The video board at Super Bowl LII uses Schöck structural thermal breaks to keep up with the heat of the game.
U.S. Bank Stadium, Minneapolis, home of the NFL’s Minnesota Vikings, opened in 2016 seating 66,200, and wows visitors with its striking asymmetrical shape, transparent roof, acres of glass, 95-ft.-high pivoting glass doors, and enormous asymmetrical video board—a stunning departure from the current-day idiom of sports stadiums. The NFL selected the stadium as the site for Super Bowl LII in February 2018. Beyond aesthetics, the stadium’s sharp angles and slopes shed and disperse high volumes of Minneapolis’ snow, while its transparent façade provides spectacular views, both of the city’s skyline to visitors inside the stadium and of the action within the stadium for visitors standing outside. The city and the team wanted to foster a sense of community among residents, visitors, and football fans.
Supporting the unconventionally large (3,000 sq. ft.) and heavy video board in its sub-zero exterior environment, are structural steel tubes cantilevered from the steel framework within the heated building envelope, requiring an inventive engineering solution on the part of HKS Inc., Dallas (hksinc.com), the project’s architectural firm, and engineering firm Thornton Tomasetti, New York (thorntontomasetti.com). They needed to prevent the structure from forming condensation and rust on the warm interior side of the insulated building envelope. Structural thermal breaks provided the answer.
The video board sits 150 ft. above grade on the exterior of the western prow, displaying game schedules, ads, upcoming concerts, and other events in extremely high resolution. The behemoth board weighs 45,000 lb. and measures 80 ft. across its top but only 48 ft. across the bottom, with the left side at 53 ft. high and the right at 45 1/2 ft., fitting neatly within the stadium’s extremities.
Thornton Tomasetti engineers were charged with devising a plan for the board’s installation and overseeing the process. “The geometry was extremely complex,” said Greg Litterick, senior associate at the firm. “We had to determine how to precisely adjust the structural supports and attach the video board so that it would integrate seamlessly with the wall.”
Adding to the challenge was the thermal conductivity of the structural steel supporting the board. The board connects to an exterior metal panel, behind which sits an array of metal studs with an insulated waterproofing barrier—all surrounded by a steel superstructure. The high thermal conductivity of steel increases thermal bridging between the sub-zero temperatures of Minnesota winters and the heated interior of the supporting steelwork. “It was imperative to prevent cold exterior steel from touching warm interior steel and causing a thermal bridge,” said Eric Grusenmeyer, project engineer.
Creating a thermal break between the exterior and interior sides of each steel cantilever is an Isokorb structural thermal break (STB) installed precisely where each support penetrates the insulated building envelope. Schöck North America, Princeton, NJ (schock-na.com), supplied the Type S22 STBs. Each module is constructed with stainless-steel bolts and a rectangular HSS within a 3 1/8-in.-thick block of HCFC-free polystyrene foam insulation. The insulation reduces the transmission of heat and cold, thus minimizing thermal bridging between the cold exterior and warm interior sides of the bolted assembly.
The same approximate width as the insulated building wall, an STB is a fabricated assembly that creates a structural insulated break between the exterior portion of a structural penetration and the interior structure that supports it to minimize thermal conductivity between the two masses while optimizing load-bearing capacity. The STBs specified are equipped with flanges and bolts for fastening to flanged rectangular steel tubes on the interior side and on the exterior side to opposing flanged steel tubes supporting the video board.
The video board’s rectangular support tubes cantilever at the building envelope to support the load of the board, which is bolstered by horizontal and vertical girts to provide additional support. The installation entailed 34 penetrations of the building envelope, each by a 6 x 4-in. steel tube. The tubes serve as outriggers that cantilever from the building structure in a grid pattern spaced approximately 9-ft. vertically and 8- to 17-ft. horizontally. Each tube is divided into two opposing flanged sections fastened on opposite sides of the STBs.
The resulting assembly reduces heat loss through the penetration by as much as 50%, reducing heat energy costs, carbon emissions, and heating-system capacity requirements accordingly. Most importantly for the video-board application, the STBs prevent the interior side of the supports from becoming cold, reaching dew point, and forming condensation that would rust, potentially compromising the structure and incurring ongoing maintenance costs.
According to Lance Evans, principal and senior vice president for HKS, “Our design had to address severe Minnesota weather conditions. Outside temperatures can dip to 20 degrees or more below zero, while the stadium has to maintain a comfortable temperature for the people inside. Preventing thermal bridging was essential to ensuring the integrity and performance of the stadium structure. STBs provided an effective barrier to accomplish that task.”
“The bolted steel plates can handle the significant structural stresses involved in securing the video board to the building,” engineer Eric Grusenmeyer explained. “They are specifically designed for this kind of application.”