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/395356
PROJECT DAVEY’S BRIDGE PROJECT A super simple span by Samir Sidhom and Greg May, Central Federal Lands Highway Division of the Federal Highway Administration PROFILE DAVEY’S BRIDGE / GARDEN VALLEY, BOISE COUNTY, IDAHO BRIDGE DESIGN ENGINEER: Central Federal Lands Bridge Office of Bridges and Structures, part of the Federal Highway Administration’s Office of Federal Lands Highway, Lakewood, Colo. PRIME CONTRACTOR: Legacy Contracting Inc., Stayton, Ore. PRECASTER: Hansen Structural Precast, Caldwell, Idaho—a PCI-certified producer BOISE COUNTY, IDAHO, OWNER BRIDGE DESCRIPTION: A single-span, 162-ft 4-in.-long and 69-ft 7-in.-wide bridge with a deck area that provided 12-ft 3-in.- and 8-ft 3-in.-wide shoulders; three, 12-ft-wide travel lanes; and an 11-ft 7-in.-wide median STRUCTURAL COMPONENTS: Eight 85-in.-deep Idaho bulb-tee girders, 161 ft 2 in. long, with an 8½-in.-thick cast-in-place concrete deck; two 5.5-ft-deep cast-in-place concrete abutment caps each supported on seven 18-in.-diameter concrete filled pipe piles; and 24-ft long and 14-ft deep wingwalls also supported on concrete filled pipe piles BRIDGE CONSTRUCTION COST: $1.67 million ($148/sq ft.) The Banks-Lowman Highway, also known as Forest Highway 24, is 35 miles north of Boise, Idaho. It is a vital 25-mile-long residential and commercial artery, and a state-designated Scenic Byway. It meanders along the South Fork of the Payette River in the Boise National Forest. Between the towns of Banks and Garden Valley, and south of the town of Crouch, the highway crossed the South Fork on the 54-yearold Davey’s Bridge. Constructed in 1960, the old Davey’s Bridge was a 150-ft-long, five-span bridge with two 12-ft-wide lanes and 2-ft-wide shoulders with a 30-ft 6-in.wide concrete deck supported by castin-place concrete girders. Each of the bridge bents was supported on six 13-in.-diameter treated timber piles with unknown lengths. The bridge was considered functionally obsolete and had a sufficiency rating of 46.9. In July of 2010, the Western Federal Lands Highway Division (WFLHD) Office, in coordination with a consulting firm, completed a study to replace Davey’s Bridge. REPLACEMENT STUDY The study recommended that the new bridge had to be widened to facilitate the complete reconfiguration of the Banks-Lowman and Middle Folk Road “T” intersection to improve traffic flow and safety. The “T” intersection is located about 100 ft west of the bridge. The reconfigured intersection has both designated right and left hand turn lanes. The study also concluded that to improve channel hydraulics it was desirable to reduce or eliminate the number of support piers in the river and evaluated several span arrangement options with different superstructure types. In March of 2011, the WFLHD assigned the design of the bridge project to the Central Federal Lands Highway Division (CFLHD) bridge design team located in Lakewood, Colo. SINGLE SPAN, BEST DESIGN After careful review of the study report, the design team decided, early on, that a single-span bridge was the best alternative for the bridge. This eliminated the two-span option presented in the study. A single-span bridge avoided the need for, significant cost of, and environmental degradation inherent in pier construction in the stream bed. A single-span bridge also shortened the construction schedule, and eliminated problems associated with dewatering, cofferdam construction, and equipment access.