Photos: Summit Engineering Group Inc.

“This is a good example of how spliced, continuous posttensioning can be used in a rail application.”

Kevin Eisenbeis

 

Non-Highway Bridges

Wadsworth Boulevard LRT Bridge and Station

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An innovative substructure design allowed the three-span Wadsworth LRT bridge to be constructed as an integral frame. The design ensured that the spliced and posttensioned precast concrete–girder bridge could efficiently support two rail lines, a bicycle lane, and a new transit station and platform directly above the street.

The bridge is part of the $707 million, 12.1 mi (19.5 km) long West Corridor expansion of the Denver, Colo., light-rail system, which, when completed, will run from downtown Denver to Golden, Colo. The bridge is one of a number along the line, but it is the only one with the station on the bridge.

The 400 ft (122 m), three-span bridge features a span configuration of two 120 ft (37 m) end spans and a 160 ft (49 m) main span crossing the boulevard. A maximum structural depth of 5 ft (1.5 m) was required by the approach grades and the traffic clearance in the main span over the road.

“This is a good example of how spliced, continuous posttensioning can be used in a rail application,” says Kevin Eisenbeis, one of the members of transportation awards jury. “It provides a good, economical solution for the rail industry.”

The substructure was designed as a multiple-pier bent with an integral transverse cap. A single drilled-shaft foundation was provided at each of the bent piers, along with integral, composite caps. The caps consisted of a lower bent cap and transverse girder diaphragm with a rotationally flexible, reinforced concrete connection at the interface. This design greatly enhanced longitudinal flexibility of the integral structural frame and eliminated the need for bearings.

The key superstructure challenge involved balancing the design loadings on the different girder lines to produce a uniform response on a relatively slender superstructure. A detailed three-dimensional analysis was performed to consider the contribution of the concrete platform in the composite cross section. Variable-depth precast concrete–girder segments over the piers added the necessary frame stiffness to allow for the shallow depth of the main span.

The platform, cast on top of the deck, was designed as a voided concrete two-way slab. Vertical reinforcing was placed between the bridge deck and platform slab ribs to develop composite action in both directions, adding strength and stiffness in more heavily loaded areas. The transverse ribs in the voided platform slab provided excellent load distribution.

Girder layouts and splice locations were designed to provide six lanes of traffic at all times during the work. Construction was accomplished on shoring with minimal disruption to traffic.

“This project offered an innovative use of continuous-girder design and integral frame,” says Nancy Daubenberger, a member of the transportation awards jury. “The biggest concern was live-load deflections, and precast concrete helped to control those deflections.”

Location: Wadsworth Boulevard, Lakewood, Colo.
Owner: Regional Transportation District FasTracks West Rail Line, Lakewood, Colo.
Engineer: Summit Engineering Group Inc., Littleton, Colo., www.Summit-Eng-Group.com
Corridor contractor: Denver Transit Corridor Group, Lakewood, Colo.
Bridge contractor: Edward Kraemer and Sons, Burnsville, Minn.
Precaster: EnCon Colorado LLC, Denver, Colo., www.enconcolorado.com
Bridge length: 400 ft (122 m)
Project cost: $4.4 million