ON THIS DAY: March 15, 1967, U.S. Steel Tower groundbreaking

PITTSBURGH — The tallest building in Pittsburgh was once the tallest building in the country, excluding New York and Chicago, a title it no longer owns. It does however, somewhat interestingly, still have the title of the tallest building in the world with a completely flat roof.

On March 15, 1967, the company held a groundbreaking ceremony for the new tower. The president of U.S. Steel, Leslie B. Worthington, called it the “most significant day in the history of two great partners in progress—the city of Pittsburgh and U.S. Steel."

U.S. Steel Tower The skyline of Pittsburgh seen from the Northside on Wednesday, June 26, 2019. (AP Photo/Gene J. Puskar) (Gene J. Puskar/AP)

U.S. Steel Tower A truck drives past the U.S. Steel Tower in downtown Pittsburgh on Tuesday, July 26, 2005. United States Steel Corp. said Tuesday its second-quarter earnings rose 16 percent on strong operating results in its European and tubular segments, as well as solid performance in the company's flat-rolled business. (AP Photo/Keith Srakocic) (KEITH SRAKOCIC/ASSOCIATED PRESS)

Detroit Red Wings v Pittsburgh Penguins - Game Six PITTSBURGH - JUNE 04: The Pittsburgh skyline during game six of the 2008 NHL Stanley Cup Finals between the Detroit Red Wings and the Pittsburgh Penguins at Mellon Arena on June 4, 2008 in Pittsburgh. Pennsylvania. The Red Wings defeated the Penguins 3-2 to win the Stanley Cup Finals 4 games to 2. (Photo by A. J. Messier/Getty Images) (Getty Images/Getty Images)

U.S. Steel Tower ** FILE ** In this April 11, 2003 file photo, the USX Tower, headquarters for U.S. Steel Corp., looms over Grant St. in downtown Pittsburgh. United States Steel Corp. said Tuesday, Oct. 28, 2008, its third-quarter profit more than tripled as higher prices led to record gains in its tubular and flat-rolled steel businesses, but the company expects softening demand to lower fourth quarter results. (AP Photo/Kieth Srakocic, file) (Srakocic/AP)

U.S. Steel Tower The full moon shines over a portion of Pittsburgh's skyline where the city's Gulf Tower at left is illuminated beside the peak of the Koppers building on Wednesday, Oct. 11, 2000. Last month, online auctioneer FreeMarkets put their company name in lights at the top of their buildings to the right of the USX building. FreeMarkets joined PNC Corp. Federated Investors Inc., and Mellon Financial Corp. who each put their company names in lights at the tops of the buildings they occupy scattered through downtown Pittsburgh. (AP Photo/Keith Srakocic) (KEITH SRAKOCIC/ASSOCIATED PRESS)

Carolina Panthers v Pittsburgh Steelers PITTSBURGH, PA - AUGUST 30: A view of the Pittsburgh skyline with a full moon during the preseason game between the Pittsburgh Steelers and the Carolina Panthers on August 30, 2012 at Heinz Field in Pittsburgh, Pennsylvania. (Photo by Justin K. Aller/Getty Images) (Justin K. Aller/Getty Images)

Los Angeles Dodgers v Pittsburgh Pirates PITTSBURGH, PA- APRIL 10: A general view of the Pittsburgh skyline with Olmedo Saenz #8 of the Los Angeles Dodgers and Sean Casey #25 of the Pittsburgh Pirates on the field on April 10, 2006 at PNC Park in Pittsburgh, Pennsylvania. (Photo by Rick Stewart/Getty Images) (Rick Stewart/Getty Images)

U.S. Steel Tower FILE – In this Jan. 9, 2003, file photo, the U.S. Steel Tower, headquarters for U.S. Steel Corp., is framed by office buildings along Grant Street in downtown Pittsburgh. The 64-story U.S. Steel Tower was on the market in January 2017, with estimates suggesting Pittsburgh's tallest building could fetch a sky-high price of $350 million, according to trade publication Real Estate Alert. (AP Photo, File) (Uncredited/AP)

U.S. Steel Tower The U.S. Steel Tower is seen in downtown Pittsburgh on Tuesday, July 26, 2005. United States Steel Corp. said Tuesday, July 31, 2012, its second-quarter earnings rose 16 percent on strong operating results in its European and tubular segments, as well as solid performance in the company's flat-rolled business. (AP Photo/Keith Srakocic) (KEITH SRAKOCIC/AP)

U.S. Steel Tower This Monday, April 24, 2017, photo shows a sign at the headquarters of US Steel at the US Steel tower in downtown Pittsburgh. (AP Photo/Keith Srakocic) (Keith Srakocic/AP)

U.S. Steel Tower Flags fly in front of the US Steel tower indowntown Pittsburgh on Monday, April 24, 2017, in Pittsburgh. (AP Photo/Keith Srakocic) (Keith Srakocic/AP)

U.S. Steel Tower The signs marking the offices for the University of Pittsburgh Medical Center, UPMC, are seen on top of the U.S. Steel tower on Monday, April 3, 2017, in Pittsburgh. (AP Photo/Keith Srakocic) (Keith Srakocic/AP)

U.S. Steel Tower A sign marks the headquarters for UPMC, University of Pittsburgh Medical Center, atop the US Steel tower, along with signs hor Huntinton Bank,and Koppers on their respective office buildings in the skyline of Pittsburgh, Wednesday, July 26, 2017. (AP Photo/Keith Srakocic) (Keith Srakocic/AP)

Protestors Hit The Pittsburgh Streets During G-20 Summit PITTSBURGH - SEPTEMBER 24: Cars move near the downtown in the morning on September 24, 2009 in the Strip District neighborhood of Pittsburgh, Pennsylvania. Dignitaries begin arriving for the G-20 Summit today while authorities vow to prevent expected protests from disrupting the meeting. (Photo by Chris Hondros/Getty Images) (Chris Hondros/Getty Images)

U.S. Steel Tower The top of the U.S. Steel Tower is covered by a cloud above the rest of the Pittsburgh city skyinle along the Allegheny River on a rainy Friday, March 31, 2017. (AP Photo/Keith Srakocic) (Keith Srakocic/AP)

U.S. Steel Tower Falling snow obscures the skyline as traffic makes its way through the snowstorm in Pittsburgh on Saturday, Feb. 14, 2015. (AP Photo/Keith Srakocic) (Keith Srakocic/AP)

U.S. Steel Tower FILE – In this April 29, 2008, file photo, the U. S. Steel Corp. headquarters tower rises above flowering cherry trees in downtown Pittsburgh. The 64-story U.S. Steel Tower is on the market in January 2017, with estimates suggesting Pittsburgh's tallest building could fetch a sky-high price of $350 million, according to trade publication Real Estate Alert. (AP Photo/Keith Srakocic, File) (Keith Srakocic/AP)

U.S. Steel Tower People stand near the entrance to the U.S. Steel Tower in Pittsburgh where the Prime Minister of Slovakia, Robert Fico, had a meeting with U.S. Steel executives on Monday, March 25, 2013. (AP Photo/Keith Srakocic) (Keith Srakocic/AP)

U.S. Steel Tower FILE – In this March 25, 2013, file photo, people walk toward the entrance to the U.S. Steel Tower in Pittsburgh. The 64-story U.S. Steel Tower is on the market in January 2017, with estimates suggesting Pittsburgh's tallest building could fetch a sky-high price of $350 million, according to trade publication Real Estate Alert. (AP Photo/Keith Srakocic, File) (Keith Srakocic/AP)

U.S. Steel Tower This Monday, April 24, 2017, photo shows the entrance to the US Steel tower in downtown Pittsburgh. United States Steel Corporation reports financial results, Tuesday, July 25, 2017. (AP Photo/Keith Srakocic) (Keith Srakocic/AP)

U.S. Steel Tower Signs for the headquarters of US Steel are displayed on the US Steel tower in downtown Pittsburgh on Monday, April 24, 2017, in Pittsburgh. (AP Photo/Keith Srakocic) (Keith Srakocic/AP)

U.S. Steel Tower FILE – This March 18, 2014, file photo shows the U.S. Steel Corp. headquarters building in downtown Pittsburgh. The 64-story U.S. Steel Tower was on the market in January 2017, with estimates suggesting Pittsburgh's tallest building could fetch a sky-high price of $350 million, according to trade publication Real Estate Alert. (AP Photo/Gene J. Puskar, File) (Gene J. Puskar/AP)

U.S. Steel Tower A sign marks the headquarters for UPMC, University of Pittsburgh Medical Center, atop the US Steel tower, . in the skyline of Pittsburgh, Wednesday, July 26, 2017. (AP Photo/Keith Srakocic) (Keith Srakocic/AP)

U.S. Steel Tower A sign marks the headquarters for UPMC, University of Pittsburgh Medical Center, atop the US Steel tower, left, above as sign for Ctizens Bank , center left, and beside the BNY Mellon building, right. in the skyline of Pittsburgh, Wednesday, July 26, 2017. (AP Photo/Keith Srakocic) (Keith Srakocic/AP)

U.S. Steel Tower ** FILE ** In this June 7, 2002 file photo, the Pittsburgh skyline looms over the Mellon Arena. The arena features the world's largest stainless steel retractable dome roof when it was completed in 1961. While players and coaches say Mellon and Joe Louis arenas are star venues in their own right, "young" is not a word used to describe two of the oldest in the NHL. (AP Photo/Keith Srakocic) (KEITH SRAKOCIC/ASSOCIATED PRESS)

U.S. Steel Tower The Pittsburgh skyline is visible through morning fog through a window of the 40th floor of the University of Pittsburgh's Cathedral of Learning, Thursday, May 19, 2011 in Pittsburgh. (AP Photo/Keith Srakocic) (Keith Srakocic/ASSOCIATED PRESS)

U.S. Steel Tower Falling snow obscures the skyline as traffic makes its way through the snowstorm in Pittsburgh on Saturday, Feb. 14, 2015. (AP Photo/Keith Srakocic) (Keith Srakocic/AP)

Steel for the building was fabricated at U.S. Steel’s American Bridge Division Plant in Ambridge and at the former U.S. Steel Homestead Works.

It was a new type of steel at the time, called Cor-ten, which is designed to resist corrosion by preemptively forming a coating of dark brown oxidation, which gives the tower its color.

Unlike other buildings that have their structure clad and hidden behind glass, stone or other decorative panels, the tower’s skeleton was intentionally left proudly bare to showcase its local steel. The building is effectively modular. Each floor has about an acre of office space and every third floor is attached to the exterior columns.

The sparse structure did require inventive ways of hiding protective systems. The 18 main columns are fireproofed, hollow and filled with a water/antifreeze/rust inhibitor mixture. It was the first building to use this technique.

After years of construction, the triangular 64-story, 840-foot-tall building was dedicated on Sept. 30, 1971. At the time, it boasted of a rooftop heliport that has not been used since 1992.

In 1988, the building’s name was changed to the USX Tower to match the rebranding of its namesake company, but this was reversed in 2002 when U.S. Steel reverted back to its original name.

Since 2007, UPMC has made the tower its corporate headquarters.

UPMC installed large signs on the building, each letter measuring about 20 feet high.

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