In the 10/18/99 issue of Design News, we posed the following no-problem problem: Given a one-gram supply of spider silk -- and nothing else -- where is the optimal weave pattern for constructing a trash-hauler-truck-proof highway crash barrier? Here are some of the best responses, including the winning letter from reader Gary Ash who will receive a one-lb bag of gummy spiders, compliments of Design News.
A tangled web
Spider silk is amazing for high strength, lightness, elasticity, and uniformity. Better than that, the spider can make both sticky and non-sticky types. The kind of spiders who make spiraling webs, such as argiope aurantia and araneus cornutus, may orient their webs using signals from polarized sky light or the earth's magnetic field. So, you've got to be a great spider wrangler to actually get the little devils to deliver the gram of spider silk and install it in the right place. Of course, the gram of spider silk has to be divided into the non-sticky kind for the basic support and really sticky stuff to actually hold the rampaging truck in place when it hits the barrier. Otherwise, the truck would just bounce back into the stream of following traffic, and we can't have that!
Many spiders want to weave an Archimedes spiral. This is great if you have a round opening, but we can expect a more rectangular opening to be blocked. We'll have to teach the spiders to put bundles of multiple strands in the center of the opening, with a decreasing number of strands in a bundle as we move to the edges. The bundles themselves should be on regular spacings in both directions so that there is a standard size opening. Designs need to take into account the additional static loads imposed by rain, snow, and dead flies. Within each square opening, an individual spider can do its work. Spiders are used to building spiral webs in small square or rectangular openings. The advantage of standard sizes is that it reduces the training time for the spiders to a period within their normal life span. Additionally, it simplifies the qualification and compliance testing to ensure that we meet impact strength specifications. Once the basic framework of bundles is in place, a herd/gathering/flock/ webbing of spiders can finish up the job in a couple of hours.
There are a few ecological and permitting problems. You didn't think that you'd just be allowed to round up thousands of spiders to produce this silk and then "do them in" later, did you? You may offend the sensitivities of millions of Americans who read Charlotte's Web and just love spiders. Each spider must be returned home unharmed after its mission is performed. The more serious issue is that the sticky silk will also collect all of the bugs that fly by. For the size of silk truck barrier that is proposed, a major environmental impact statement would have to be prepared.
You'd need to detail how the removal of so many flies, moths, and other bugs would not upset the ecological balance of the region. Worse than that, you'd no doubt also collect hummingbirds from someone's endangered species list. And what about small children wandering by? Who would feed them or free them from the web? What would stop parents from sending their ill-behaved offspring in the general direction of such immobilizing traps? The debate over permitting, ecological impact, and child raising would stretch on for years.
Meanwhile, articles in the New Yorker, People magazine, and the National Enquirer about the fiendish plans of spider web truck barrier builders would create a storm of public protest. Sorry, another great idea that will never get built! (Special thanks to Anne Helmenstine at http://geocities.com/CapeCanaveral/Launchpad/3877/ for info on spiders and silk.)
Gary Ash
Director of System Technology
Helix Technology Corp.
Mansfield, MA
The diva decoy ploy
Use counted cross-stitch to weave the silk into a net that says, "Martha Stewart." The repulsive forces between a teamster and Martha are so high that even the heaviest trash hauling truck would be repelled from the barrier.
Gerard Vaerewyck
Add a retaining wall
The answer to this question is obvious. The silk should be woven into a nice ribbon (preferably red), which is attached to a medal of commendation. This metal is then presented to the highway designer who routed the highway through a narrow canyon, the walls of which serve as the required crash barrier.
David Polakowski
Reliability Engineer
Hewlett-Packard
Everything but the flies
Before I started on this problem, I did what every design engineer should do go see what the experts recommend. In this case, the "experts" have eight legs and eat insects. As I watched them work, I noticed a disturbing trend. They were catching everything in their webs except what they wanted -- sticks, dirt, leaves, trash, etc.
This led me to the conclusion that even if you wove a perfect pattern for a trash-hauler-truck crash proof barrier, you would never be able to test it. You would end up catching VW Beetles, Vipers, Cobras, Sunbirds, and if you were really lucky, you may catch something bigger such as a Jaguar or Ram.
Even if you wove your barrier in a perfect place for a test, you would probably end up catching a low flying Whirly-Bird instead. If you don't believe me, just go and ask the eight-legged experts.
D. O'Brien
Engineering Manager
North American Capacitor
Greencastle, Indiana
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