Editor's note: One of the hallmarks of Gary Everhardt's career as superintendent of the Blue Ridge Parkway was the design and construction of the Linn Cove Viaduct around Grandfather Mountain. Randy Johnson describes the significance of this span.
Viaduct to History
The Linn Cove Viaduct on the Blue Ridge Parkway was featured on the History Channel’s Modern Marvels series, for heaven’s sake. Nevertheless, it’s not widely understood why or how it’s noteworthy. The High Country landmark might be nothing less than the combined genius of the 20th century’s two top bridge designers.
The Parkway’s chosen route across the mountain was especially problematical below Black Rock Cliffs where steep slopes and awesome boulders would seem to require massive excavation to build a conventional road. Fortuitously, in part due to Hugh Morton’s battle with the Parkway over placement of the road, by the late 1970s, when funds came from Congress, the Federal Highway Administration was able to call on unique, previously unavailable technology and technique. Not only was major damage avoided, but the resulting structure can actually claim to be environmentally sensitive.
The viaduct cost more than $8,000 a foot for the 1,243-foot-long bridge.
The bridge might be the best, albeit one of the shortest, examples of designer Figg and Muller’s essential method—described as a “complex precast concrete segmental and cable-stayed bridge design.”
What that means is that each of the viaduct’s 153, 50-ton segments, was cast abutting its mate to create a perfect fit. Each section of the bridge was epoxied to the previous segment, then clamped tighter with cables. A cantilevered construction method was another interesting element. Each piece of the bridge was lowered out from the end of the viaduct and attached. Only the piers that support the road rest on the ground, which means that the viaduct soars over the awesome boulder field with minimal impact. The pieces were tinted with black iron oxide to more closely match the mountainside.
Beyond the use of pre-stressed concrete segments and cable tensioning, the two men behind the viaduct took advantage of the emergence of commercial computers in the 1970s to reinvent bridge design. As a result, the viaduct winds and weaves in a very unique and graceful way.
In a 40-year career, Eugene “Gene” Figg, Jr. (1936-2002) ultimately won more than 150 national and international design awards, among them the Presidential Design Award under the National Endowment For The Arts. Just five bridges have been honored by the Presidential Award Program, and Figg Engineering designed three of those (the Linn Cove Viaduct, the Interstate 27 Sunshine Skyway Bridge in Florida in 1988, and in 1995, the Natchez Trace Parkway Arches bridge in Tennesseee, the longest precast arch bridge in the country.) Figg cut his teeth on the countless bridges needed to complete the Interstate Highway System.
Figg’s partner, Paris-based Jean Muller (1925- 2005), helped create Figg & Muller Engineering Group in 1978. Muller too was a proponent of building with pre-stressed and precast concrete, having started his career after WW II as a protege of Eugene Freyssinet, the inventor of prestressed concrete. He also “developed the original concept of precast segmental construction using glued match-marking joints.”
Like Figg, Muller refined his skills and techniques in Europe and the United States in the post-War boom in bridge building. Photos of his many projects, including the construction of viaducts in the Alps, include bridge segments and cantilever construction methods that are strikingly reminiscent to photos of the Linn Cove Viaduct.
When Figg & Muller “coupled the precast, prestressed concrete techniques with cable-stayed supports, they ... helped change the way bridges were built in North America,” concluded on engineering journal. Figg once said, “We are designing bridges for 100 years or more ... It needs to be a piece of art.”