South Spokane Street Viaduct Off-Ramp to 4th Ave South: Unique Design Considerations, Seattle, WA

摘要

The Seattle Department of Transportation (SDOT) is constructing a new two-lane eastbound off-ramp from the South Spokane Street Viaduct (SSSV) to 4th Avenue South near downtown Seattle. The ramp project encompasses a length of six (6) city blocks and includes surface street improvements. This paper presents the parameters and methodology used in an Alternatives Selection Worship for this 9-span tapering cast-in-place concrete t-beam and 5-span continuous post-tensioned cast-in-place concrete box girder ramp. Although the project originally required complete separation between the existing viaduct (circa 1941) and new ramp structure, also included herein is an overview of the seismic analysis performed to determine impacts of a closure slab. The post-tensioned concrete box girder portion of the bridge has an unbalanced span arrangement governed by cross-street geometry. The box girder is on a tight 56 meter minimum radius horizontal curve requiring special design methodologies that are also included. The engineer's estimate was $19.5M.