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'An Engineering Feat': The Doors At U.S. Bank Stadium

MINNEAPOLIS (WCCO) -- With construction now complete, U.S. Bank Stadium will soon open its doors.

Those doors might not be what the stadium is most known for, but maybe they should be.

Since the beginning, all the way from design through construction, the stadium's clear, see-through roof has been the headliner grabbing all the attention.

Which has caused the stadium's doors to sort of slip under the radar. Which is kind of incredible.

Because on any other stadium, they'd be the star.

"You hesitate to say that something is unique," said author Steve Berg. "But these are."

Berg wrote the book on U.S. Bank Stadium – literally, it's out in October – and is the resident expert on it. And recently, while collecting material, he got the chance to walk through those massive glass doors – ahead of just about everybody else.

"Passing through a door like this is like nothing else you've ever experienced," Berg said. "Doors are about transition. You go from a bright sunny day like today, to a dark interior. [But] that's not what these doors are like. You don't know whether you're inside or outside. It's the absolute absence of contrast. That confuses you."

Who knew that a door could be so exciting.

"Well that's true," Berg said with a smile.

"They were looking for something that was animated. Something that would move. And these doors, because they pivot like this, they move. And they're actually more dramatic than a roof," Berg said.

Rotating on hydraulic pistons, they are the five largest pivoting glass doors in the world, 55 feet wide and ranging from 75 to 95 feet high, consisting of 30,000 square feet of glass from Owatonna, attached to door frames manufactured in Tennessee, and weighing, altogether, 40,000 tons.

"Enormous," Berg said. "And very impressive when you see them open."

And rather unique to sports stadiums.

"They have a big sliding door at the Miami Marlins ballpark in Miami," Berg said, "that was designed by the same company that built this door. The company said that their first inclination was to run away from this project. They didn't want it -- it was going to be too hard. But it was too alluring to turn down. It was too big of a challenge.

"They had never done pivot doors like this, they had done sliders. They've done a lot of aircraft hangars and big, big defense department buildings. But as far as clear glass, and a door that pivots, so it's indoors-outdoors, it's a first for them. Very risky for them."

Risky, why?

"A building like this is designed to move, a little bit, with the stress of temperature variation, moisture, all of those things," Berg continued. "But these doors had to be built into a wall in a way where the measurements were extremely precise, in order for them to fit, and in order for them to work. And so, it was an engineering feat, to get the doors in there."

The Vikings initially thought the NFL might need to create a new policy for their first-in-the-league doors, similar to the one for opening and closing retractable roofs. But the NFL informed the Vikings in May that its existing retractable roof and wall policy applies: The Vikings must make a decision -- doors open or doors closed -- at least 90 minutes before kickoff.

As for the factors that will go into that decision? The Vikings are planning to do some testing to determine what happens when the doors are open. Any wind, or other impact?

"I think they might have an effect," Berg said. "Certainly the architects know that there's a ventilation effect, to having the doors open.

"I suppose there's a chance that that might affect the game, [for example] the flight of a field goal kick."

If that ever happens, no doubt the doors would surpass the roof as the U.S. Bank Stadium's most famous feature.

"Well the doors are a little underrated," Berg said.

Berg's book is available for pre-order right now from the Minnesota Historical Society Press, or the Vikings website.

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