A trip to the roof of Mercedes-Benz Stadium

1. The moving roof panels ("petals") weigh 500 tons each. 2. The roof is believed to have cost hundreds of millions of dollars. 3. The roof petals move on rails, like a railroad car. 4. The stadium opening was delayed to fix a gap in the roof. 5. The opening and closing of the petals was designed to resemble a camera shutter.

Take a ride to the top of Mercedes-Benz Stadium, about 340 feet above what will become the playing field, and you see first-hand the challenge, the complexity and, yes, the marvel of the building’s retractable roof.

You see the eight movable panels, called petals, each weighing about 500 tons. You see the rails on which the steel petals will move in straight lines when the roof opens or closes. You see workers making adjustments and preparing the petals for installation of a translucent covering.

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And you look down, through the roof’s 100,000-square-foot opening, and see the ground on which a Falcons exhibition game is scheduled to be played Aug. 26, which was 100 days away as of Thursday.

To get this vantage point, to get an up-close look at the roof that has delayed the massive stadium’s opening three times and ultimately figures to be one of its signature features, an Atlanta Journal-Constitution reporter and photographer were lifted in a crane basket from field level to the top of the building.

The roof is about 180 feet above the highest row of upper-deck seats. It measures 14 acres, including the approximately 2 1/2-acre retractable portion, which currently is in the open position. And it is believed to account for hundreds of millions of dollars toward the $1.5 billion cost of the stadium.

Already standing on the roof when the reporter and photographer landed was Bill Darden, president of Darden & Company, the project-management firm overseeing development of the stadium for Falcons and Atlanta United owner Arthur Blank.

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“It’s just an incredibly one-of-a-kind thing,” Darden said of the roof.

More than once, Blank has called it “the most complicated roof design in the history of the world.” No one on his construction team has disagreed.

It is so exacting that Darden, in a 45-minute rooftop interview, compared its construction to “a Swiss watchmaker working with micro-ounce pieces that are so small you can barely even know they’re in your hand.”

Except, he added, for this large difference: “There are 4,000 tons of steel in these eight petals, and we’re trying to accomplish the same exact thing because these pieces have to move at the exact precise time and have to have very tight tolerances between the bogies and the rails. They can’t be (loose), like you see in an amusement park sometimes. It’s very precise. I was in a meeting earlier this week, and we were literally talking about 1/16th and 1/32nd of an inch.”

The eight petals — each more than 200 feet long — rest on the bogies, mechanisms that sit on the rails. For the roof to open or close, the bogies move the petals along eight separate tracks, which are attached to the fixed portion of the roof.

“It’s like a railroad car on a railroad track,” Darden said.

Or eight railroad cars on eight tracks.

The roof is powered by many electric motors — 12 motors per petal. Each petal is moved independently but in unison with the others.

Eventually, opening and closing the roof is supposed to be a routine process that takes nine to 12 minutes.

“We can move it today,” Darden said. “But the tighter those tolerances are, the longer the life span of the bogies. So it’s important to drill down and get them right, right out of the gate.”

Darden said the stadium will be ready for what is now scheduled as its first event, a Falcons exhibition game against the Arizona Cardinals in late August.

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“Like anything this complicated, it’ll be a challenge. But we’ll get it done, yeah,” he said. “It’s exciting to see how many bodies are up here working. When these people go home, a whole other group comes up here and just keeps going.”

Even if the Aug. 26 opening is achieved, there has been much speculation — denied by the Falcons organization — that the roof might not be ready to retract then and that part or all of the stadium’s first season might be played with it closed.

“Day 1, I think we’ll be able to operate both ways,” Darden said, meaning with the roof open or closed.

Adding to the complexity of the roof is that a 58-foot-high, 360-degree video board is being built into the structure. The steel to support the halo-shaped board has been erected, and installation of the video screens is underway. The board, shipped in more than 40 truckloads from manufacturer Daktronics’ headquarters in Brookings, S.D., will ring the roof opening, measuring 1,100 feet around.

All of the stadium’s structural steel is in place now, including 18,000 tons in the fixed roof, 4,000 tons in the retractable portion, 4,000 tons in the “skin” of the building and 580 tons to support the video board.

The final structural-steel piece was installed early this month. Attached to one of the roof petals, it is designed to cover and seal the spot where the eight triangular petals come together when the roof is closed. The construction team calls this piece the "button" because, although it weighs eight tons and measures 22 feet in diameter, it is expected to look like the button on the top of a ball cap from far overhead.

The completion of structural steel was cause for celebration by the workers on site. But as the calendar moves rapidly toward football season, there is still plenty of work to be done up on the roof.

On a recent 88-degree afternoon, a gentle breeze blew across the roof as some workers gauged alignments, made adjustments, checked water-tight seals. Others prepared for the installation of multiple layers of ETFE, a plastic-like material that will filter the sun’s rays while letting in some light when the roof is closed.

The roof was meticulously moved to the open position for this phase of work. Next month, it’ll be moved back to the closed position for other work.

The stadium originally was scheduled to open March 1, which was pushed back to June 1, then to July 30, then to Aug. 26 — a total of about six months in delays, all said to be related to roof steel work.

Demolition of the Georgia Dome, originally slated for July, has been put on hold as an “insurance policy” against further delays. Steve Cannon, CEO of Falcons parent company AMB Group, said it should be known in June when preparations for demolishing the Dome can resume.

In announcing the latest delay last month, Cannon acknowledged the roof has required extra work beyond the original drawings to make the pieces fit and align.

“You install a shim that closes a gap or addresses a gap,” Cannon said. “So, yes, there was a shimming process that took place.”

On the roof, you see an example of that improvisation: a spot where an additional chunk of steel had been bolted to a petal to make an adjustment in the slope.

From the start, the architects wanted the roof to be a significant, even iconic, design feature rather than just a utilitarian cover. The lead architect, Bill Johnson, has said the roof will resemble a camera shutter when it opens and closes.

“Even though the petals are going in a true straight line, the geometry allows them to look like they’re moving in a curved motion,” Darden said.

While each of the eight panels moves a shorter distance than the fewer pieces on other retractable roofs, the oculus design and geometric angles have made construction more complex, more intricate.

“More tedious and more time-consuming,” Darden said. But the progress heartens him. “I see the end of the tunnel and see the daylight coming out.”

When the roof is closed, the Mercedes-Benz emblem will appear on the outside top of the retractable portion, an image sure to be prominent in TV’s aerial shots. But that large logo will be spread across all eight retractable panels, forming the Mercedes star only when the pieces come together.

“It is literally part of the puzzle,” Darden said. “When it is closed, it will look just like you painted it on.”

As you look down from the roof into the stadium now, you see other important work yet to be done: Many of the lower-level seats aren’t in place, and the artificial turf hasn’t been installed.

But those are simple and swift tasks, at least by comparison to what’s up top.

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