- Supply and installation of external post-tensioning
- Design assist for section enlargement, epoxy injection and FRP composite strengthening
- Robert Sillman Associates and Schupack Suarez
- Western Pennsylvania Conservancy
- STRUCTURAL TECHNOLOGIES / VSL
Material Supply, Design Support & Installation
When one of America’s most treasured landmarks experienced severe cracking and deflections, STRUCTURAL TECHNOLOGIES / VSL was selected to help restore and strengthen Frank Lloyd Wright’s Fallingwater. Completed in 1939, Fallingwater is comprised of a series of concrete cantilever “trays” 30-ft. above a waterfall. Previous efforts failed to permanently address excessive deflections of the cantilever and repair the cracks. After a thorough design review, the owner and engineer selected an external post-tensioning solution for its durability, aesthetics and structural unobtrusiveness.
To preserve existing building elements and minimize incidental damage, the team “gently” chipped and drilled openings, while keeping construction debris from falling into the stream.
Construction plans called for strengthening of three support girders spanning in the north-south direction with multistrand post-tensioning tendons consisting of multiple 0.5” diameter strands. Thirteen-strand tendons were placed on each side of two girders. One 10-strand tendon was placed on the western side of the third girder (access on the eastern side of this girder was not available). Eight monostrand tendons, 0.6” diameter, were slated for the east-west direction.
The monostrand tendons were stressed in the east-west direction and then the multistrand tendons were stressed in the north-south direction and grouted with a high quality, low-bleed cementitious grout mixture.
Additional work items included welding steel cover plates, attaching structural steel channels, injecting epoxy grout, installation of near surface mounted carbon fiber rods and carbon fiber sheets.
Challenged with maintaining Fallingwater’s original setting, furnishings and artwork, the project was successfully completed in six months.