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Model Project Test Results
Global instability

Arch 324, Introduction to Structural Design, University of Virginia
Last updated Monday, March 11 1996, at 9:59 PM Copyright © 1996, Kirk Martini

Global Instability

At the level of overall form, the project required the designer to find proportions that struck an appropriate balance between high depth and slenderness for strenght, and low depth and compactness for stability. Many projects opted for too-slender proportions, resulting in global instability. The projects below toppled, undamaged, under relatively small loads.

This beam simply rolled over under a relatively small load. Although the structure failed, the material was undamaged.
This tied arch structure suffered a similar failure
This cable structure worked well until it swayed in the direction parallel to the span, it was internally unstable because the connections at the top had little resistance to rotation.

Other projects had even more difficulty dealing with the stability issue. The images below show a model that was unable to carry it's own weight, collapsing immediately into the loading bucket. The basic concept for the structure was sound in two dimensions, but the implementation did not provide necessary lateral bracing.

Unable to stand on its own, the ill-fated structure is held in place by its anonymous authors.
The self-disposing structure collaapsed into the empty loading bucket.

Next: Local Instability

Last updated Monday, March 11 1996, at 9:59 PM
Copyright © 1996, Kirk Martini
Please send comments or questions to Martini@virginia.edu
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