoughts are 1) they seem too susceptible to the tornados we 
> > have here in south-central Texas and 2) they do not appear to be good
> > for do-it-yourselfers like me...my plan is to build several small
> 
> 1)   I live in north Texas...Dallas.  The shopping mall I mentioned is
> in Sherman, which is part of the big silver trophy buckle of the tornado 
> belt.  They've held up fine, through many tornadoes.  They do *look* 
> fragile though, don't they?
> 
> Think about it this way...the fabric functions almost exclusively in
> tension.  There are threads (Kevlar springs to mind) which can
> support a full grown adult, individually.  Now, weave them into a
> cloth, and "spread" the load a bit.  Imagine the forces needed
> before you could break even a single thread, much less rip that
> cloth.
> 
	Chuck is right. The material most large fabric structures are made
of is teflon-coated fiberglas. The fiberglas is woven into extremely strong
fabric, then dipped in molten teflon, which seals the gaps in the fabric
and makes it more rigid. This is also what gives the fabric structures
their brilliant white color. The teflon starts out tan-colored, and
bleaches out to pure white after a few weeks, and after that, it doesn't
stain, discolor, or even get dirty for 25-30 years or more. (Almost nothing
sticks to teflon, so any dust or dirt washes off with each rain, leaving it
sparkling white.)

	Most of the really big fabric structures you see, including the Haj
terminal and the Millenium Dome were made by Birdair Corporation.
http://www.birdair.com/  My fabric structures class toured their plant in
Buffalo, NY about 10 years ago. 
	One humorous note about the Haj terminal was that the Sheik who
ordered the thing built in Saudi Arabia didn't know about the bleaching
process, so when he came to the construction site, and saw the first 2 of
the 130 or so pavillions going up, he saw that they were tan and said "No,
no! I ordered a white one! Take those down and bring me a white one!" They
then had to convince him to wait the 2 weeks and that it really *was* a
white one. :-)  
	
> I'm trying to do the same thing, but from fabric...it's such an
> interesting
> way to build, but patterning has to be very precise.  (like domes don't
> require precision and math...)  Unfortunately, noone that I'm aware of
> has published a book called "tensile math and how to use it," as Hugh
> Kenner did for geodesics.
> 
>       -- Chuck Knight
	Sounds like a great idea! Realistically, the math is all
triangle-mesh iterations. The calculations are done over and over and over
to "relax" a shape into its minimal surface configuration. It's not the
sort of thing anyone would want to do by hand. I'm still not aware of any
shareware/freeware programs that do this, but it seems like it wouldn't be
all *that* hard to do. You'd just need arrays of numbers that describe
points on the surface that you're modeling, and as you put it under a
stress or load, it will respond and shift in various ways, depending on the
load, elasticity of the fabric, etc. There are certainly engineering
programs that do this. We used some from Birdair while in college. I'm sure
they've improved in the last 10 years. They even did things like wind and
snow-loading calculations.

	Some of the books that we studied dealt a lot with bubble systems
and the minimal surfaces they form. Bubbles are really quite fascinating,
and they follow some interesting rules regarding the geometries they form
at intersections and in clusters, etc. Frei Otto's work is the foundation of
much in modern fabric structures. Look for his books to get a good insight
into many of the forms. 

	Just found this rather cool page detailing some people's work on
determining different forms for fabric structures:

http://fibers.philau.edu/ntc/f00p01/


-- 
Pat
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