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| STORY OF FALLINGWATER CHRONOLOGY OF CONSTRUCTION BUILDING PRESERVATION BUILDING DRAWINGS |
BUILDING PRESERVATION The Preservation of Fallingwater began with the Kaufmann family, who continually monitored the cracks in the master terrace parapets as well as the movement of the cantilevers, a practice continued by Western Pennsylvania Conservancy. Up until the 1980’s, the majority of the preservation projects undertaken first by the family and then Western Pennsylvania Conservancy concerned the concrete surfaces: patching and repainting. Beginning with the 1981 installation of new roofs, recent preservation and conservation projects have focused on areas such as the structural system, the replacement of the original glass with ultraviolet-filtering glass, and the conservation of all of the woodwork in Fallingwater.In 1994, our continued concerns about the structural integrity of the house led us to engage the engineering firm, to conduct a comprehensive analysis of the master terrace cantilever using non-destructive testing methods. The results of the study indicated that the master terrace could not function as an independent cantilever, and that it was transferring its load to the living room level. Furthermore, the study predicted the ultimate failure of the living room cantilevers if no remedial action was taken. The study recommended that the structure be repaired. In order to stop the deflections and provide a margin of safety, Western Pennsylvania Conservancy installed temporary shoring in 1997. A 1999 peer review approved the proposed plan for the structural repair, which will strengthen the living room using post-tensioning, and waterproofing the building. Preservation Philosophy A primary goal of Western Pennsylvania Conservancy’s preservation efforts at Fallingwater is to maintain Frank Lloyd Wright’s designed relationship of the house with the surrounding natural landscape. The most defining features of this relationship are the cantilevers and the pristine, smooth concrete finishes indicative of the Modernist Style. The results of Wright’s innovative use of technology, however, can sometimes make traditional repair methods at Fallingwater difficult. Western Pennsylvania Conservancy makes every effort to maintain the structural integrity of the cantilevers and their relationship to the site as well as retain the smooth appearance of the concrete surfaces. In addition, the WPC makes every effort to make all conservation of the building as noninvasive as possible. No effort shall be made to revise or improve upon the original design for aesthetic purposes. However, changes to original building systems can be made if such changes contribute significantly to the long-term preservation of the building. Preservation Projects
Analysis of the Master Terrace  Over the years all of the cantilevers at Fallingwater have deflected (or sagged) by varying amounts. Though a certain amount of initial deflection is normal after the framework has been removed, the cantilevers stabilize after a short period of time. The living room, master bedroom terrace, and Edgar Kaufmann, Sr.’s terrace, however, are continuing to deflect and there is no indication it will stop.Edgar Kaufmann, Sr., himself, was concerned about the continuing deflection of the house and engaged engineers to make yearly surveys from 1941 to 1955. When Western Pennsylvania Conservancy (WPC) was entrusted the site in 1963, they continued to monitor the structure. Further concern about the structural integrity of the house lead WPC in 1994 to engage Robert Silman Associates (RSA) of New York, an engineering firm widely recognized for their preservation work. Since 1936, there has been much confusion regarding the exact construction details of Fallingwater. In particular there were questions regarding the number, size and arrangement of the reinforcing bars in the concrete work of the house. In addition, new questions had arisen about the strength of the concrete and whether any internal deterioration of the materials had occurred over time. In a National Historic Landmark building such as Fallingwater, questions like these are best answered by using methods that do not destroy or damage any parts of the building. Although all questions could be answered by chipping away sections of the concrete, this is unacceptable because vital original fabric would forever be lost. Therefore, RSA used non-destructive testing methods to provide the answers. RSA’s investigation consisted of four phases: historic research of the original plans, and Wright’s instructions to the builder, non-destructive testing, computerized monitoring, and a sophisticated computer analysis of the master terrace. Using impulse radar and ultrasonic pulse testing, they were able to confirm the size and location of the reinforcing steel and found the concrete in generally fair condition. Moreover, the measured deflections of the cantilevers proved to be consistent with those predicted in the computer model developed by RSA. Unfortunately, that computer model also predicted the ultimate failure of the living room cantilevers. The study also discovered that the master terrace could not function as an independently supported cantilever with its existing reinforcement. It was in fact the design intent, structurally, to transfer the loads of the master terrace down to the living room level through four structural "T" sections encased in the larger window mullions on the south elevation. To further monitor the situation, RSA installed crack meters on two of the most prominent cracks on the parapet of the master terrace and a tilt meters on the wall at the southern end of the living room and master bedroom cantilevers. These instruments take readings every half-hour and indicate whether the cracks are expanding or the cantilevers are tilting further downward. RSA eventually concluded that the problems found at Fallingwater stem not from oversights in basic geometry or flaws inherent to the structural concept, but were instead mistakes in the design and detailing of the reinforcement. They recommended that the structure be repaired. In the meantime, in order to stop the deflections and provide a margin of safety, WPC installed temporary shoring in April 1997. Peer Review On April 10, 1999 a peer review and forum was held to review Robert Silman Associates’ (RSA) plans to stabilize the cantilevers and Wank Adams Slavin Associates’ (WASA) waterproofing plans for Fallingwater. Because of the architectural importance of Fallingwater, and the possible controversy over its repair, Western Pennsylvania Conservancy understood the need to present this information to a qualified panel for review and announce the plans to the public. In his opening remarks, panelist and internationally known conservator Martin Weaver stated, "The Conservancy should be congratulated for adopting this process of peer review on the conservation proposals, and I firmly believe that this should be a standard process for all historic resources of national and international significance." The panel, composed of individuals recognized for their outstanding achievements in architecture, engineering, academia, and preservation, unanimously endorsed the proposals to strengthen and restore Fallingwater. Panelists were: Randall Biallas, the Chief Historical Architect for the National Park Service; Nick Gianopulos, a structural engineer and founding member of the firm Keast and Hood; Neil Levine, Gleason Professor at Harvard University; John Thorpe, restoration architect in Oak Park, IL; Dr. Bruno Thurlimann, a Swiss structural engineer who specializes in building failures; Martin Weaver, an international specialist in the conservation of historic buildings and sites; and Eric Lloyd Wright, architect and grandson of Frank Lloyd Wright. Stabilizing and restoring Fallingwater does not diminish the genius of Frank Lloyd Wright and the mastery of Fallingwater. As panelist Randall Biallas so eloquently stated, "The problems at Fallingwater inform us about Mr. Wright’s practice at a particular point in time, about the people that he had in his office at a point in time, and about how he was constantly pushing the envelope in terms of design and materials and concept and form … Mr. Wright was doing something dramatically different in terms of residential architecture at Fallingwater." Structural Repair: Proposed Plans to Stabilize the Cantilevers:  RSA proposes a technique called post-tensioning to halt further deflections of the living room and master bedroom cantilevers. No effort will be made during the stabilization to raise the cantilevers back to their intended position. As panelist Dr. Bruno Thurlimann remarked during the forum, "Post-tensioning is the way to go. No one will come up with a better solution." The reinforcement will remain in the floor depth with minimum disturbance to the existing concrete fabric. Panelist Eric Lloyd Wright, grandson of Frank Lloyd Wright, agreed and said, "The most important thing in Frank Lloyd Wright buildings is the space that is inside the building and the space that is outside the building, not what is in the floor." In order to post-tension Fallingwater, high strength steel cables will be placed along each side of the 3 major north/south concrete beams in the living room. The strands follow a bent path where they start and end at points near the bottom of the existing concrete beams and rise up to the top of the existing beams at the middle. This path locates the strands at the top and middle of the beam where they are most needed for strength. The geometry of the strands’ placement is carefully calculated to ensure that the large post-tensioning forces will always oppose the inner stresses now present in the beams. The strands are attached to the side of the concrete beams with anchor blocks.The strands will extend outside the face of the south living room parapet and a post-tensioning jack will be installed. The jack will be used to tension each group of strands on either side of the beam until the required 200,000 pound or 100 ton force is reached, which places 400,000 pounds or 200 tons of tension on each beam. The jack will then be removed and the strands will be cut off inside the parapet. The concrete will be patched, leaving little trace of the work performed. In order to achieve proper transfer of forces from the living room to the master terrace, the concrete joist directly above the four steel "T" mullions will be reinforced by bolting a steel channel to each side. Architectural Restoration Needs: The stabilization of the cantilever is clearly a dramatic project, but the restoration of the structure includes many other vital components:
Waterproofing |
Another major issue facing Fallingwater is moisture penetration. Lynda Waggoner, vice president of Western Pennsylvania Conservancy and director of Fallingwater, said during the forum, "Inside the house, this on-going problem is responsible for warped doors, peeling paint, stains and cracks on the walls. It’s a serious problem that rivals our structural challenges in its importance." To remedy that, WASA proposed to replace the current one-ply rubber membrane roof with an IRMA (inverted roofing membrane assembly) roof. The IRMA system employs three plies of modified bitumem that is surmounted by a drainage mat (to guide the sub-surface water), insulation, filter fabric and gravel. The terraces will be waterproofed similarly with three plies of modified bitumem and a drainage mat. Flagstones will then be laid over filter fabric and sand. | ||||||||||||||||
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