By Cass Jacoby.
Roofs are very particular. They are strong and protect us from the elements, yet can be taken down by the smallest trickle of water or incorrect airflow. With how precise a roof needs to be in order to properly do its job, the engineering of something like a retractable roof seems more like sci-fi than an achievable engineering feat.
Engineer Mark Sharamitaro knows this fact intimately. He has been instrumental in the design of both the Arthur Ashe Stadium and the Louis Armstrong Stadium systems — two retractable roofs that fully embody the engineering challenges of building something that can be load-bearing and watertight at one moment and gone the next.
“I worry about unexpected storms because of the wind,” he tells Popular Mechanics. “It is not because of the wind and the structure, but because the wind pushes water places where I won’t want water. That is pretty much my overall concern, that something abnormal would get into the system.”
Yet, despite these design challenges, retractable roofs are quickly becoming a reality over plenty of stadiums, be it the Bilie Jean King National Tennis Center, the Arthur Ashe Stadium, the Louis Armstrong Stadium or the Globe Life Field. These stadium roofs can be rolled out the moment a venue recognizes a storm is blowing in, allowing the game, the show or the concert to go on.
“That is definitely a bit of an art and science together, for sure,” Sande Frisen, a partner at Detroit, Michigan-based Rossetti Architects, tells Popular Mechanics. “It is a very complicated piece.”
There's no single answer to that question because no two retractable roof stadiums are exactly alike. While these roofing structures have plenty of differences, from low slope to steep slope, being made up of two movable panels or the number of winches, they all share the similarity of requiring a roof that weighs thousands of pounds over the sizable opening of the stadium.
These roofs all slide on railroad-style rails that require rail clamps to hold the roof in place. Mark’s designs, however, use winches and a rotating spool driven by a motor that can tighten or loosen a cable.
Winches are driven by ten electro-mechanically powered motors with independent controls so the panels can coordinate and meet in the middle at the exact same time, creating a smooth visual effect. The Billie Jean King National Tennis Center has four winches, while Ashe Stadium only has two.
“It is like pulling a wagon up a hill with two ropes, one on each side, and then trying to keep them center, with no skew,” Mark says. “You don’t want one side to crawl up the hill faster than the other.”
Alternately, to deal with the higher slope at the Armstrong Stadium, four 40-horsepower motors operates four ropes for the one winch, each connecting to one end of each panel. The steel rope doesn’t allow stretching and keeps each of the roof panels in the exact same configuration for opening and closing.
With sensors on the roofs monitoring everything from skew to winch power, they must also be careful to not operate the roof in high winds since the rail clamps aren’t set when the roof is moving.
“The roof could theoretically be repositioned by the wind due to the fact it is kind of like a wing of a plane,” Mark says. “We have never had to stop because of wind during the event, but have had to during commissioning and maintenance times.”
While a drop of water is no big deal for baseball and football, in the world of tennis it is unacceptable. A watertight retractable roof is conceptually quite simple, however, the reality of making a watertight roof work is complicated, especially given how retractable roofs don’t typically need a 100-percent watertight solution.
So, these retractable roofs feature panels that overlap, with sets of bristle brushes covering the overlap and helping stop wind and rain. Blowers then inflate an air bladder to fill the gap on the back side of the bladder and a gutter catches any escaping water and sends it away from the court.
Globe Life Field, home of the Texas Rangers, has one of the world’s largest retractable roofs. KPost Roofing and Waterproofing originally completed this job, writing that the complex scope of work included installing approximately 450,000 square feet of Carlisle’s single-ply KEE PVC, a fleece-backed membrane for hail damage protection, and Liquiseal in gray to waterproof the steel structures penetrating the roof.
This year, the project for the Roofing Alliance’s Student Competition at the 2023 International Roofing Expo (IRE), is the Globe Life Field. The student competition is a hallmark event that exposes upcoming generations of roofers to the world of roofing by giving them a chance to submit a qualified bid package proposal. This competition offers a look into roofing as a career as well as a valuable opportunity to network and exposing future of roofing to projects that foster their creativity and allows them to elevate where the industry is headed.
Given their popularity, it's likely we will see many more of these convertible stadiums built in the future.
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Cass works as a reporter/writer for RoofersCoffeeShop, AskARoofer and MetalCoffeeShop. When she isn’t writing about roofs, she is putting her Master degree to work writing about movies and dancing with her plants.
Photo credit: Tim Clayton - Corbis//Getty Images
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