Fiber bridge connects Incan, student engineers


A technology that once brought the bold conquistadores of Spain to their knees in fear in the jungles of South America has come to the dry moat behind the Stata Center.

Students in Course 3.094 (Materials in Human Experience) have built a fiber bridge in the style of the Incan Empire. They call it Chaka Stata--chaka being the word for bridge in Quechua, the native language of Peru.

The Incas had no wheel, no arch and no system of writing. But they knew how to twist and braid countless miles of grasses and slender branches into ropes--sometimes as thick as a wrestler's waist.

From these ropes they built a system of long-span fiber suspension bridges that connected 15,000 miles of road across a distance greater than the width of the Roman Empire. The bridges, appropriate to the vertical landscape of the Andes, made possible a system of messenger service unmatched until the 19th century.

But the bridges swayed under the weight of traffic--and that's what terrified the Spanish and their horses, even though, as one Spaniard observed, they were almost as "sturdy as the street of Seville."

John Ochsendorf, assistant professor of architecture, has been studying these rope bridges since his undergraduate days at Cornell. This semester, Heather Lechtman, professor of archaeology and ancient technology, and Linn Hobbs, professor of materials science, have been guiding their students in Course 3.094 in the construction of the 70-foot Chaka Stata.

The project made a few concessions to modernity, however: They used sisal twine from the Yucatan Peninsula instead of the grasses the Incas used. And whereas the Incas chiseled into stone to anchor their bridges, the MIT students anchored Chaka Stata by wrapping it around some massive concrete blocks contributed by A.J. Welch Corporation of Brighton.

The weekend's burst of activity was preceded by what the students estimated was 360 hours of rope-twisting as the 50 miles of sisal twine was turned into rope.

Working together as a group was part of the exercise. "A third of the time was spent learning to work together," one of the students said. "But after a while, we were banging those cables out."

A version of this article appeared in MIT Tech Talk on May 16, 2007 (download PDF).


Topics: Mechanical engineering, Students

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