Case Study- Zilwaukee Bridges
The Zillwaukee Bridges are twin high level viaducts crossing the Saginaw River and its floodplain
in the state of Michigan. They carry 8 lanes of i-75 and US 23, 4 lanes in each direction. The
total length is 8061 feet NB and 8085 feet SB. There are 26 NB spans and 25 SB. The river span
is 392 feet with a navigation clearance of 120 feet.
Construction began in late 1979 but was not completed until September 1988. Construction
was delayed in 1982 due to a major construction accident. The erector lost control of a 150
foot, 6,700 ton precast concrete section. After settlement of claims, a new contractor and
construction engineer were engaged to complete the work.
The structure was constructed by using an overhead truss and placing precast concrete
segments by the balanced cantilever method. The segments were 8 or 12 feet long, 73.5 feet
wide and weighed 120 to160 tons. The last segment of each span was cast in place.
Shortly after completion in 1988, problems arose due to the amount of creep and shrinkage in
the bridge. Pot bearings began leaking elastomer and the ptfe disks ground against the steel
pot. The bearings became over rotated and over translated. There was significant movement in
the first 12 years of use.
In 2013 and 2014 the bridges were retrofitted to replace the failed bearings and pressure grout
the joints. This required a major underpinning operation. The cost of the bearing replacement
and other rehabilitation work was $70 million.
The Michigan DOT had issued a moratorium on the construstion of concrete segmental bridges
after the 1982 accident but rescinded it after the successful reconstruction.
References
Wikopedia. Zilwaukee Bridge
Kwong Chen & Frandcis Drouilard, OPAC. Zilwaukee Bridge Construction Engineering
Ken Haddad. The Z-Bridge: The turbulent history behind Michigan’s Zilwaukee Bridge
Michigan Highways. The Zilwaukee Bridge: From the Beginning
American Segmental Bridge Institute. Retrofit Ends Michigan Moratorium
The Zilwaukee Bridges