Five-Rail Rolling Roof Is Extra Tough to Align
Indiana Stadium and Convention Building Authority

Lucas Oil Stadium, opening next month in Indianapolis, will reign for only a year as the sports venue with the steepest rolling roof and the tallest retractable end-zone wall. Next August, both titles will pass to football’s Dallas Cowboys stadium, under construction in Arlington, Texas. Indianapolis and football’s Colts might be upset about the upset, but the firms responsible for the fleeting bragging points aren’t: Working on both jobs, they are breaking their own records.

There are some distinctions that might lastfor Lucas Oil Stadium. The building has the largest roof opening of any National Football League stadium with a retractable roof, says Tarek A. Ayoubi, a principal of the roof’s structural engineer, Walter P Moore, Houston. At 180,000 sq ft, the opening is 10,000 sq ft greater than the sun roof of Houston’s Reliant Stadium, another WPM project, completed in 2002.

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  • The Colts’ generous opening is a consequence of still another distinction: The building’s field-house look, designed by Dallas-based HKS Sports & Entertainment Group, inspired a new direction in panel movement thanks to its gabled roof. The panels separate along the roof’s longitudinal ridge and roll away from each other down the straight, 13.2° pitch. They land along the sides of the building. In other retractable football stadiums in the U.S., panels part along the 50-yd line and roll toward the end zones.

    The directional difference created some challenges for the three roof designers, the third of which is kinetic architecture supplier Uni-Systems LLC, Minneapolis. But it avoided having the panels overhang at the ends of the stadium, which would have ruined the field-house look, says Ayoubi.

    The biparting panels of the pitched roof of Lucas Oil Stadium in Indianapolis meet along the roof's longtitudinal ridge. This joint created a potential for water leaks.
    Uni-Systems LLC, Minneapolis, designed an operable ridge cap and rubber seal that lift up when the roof panels part or come together.

    Each 600-ft x 150-ft panel rides on five parallel rails along pitched transverse trusses. Other rolling panels run on only two rails. The extra rails created more erection and alignment challenges, but they also reduced the panel’s required clear span, say the designers.

    Another challenge is the three center transverse steel-box trusses are unbraced across the field. WPM suggested adding a ridge beam but the architect rejected the idea for aesthetic reasons, says Ayoubi. The lack of bracing meant a stronger box truss, he adds.

    One of the consequences of the 90° switch in movement direction has to do with basketball, not football. The 600-ft-long ridge joint opened up the potential for a leaky roof. That would not have been so bad if the stadium weren’t going to have a wood floor for basketball games. Leak prevention translated into an operable ridge cap with a drip pan below it that doubles as a catwalk.

    + click to enlarge
    Operable ridge cap is designed to prevent water leaks.
    + click to enlarge
    Operable ridge cap is designed to prevent water leaks.
    Operable ridge cap is designed to prevent water leaks.

    Primary roof support consists of two steel sideline superframes, 300 ft apart. Each spans 760 ft. The top of each frame is 241 ft above the event floor. Superframe columns are 217 ft tall and supported at the street level by 35-ft-tall concrete shear walls. Five peaked transverse trusses, exposed at the center when the roof is open and at their ends when it is closed, span over the superframes.

    A 960-hp cable-drum drive system, which operates like a yo-yo, moves the retractable panels—each weighing 1,450 tons—up or down the roof in nine to 11 minutes, depending on wind conditions.

    Cable drums move with the panels, as do all the transporter systems, including the control panels. “We moved the cable drums with the transporters because if they were fixed, the drums would have messed up the looks of the open roof,” says Alan Wilcox, Uni-Systems project manager. Cables are anchored to the structure near the peak of the transverse trusses. Each roof panel has 480 hp, or 1.4 million ft lb of torque. “It’s like driving a new Corvette in first gear,” says Wilcox.

    The Colts’ retractable endwall consists of six glazed panels that move to create an 88-ft-tall and 214-ft-wide opening. A traction drive, similar to a push lawnmower, opens or closes the wall in four minutes. The system’s steel wheels ride on a single rail. At the top, there is a system of guide-roller assemblies. Each assembly telescopes vertically 6 in. to handle building movement.

    + click to enlarge
    Open Roof
    Walter P Moore
    Shed shape inspired new direction for panels.
    Indiana Stadium And Convention Building Authority
    Shed shape inspired new direction for panels.

    Construction of the $580-million building began in September 2005. Robert K. May, contract manager for the local office of Hunt Construction Group, the job’s construction manager, says one of the bigger challenges of the project was getting the five wheel rails installed to stringent, 1⁄8-in. tolerances so the panels would roll smoothly. “It was an effort to get it aligned,” considering variations in temperature and changing weather conditions, says May.

    The transporters weren’t easy to install, either. Uni-Systems miscalculated the transporter weight. “We exceeded the capacity of the crane,” says Alan Wilcox, Uni-Systems project manager. The situation required a work-around, but there was no time lost, says Wilcox.

    The project benefited from cable-system prototyping performed on the sloped and rolling Arizona Cardinals roof, which was Uni-Systems first cable drive. The wheelbox and top-guide rollers developed for the Colts wall are being used on the Cowboys job. Eventually, “we will have a kit of parts, like Legos, so we don’t have to reinvent the wheel each time,” says Wilcox.