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University of Phoenix Stadium
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Peter Eisenman
HOK Sport + Venue + Event |
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When the University of Phoenix Football Stadium design team began its work, they were told to not think of it as a football stadium at all. Think of it, rather, as a multi-purpose facility, configurable for any type of show or convention, including football. Where some traditional football stadiums are used no more than 10-20 dates a year, the University of Phoenix designers were asked to create a stadium that is available for scheduled events 365 days a year. The opening in 2006 of the home of the NFL’s Arizona Cardinals marked a new era in stadium design, and with it an innovative approach to sports facility management.
The 365-day design criteria was brought about to improve income opportunities and optimize event scheduling flexibility by hosting non-football events throughout the year. Two challenges were presented to Uni-Systems – Arizona’s scorching summers and mild winters, and the trend towards “live grass” playing fields. The resulting stadium design included a retractable roof as well as the first retractable “live grass” playing field in an NFL stadium.
Some very unique design changes were selected for this stadium, based more on desire than need. Twin translucent roof panels effortlessly angle toward one another from a 14 degree tilt above the end zones to a flat 0 degrees at the center of the stadium. While pleasing to the eye, the structure needed to work in a completely new way because of the arch. Designers also hid the massive cables that move the panels into position.
On non-game days, the playing field resides outside the stadium where conditions for maintaining grass are ideal. Engineers designed the field to react like a traditional grass playing surface, so that players feel comfortable, whether they are running, jumping or tackling each other. At the touch of a button, the 9,300 ton retractable grass playing field can be “driven” into the stadium for football games. The 2.1-acre field moves into or out of the stadium in approximately one hour.
This design provides an attractive space for convention planners. The field rides on thirteen steel rails embedded in concrete that sit nearly flush with the facility’s floor. The low-profile field is designed with the grass surface a mere 42 inches above the concrete. After the field is driven outdoors, a clean, flat, well-positioned event floor is exposed, ready to fully support public venues.
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University of Pheonix Stadium
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RETRACTABLE ROOF
The University of Phoenix Stadium retractable roof consists of two translucent, fabric covered panels (185 feet by 285 feet each) that meet directly over the 50-yard line when in the closed position, and roll downhill to reside over each end-zone when in the open position. The roof operates at a maximum speed of 25 feet per minute and fully opens or closes in approximately 11 minutes.
The retractable roof is moved by 16 transporters, each riding on two steel wheels. Half the transporters are equipped with cable drums that spool cables anchored to the fixed roof above the 50-yard line. Each cable drum is powered by electric induction motors with fail-safe DC electric brakes that automatically engage when roof movement stops.
Linear bearings on the west side of the stadium allow up to 36 inches of relative movement between the roof panels and the transporters. This allows the wheels on both sides of the roof to stay engaged with the rails regardless of roof movement caused by thermal expansion, wind, and other forces.
The control system is fully redundant to ensure 100% reliability at all times. Real-time feedback and other diagnostics allow easy operation and troubleshooting.
PLAYING FIELD
The retractable field normally resides outdoors, on the south side of the facility, where conditions for maintaining its natural grass playing surface are optimal. The field structure measures 403 feet by 234 feet and includes all components required for a healthy grass playing field, including irrigation, drainage and an optimized growing surface. When the field resides outside, the stadium can be configured for a multitude of events, including conventions, monster truck pulls, and concerts.
The retractable field is equipped with 542 steel wheels that ride along 13 rails embedded in the concrete facility floor. Guide wheel assemblies located on the center guide rail keep the retractable field in alignment as it moves in and out of the stadium. The field is driven 11.5 feet per minute by 76 one-horsepower motors into the stadium through field doors on the south side of the facility in approximately one hour.
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