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To Reduce Swaying In Chicago Winds, Vista Tower Getting Empty 'Blow-Through' Floor

CHICAGO (CBS) -- Vista Tower, which will be the city's third-tallest building, is getting a unique feature for a Chicago skyscraper to prevent the 1,191-foot building from swaying too much in the wind.

In a rare opportunity, CBS 2 Morning Insider Vince Gerasole traveled to Lakeshore East, where the city's newest skyscraper is rising through the winds of change.

Rising 101 stories above the city, each day Vista Tower looks less like a steel skeleton and more like the third-tallest building in Chicago, but before it's complete, we want to point out one floor in particular.

Vista Tower
When complete, the 101-story Vista Tower will include an empty "blow-through" floor on the 83rd floor, to reduce swaying in windy conditions. (Credit: CBS)

From the ground, it already looks a bit different, and it's unique to the city.

"We call this the blow-through floor. This is the 83rd floor of the building," said Sean Linnane, executive vice president of Magellan Development Group, which is developing Vista Tower with China-based Dalian Wanda Group.

Like its name implies, the blow-through floor will remain mostly open, allowing winds to blow through and keep the building's three connected towers from swaying too much under the force.

"A blow-through floor is a way to – as the structural engineer and the wind engineers describe it – confuse the wind, and basically dissipate some of the effects of the wind," Linnane said.

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The need for a blow-through floor was discovered after construction began, when a model of acclaimed architect Jeanne Gang's thin elegant structure was placed in a wind tunnel for analysis.

The blow-through floor will include 24-foot vertical grates spaced out around the perimeter, matching the window colors of surrounding floors.

The floor was designed to encourage winds to come its way and pass through.

"If you want to get technical, it reduces some of the acceleration. So it's kind of the whippiness factor of the movement," Linnane said.

Though they exist in other cities, the Vista's blow-through floor will be a first for Chicago. You can find a hole at the top of 515 N. State St., but it's only an asthetic feature.

The Council On Tall Buildings said most of the city's taller structures, like the Willis Tower, sway several inches each day.

"Whatever direction the wind comes through, or comes from, we can alleviate that pressure," Linnane said.

Creating a blow-through floor cost developers a lot of cash. The floor is roughly 8,000 square feet in a building where property can sell for upwards of $1,000 per square foot.

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