The 66,200-seat U.S. Bank Stadium in Minneapolis, Minnesota, was completed in just 30 months and six weeks ahead of schedule. Photo John Aniol /Thornton Tomasetti
After nearly three years of construction, U.S. Bank Stadium, the new $1.1-billion home of the Minnesota Vikings, has thrown open its doors, including five 55-foot wide glass operable panels some as high as nine stories tall. The massive pivoting doors and the largest transparent ETFE roof in North America are among the innovative design elements unveiled at the Minneapolis stadium’s ribbon cutting and grand opening celebration this past weekend.
On hand for the festivities were members of Thornton Tomasetti’s structural engineering, façade engineering, sustainability, construction engineering and kinetic mechanization design teams, all of which collaborated with the architects at HKS Sports & Entertainment Group to create a state-of-the-art venue and a unique experience for fans. Also on the project team are developer Minnesota Sports Facility Authority and general contractor Mortenson Construction.
“U.S. Bank Stadium raises the bar for stadium design on so many levels,” Chairman & CEO Tom Scarangello said. “Its complex geometry, iconic moveable doors and innovative EFTE roof—not to mention amazing sight lines that every fan dreams of—make this venue is truly unique. Thornton Tomasetti is proud to have played an integral role in such a world-class structure.”
The stadium’s ribbon-cutting ceremony on Friday, July 22 was followed by a two-day open house for fans and the community. U.S. Bank Stadium, which finished six weeks ahead of schedule, is nearly twice the size of its predecessor, the Metrodome. In addition to Vikings football, the facility can accommodate professional and collegiate sporting events, concerts, motocross racing, conventions and trade shows. It can seat 66,200 people for Vikings games, 58,000 for concerts and up to 70,000 for the Super Bowl or similar events. The stadium also features 8,200 club seats and 131 premium suites. Fans will be able to get up closer to the action than at any other NFL venue with seats 41 feet from the sideline and turf suites just 25 feet away.
Photo John Aniol /Thornton Tomasetti
With its glass doors and transparent roof, the 1.7-million-square-foot venue was designed to convey the feeling of being outdoors while protected from the elements and connected to downtown Minneapolis. The stadium stands 214 feet above grade at the eastern end and rises to a peak of 284 feet on the western end. The steeply lofted steel roof, a principal architectural feature, will shed snow more easily, reducing snow loads by some 25 to 30 percent. Our design team used parametric modeling techniques to perform slope optimization studies to create one of the lightest structural steel stadium roofs in North America. A single steel ridge truss, measuring 970 feet long and 15 feet wide, is the primary support for the roof structure. The seven-level superstructure consists of precast concrete seating units and cast-in-place concrete frames and concourses. The first seating level above the main concourse is elevated to provide an open view of the field when entering the stadium.
“Thornton Tomasetti’s structural engineering and construction engineering teams worked closely with the design team, Mortenson Construction and the roof steel fabricator/erector in a collaborative process,” Vice President John Aniol said. “This resulted in the completion of the long-span roof one month ahead of schedule and within 100 tons of the design development/GMP steel tonnage allowance.”
Photo Thornton Tomasetti
The Moveable Doors
The stadium’s main entrance at the western end of the building features five steel-framed glass panels that range between 75 and 95 feet high. The doors, said to be the largest in the world, pivot 90 degrees to create a large plaza with views of downtown Minneapolis. The panels consist of a series of stacked steel trusses that incorporate five of the building’s columns as the pivot points. They are operated by three pairs of hydraulic cylinders and will take five to seven minutes to open and close, depending on wind, weather and other conditions. Tapered seals along the edges and operable sills that rise two inches when in motion will keep the panels tightly closed. There are 10 smaller doors within the panels that allow people to enter and leave the stadium when the larger doors are closed.
“Although operable walls exist in a few other stadiums, the panels at U.S. Bank Stadium are unprecedented in scale,” Associate Principal Tom Duffy, who specializes in kinetic structures, said. “The design team also developed an alternative approach, making them pivot instead of slide which has never been done before. This presented a few challenges, including figuring out how to make sure there was a tight seal when the panels were closed. And we needed to devise a way to gain a few inches of clearance from the floor as the panels moved. In the end, we came up with a separate mechanization system that lifts the bottom of the smaller doors by a few inches. There were a lot of new ideas that went into this project, which made it a very exciting one to work on.”
Photo Thornton Tomasetti
Approximately 45 percent of the stadium’s roof will be clad in ETFE (ethylene tetrafluoroethylene) pillows. The clear, lightweight polymer covers some 240,000 square feet on the south side of the building. The ETFE pillows, which are approximately 10 feet wide and 320 feet long, create a continuous surface from the ridgeline to the eaves, which along with the roof’s steep pitch, helps the snow glide off and into a gutter, maintaining transparency year round. The north side of the ridge is a traditional steel deck and membrane roof. The transparent roof allows for panoramic views of the city, increases natural light and produces additional solar gain to warm the stadium and drive natural ventilation as excess heat will be vented out as part of a coordinated sustainability strategy.
“The extensive transparency both in the facades and roof represents a change in stadium design from one that is centrally focused on the event to one that engages a city and the environment,” Vice President Edward M. Peck of our Façade Engineering practice said. “The ETFE design is a result of extensive study to optimize transparency and connection to the city while intelligently developing solutions for spectator comfort. Heat-gain is addressed by integrating a frit pattern on the ETFE itself and by developing a strategy for natural ventilation. These strategies create a unique spectator experience.”
Now that the stadium is completed, let the games begin. The first event at U.S. Bank Stadium will be a 2016 International Champions Cup soccer event between AC Milan and Chelsea FC on August 3. Concerts by Luke Bryan and Metallica are scheduled for later in the month. The Vikings will take to the field for the first time on August 28 in a pre-season game against the San Diego Chargers. Their first regular season game, against the Green Bay Packers, will be broadcast from the new stadium on NBC’s Sunday Night Football on September 18. The stadium will also host Super Bowl LII in February 2018, the Summer X Games in 2017 and 2018 and the NCAA Final Four in 2019.
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