The historic bridge carrying Franklin Avenue over the Mississippi River is getting a makeover in an innovative way meant to lessen construction time and driver detours.
Hennepin County shut the bridge to all traffic Sunday night. But it’s planning for the detour to last just 17 weeks, targeting Labor Day weekend for the reopening.
The detour is diverting almost 10,000 drivers daily, but it would last far longer if the county had stuck with traditional construction methods of building forms and pouring the concrete on the bridge, according to Paul Backer, a county project engineer. That would have closed the bridge for two construction seasons, he said.
Instead, contractor Kraemer North America has been precasting 366 panels of the new concrete bridge deck just upstream at Bohemian Flats. From there, they’ll be barged to the bridge and hoisted to the deck by cranes. The cranes are also being used to lower 25-ton sections of the old 1970s bridge deck to barges below, to be ferried upriver and trucked to a crushing yard.
The 45 cross beams of reinforced concrete that support the deck will also be exchanged. The newly cast beams will feature scrolled ends that mimic the bridge’s original 1923 design. New side railings in the original design also will be installed, along with reproductions of the original ornamental streetlights.
“I give the engineers the credit here,” said County Commissioner Peter McLaughlin, who said the short but intense closing was chosen after consulting with nearby businesses and residents.
Staff at Seward Co-op and neighboring stores west of the bridge warned customers in advance and suggested detours. But they may step up publicity if business is affected.
“We’re in a little bit of a wait-and-see mode now,” co-op marketing manager Tom Vogel said. “It’s going to take a couple weeks to know what the real impact is.”
The bridge, known officially as the Cappelen Memorial Bridge, joins others in the metro built with techniques that accelerate construction and minimize disruption for bridge users.
In 2012, barges floated a 545-foot main span for the Hwy. 61 bridge at Hastings to the partly built bridge, where it was hydraulically lifted into place. Similarly, in 2012 a self-propelled motorized platform rolled the new Maryland Avenue bridge into place on Interstate 35E in St. Paul, limiting the closing of 35E to one weekend and Maryland’s closing to two months.
The $51 million cost of the Franklin bridge project is comparable to what it would be under a more traditional approach, Backer said.
Innovative construction methods fit with the Franklin Avenue bridge’s history. It’s one of a series of bridges built by Minneapolis from 1914 to 1929 that attracted engineers from around the world. The five-span bridge stood out for its 400-foot central arch, the longest reinforced concrete arch in the world when it opened in 1923, something that later made barge traffic easier.
The rehabilitation also attempts to reverse some of the downsides of a 1970s rehab that occurred just before historic preservation efforts gained momentum. At the time, some of the vertical supports known as spandrels that supported the deck were removed, changing its look, and 1970s-style railings and lighting replaced vintage features.
The current rehab aims to restore some grandeur while complying with modern standards such as safety and accessibility, said Kristen Zschomler of MnDOT, who worked with the county to comply with federal standards for historic properties. The bridge is a designated local landmark and on the National Register of Historic Places.
Watching the timeline
The new bridge will make other accommodations to 21st century transportation. For example, the number of traffic lanes is being reduced from four to two, with turn lanes at the eastern end’s complicated five-way intersection. The remaining space will be converted for pedestrians and cyclists separated from cars and trucks by a 2-foot-high barrier of concrete and tubular steel.
Reopening the Franklin Avenue bridge also has implications for West River Parkway, which has been closed to all traffic upriver from the bridge since a mid-2014 mudslide. Park officials say their long-awaited stabilization of the river bluff will be completed in time to reopen the parkway as Franklin reopens.
The planned reopening of the bridge and parkway around Labor Day weekend is also on the calendars of fall event organizers. The Oct. 9 Twin Cities Marathon is planning to retain its traditional crossing of the river at Franklin, and plans for its companion 10-mile race to return to its normal parkway route, although a spokesman said there are contingency alternate routes. The Sept. 18 Minneapolis Bike Tour also is routed along the parkway.