Penn State Engineers Lend Fallingwater A Helping Hand
April 18, 2002
University Park, PA--Constructed in 1937 for Pittsburgh department store owner Edgar J. Kaufmann, Frank Lloyd Wright's architectural masterpiece Fallingwater was meant as a haven for the family from the hustle and bustle of city life.
The building was erected on a site in Bear Run, PA, where the Kaufmanns often enjoyed it as a picnic spot. Fallingwater became famous for its floating terraces which echo the cascading flow of the stream it sits over.
In the years since, however, the structure's famed terraces began sagging and many believed that without help, the terraces would eventually collapse.
With the help of Andrea Schokker, Henderson Chair Professor of Civil Engineering, and Justin Brennan, a civil engineering master's student, an effort began in fall 2001 to save Fallingwater. Schokker was brought in by engineering firm Robert Silman & Associates for her expertise on post-tensioning.
"Over the history of the structure, it's continued to sag," Schokker explained. "They were starting to worry about the structural integrity of the building."
She said the lack of tensile reinforcement led to the deflection, or sagging, in the terraces. To keep the terraces from deflecting further, engineers temporarily shored the structure with steel scaffolding.
As planning started on how to save Fallingwater, Schokker was asked to join the effort. "Our job was to come in and monitor what was happening during the retrofit," she said.
Schokker and Brennan installed a series of gauges throughout the building and began monitoring Fallingwater before construction work began. The two used dial gauges to measure deflection in the structure and vibrating wire gauges and Demec strain gauges to keep an eye on strain.
The engineering team devised a solution using a method called external post-tensioning. Although other possibilities exist for fixing the structure, external post-tensioning was chosen because it would not alter the original appearance of Fallingwater. Using high-strength strands, engineers anchored one end of the lower terrace with cables. By adding tension to the other end of the strand, the lower terrace's sag is reduced.
Engineers chose to raise the lower terrace by about an inchenough to make the structure safe. Raising it any higher would have caused non-structural materials, such as windows, to crack since they have had years to sag.
The high-strength strands supporting the terrace won't be seen by visitors, however. The strands run under the lower terrace's stone floor, which was removed and replaced for the restoration project.
"It causes very little disruption to the original structure," Schokker said, adding that composite fiber will be used to strengthen the secondary balcony.
"Frank Lloyd Wright loved to incorporate overhangs into his buildings. This particular house is built over the falls and it just hangs over the water," she said. "It's a piece of architectural history that we're glad to help save."
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Curtis Chan Phone: (814) 865-5544 FAX: (814) 863-4749 http://www.engr.psu.edu/news