A Smarter Stadium: Retractable Advances Hurricane Engineering
Location: Miami, FL
Client: Florida Marlins
Roof Size: 338,000 sf
Budget: $600 million
Services: Structural Engineering, Retractable Roof
Firsts: 1st LEED Gold-certified stadium in MLB
- Largest retractable roof in major league sports (7.7 acres)
- Three-panel, 8,000-ton steel roof
- Roof opens or closes in 13 minutes
Miami is a tropical city. Its sweltering summer heat, frequent rain, and the occasional hurricane dictated a roof over the Florida Marlins’ new stadium. Their first home, Sun Life Stadium (aka, The Orange Bowl) had been designed primarily for use in the fall and winter – football weather. And since serious baseball fans like their games in the open air, the roof had to be retractable. Furthermore, owner Jerry Loria wanted a building with LEED-standard sustainability, as well as one that did not use a nostalgic motif.
In challenging the design and engineering team to create something fitting the South Florida aesthetic, Loria stressed, “No retro. No Art Deco. No looking back. Miami is a forward-looking city… I’d like to see us build a great, contemporary building.” Between the architecture and engineering, Loria, the Marlins, and Miami got this and more.
Engineered for Fly Balls and Hurricanes
Marlins Park is Walter P Moore’s sixth retractable roof stadium, and our second one, after Houston’s Minute Maid Park, for Major League Baseball. We engineered this latest generation of retractable roofs to be hurricane resistant, energy efficient to operate, and to give a thoroughly modern, dispensable cap to a thoroughly modern ballpark. Both stadium and roof are unlike anything else in Major League Baseball.
The roof’s three panels operate independently of each other. When fully open, the two lower panels nest under the larger upper panel at one end of the stadium. Instead of sealing the panels, the design provides space between the upper and lower panels. This prevents pressure buildup from high winds. It also reduced construction costs by some $5 million. Furthermore, the ability to reconfigure the panels permits some shading below. The upper panel or one of the lower panels can be separately repositioned to create a kind of moving sunshade for the seating and playing field below–good budgetary stewardship, as well as good engineering.
The roof panels span between 530 - 560 feet over the playing field, at heights ranging from 128 feet in deep right-center to 210 feet over second base. The heights are critical. Our engineers gathered variables from the Miami environment such as air density and temperature, and by combining them with equations from NASA, we determined how high the panels had to be to keep from interfering with fly balls—and potentially, the outcome of a game. We even wrote an algorithm to generate a volumetric approximation of all the possible batted ball flight paths and used it against our BIM to determine the final geometry of the roof structure.
Silver or Gold?
A major goal of the owner was sustainability. The stadium had to score a minimum LEED certification of Silver. Marlins Park passed up Silver for Gold. One important element in reaching this rating level was the retractable roof. Its regenerative drive systems conserve excess power generated by the retractable roof during braking and at times when the panel is being pushed by the wind, by returning it to the electrical grid. To open or close the roof it is estimated to cost less than $10, depending on wind conditions.
Key to meeting these challenges was the collaborative nature of our working relationship with the architect, Populous, and the mechanization consultant, Uni-Systems. We’ve worked with both before, including on Minute Maid Park. Clear, continuous communication on projects of this scale and complexity is paramount. We operated as a close-knit team in which the players understood each other’s needs.
This enabled the architects to move ahead with the stadium’s overall design, while our engineers teamed with the fabricator and erector to deliver a complex roof that made open-air baseball possible.