HomeMy WebLinkAboutPN_South_Bridge_Project_Narrative_240202_v1.pdfRenton South Bridge Seismic Retrofit Project Narrative
Global Project Information
Title: South Bridge Seismic Retrofit
Location: Renton, Boeing South Bridge
Boeing Permit Contact: Mark Clement
Contact Phone: (425 ) 229- 4274
Summary Program
The Boeing South Bridge spans over Cedar River approximately 0.75 miles south of
the river mouth at the south end of Lake Washington. The bridge connects Boeing
Apron D to the Renton Municipal Airport. The bridge was originally constructed in
1966 and retrofitted with a lifting mechanism in 1997.
This project will retrofit the Boeing South Bridge in order to increase the structure’s
capability of resisting modern seismic design forces. The bridge foundations will be
extended north and south at each end of the bridge and 56 new steel micropiles will
be driven as part of the work. The retrofit concentrates on work outside of the
ordinary high water (OHW) of the Cedar River.
• Overall Size: Existing 170’ bridge with 86’ of new retrofit additions at each end
• Building Codes
o AASHTO Guide Specifications for LRFD Seismic Bridge Design, 2nd
Edition (2011 – with 2012, 2014, and 2015 Interim Revisions)
o AASHTO LRFD Bridge Design Specifications, 9th Edition (2020)
o FHWA Seismic Retrofitting Manual for Highway Structures: Part 1 –
Bridges, FHWA-HRT-06-032 (January 2006)
o WSDOT Bridge Design Manual, M 23-50.20 (September 2020)
o WSDOT Standard Specifications for Road, Bridge, and Municipal
Construction, M 41-10 (2022)
• Major Design Components:
o Structural
o Mechanical
o Civil/Site
o Geotechnical
• Soil Type and Drainage
o Not applicable. No modification to existing soil/drainage conditions are
expected for this project.
• Zoning Designation
o The west abutment is zoned for Air Terminal and Hangars
o The east abutment is zoned for Industrial (Heavy)
• Proposed Off -Site Improvements
o Not applicable. No off-site improvements are expected for this project.
• Construction Cost
o Construction cost is estimated at 3.9 million.
• Quantities of cut/fill
o 985 CY of native soil is being excavated.
o 420 CY of native soil is being used as fill.
o 120 CY of riprap is being used.
• Number, type, and size of trees to be removed.
o No trees are planned to be removed.
• Land Dedicated to the City
o Not applicable. No land to be dedicated to the city.
• Existing Shoreline
o The bridge crosses the Cedar River
▪ The shoreline is a river shoreline.
▪ The shoreline material is a mix of sand, gravel and riprap at the
site
▪ Current bridge abutments exist along the shorelines.
o The structure will not obstruct any views.
o Temporary erosion and sediment control, including straw waddles and silt
fence, will
be installed to prevent erosive conditions during construction and reduce
impact to the
existing adjacent vegetation and habitat.
The buffer area temporarily impacted will be replanted with native
vegetation and seed mixes that will improve LCR habitat value and result in a
net environmental uplift.
C urrent Site
Originally constructed in 1967, the South Bridge is a 170 -foot long, three-span, steel girder
bridge spanning over the Cedar River at Boeing’s Rento n plant. The bridge width is 50 feet
from face-to-face of curb, and the span configuration consists of a 120-foot-long main span
with two 25-foot long approach spans. The superstructure is composed of a 7.5-inch cast-in -
place concrete bridge deck supported by nine welded plate girders. In the original
configuration, the superstructure was pinned at Abutment 1 and had expansion connections
at the Pier 2, Pier 3, and Abutment 4 bearings. The bridge is founded on timber piles with
cast-in -place concrete pile c ap footings at both the abutments and intermediate piers. All the
piles at Pier 2 and Pier 3 are driven vertically with exception of the exterior piles which are
battered 4:1 away from the centerline of bridge.
In 1998, the bridge was retrofitted to add the capability for the superstructure to be lifted
vertically up off the piers and abutments using a hydraulics system in the event of a high flow
condition in the Cedar River. This was achieved by strengthening the pier walls, modifying the
bearings at th e piers and abutments, and adding the necessary hydraulic and mechanical
systems. No significant changes were made to the earthquake resisting elements of the
bridge.