Interstate 25 FlyoverDenver |
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In Denver, a recently completed flyover ramp, which features U-shaped precast concrete girders, may open an entirely fresh chapter in bridge designers’ search for additional ways to use precast components. “We designed a bridge with several design features that have never been done before in Colorado. [These features allow precast concrete girders to compete with steel in the design of longer span interchanges, with complex geometry],” says Gregg Reese, president of Summit Engineering Group in Littleton, Colo. The project, completed this summer, spans Interstate 25 just north of the US- 36 and I-76 interchanges. Traditionally, such structures have used structuralsteel girders. The Colorado Department of Transportation took a bold step by offering contractors the option of using precast components on the 1,428-footlong bridge — and while contractors had the option of bidding the project with steel girders or precast, they were limited to one or the other. |
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The contract went to SEMA Construction Inc. in Centennial, Colo. “As we were working on our bid, steel prices were on an upswing,” explains Brad Spies, SEMA president. “We analyzed the costs for steel and concrete, and we determined that concrete would be less costly.” Ironically, on the morning that SEMA submitted its bid, steel prices dropped, Spies says, and the differential between the two materials appeared negligible. However, by this time SEMA and its partners — Summit and precaster EnCon Bridge Co. in Denver, had committed themselves to the concrete alternative. Even so, when the bids were opened, the team’s bid came in approximately $200,000 lower than the next-lowest bid, which used steel girders. In fact, due to competition between steel and concrete options, the contractors had to sharpen their pencils at bid. The bid price of structural steel came out at $1.14 per pound, which is unprecedented in recent history for structural steel box girder. The winning design called for 28 Ugirders, each approximately 100 feet long. Of those, only six were straight. The other 22 were cast with a super elevation and a radius to create a graceful structure with an uninterrupted curve. The 7-foot-deep girders featured 10-inch webs, according to Jim Fabinski, vice president of EnCon Bridge, a PCI-certified plant in Denver. The two-lane, eight-span structure consists of two girders spanned by 17-foot- 8-inch-long and 8-foot-wide deck panels that vary from 4½ to 6 inches deep. Of these panels, 131 were pie-shaped to accommodate the structure’s curve. Full Article Download
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