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/306894
36 | ASPIRE , Winter 2007 profile U.S. 97 over Union Pacific railroad trackS/ Chemult, OregOn e ngineer David evans and Associates Inc., Salem, Ore. Prime contractor hamilton Construction Co., Springfield, Ore. Preca S ter morse Bros. Inc., harrisburg, Ore. Faced with twin challenges of a long span and short construction time to design and build a replacement bridge to carry a busy highway over an active railroad in Chemult, Oregon, project engineers turned to precast, prestressed concrete girders to create the best solution. One of 11 bridges in a design-build project for the Oregon Department of Transportation (ODOT), the structure features a single-span precast, prestressed concrete design. That approach avoided activity near the main line of the Union Pacific Railroad and sped up construction as well, according to Terry Stones, lead engineer from David Evans and Associates Inc. of Salem, Oregon, the design- build engineering firm. The precast design eliminated any need for intermediate bents, allowing the contractor, Hamilton Construction Company of Springfield, Oregon, to stay clear of the railroad track, which carries both freight and passenger trains and remained operational during construction. A new roadway alignment was added to the plans, leaving the existing bridge in place during construction. The old three-span bridge was considered structurally deficient and too narrow, with practically no shoulders. It had two intermediate piers, which designers wanted to avoid by using the longer precast concrete design. "The three-span design left significant concerns about the falsework adjacent to and above the rail mainline," Stones adds. A single span nearly 182 ft long would be needed to cross the tracks at a 60-degree skew and it would have to be constructed quickly enough to open to traffic in less than seven months. new casting Bed Provides Solution Fortunately, the precast manufacturer, Morse Bros. Inc., of Harrisburg, Oregon, had just installed a new casting bed that could fabricate bulb-tee beams up to 96 in. deep and 190 ft long. It was just what was needed for this project. The final design called for seven precast, prestressed concrete bulb-tee beams, each with a 90 in. depth and a length of 183 ft-3 in., the longest ever used in Oregon bridge construction. Each beam has a top flange width of 5 ft, a bottom flange width of 2 ft 6 in. and contains fifty-six 0.6-in.-diameter strands. Beam spacing was at 6 ft-10 in. The beams were cast with concrete having a specified compressive strength of 9000 psi at 28 days and 7000 psi at prestress transfer. The beams, each weighing 93 tons and two-thirds the length of a football field, were delivered one at a time on a transporter with 13 axles with the rear units steered remotely by an operator in the truck. The spans were transported from the Morse facility in Harrisburg, near Eugene in the western part of the state, along the 125-mile delivery route over the Cascade Mountains to the bridge site on U.S. 97 midway between Bend and Klamath Falls near the center of the state. RecoRd Length PRecast Beam ensures Project meets deadline by Donald P. Merwin Single-span design of nearly 182 ft on a 60-degree skew replaces bridge on major Oregon highway over railroad tracks in less than seven months UPRR_Oregon.indd 36 1/3/07 11:49:33 AM