New football arenas push bounds of stadium engineering


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Sep 18, 2002
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Margaritaville,north of Tucson

Alex Frangos
Wall Street Journal
Aug. 29, 2005 10:55 AM

At the Arizona Cardinals new stadium in Glendale, Ariz., a half-dozen of the team's 300-pound linemen will jump up and down in unison next month, hammering a 30-foot patch of turf under their cleats.

Training for a new quarterback blitz? Nope. Testing the limits of the playing surface the Cardinals plan to use as the centerpiece of their $450 million stadium when it opens in 2006: a retractable field. Imagine a gigantic rectangular planter 18 inches deep with dirt and grass, and mounted on rails.

"We've got marching bands marching, and big gorillas tackling each other - we've got to make sure the floor doesn't move beneath them," says Larry Griffis, president of the structures division of Walter P. Moore, one of the leading stadium engineering firms in the U.S. Mr. Griffis is currently working on three National Football League projects and is a leading expert on retractable stadium roofs.

Now he has to deal with a retractable floor - the first of its kind for a stadium in the U.S. Mr. Griffis is worried not so much that the field will collapse under the weight of the titans, but that the vibrations will make the players feel uneasy. "It's not a structural issue, but a perception issue," he says.

The next generation of NFL arenas is pushing the bounds of stadium engineering way beyond the old bowl-like, exposed-to-the-elements structures of the past, and even beyond more recent indoor venues. Football stadiums these days must serve as team icons, with bold, distinctive designs that render them easily recognizable for brand identity. They also have to be functionally and environmentally versatile, to tap other kinds of event revenue than just football.

The Cardinals, for their part, hired New York architect Peter Eisenman, something of a maverick in design circles as well as a football fanatic. The architect responded by conjuring a vision inspired by the team's Southwest desert setting: a barrel cactus. Curved metallic panels will alternate with glass strips around the exterior of the building, scheduled for completion before the 2006 season. A retractable roof will let air in on temperate winter Sundays. And in a bid to have both natural turf and a building that makes money year-round, the Cardinals are betting on their grass field on wheels. Even during football season, the field will be able to roll outside next to the parking lot during the week so it can soak up the warm Arizona sun while conferences and meetings take place indoors.

This is relatively new territory for engineers. Only a handful of stadiums in Japan and Europe have experimented with retractable fields. Mr. Griffis tried to learn about the Veltins Arena in Gelsenkirchen, Germany, near Munich. But the tight-lipped builders didn't want to compare notes, Mr. Griffis says. "We're sort of inventing the wheels ourselves," he says, referring not only to the field but the rollers underneath.

The NFL's two other teams with funds to move forward with new stadium blueprints are Indianapolis and Dallas. The Indianapolis Colts unveiled their design this year, by Dallas architects HKS Inc. The shape is inspired by the classic Indiana field house, a square building with sloped roof, which in this case will be retractable.

The sloping roof, in fact, poses a challenge to the engineers since it also has to move. "It's basically a combination of crane and railroad technology being utilized on a moving roof rather than, say, unloading containers on a ship," says Brian Trubey, the architect on the Indianapolis and Dallas stadiums. Every retractable roof is a challenge, Mr. Trubey says, because each stadium's shape is different. Mr. Trubey says he lets his buddy Mr. Griffis worry about the particulars. "There's some good engineers who know how to do that," he kids.

Mr. Griffis responds, only half-kiddingly, with a complaint often heard from engineers: that architects come up with designs that are difficult to build while staying within the budget. "A lot of these architects are great at getting them to look good," Mr. Griffis says of modern stadiums, "but not so good at the price tag. It can get pretty tense. We're going through that with Mr. Trubey right now."

Before Arizona, Mr. Griffis's biggest football-stadium challenge was for the Houston Texans' Reliant Stadium - the first NFL venue with a retractable roof. As in Arizona, financial pressures forced the stadium owners to seek additional revenue from other kinds of events. The solution: the Houston Livestock Show and Rodeo, an annual 2 1/2-week run of lassos and bucking bulls that sells out every night. The show actually brings in more money than football, so it demanded some design changes.

Having multiple uses "adds a level of complexity to the design," says Mr. Griffis. For the rodeo, for instance, "we had to design for all the speakers and lights and banners they wanted to hang." That meant the retractable roof needed to support an additional 180,000 pounds. The solution: more steel supports.

Other recent proposals pushing at the edge of stadium design include the New York Jets' ambitious plan for a multipurpose stadium on the west side of Manhattan, an idea that was scuttled earlier this year. Designed by New York architects Kohn, Pedersen, Fox and by engineers Thornton-Tomasetti Group, also of New York, the retractable-roof stadium would have been built atop a busy railyard. The stadium also would have served as a convention center, concert hall and giant ballroom. And an early version of the plan envisioned a structure transformable from a 75,000-seat stadium into a 20,000-seat basketball or hockey arena.

While that project is unlikely to move forward, the Jets are considering other possibilities. One is to build a stadium in the borough of Queens. A potentially more innovative option would be to share a new stadium in East Rutherford, N.J., with their rivals the New York Giants-next to the facility the two already share.

The current situation has the Jets playing in Giants Stadium, the name clearly emblazoned on the outside of the structure. The Jets have long complained about the arrangement, saying the NFL is all about home-field advantage. The teams have been willing to discuss sharing a new stadium, however, because of design ideas being discussed that would make it a home for both franchises, such as massive changeable light displays that would mutate from one Sunday to the next: green for Jets, blue for Giants. After all, it's cheaper to build one stadium than two.

Recently at the Cardinals' practice facility in Phoenix, stadium designers kept their focus firmly on the floor as they tested a prototype for vibrations. The design calls for a series of steel rails running under the length of the field, from end zone to end zone, and serving as the tracks. Running crossways under the tray of dirt and grass are steel beams that will rest on boxes containing railroadlike wheels.

Before the test, Mr. Griffis's calculations said the span from rail to rail should be 23 feet in order to minimize the vibrations.

Thomas M. Murray and Mehdi Setareh, professors from Virginia Polytechnic Institute, brought a special shaking machine to simulate different intensities of vibration atop the section of the field. Volunteers from Mr. Griffis's team and the Cardinals' front office moved around on the shaking field to see whether the vibrations were perceptible to humans, while accelerometers measured the exact level of vibration.

One thing they found: The worst sort of event is coordinated jumping exercises - the kind of thing that football players or marching bands often do. With everyone moving in unison, it increases the force and thus the vibration.

Shaking-building phenomenon is a product of modern construction material, and thus is not limited to stadiums. Convention centers, shopping-mall atriums and aerobics studios are notorious for their perceptible vibrations. Engineers say buildings weigh 40 percent less than they did before World War II, after which construction methods changed. Light steel and concrete have replaced brick and steel. Drywall has pushed aside masonry. Feather-light metal studs stand in for heavy pine.

For the Cardinals and their field, however, the challenge goes beyond vibrations. Because the tray of dirt and grass is exposed top and bottom to Arizona's desert heat when it's outside, the roots and stems of the grass can fry. Part of the experiment at the practice facility also was to determine how much water the grounds crew will need to sprinkle in order to keep the field fresh and green.

Another obstacle for the engineers was attaching Mr. Eisenman's unique cactus-shaped panels to the frame of the building. Despite the difficulty, the Cardinals think the result will be worth it, since beginning in 2006 millions of football fans will identify the team with televised blimp shots of their new stadium.

Mr. Trubey, the architect for the Colts, says television exerts a powerful force on stadium design. "You can argue that NFL venues are the most-seen type of architecture on television," he says. "As much time as we spend making it incredible for the people actually physically there, we believe the balance of the audience - which is probably 99 percent of it - hadn't been leveraged as a participant in terms of enhancing brand through the stadium."

Of course, even with a great brand, football can't take place without a big hunk of solid turf.

The Cardinals initial field vibration test proved crucial. Mr. Griffis and his team discovered that the 23-foot span between the rails was too wide. The fix: more rails spaced more closely together.

But that doesn't have them satisfied. On Sept 19 and 20, the team will do a "confirmation test" on a 30-foot-long, full-width slice of the actual field, this time with real players - not engineers - jumping around. If the pitch passes, workers will go ahead on the rest of the field without changes.

Mr. Griffis is philosophical about all the tests. "We know from past experience that if you don't pay attention early in the design, it'll bite you in the end."