Standing in the rain on Feb. 19 to witness the slow-motion roof lift for the $450-million Arizona Cardinals Stadium development was about as exciting as watching the grass grow. That was just fine with the "gardeners." They had toiled, some for five years, on this unusual roof-raising. And they were thrilled that the superficial tedium of the maximum 20-ft-per-hour lift was not shattered during the 120-ft lift and positioning of the 5,400-ton mega-assembly, which was jacked up in slots in its corner supercolumns.
|Popped Up. Roof, preassembled on the field and lifted, appeared on the landscape late last month.|
Bad weather, including hail, and a minor mechanical problem drew out the operation from four to almost seven days (ENR 2/28 p. 10). But even that could not dampen spirits. The milestone, achieved on Feb. 24, lifted a huge weight from the teams collective shoulders, freeing everyone to concentrate on remaining work. This includes construction of the first playing field in North America that will roll out of the stadium, like a crumb tray from a toaster, so field grass can soak up the sun.
|Starchitect Form. Football stadium is shaped to evoke a barrel cactus.|
Designed by football junkie Peter Eisenman to resemble a barrel cactus, the 65,000-seat stadium in Glendale, outside Phoenix, is the first National Football League venue claiming "starchitecture" status. Thanks to Eisenmans bulbous design, the bi-parting twin panels of the roof will be the first to roll on a slope.
The arc forced the roofs structural engineer and mechanization consultant, Uni-Systems Inc., Minneapolis, to "take [transporter] technology to another level," says Lawrence G. Griffis, president, structures division, in the Austin office of Walter P. Moore and Associates Inc. Click here to view images
The roof lift was the brainstorm of David A. Schuff, chairman of the local steel fabricator-erector that bears his name. Schuff, no stranger to lifts, conceived of it at least a year before he won a design-build contract for the roof with WPM and Uni-Systems. That was in 2001 when the stadium site was in Tempe. Schuff pushed the idea primarily for safety, but also to ease erection. The approach "was a natural," says Griffis.
To work, Schuffs brainstorm had to drive the whole project, not just roof design. "Everything evolved around the lift," says Corissa Anderson, project engineer for the Phoenix office of Hunt Construction Group Inc. Maricopa County legislation had allowed "direct selection" of Hunt, a long-time construction adviser to the Cardinals, as the jobs guaranteed-maximum-price design-builder.
Key to execution of the roof lift was Schuffs nontraditional involvement in the roofs design and WPMs and Uni-Systems nontraditional involvement in means and methods. "With this project, we reached a new level" of interaction with the fabricator-erector, says Griffis. "Some would think us stupid because of liability issues, but we feel we reduced our risk," he adds.
|On High. End bearing of roof assembly is inserted into notched top of supercolumn.|
Because the assembly bears on four concrete supercolumns, the lift team also wrapped in TLCP Structural Inc., the local engineer for the concrete stadium, and Kiewit Western Co., Renton, Wash., the concrete contractor. The strategy required collaboration, communication and "planning on planning on planning," says Scott Schuff, Davids son and Schuffs president.
But the best laid plans nearly imploded because of fallout from the 9/11 terrorist attacks. In mid-2001, with roof design work under way, the Arizona Stadium and Tourism Authority, which owns the stadium, shifted the projects Tempe location near Sky Harbor Airport to address Federal Aviation Administration concerns about proximity to flight paths. FAAs deadline for approving the site was Sept. 11, 2001. But after 9/11, it nixed the plan.
It was back to the drawing boards, both for a locale, a design and contracting arrangements. But when the project went on hold, roof design was 25% complete, with steel ordered. "We were three weeks away from starting fabrication, with shop drawings in hand," says Scott Schuff. "We had to lay off about half of our 123 employees and we ended up carrying $3.5 million in steel for one and a half years until we got reimbursed." Click here to view image of Stadium's Steel Roof
For the Glendale site and a scaled-back design, Hunt bid the roof conventionally. WPM would contract with the stadium architect of record, HOK Sport, Kansas City, Mo., not with Schuff.
Schuff says he almost lost the job to another bidder. He declines to say just how much the price came down to win it.
Hunt says its role as design-builder also was temporarily suspended, until August 2003, so the owner could control the redesign. The switched strategy was in large part a response to "significant" budget problemsprimarily cost escalationcaused by the delayed construction start, says Hunt.
The whole process was "very painful," says Griffis. "When the roof was design-build, we had done a lot of planning," he says. "Then the rules changed and we asked ourselves, Now what do we do? We couldnt just walk away."
And they didnt. Prior to signing a $43-million contract in July 2003, Schuff participated in a design-assist role, which continued. Thanks in part to that, Schuff was able to reuse 99% of the roof steel.
The stadium is financed by a 1% hotel occupancy tax and a 3.25% car rental tax, authorized by a county referendum in November 2000. Legislation put a statutory limit on the amount of public funds for the stadium proper at $266.6 million. The Cardinals, as tenant, have a $104-million share, with naming rights and all revenue from game days. The team, also the landowner, is responsible for any stadium costs over $370.6 million. The investment for the 165-acre site, including infrastructure and onsite parking for 14,000 cars, is $450 million.
The stadium is being clad in alternating metallic panels and recessed glass strips. The roof will be clad in fabric.
|Record Span. Sideline trusses span 699.5 ft, a record for an operable-roof stadium.|
The 500,000-sq-ft roof assembly consists of tear-drop-shaped, twin sideline trusses, called Brunels. They are 699.5 ft long, up to 87 ft deep and 257.5 ft apart. The Brunels create the longest clear span of a retractable roof, claims the engineer.
Spanning between Brunels are eight teardrop Vierendeel trusses for each 270 x 180-ft operable panel. Panels are supported at each Brunel end by eight sets of wheeled transporters that ride on crane rails. Rails are clamped at 1-ft intervals to a built-up box girder running the length of the Brunels top chord.
The top chord is a 15-ft-square "laced" member, in compression. The bottom chord, in tension, is a double wide-flange beam. Hollow posts with rod X-bracing connect chords.
Structurally, the Brunel is "hardly a truss" at all, says Joseph M. Ales Jr., WPMs project manager. It works essentially as a "superposition of an arch and a catenary...