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May 18, 2015

Public Works: Bridges

Photo courtesy of WACA
The bridge’s outside curve has a 152-foot radius and its inside curve has a 94-foot radius.

Montlake Triangle pedestrian bridge

Location: Seattle

Owner/developer: Sound Transit

Team: Hoffman Construction Co., general contractor; Hoffman Structures, concrete contractor; LMN Architects, architect; Aecom, structural engineer; Cadman, read-mix supplier; Gerdau, rebar supplier and installer; Peri Formwork Systems, specialty formwork

The Montlake Triangle pedestrian bridge is a highly curved, 427-foot-long bridge spanning Montlake Boulevard between the Sound Transit light rail station and the University of Washington campus.

The bridge was designed and built as part of the University Link project to extend light rail from downtown Seattle to the UW. Its layout consists of an outside curve with a 152-foot radius and an inside curve with a 94-foot radius.

Its span hinges divide the bridge into three segments. The inside and outside curves are cast-in-place, post-tensioned concrete single-cell box girders that transition to a three-cell box where the curves converge.

Post-tensioning was chosen to allow a shallow section of the bridge to meet vertical clearance requirements. It also produced a high-level architectural finish without the typical cracking associated with reinforced concrete bridges.

Crews had to form and construct the bridge over a main arterial road without interrupting traffic.

Design and construction of the project pushed the limits for use of post-tensioning in highly curved bridges, demonstrating that durable, low-maintenance, high-aesthetic post-tensioned bridges are a viable option for transportation projects.

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