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	<title>John Zerning &#187; Prestressing</title>
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	<description>Garden Trellises - Architectural Space Frames</description>
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		<title>Prestressing: Dodecahedral cage made rigid via prestressed wires</title>
		<link>http://www.johnzerning.com/prestressing-dodecahedral-cage-made-rigid-via-prestressed-wires/</link>
		<comments>http://www.johnzerning.com/prestressing-dodecahedral-cage-made-rigid-via-prestressed-wires/#comments</comments>
		<pubDate>Sun, 23 May 2010 11:03:34 +0000</pubDate>
		<dc:creator>John Zerning</dc:creator>
				<category><![CDATA[Prestressing]]></category>
		<category><![CDATA[dodecahedron]]></category>

		<guid isPermaLink="false">http://www.johnzerning.com/?p=208</guid>
		<description><![CDATA[Once again, curiosity and the pleasure of finding and working things out motivated this DIY project.
Being a keen cyclist, I am fascinated by the lightweight efficiency of the bicycle wheel with tension spokes. This small and inexpensive project is about applying the structural principle of the bicycle wheel to a spatial closed system.
The starting point [...]]]></description>
			<content:encoded><![CDATA[<p>Once again, curiosity and the pleasure of finding and working things out motivated this DIY project.</p>
<p>Being a keen cyclist, I am fascinated by the lightweight efficiency of the bicycle wheel with tension spokes. This small and inexpensive project is about applying the structural principle of the bicycle wheel to a spatial closed system.</p>
<p>The starting point were the two polyhedra: the great stellated dodecahedron inscribed in a dodecahedron. For the dodecahedral cage I used Herringbone struts (manufactured by Simpson Strong-Tie) and for the great stellated dodecahedron I used galvanised wires.</p>
<p>Instead of the turnbuckles I used long eye bolts with two nuts. To fix the wire end to the eye bolt I threaded the wire through the eye and bent it over by 180 degrees, then pushed a washer over the two wires and bent the end again.</p>
<p>I began by assembling the dodecahedral cage (the ends of the struts had prepared holes). As the form had &#8220;hinged&#8221; joints and no triangulation it collapsed! To make it stand up I temporarily stabilised all the 12 pentagonal faces with thin wires (radiating from the centre to each of the five vertices).</p>
<p>Next, piece by piece, the 90 prepared wires, with L-shaped ends, were fixed into their correct positions.</p>
<p>Finally, the exciting bit could begin – prestressing the structure one vertex at a time. With each complete cycle the structure became progressively stronger and stiffer – magic. Indeed, prestressed wires resist forces like columns! The larger the structure the more efficient it becomes.</p>
<p><strong><em>Yes, I do, and I understand!</em></strong><em></em></p>
<p>This is a good model of the <em>synergy</em> between the opposing forces (tension and compression).<br />
The working together of the two forces to produce an effect greater than the sum of their individual parts.</p>
<p>The constant interaction between two opposing balancing forces in this closed system can stand as a metaphor for Yin and Yang!</p>
<div id="attachment_183" class="wp-caption alignnone" style="width: 510px"><em><strong><em><strong><img class="size-full wp-image-183" title="dodecahedron_stellated" src="http://www.johnzerning.com/wp-content/uploads/2010/05/dodecahedron_stellated.jpg" alt="Dodecahedron filled with a stellated dodecahedron. Straw model." width="500" height="338" /></strong></em></strong></em><p class="wp-caption-text">Dodecahedron filled with a stellated dodecahedron. Straw model.</p></div>
<div id="attachment_182" class="wp-caption alignnone" style="width: 510px"><em><strong><em><strong><img class="size-full wp-image-182" title="dodecahedron_spatial" src="http://www.johnzerning.com/wp-content/uploads/2010/05/dodecahedron_spatial.jpg" alt="The principle of the bicycle wheel applied to a spatial closed system." width="500" height="377" /></strong></em></strong></em><p class="wp-caption-text">The principle of the bicycle wheel applied to a spatial closed system.</p></div>
<div id="attachment_179" class="wp-caption alignnone" style="width: 510px"><img class="size-full wp-image-179" title="dodecahedron_constr1" src="http://www.johnzerning.com/wp-content/uploads/2010/05/dodecahedron_constr1.jpg" alt="Constructional details" width="500" height="388" /><p class="wp-caption-text">Constructional details</p></div>
<div id="attachment_180" class="wp-caption alignnone" style="width: 510px"><img class="size-full wp-image-180" title="dodecahedron_constr2" src="http://www.johnzerning.com/wp-content/uploads/2010/05/dodecahedron_constr2.jpg" alt="Constructional details" width="500" height="338" /><p class="wp-caption-text">Constructional details</p></div>
<div id="attachment_181" class="wp-caption alignnone" style="width: 510px"><img class="size-full wp-image-181" title="dodecahedron_fig4" src="http://www.johnzerning.com/wp-content/uploads/2010/05/dodecahedron_fig4.jpg" alt="Struts and “spider webs”, the latter being almost invisible." width="500" height="392" /><p class="wp-caption-text">Struts and “spider webs”, the latter being almost invisible.</p></div>
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