An innovative retractable roof for a baseball stadium in hurricane country
Marlins Park is a 37,400-seat baseball stadium, home to Florida’s Major League Baseball franchise, the Miami Marlins. The first baseball stadium to earn LEED Gold Certification, Marlins Park is said to be the greenest ballpark in America. The stadium has also earned praise for its innovative contemporary design. Marlins owner Jeffrey Loria encouraged architects, engineers and designers to run against a trend toward nostalgic architectural design in American ballparks at the time the stadium was being conceived. “No retro…no looking back,” he recalls saying. “Miami is a spectacular city, looking ahead.”
The central challenge in the roof’s design was to support the facility’s exciting architectural ambitions and satisfy its operational demands--all while ensuring that the structure could survive major hurricanes. A hurricane comes within 50 miles of Miami every five to seven years on average. Our task was to work closely with the Marlins Park design team to develop an economical retractable roof that would suit the stadium’s bold, contemporary architecture and also withstand the sometimes extreme weather the facility is expected to experience.
Having developed retractable roofs for a range of climates and conditions, we began with a clear picture of the project’s demands. We collaborated closely with the structural engineers on the project, communicating systematically so that every part of the team could understand the competing priorities of their own scope of work--including design, efficiency and cost--in the context of the entire roof and the demands from a wind engineering perspective. This close collaboration was critical to the development of a successful and efficient engineering solution.
Protection, visible and invisible
When Marlins fans look up, they see the roof’s basic components: three metal-decked panels, supported by two horizontal concrete track beams approximately 550 feet apart and 750 feet long. The east and west panels sit at a lower elevation over the stands, while the center panel rests higher, offering 200 feet of clearance over second base for pop-flies. When the roof is opened, the center panel moves along the track beams toward the west side of the stadium while both the east and west panels retract underneath it. Each of the three panels can be moved individually to provide partial shade to the field and patrons.
What fans do not see when they look up is the extent of the protection the roof provides for the stadium in all weather, up to and including hurricanes. The first step in ensuring the performance of the roof in all conditions was thorough wind tunnel testing; we conducted our tests using both a pressure model and an aeroelastic model. We needed to address two key challenges. One was to ensure the building’s safety during a sudden intense windstorm that is not a hurricane. Whereas Miami usually receives ample notice of approaching hurricanes, such weather is less severe but still potentially dangerous as high winds can develop with very little warning. This meant that in some cases, there would not be time to execute a storm preparation protocol and move the roof into optimal position before a storm. We had to design a roof that would withstand severe weather in an open, closed, and partially open position.
The second challenge was hurricanes. Here the value of our extensive wind tunnel testing revealed itself even more fully. Because we had worked to deeply understand the possibilities the roof system presented for aerodynamic optimization, we were able to identify an opportunity that engineers using another approach might have missed.
A surprising, but effective, aerodynamic strategy
Depending on the sun’s position or the threat of a rain delay, the Marlins Park roof can be totally open, open with targeted shade, or closed. But in the most extreme conditions, hurricanes, the roof assumes another position. In collaboration with the design team, we developed an innovative storm preparation protocol that shifts the roof into a “gapped” position. The gapped hurricane position is a closed position with a difference: the panels of the operable roof panels are left slightly ajar instead of being fully closed. It may seem counter-intuitive to leave the stadium “open” during a hurricane, but our investigation using wind tunnel simulations identifed these air gaps alter the internal pressure within the stadium and reduce the net wind loads acting across the roof surface (as compared to the sealed and closed position). The identification of the gapped position enabled the structural engineer to significantly improve the efficiency of their design for the expected wind loads imposed by hurricanes.
Because of its innovative functionality, the Marlins Park roof exemplifies a new generation of retractable roof design. It offers an array of options for keeping players and fans safe and comfortable, and ably withstands major tropical weather events. It is a fitting crown for a stadium designed for a city with its eyes on the future.