Best Non-highway Bridge Cowinner - Seattle Sound Transit Tukwila Segment, Seattle, Wash.

This 4.2-mi-long precast concrete segmental bridge was designed to complete the 20-mi-long light-rail mass-transit system connecting the Boeing airfield to the City of Seattle Airport. This projects light-rail alignment faced significant technical challenges, including the minimization of disturbance to major crossing thoroughfares, a large rail yard, and environmentally sensitive waterways. Further complicating the project is the high seismic zone in which it is located. Additionally, this project created unique vibration concerns resulting from the light rail and structural interaction, which had to be minimized to maintain passenger comfort. Because of the unique constraints and contextually required long spans, a precast segmental concrete V-box bridge type was chosen. By using precast concrete, a reliable high-strength concrete could be used (6500 psi) and the dimensions of the box girder were streamlined, allowing for a lighter structure and reduced seismic loads. This resulted in significant cost savings. The choice to use precast segmental concrete V-box girders saved approximately 15% of the original construction cost and accelerated the original construction schedule by six months. For aesthetics, the use of precast concrete allowed for the development of the unique cross-sectional shape of the box girder and architecturally appealing column treatment on this highly visible project. Precaster: Bethlehem Construction Inc., Cashmere, Wash. Website: www ...

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