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Aluminum

Unveiling the wind

By Nick Wright

Gusts set thousands of aluminum tiles in motion as the Minnesota Twins play ball

December 2011 - If you have ever been a part of the wave at a sporting event—a cascade of fans collectively throwing up their arms—you know a wave’s travel depends on fan enthusiasm and ultimately the game. Just over the right field wall at Target Field, the home of the Minnesota Twins, is a kinetic, veil-like aluminum sculpture that relies not on fans’ emotions but rather wind gusts to set it in motion.

Facing south above Target Plaza, the aptly named “The Wave” is affixed to the Ramp B parking garage adjacent to Target Field in downtown Minneapolis. According to Mike P. McGrath, project manager at Maplewood, Minn.-based M.G. McGrath, the construction firm that assembled The Wave, it is comprised of 51,000 machined aluminum pieces 4 inches wide by 4 inches long. “Each flapper assembly has 10 parts that are fabricated or machined and then assembled into one unit,” McGrath says. He adds all of the tiles hang on 4 millimeter stainless steel cables, which are hung at 6 inches on center from a steel tube truss attached to the garage’s roof.

Ned Kahn, a Sebastpol, Calif.-based artist who creates works that respond to natural elements such as wind, heat, water and fog, designed The Wave. Kahn has installed several structures around the world composed of thousands of hinged metal elements that move in the wind. He collaborated with Minneapolis-based architecture firm Oslund and Associates.

“Aluminum responds to the wind exuberantly and really reveals subtle, delicate changes in the wind when there’s not a fierce storm,” Kahn says, noting the metal’s light weight and strength are ideal. Colorful LED lights add effects at night.

When a gust of wind hits The Wave’s façade, which measures 285 feet wide by 60 feet high, it produces a textured, pixelated ripple, revealing the wind’s contours. “It is engineered to withstand normal loads typical of any other building in downtown Minneapolis,” says McGrath, noting the tiles are machined from 5005 AQ aluminum.

North Central Stampings and Manufacturing Inc., Blaine, Minn., machined and formed each of the tiles, which are 0.02 inch thick, according to Steve Rutherford, the company’s president. “There were three operations total: we blanked them, made a starter curl and a final curl with a punch press,” he says. It took two months to form the tiles, after which NCSMI sent them out for anodizing.

The nature of the cable system allows for play, so the design required the roof trusses keep The Wave suspended away from the garage to keep the tiles from hitting it during strong winds, Kahn says. “The trusses have a bar with rig points for the cables every 6 inches, so then you string all the cables. It’s like a giant harp,” he says. It took two months for four workers to manually hang the pieces from a window-washing platform. Because of construction delays, assembly took place in the winter before the 2010 opening season. “Basically, it’s a tiling job. You’ve got index marks and a laser level to keep the pattern consistent.”

Flawless finish
Accurately aligning thousands of tiles posed plenty of difficulty, and in addition, Kahn says ensuring each one received a uniform, clear anodized finish was tricky. “It’s a bit of a challenge to make sure all the metal you get is from one metallurgical batch from the mill so there aren’t various alloys in the anodizing,” he says. “A lot of anodizers will let the bath naturally get contaminated, so as you do a huge run, each one has to be anodized individually. If you don’t keep an eye on the batch of chemicals, the anodizer can slowly drift.” Because Target Plaza straddles Interstate 394 where it passes through Minneapolis, the Minnesota Department of Transportation initially was worried The Wave would distract drivers or tiles could fall onto the freeway. But the design team convinced MDOT it wasn’t any more distracting than a billboard, according to Kahn.

Similarly, Major League Baseball was concerned that The Wave would distract batters from opposing teams. “They were worried the Twins would get used to it but other players would be looking at the beautiful wind patterns as strike three got called,” Kahn says. “Mercifully, this wasn’t even anywhere close to the area they were concerned about, which is behind the pitcher.” MM

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