Ivan Farr designed and supervised the erection of a nucleated tensegrity mast at Texas A&M. The tower honors Alan Stacell.
Statistics:
Height: 25-foot
Tendons: 250 feet galvanized steel cable
Nucleated struts: steel pipe, 1/8"
Its nucleated units look like airplane propellers. The new tower replaces one Stacell erected that stood for 6 ½ years. The new Farr tower is half the height of the original tower, due to practical considerations of construction, namely limitations of the off-site assembly area.
“It couldn’t have been made any bigger because when we raised it at the ranch, it came in a foot under the ceiling and it was within one-half inch of the maximum delivery truck space,” Farr said.
Farr’s initial designs of the tower called for high-strength plywood, but for structural and financial reasons, steel had to be used instead.
“Purchasing carbon steel from local Aggie-friendly suppliers proved far more cost effective than importing prime plywood from other states,” said Farr. “Choosing to construct the tower exclusively of steel gave one more crucial advantage, because it weighs less than wood in the manner used.”
To give the tower the necessary stability with wood said Farr, significantly greater quantities of it would have to be used, whereas a 1/8” steel propeller weighing just a few pounds could serve the same purpose.
“Selecting the cable was a challenge, as it had to be sized in relation to the pipe’s inner diameter,” said Farr. “A thin cable will rattle and be unable to provide the necessary shear resistance to the pipes in compression, and a thick cable will cause threading problems or may simply be too inflexible for general use.”
Externally tensioning the final cables proved to be another challenge, as well as finding an engineer willing to sign off on the tower. “No signature, no tower. When I had visited with about 10 engineers who were hesitant to sign up on the project, I started doubting it would go through at all.”
Others integral in making the tower a reality were engineers Thomas Gessner and Mikael Olsen, sponsors Jorge Vanegas and Rodney Hill, and suppliers Brazos Industries, Mack Bolt & Steel, Suncost Post-Tension, Harbor Freight and Texas Custom Coasters.
http://archone.tamu.edu/college/news/newsletters/spring2010/stories/stacell_tower.html
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