The massive strong back beams that support the superstructure in order to unload the expansion hinge to replace the bearings.
It’s said the two brothers who founded the small Michigan township of Zilwaukee in the mid 1800s deliberately named it thus in the hope of confusing settlers who, mistaking it for Milwaukee in Wisconsin, would arrive there to work.
So it is indeed Zilwaukee with a zee, and work on its bridge forms part of a Michigan Department of Transportation (MDOT) project under a relatively new contract delivery method used only a few times in the state, and never before on a project this large or complex.
The Zilwaukee Bridge is a 8,100 ft. (2,469 m) long post tensioned concrete segmental structure, consisting of 1,592 concrete segments, each with an average weight of 160 tons (145 t). This complex structure was one of the largest post tensioned concrete segmental bridges in the United States at the time of its construction.
The overall cost of about $65 million represents $36 million for work on the Zilwaukee Bridge and $29 million in related I-75 road improvements.
The latter job includes not only reconstruction of 4 mi. (6.4 km) of the highway but also storm drainage and guardrail improvements and work on the bridge ramp shoulders, while the Saginaw County span will have all the pier, expansion hinge, and abutment bearings replaced as well as concrete overlay work and barrier repairs.
“The project is being built using an innovative contracting called Contract Manager/General Contractor (CM/GC),” said Matthew J. Chynoweth, MDOT engineer, bridge field services.
“MDOT contacted national renowned qualified contractors to make them aware of this project and encouraged them to solicit proposals if their team had the expertise and knowledge to successfully complete this project,” he went on, explaining that “CM/GC involves selection of the contractor team via qualifications-based selection as opposed to low bid. The qualifications were dictated by MDOT, and the scoring of each team included items based on the qualifications of the team, innovations, understanding of the work that needs to be done, and past experience on segmental construction and rehabilitation.”
Chynoweth described the process as allowing the contractor to provide input at the design phase as opposed to the designers producing the plans, and then handing them off to the contractor. This permits the contractor to provide information on constructibility, means and methods, specialized equipment, and market conditions for materials, as well as providing independent cost estimates throughout the design phase.
As an example of this team work, the contractor’s engineer independently looked into the designer-proposed strengthening procedures, and provided input on other means and methods on other items.
As a result, efficiencies mitigating costs and possible risks were developed, including:
• Eliminating proposed shoring towers and temporary support structures
• Reusing strengthened support beams used on a 2007 Zilwaukee Bridge project rather than fabricating and building new support beams
• Developing bearing removal and replacement procedures to significantly reduce or eliminate completely the risk of impacting critical steel tendons or reinforcement.
In connection with this latter aspect of the project, said Chynoweth, “The project team contacted all the major bearing manufacturers in the U.S. to solicit input on bearing designs given the vertical and horizontal constraints. This has led to consideration of innovative material such as self-lubricating Teflon sheets to reduce friction and using the same temporary shoring system on the abutments and expansion joints, to eliminate custom built and fabricated shoring system for the abutments only.”
“When the design phase was substantially complete, MDOT negotiated a Guaranteed Maximum Price proposal with the contractor. Had the negotiations been unsuccessful, the project would have been advertised via low bid, however, the project would still have the overall benefit of having a contractor as part of the design phase,” he continued.
Prime contractor for the job is PCL Civil Constructors, based in Tampa, Fla. However, a large portion of the work was subcontracted to the Michigan bridge contractors Walter Toebe Inc., of Wixon, Mich., and C.A. Hull of Walled Lake, Mich.
Bridge work includes replacing 34 expansion joint bearings (16 on the north bound structure, 16 on the southbound structure, and two on the entrance ramp to southbound), 106 pier bearings (48 on the northbound structure, 50 on the southbound structure, and 8 on the entrance ramp to the southbound), and 10 abutment bearings (4 on the northbound structure, 4 on the southbound structure, and 2 on the entrance ramp to the southbound).
“Although the bridge opened to traffic in 1987/1988, segments and bearings at the north end of northbound were erected as early as 1980. Bearings support as little as 700,000 pounds at the abutments, to as much as 8,100,000 pounds at the piers. The existing bearings’ service life included capacity to facilitate the construction sequence, and also facilitated 24 years of the finished structure’s movements due to thermal gradient, and volumetric changes due to creep and shrinkage of the concrete during the service life of the structure. The loads on the bearings during construction were larger than any in-service load the bridge will ever experience,” Chynoweth said.
In addition, approximately 10,000 ft. (3,048 m) of bridge barrier will be repaired or replaced and 3.2 percent of the concrete overlay surface will be repaired, while mainline I-75 and southbound entrance ramp bridge decks will receive a coating of penetrating water repellent treatment to further enhance the serviceable life of the latex modified concrete overlay riding surface.
The southbound work began in April 2013 and will be completed by January 2014, at which point the northbound work begins with an expected completion date in January 2015.