Aware of all those high-tech sports domes that stick, leak and squeak, the architects who dreamed up the new proposal for a retractable roof over Soldier Field went decidedly low-tech in their mechanical scheme and classical in their design.
It’s no dome, retractable or otherwise.
Think of it more as a 72,700-seat greenhouse with a roof that rolls back and forth on tracks.
Its designers call it a field house, as if it were a larger version of the quaint buildings in Chicago’s parks.
This latest bombshell proposal from Mayor Richard Daley, made Friday afternoon, would raise a plastic, translucent roof over the distinctive classical columns of Soldier Field.
It would create a maw that could be opened up to let in Bear weather, yet closed to keep out duck weather.
And it would do that under a gently sloping roof line that would be familiar to anyone who has looked down Michigan Avenue at the Art Institute of Chicago.
But the nearly $400 million renovation, which Daley said could be completed in three years without disrupting a single football game, is a bundle of compromises.
Moreover, it isn’t the state-of-the-art sports mecca Bears president Michael McCaskey has longed for.
It would help only a few thousand of the fans who complain that too many seats are in the end zones.
And though the simple design is based on technologies that are virtually Victorian, it would employ them on a scale never before tested.
But Daley hopes the combination of natural grass, improved skyboxes and a movable roof will create the right blend of modern amenities and traditional ambience. That, he hopes, will prove more attractive to the Bears than the open-air renovation proposal he made last October.
“This is the new concept going into the next century,” Daley said.
The technology for the sliding roof is appropriate for Chicago and the Bears’ blue-collar image–the roof operates on the same principles used inside the great steel mills on the southern tip of Lake Michigan.
There, gantries–bridgelike frameworks that span great lengths–roll across the mammoth mills with cranes on them, moving hot metal and machinery.
The same rolling gantry design, on an even larger scale, would slide the massive, one-piece moving roof on parallel tracks.
“There is nothing fancy about this structure,” said Robert Wesley, a partner at the Chicago architectural and engineering firm of Skidmore, Owings & Merrill, which designed the plan. “It is all based on tried and true technology.”
Skidmore, which shaped the Sears Tower and John Hancock Center, has a history of solving complex architectural and engineering problems. The retractable roof would appear to be child’s play for the firm, but there are doubters, nonetheless.
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The roof is “a huge thing to move, and I think there’s a lot of things that could go wrong,” said Scott Pratt, a senior vice president at Murphy/Jahn of Chicago, which has floated its own retractable roof plan for Soldier Field.
“If it gets stuck, you can’t just go and give it a push,” Pratt said.
But another architect described the Skidmore plan as fairly simple and viable.
“It seems pretty straightforward,” said Michael Wright, a project manager for Kansas City, Mo.-based Ellerbe Becket architects, designers of the Bank One Ballpark in Phoenix, which will have a retractable roof when completed.
He found it highly unlikely that the roof structure would derail, causing it to get stuck. He said this was especially true because of the simple motion required of the roof.
Under Skidmore’s design, the roof would have two pieces. One would be a fixed half-circle covering the seats in the south end zone.
The other would be a movable rectangle, about 6 acres in size, covering the field and north end zone when closed. It could be opened, a process the architects said would take about 20 minutes, to expose the field and sideline seats. (When in the open position, the movable roof would still cover the north end zone and the open stadium space behind it.)
None of the existing walls or columns at Soldier Field would be used to hold up the roof. Instead, the new structure would be set around the stadium on columns, almost like a table on legs.
That would leave intact the enormous classical colonnades on the east and west, the visual trademark of the building designed by Chicago architects Holabird & Roche and completed in 1926.
The key to raising this roof, of course, is building a suitable foundation for the columns.
Long ago, Chicago builders learned how to deal with the soggy, unstable soil around the city, much of which was created by landfill.
While the design isn’t complete, engineers believe the new foundation could be created with about 100 caissons–round holes that are drilled into the earth and filled with concrete and reinforcing steel bars.
Each of the caissons would be between 4 and 6 feet in diameter and would be drilled 90 feet to hardpan clay, the same geologic structure that supports most of the city’s skyscrapers.
Atop the caissons would be the new columns that bear the load of the roof. On each side of the field, massive “super columns” would be set about 100 yards apart to support the roof’s track as it rides over the top of the new skyboxes.
The roof itself is a simple truss design created with translucent, extruded plastic panels placed into an 11,000-ton steel frame.
Could it handle a 26-inch snowfall?
Wesley said that wind off the lake, the pitch of the roof and the lack of places for the snow to drift would keep snow from piling up.
The sightlines that would be offered by the renovated Soldier Field are a major issue for the Bears, especially because of the ongoing fan dissatisfaction with the upper deck at Comiskey Park.
As Daley proposed in his last plan for Soldier Field, the playing field would be dropped by about 21 feet to improve the fans’ view.
But the plan does not rotate the field 90 degrees to decrease the number of end zone seats, a step suggested last year.
Skidmore associate partner Brian Jack said that 53 percent of the seats in the renovated stadium would be considered “sideline seats,” while “about half” are sideline seats now.
Most National Football League stadiums have 55 percent of their seats along the sidelines, Jack said.
The new configuration would raise the current two rows of skyboxes, creating room for nine additional rows of seats along the sidelines.
Buildings often start with an architect drawing on the back of a cocktail napkin, and this one doesn’t appear to be much different.
When Edgar’s proposal for a $465 million domed stadium pushed Daley’s plan for renovating Soldier Field to the sidelines in February, it sent the plan’s architect–Skidmore partner Adrian Smith–back to the drafting board.
Smith–whose credits include Chicago’s popular towers for NBC and AT&T, the ongoing redesign of State Street, and the under-construction Jin Mao tower in Shanghai, which will be one of the world’s tallest buildings–came up with a “dome” plan of his own.
Smith took his rough idea to Daley administration officials and was told to work it out, architects from the firm said.
Now that it is in the public domain, however, the Skidmore plan will have to overcome both political hurdles and public mistrust of retractable roofs.
The most notorious precedent is Olympic Stadium in Montreal, built for the 1976 Summer Games and designed by Roger Taillibert, a Paris-based architect.
This is what Taillibert predicted: “A strong synthetic fabric attached to cables suspended from the tower will cover the central opening, folding and unfolding easily and quickly.”
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This is what the Montreal Gazette reported in 1991: “In practice, however, the roof has never performed as promised. Opening and closing it has always been so precarious a business that when it works it still takes twice as long as the time required to roll around the retractable roof on Toronto’s SkyDome.”
Earlier this month, after years of tearing proved the roof could not withstand Montreal’s winds, the managers of the stadium announced plans to replace the retractable roof with a fixed one.