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Wednesday, March 30,2011

Skeleton crew

Dancing delicately with the Ottawa Power Station’s steel bones

by Lawrence Cosentino

 

Imagine replacing a dinosaur’s skeleton, working through a small hole in the top of its head, while the dinosaur is still alive.

That’s pretty much what steelworkers had to do when they set about to convert the Ottawa Street Power Station to the world headquarters of the Accident Fund Insurance Co. of America.


To protect the plant’s flame-colored masonry shell, a crew from Lansing’s Douglas Steel Fabricating Corp. used a technique some workers compared to building a ship in a bottle.


“I don’t imagine any of us will run into something like that again in our careers,” foreman Judd Converse said.


Converse didn’t know what to expect when he looked at the job site for the first time in early spring 2008. The plant’s turbines and heavy equipment were gone, but tons of debris and scrap beams littered the floor.


“I walked down in the basement, I looked all the way up through the building and I could see the roof,” Converse recalled. “There wasn’t much iron left in there. I kind of had my doubts there for a minute.”


Normally, if a building’s shell needs to be preserved during interior work, engineers buttress the walls from outside, using structural scaffolding that can transfer weight loads to the ground.


But the Ottawa station is stacked like a wedding cake. Instead of holding the walls up, the scaffolding would have rested on the walls below — except at the lowest level, where some of it would have sunk into the Grand River.


The only other way to get nine floors’ worth of beams and girders into the building was through the roof.


The steel team wanted to tear the roof off, but that would have let rain and snow pour into the building for two years, complicating everyone else’s work and getting the masonry wet on the inside.


They decided to cut two hatches, each 14 by 40 feet, into the roof, to be open by day and covered by night. The steel would be threaded through the holes and gently lowered into place.


Once the method was settled, the entire work schedule was penciled out in one afternoon, said Lawrence Kruth, vice president of engineering at Douglas Steel.


A crane operator 200 feet below the roof worked blind as he lifted the beams and threaded them through the hatches.


“He can’t see what he’s lowering or where it is,” Kruth said. “He’s being directed verbally by the ironworkers inside.”


The plant’s vertical beams were sound, but a lot of steel, including service platforms for boilers and generators, wasn’t where the new floors needed to be.


From April to September 2008, the Douglas team worked with a computer model developed by Ruby & Associates of Farmington Hills to map all 2,000 beams in the building.


A delicate ballet of removal and construction, known as surgical demolition in the trade, was under way.


To complicate matters, the steel team had to work around the Lansing Board of Water & Light’s water chilling plant, the only source of chilled water downtown for nine months into the project.


Christman vice president John Holmstrom said most of the building’s columns stayed put, but about 85 percent of the beams and girders were taken out and replaced with 2,500 tons of new structural steel and decking.


Kruth said he constantly asked himself the same question: “How much can we take out safely and have this building still stand during construction, with wind loads and other loads we’ll be experiencing?” It wasn’t enough to avoid pulling out a crucial beam or swinging a girder into a wall.


Take out too much support, Kruth said and you end up with “drift.”


“You can have a building that’s stable, but it can still move around a lot,” Kruth said. “Too much drift would crack the masonry, so a lot of braces had to stay until the new steel was built up around them.”


As they worked their way up, the steel team found features that didn’t show up on the original 1939 drawings. But the top of the steel skeleton exactly matched the height indicated on the old plans.


Converse contrasted the building techniques of 1939 with today’s assembly of pre-fabricated sections. “They built everything out here on site,” he said. “They got raw material in place and riveted it, and they were tremendously close on everything.”


When the steel crew got to the Hall of Turbines on the plant’s west and south sides, they a new set of challenges, including hanging the third floor from the fourth to keep from breaking up the space near the towering west windows. Here, they couldn’t drop the steel through the roof, as they did in the main building, because the chiller’s cooling towers had not yet been taken off the plant.


When in Rome, use the aqueduct.


Engineers put the hall’s 72-year-old overhead crane rails, once used to service the turbines, back to work, building a custom crane that fit the rails. (The old crane wasn’t usable anymore but was left in the building, welded into place, as a giant museum piece.)


Starting from the bottom, the floors were lowered into place. Getting the first floor in was a relief, but Kruth didn’t feel the job go over the hump until the team did “some jacking and shoring that was very scary” was done higher up.


The job got tense when a hydraulic jack was brought to the eighth floor to hold a crucial beam up while work progressed.


“In the process of putting the hydraulic jacks on, we were actually taking the support out that was holding that beam up, and that beam was holding quite a bit of the eighth floor up all by itself — A very challenging situation,” Kruth said. “When we got it done we all felt better.”


Kruth said the Ottawa job employed about 30 steelworkers on the job site and 40 in the steel plant, including a team of 10 engineers.


“I really have to compliment Christman on their vision, to see the beauty in this building,” Kruth said. “When I walked in, I never would have dreamed it would turn out the way it looks right now.”


Kruth is especially pleased that so many beams and cross-braces were left visible on purpose, as reminders of the building’s history.


“Once it’s up, usually nobody ever pays attention to our work anymore,” Kruth said.


“I’d like to get in there and see it,” Converse said. “I hear it’s pretty nice now.”

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