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Rays ballpark engineers computer-modeled fly balls to design a roof that would stay out of play

TAMPA — The roof at the Tampa Bay Rays' proposed ballpark in Ybor City is about the same height at its peak — 230 feet, give or take — as at Tropicana Field, but the similarities end there.

One big difference: No catwalks. Nothing to get in the way of fly balls that began hitting the rafters just four days after the Rays' debut at the Trop in 1998.

Since then about 160 more have bounced off the catwalks. Five got stuck. This season, one hit a speaker attached to a catwalk, took a crazy bounce and ended up bonking the Rays' Adeiny Hechavarria just above the eye, putting him out of the game.

So when the Rays commissioned a design for a new stadium, they had a simple instruction about the roof.

"That cannot happen," said Dylan Richard, a principal in the Tampa office of the structural engineering firm Walter P. Moore, which worked on plans for the $892 million ballpark. "The first thing they put on the list is it's got to accommodate the ball flight."

COMPLETE COVERAGE: Rays unveil their plans for an Ybor City ballpark

To make sure it would, designers did something they think is unprecedented.

Using huge amounts of data that Major League Baseball collects through a system called Statcast, they modeled the flight of 7,736 fly balls hit in fair territory at the Trop.

Launched in 2015, Statcast uses radar and video shot at 20,000 frames per second to track a wide range of things that happen when pitchers pitch, hitters hit and fielders field. They include the speed and spin of a pitched ball, the speed of base runners and fielders, how hard fielders can throw a ball, how long it takes catchers to get the ball out of their mitt for a pick-off throw to second-base and more.

When engineers at Walter P. Moore downloaded this data, it filled 90 columns on their spreadsheet. They factored key elements of it — the speed and angle of each ball as it came off the bat — into some complex mathematical equations to project the parabola of every single fly ball. They had previously done something similar but more hypothetical when designing the retractable roof at the Miami Marlins new ballpark, but data from actual hits wasn't available for that previous exercise.

Mapped into a computer model, the re-created hits form a digital "dome" of fly balls the designers could overlay onto their plan for the new stadium.

They didn't stop there. They also put in data for every ball hit in every ballpark by two of baseball's best sluggers — the New York Yankees' Aaron Judge and Giancarlo Stanton — and superimposed that on the dome of hits from the Trop.

"We wanted to make sure we caught any crazy outliers from the hardest hitters in baseball," said Aaron White, a principal and director of digital practice in the firm's structures group. And, yes, the models showed that Judge and Stanton do sometimes hit the ball higher and farther than most other players who pass through the Trop.

Along with keeping the Ybor ballpark's roof higher than the dome of hit balls, the design team also built a cushion of maybe 20 feet in case MLB changes the composition of the ball or players get stronger or start hitting the ball with more backspin.

"Very mathematical. Very precise," says Tampa Mayor Bob Buckhorn, who saw a detailed presentation on the computer modeling. "They did their homework on this building."


So if the goal was to keep fly balls from hitting the roof or its supports, why not build the stadium with a retractable roof that could simply be moved out of the way?

Two main reasons, say the team and its designers:

It would cost a lot, and often it would be closed.

"There would be really very limited opportunities to open an operable roof," Rays' chief development officer Melanie Lenz said. A study done during stadium planning concluded that rain or lightning would affect 45 percent of daytime games and 61 percent of night games at an open-air Tampa ballpark. (For comparison, consider Marlins Park: During the 2017 season, six out of 78 home games started with the retractable roof open. That's less than 8 percent. And, for what it's worth, the Marlins lost all six of those games.)

Instead designers made the roof translucent, with 30-foot-tall glass walls below the roofline that can be opened up on nice days.

And then there's the cost. A retractable roof would need heavier girders and a foundation capable of supporting the extra weight. That could add $100 million to $150 million to the cost of the roof, which already is projected to cost about $245 million, or 30 percent of the estimated cost of the ballpark.

MORE: Roof drives lofty cost of Rays' proposed Ybor City ballpark

A retractable roof would have been different than the proposed roof in a couple of other key ways, too.

For one, roof panels that slide out to the side of the stadium, as in Miami, end up giving a stadium a bigger footprint, and the 14-acre site in Ybor isn't big enough for a building of that size.

The skeleton of the roof consists of a grid of criss-crossing arches. Known as catenary arches, each has the shape formed by a cord suspended between two fixed points (to picture this, think of the Gateway Arch in St. Louis, but turned upside down).

As those arches bear weight, they want to press out, so they would be secured at the base by a tension ring that acts like a belt. The grid is covered with a translucent synthetic fluoropolymer known as polytetrafluoroethylene, or PTFE. At the southern end of the building, over home plate and the stands, a solid curved canopy over the roof would provide some shade.

THE RAYS' VISION: A ballpark with windows that open, a translucent roof, spaces to play — and a $892 million price tag

One advantage of the design is that roof structure is only about 5 feet thick and requires 35 percent less steel per square foot than a traditional truss-supported roof like at Marlins Park.

And even if it could fit on the site, a retractable roof would be taller, maybe 90 to 100 feet taller, than what's proposed. That would be a problem, since the Rays want a stadium that won't clash with or loom over Ybor's smaller, older and often historic red-brick buildings.

So, as planned, the view from home plate is toward Ybor City. From the roof downward, the building is designed to "step down" from the side of the stadium closest to Adamo Drive to "gently connect to the historic district," Lenz said. The ballpark's design also calls for the use of brick facades and similar features that would help integrate the part of the stadium nearest Ybor into the neighborhood.

"We think, quite frankly, anything more than this (roof) wouldn't have fit aesthetically in the neighborhood and might have actually blown the budget out of the water," Richard said. "It did save money. A retractable roof would have probably pushed us over a billion dollars."

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Contact Richard Danielson at or (813) 226-3403. Follow @Danielson_Times