The Portage Lake Bridge is being recognized as one of the most significant historic civil engineering works in the country thanks to three Michigan Tech researchers.
The American Society of Civil Engineers (ASCE) will dedicate the Portage Lake Bridge as a National Historic Civil Engineering Landmark at 10 a.m. Friday, June 17, in a ceremony at Houghton’s Bridgeview Park. The public is invited.
“The lift bridge,” as it’s regionally known, links Houghton and Hancock and is the only structure spanning the Keweenaw Waterway. At 4,584,000 pounds, built with more than 35,000 tons of concrete and 7,000 tons of steel, the bridge was the heaviest double-decked vertical-lift span in the world at the time of its construction in 1959. It was also the first bridge in the United States to use an intermediate lift span position.
Officially named a State Historic Landmark in summer 2019, the lift bridge was recognized as an ASCE National Historic Civil Engineering Landmark later that year thanks to the efforts of Tess Ahlborn, professor of civil, environmental, and geospatial engineering at Michigan Technological University, and two of her former students: Michael Prast ’19 and Emma Beachy ’19. The public dedication and celebration were delayed due to COVID-19.
The trio of Ahlborn, Prast and Beachy submitted the required 300-page application to obtain the ASCE designation. Prast is now a timber structural engineer at Fire Tower Engineered Timber in Calumet, Michigan, and Beachy is a design engineer at Corbin Consulting in Beaverton, Oregon. Both earned their bachelor’s and master’s degrees in civil engineering at Michigan Tech, completing their degrees in 2019.
“I mentioned the topic of national historic landmarks during Bridge Design class and let the class know I would be delighted if someone wanted to work on a nomination application for the Portage Lake Lift Bridge,” said Ahlborn. “It didn’t take long for Emma and Michael to speak up, and the rest is history. I can’t thank them enough for taking on this project and seeing it through the application process.”
Prast and Beachy started preparing the application in spring 2019. It took them about four months to gather all the required information.
“We had to prove the historical significance of the Portage Lake Bridge and describe its unique features,” said Prast. “We also had to show what the building of this bridge did to elevate the civil engineering profession — as well as its social and economic impact on the region and the nation.”
The Portage Lake Bridge took its name from the bridges that came before it. Like them, it was crucial in helping facilitate the transport of copper, timber and other raw materials during the region’s industrial heyday. But Beachy said the continued importance of the lift bridge is unique.
“Most of the bridges of this type — because they’re so old — are mostly converted into either pedestrian or bike bridges, or just demolished entirely,” she said. “In contrast, the Portage Lake Bridge is really well maintained. It also has a really high level of use. Not only in comparison to other vertical lift bridges, but also just in comparison to other notable Michigan bridges, like the Mackinac, the Blue Water, and the International Bridge.”
“Today, we have a very active tourism industry,” Prast added. “Especially in the summer, traffic on the lift bridge increases quite significantly. In the winter, when the lower deck is used for snowmobiles, it makes it a much safer crossing for everyone involved.”
Some of the earliest crossings across Portage Canal included a ferry service and a floating gondola-style bridge, said Prast. “In the 1870s citizens created a wooden swing bridge. It had only one deck originally, for animal carts and pedestrians. In 1892 it was adapted for rail.”
The swing bridge allowed pedestrians, cars and trains to cross. Its center span rotated to open the waterway to boats passing through.
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