This project replaced a 100 year-old single-track timber trestle with a dual-track concrete structure. Approximately 2/3 of a mile of elevated structure was replaced adjacent to Freighthouse Square in Tacoma, Washington. The upgrade significantly improved reliability for Sound Transit Sounder and Amtrak trains.
The substructure consists of cast-in-place abutments and columns supported by drilled shafts. The superstructure consists of multiple precast concrete component types, including; box girders, fascia girders, flat slabs and WF42G girders. The track was installed on ballast that was placed on top of the precast components.
The project is an excellent example of design flexibility with precast concrete. The heavy-duty box girders on the interior of the superstructure support significant rail loads. The outermost box girders had 2nd –cast curbs to retain ballast under the tracks.
The box girders are framed by exterior fascia girders that incorporated many features including; utility chases with access ports, a broom-finish on the top walkway and integrated curbs for connection of the pedestrian guardrail.
296 pcs. – 36” deep x 38” wide Prestressed Box Girders
56 pcs. – 52” deep Fascia Girders
7 pcs. – WF42G at a long-span crossing over the roadway
28 pcs.-Flat Slabs at the platform support