A colleague just asked me how many aluminum-mesh panels make up the Walker’s crinkly facade (answer: 2,878), which reminded me of the piece I wrote for the July/August edition of the Walker calendar. To complement artist Frank Gaard’s reflection on the Walker’s architecture at the Visual Arts blog, here it is:
Dick Dotterweich understands complicated architecture. As a project executive with M. A. Mortenson Company, he oversaw construction of the facade of the Frank Gehry-designed Walt Disney Concert Hall in Los Angeles, a building that involved the assembly of 500,000 individually numbered parts on its wavelike stainless-steel exterior. But he’s never seen a job like the Walker expansion. Likely the most complex engineering project currently underway in the United States, Herzog & de Meuron’s new structure has presented Dotterweich and his colleagues at Mortenson and Hammel, Green and Abrahamson, Inc. (HGA) with some rare challenges. From its pioneering skin of undulating aluminum to a cantilevered structure dotted with asymmetrical custom windows, it’s proving to be an engineering and construction marvel.
The shimmering aluminum facade–made up of 2,878 individual sheets–represents one of the design’s most visible challenges. Each “ expanded aluminum” panel is created not by punching holes, as it would appear, but by puncturing and stretching a sheet of aluminum into a field of diamond-shaped perforations. The creases are mapped by computer so that each fold matches one on the adjoining panel, and are made using a custom-designed stamping machine that can create eight different patterns from one die. But it’s not the involved construction of the panels that’s tricky; it’s the fact that the material has never been used before on a building’s exterior.
Since this is its first outdoor architectural use, the material’s structural properties have never been defined (the closest data Dotterweich could find on its weatherability was on aluminum patio chairs). So he embarked on an extensive research project to see how the material would withstand Minnesota’s temperature swings and the high winds that funnel along Hennepin Avenue. Since February, the panels have been undergoing continuous vibration testing–a single panel will be rattled 700,000 times, once every 4.8 seconds–and periodic inspections under a microscope by a metallurgist. As Kendall Griffith, Mortenson’s senior project manager, says, “ Two or three months ago, Dick was seen in Bloomington in a testing agency’s pickup truck with one of these panels mounted on the front end, and two technicians in the cab with him. And they were driving around assessing wind forces on these panels.” What’s the top wind speed the material can withstand? Dotterweich won’t say: “ We didn’t test 90-mile-an-hour winds, I can tell you that.”
Another challenge is the new building’s “ cantilevered” design. Nearly 50 feet of the building juts over the Hennepin Avenue entrance, without visible support. An engineering feat by itself, this design feature is key to Herzog & de Meuron’s aesthetic vision. “ When we first met with lead architect Christine Binswanger, she said I only have one rule for my structural engineers: no columns in the corners of buildings,’” recalls Paul Asp, HGA’s structural engineer on the project. “ It’s a statement I took literally, but I also understood what she meant by that. If they want a window in the corner of the building, there’s not going to be a column there. We’re willing to create a complex structure to accomplish the architecture.”
To realize this vision, all of the structural support had to be concealed within the building. Two columns just inside the main entrance serve as anchors for the cantilevered section, and a complex network of diagonal beams within the building’s side walls support the projecting portion of the cube much as steel trusses brace a railroad bridge. This cantilevering, not to mention the asymmetric windows (initially inspired by patterns made by folding and cutting paper snowflakes), require the rest of the support structure to be unusually rigid. And it is: in March, when 12 temporary columns were removed, the suspended part of the building settled almost imperceptibly–less than one-half inch and well within the parameters set by the structural engineers.
The new Walker is filled with inventive ideas in less visible ways as well–from the uncommonly slim window mullions that support glass walls along Hennepin Avenue (a solution invented specifically for the Walker) to the challenges the sloped sidewalk presents in linking the present building to the expansion. For engineers and construction experts, the complexity of the problems they grapple with is rarely fully appreciated–or even noticed–by museum visitors. But Griffith says that while he gets plenty of thanks for his work, the real satisfaction is in seeing the building take shape. “ Every day when I go home, I walk through and I see the progress that’s been made. It’s the most gratifying work you can get.” Asp agrees, adding that working on such a prominent building is an honor. “ I have a lot of respect for the people who worked on the original Walker [designed by Edward Larrabee Barnes]. I look at what they did and the structure that’s in there and say: that’s clever, that was a good idea, they did this nicely. Someday when this gets renovated, another wing is added, somebody will be looking back at our work and I hope they have the same appreciation for it.”
Construction stats:
A look at startling statistics from the Walker expansion
Square footage of the new Walker facility: 260,000
Cubic yards of earth excavated: 285,000
Cubic yards of concrete poured (new building and parking ramp): 26,000
Tons of rebar used: 2,000
Rebar’s weight measured in Honda Civics: 1,538.5
Pounds of aluminum to be used for the facade: 70,000
If recycled, number of soda cans facade could make: 2.31 million
Number of rivets to be used to install facade: 230,000
Pounds of sheet metal in the heating, cooling, and exhaust systems: 200,000
Number of football fields this sheet metal could cover when unfolded and laid flat: 3.5
Miles of piping: 5.1
Miles of wiring: 123
Miles of track lighting: 1+
Photo: ©2005 Paul Warchol
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