Closing the Gap

Pfuntner, Jerry; ,

Closing the Gap

by Jerry Pfuntner, P.E., (A.M.ASCE), Sr. Bridge Engr.; Finley McNary Engineers, Inc., Tallahassee, FL,

Serial Information: Civil Engineering—ASCE, 2001, Vol. 71, Issue 11, Pg. 62-67

Document Type: Feature article

Abstract:

In 1944 Congress authorized construction of the Foothills Parkway, a 116 km highway through the Tennessee mountains along the northwestern edge of Great Smoky Mountains National Park. Fifty-seven years later, the National Park Service has completed about 37 km of the parkway, but a large central portion of the alignment remains untouched, and a 2.7 km gap�the missing link�renders one partially completed segment inaccessible to motorists. Two of the 10 bridges needed to finish the missing link were completed in June. The original design for the bridges called for a precast segmental superstructure built partially on falsework, the rest to be erected using the progressive placement technique. Finley McNary Engineers, Inc., of Tallahassee, Florida, teamed up with PCL Civil Constructors, Inc., of Edmonton, Alberta, to develop an alternative construction scheme. The challenge was to build the bridges without having ground access to most of the site and without inflicting any environmental damage. The team decided that a cast-in-place alternative would be the most economical. They developed a construction scheme whereby a derrick crane would be used to build the bridges linearly using cantilevered cast-in-place segments with form travelers. The original substructure design developed by the Eastern Federal Lands Highway Division of the Federal Highway Administration, which consisted of posttentioned piers made up of precast-concrete segments, was retained. However, the change in construction method required that all aspects of the superstructure be redesigned. The cast-in-place erection scheme used 60 percent less longitudinal posttentioning, resulting in a simpler posttentioning layout in which the top slab anchor blisters were eliminated. The temporary towers in each span, the segment precasting, and associated transportation were also eliminated. The mountainous terrain severely limited crane access to the bridge alignment. During construction of most of the superstructure, the team had to either use a nearby dirt road for access or rely on the superstructure elements that had already been built to support additional construction, placing an increased structural demand on these elements.

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