Stopping That Sinking Feeling At Milwaukee City Hall
Milwaukee City Hall was completed in 1895. But if you've seen the building over the years, it may seem like it's been under constant construction. So, let's look at the work that's been done on City Hall and what's still in store.
That's what Kim Marggraf wants to know, so she reached out to Bubbler Talk — our series where you ask, we investigate and together we unveil the answers:
"Why has City Hall been under some form of construction or reconstruction, for what seems like decades?"
The answer to Kim’s question is long, and continuing.
First, there was the $76 million renovation of the exterior of the building that started in 2005 and wrapped up in 2008. Except it didn't wrap up for long. In 2011, chunks of stone started falling off and there were a few more years of repairs.
Once that public safety problem was fixed, another huge project began about three years ago, mainly in the City Hall basement. The northeast section of the basement, where some mechanical equipment used to be, is busy with construction workers. Their mission is to take the weight off the long wooden piles that were driven into the soft, river valley ground when City Hall was built.
There are about 2,600 of the 25-foot long pieces of white pine. The piles, along with oak planks and slabs of limestone, help support the 50,000-ton weight of City Hall that rises 393 feet in the building's bell tower. Department of Public Works (DPW) Engineer Craig Liberto says even though the vertical piles have long been submerged in water to protect them, they are slowly decaying.
"Well, it's just wood in itself, it fungal rots. Things in the soil itself causing deterioration. Keeping them submerged will prolong their length. But again, we have a building that's built in 1895,” Craig says.
He says the first signs of wood decay were spotted in the 1950s and some limited repairs were done. More recently, measurements showed the north end of the building sinking more than 2 inches and the south half nearly 1 inch.
Craig says what's known as "differential settlements" were causing problems. "We were having areas that one column over would have a little more settlement than the other one, and that created stress in the building and cracks in the building, as evidenced by cracks in the mosaic tile, by cracks in the plaster, “ he explains.
While some communities might have thought of tearing down their city hall and moving to higher and firmer ground, Milwaukee's center of government is on the National Register of Historic Places and is a National Historic Landmark.
So, into the basement went the ironworkers, carpenters and other tradespeople. Not to jack up the building, but to try to stop the sinking.
Mary Collins is senior project manager for Gilbane Building Co., the general contractor on the City Hall project. She describes the basic fix.
"So, the existing foundations for the building are not being removed. What we're installing is a new foundation system around the existing. What it's called is a passive load transfer design. It's actually the first time this design is being used in North America. They've used this design in Europe where there are other buildings similar to City Hall," Mary says.
The new foundation system consists of long steel tubes called micro-piles that are covered by grout and driven 75 feet deep. Then, a cage of metal rods, known as rebar, is built around existing steel vertical support beams and concrete is poured over the rods.
Later, metal tension rods are installed horizontally to tie the old wooden pile foundation to the new foundation. Over the next decade, as a protective water system is disconnected and the wood continues to rot, the weight of City Hall will transfer from the old base to the new one.
Despite being three years into the work, the City Hall project is only about half done. Mary says the confined space of the basement makes going faster too difficult.
“We have a limited amount of space we can work in at any given time. That causes us to have to consider the amount of activity that can happen. We can't overlap certain activities like you normally could on a new construction project, and that does limit the number of tradesmen we have on-site at any given time," she says.
DPW adds that keeping City Hall open, and restricting very loud work to nighttime, also slows things down.
While the foundation project moves along, workers are also restoring basement stairways, doors, and outdoor iron grills at the north end. They’re also filling in and replacing old outdoor walkways that had nothing underneath them except part of the basement. Plus, the tunnel between City Hall and the city Municipal Building is being renovated.
Still ahead, is the south end of the basement, and patching the cracks upstairs.
So far, $35 million has been spent, with a projected overall cost of $58 million by the time things wrap up in 2022. A sizable burden for city taxpayers, perhaps, but officials say it's needed to protect a 123- year-old symbol of Milwaukee.
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