Photos; Tsiouvaras Simmons Holderness (TSH) Inc. 2012

“This is an excellent example of how precast can be used to reduce cost and provide an innovative solution.”

Kevin Eisenbeis

 

Harry H. Edwards Industry Advancement Awards

Best Bridge with a Main Span Greater than 150 ft

I-25 Trinidad Viaduct Replacement

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Replacing the I-25 Trinidad Viaduct in Colorado required spanning a variety of obstacles along a long, curved path. The resulting design used precast concrete tub girders and deck panels to span the Purgatoire River, three existing rail lines, a planned rail line, and four city streets.

The needed alignment required a variety of highly skewed substructure elements and reversing superelevated curves. The design solutions proved so innovative that the project was selected to receive both the award for Best Bridge with a Main Span Greater than 150 ft (46 m) and the Harry H. Edwards Industry Advancement Award.

The tub-girder design was selected after a second round of bids that were opened to alternative-structure designs. This design created an $8 million savings over the engineer’s estimate. The design features four bridges over the river (two for the interstate mainline and two on/off-ramp bridges), two viaducts carrying the interstate over the city streets and rail lines, and two on/off ramps connecting into the viaducts.

“This is an excellent example of how precast can be used to reduce cost and provide an innovative solution,” says Kevin Eisenbeis, a member of the transportation awards jury. “It overcame a challenging situation and came in well under the estimated cost.”

The largest spans, highest skews, and tightest horizontal curvatures involved unit 1 sections along the northbound and southbound viaducts. The skews needed for the railroad lines and city streets, combined with the aesthetic requirement for hammerhead piers, created a staggered substructure configuration that supports the four-girder superstructures.

The five-span, 855 ft (260 m) northbound unit had a span configuration of 115, 131, 250, 175, and 181 ft (35, 40, 76, 53, and 55 m) for girders 1 and 2 and a configuration of 115, 181, 256, 121, and 182 ft (35, 55, 78, 37, and 55 m) for girders 3 and 4. The 486 ft (148 m) southbound unit had a configuration of 107, 228, and 148 ft (107, 69, and 45 m) for girders 1 and 2 and a configuration of 117, 232, and 134 ft (36, 71, and 41 m) for girders 3 and 4.
As the configurations made economical simple spans unfeasible, a spliced, variable-depth, curved tub-girder superstructure was selected. The design, featuring nine girder segments on the northbound unit and five for the southbound unit, was the first of its kind.

The partial-depth, prestressed concrete deck panels played a key role in minimizing costs. The panels were used for both the interior panels and the deck overhangs, which varied up to 6 ft (1.8 m). They would have required costly formwork, especially for the deck portions within the curves. The overhang panels were supported over the exterior girder’s two flanges while cantilevering to match the overhang length.

“Precast concrete overcame this project’s challenges in a unique way,” says Dennis Andrejko, a member of the special awards jury. “The fact that this project could use precast puts it at a stage where it can be competitive with other approaches that have been more traditionally used.”

Location: I-25 over the Purgatoire River, Trinidad, Colo.
Owner: Colorado Department of Transportation, Pueblo, Colo.
Engineer: Tsiouvaras Simmons Holderness Inc., Greenwood Village, Colo., www.tshengineering.com
Contractor: Lawrence Construction, Littleton, Colo.
Precaster: Plum Creek Structures, Littleton, Colo., www.plumcreekstructures.com
Bridge length: 855 ft (260 m)
Project cost: $79.5 million