ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/297033
The Foothills Parkway was authorized by Congress in 1944 to provide beautiful vistas of the Great Smoky Mountains National Park from the Tennessee side of the park. The missing link of the Foothills Parkway is a particularly rugged 1.6-mile stretch of the Foothills Parkway traversing steep mountain-sides that overlook Wears Valley, Tenn. Foothills Bridge No. 2, is located in Blount County, Tenn., approximately 10 miles west of the north entrance to the Great Smoky Mountains National Park. Construction of this bridge is instrumental to completing the missing link in that it crosses the most difficult terrain and is needed to access the construction of the missing link. Project Development The Eastern Federal Lands Highway Division (EFLHD) bridge staff prepared the preliminary design for the Foothills Bridge No. 2. The design envisioned a precast concrete segmental, single-cell, box-girder bridge, built with minimum disruption to the site. The Recovery and Reinvestment Act of 2009 provided needed construction funding for the project, and the National Park Service (NPS), Federal Highway Administration (FHWA), and EFLHD moved to develop the project in a design-build format. Bridge Layout The new Foothills Parkway Bridge No. 2 is a 790-ft-long precast concrete segmental bridge built using the b a l a n c e d c a n t i l e v e r m e t h o d o f construction. Lengths of the five spans of the bridge are 125 ft, three at 180 ft, and 125 ft. The bridge follows an S-shaped alignment with curve radii of 262 and 650 ft. Superelevations vary from 7.8% (right) to 5.8% (left) over the length of the bridge. The vertical profile of the bridge begins at a +6.75% grade and transitions through a vertical curve to a +8.02% grade. The superstructure of the bridge is a 9-ft-deep single-cell, precast concrete segmental box girder with a top slab width of 36 ft 10 in. The width of the segment bottom slab is 16 ft. The slope of the 1-ft 4-in.-thick webs is one horizontal to three vertical. The thickness of the top slab is 9 in. at the cantilever wing tips and in the middle of the top slab, and 1 ft 6 in. at the faces of the webs. The top slabs of the segments were transversely post- tensioned in the casting yard with two tendons consisting of four 0.6-in.- diameter strands. profile FOOTHILLS BRIDGE NO. 2 / BLOUNT COUNTY, TENNESSEE BRIDGE DESIGN ENGINEER: Corven Engineering Inc., Tallahassee, Fla. PRIME CONTRACTOR: Bell and Associates Construction, Brentwood, Tenn. CIVIL AND ENVIRONMENTAL ENGINEER: Palmer Engineering, Winchester, Ky. GEOTECHNICAL AND FOUNDATION ENGINEERING: Dan Brown and Associates, Sequatchie, Tenn. PRECASTER: Ross Prestressed Concrete Inc., Knoxville, Tenn., a PCI-certified producer SEGMENT ERECTION AND POST-TENSIONING CONTRACTOR: VSL, Hanover, Md. Foothills Bridge No. 2 Filling in te "Mising Link" Durability for 100+ Years Enhanced durability measures used on Foothill Bridge No. 2 included the following: • Post-tensioning design for no longitudinal or top slab transverse tension under service loads • Concrete with a high cementitious materials content including fly ash for reduced permeability • Post-tensioning details and corrosion protection system to enhance durability • Post-tensioning system installed, stressed, and grouted by certified technicians • High-performance concrete overlay for an additional layer of protection by John Corven, Corven Engineering Inc., in cooperation with the Eastern Federal Lands Highway Division, Federal Highway Administration 38 | ASPIRE , Fall 2012 P R O J E C T AspireBook_Fall12.indb 38 9/18/12 8:58 AM