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June 3, 2016 — A year of planning and one-and-a-half years of construction came to a close in May with the completion of the $8.4 million Portage Lake Lift bridge project.
The Michigan Department of Transportation (MDOT) project included upgrades to the bridge’s mechanical and electrical systems, along with concrete and steel structural improvements. It was one of the biggest overhauls of the iconic bridge since its construction in the late 1950s. Modjesky and Masters from Pennsylvania served as MDOT’s design consultant, with Zenith Tech from Wisconsin was the prime contractor.
Mobility was a primary concern, as the project required 400 brief closures of the bridge – the sole link between the Keweenaw Peninsula and the mainland. While these closures lasted less than 20 minutes each, 20 two-hour closures and two all-night closures were also necessary. Various lane closure configurations on the bridge also strained the road system and caused periodic backups. Extensive coordination was undertaken to ensure the community had access to essential services and the local economy could continue to function during bridge closures.
“MDOT’s $8.4 million spent in keeping the Portage Lift Bridge in top working order has been an important investment for the 24,000 daily vehicle users and is appreciated by the 22,000 residents who live on the north side of the bridge,” said Hancock City Manager Glenn Anderson. “In addition, the coordination and public communication between MDOT, the contractor, and the community was extremely effective in assuring minimal interruptions and impact on the residents and businesses of the area.”
MDOT organized a communications working group eight months prior to construction and the group continued to meet throughout the project. The panel included MDOT engineers, local government officials, law enforcement, Coast Guard staff, and hospital and emergency personnel, plus representatives from airport and bus services, surrounding school districts, colleges and many other organizations.
Construction engineer Alan Anderson, the project manager for MDOT, said he attributes the smooth progress of the Lift Bridge project to this group.
“Key players in the community became engaged,” Anderson said. “And once they knew the impacts they were dealing with, they adjusted to provide successful solutions for things under their immediate control.”
Houghton County Sheriff Brian McLean was one of the participants in the working group. “For such a large, expensive and extended project, things went quite well from our perspective,” he said. “The pre-planning, planning and re-planning went very well – we were always in the loop of communication and everyone worked well together. Hats off to the team that put this together.”
The list of work performed on the bridge is extensive: new barrier gates were added, as well as additional security cameras. Mechanical component upgrades included lift cable replacements, pinion and pinion shaft replacements, balance chain improvements, new hydraulic cylinders and brake upgrades. The electrical work included new lift motor drives, motor upgrades, sensors, cabling, and fiber optic lines connecting the two bridge towers.
The upgrades will make for more precise, reliable and automated bridge operations, MDOT’s Anderson said. The bridge’s massive 4.5 million-pound central lift span is now balanced by the counterweight to within 5,000 pounds on each end. Precise shimming ensures the span sits down equally on all four corners simultaneously. New pinion designs reduced the amount of backlash — or “slop” – in the system, tightening up the operation of the mechanical components.
One amazing byproduct of such precision: Anderson noted that a person could actually lift this bridge, one of the world’s heaviest lift spans, with a hand tool.
“The gear series gives you enough mechanical advantage and the counterweights are balancing the span so closely that you could put a strap wrench on the shaft that comes out of the motor and actually lift the bridge by hand – slowly,” Anderson said.
