When one of America’s most treasured landmarks experienced severe cracking and defl ections, the Western Pennsylvania Conservancy added VSL to the team 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 defl ections 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.

For the fi rst time since original construction, the stone floor was removed to expose the inner workings of Wright’s design. 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. Thirteenstrand 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.

VSL’s scope of work also included welding steel cover plates, attaching structural steel channels, injecting epoxy grout, doweling reinforced cast in place concrete blocks and the installation of near surface mounted carbon fi ber rods. Challenged with maintaining Fallingwater’s original setting, furnishings and artwork, the project was successfully completed in six months.