On Dec. 23, 2023, I had the pleasure of interviewing Steve Reichwein, P.E., S.E., principal with Severud Associates and the lead engineer on the Sphere in Las Vegas.
There have been many articles and news stories about this incredible new venue and its amazing architecture, audio and visual systems, stunning outer LED shell, and even the structural steel framing. In this article, I’m sharing highlights from this enlightening interview that looks at the Sphere from the lead engineer’s perspective, but I highly recommend watching the full interview found above or at bit.ly/427BFwJ
After graduating from Penn State with bachelor’s and master’s degrees in architectural engineering, Steve Reichwein landed an internship with Severud Associates in New York City in 2008 and joined the firm in 2009. His first project was the $1.2 billion renovation of Madison Square Garden. He spent five years on that project, gaining invaluable experience in a variety of areas.
“I was not only doing all the engineering work in the office with a huge team, but I was also going out there and living it onsite as it was being built,” he explains. “I quickly gained a ton of experience about how things get put together and how to make decisions very quickly and work collaboratively with the team, which were invaluable lessons.
“After that project, Madison Square Garden became a very key client for the [Severud] partner I worked directly for, Cawsie Jijina, and myself. We did everything for them, including LA Forum. They eventually bought Radio City, we did that. They bought Beacon Theatre, we did that. And then they had this crazy idea to build to the Sphere.”
According to Reichwein, the Sphere was the dream of James Dolan, the executive chairman and CEO of Madison Square Garden Sports and Entertainment. A deal was made between Madison Square Garden and Sands Casino (Venetian) to use a large parking lot behind the Sands Expo and Convention Center in Las Vegas. The dream now had a location, but there was still a lot of work to do to create a viable design.
From the initial concept, the project morphed into a 200,000-square-foot 16K media plane with 18,000 people able to attend any given event. The outer sphere is a 650,000-square-foot LED screen that’s the largest continuous LED screen in the world. With a final expected cost of $2.3 billion, it’s the most-expensive entertainment venue in Las Vegas history, edging out the $1.9 billion Allegiant Stadium, home to the NFL’s Las Vegas Raiders.
“It should be no surprise [to engineers] that a geodesic sphere is a very efficient structure,” says Reichwein. “It’s the most efficient shape as far as we’re concerned in our perceivable notion of the universe. Planets are spherical for a reason. Fruits are spherical for a reason. It’s just the natural shape that produces the most-efficient structure. It’s how nature evolved from some sort of spherical form, even at the cellular level.”
Creating the general structure wasn’t that difficult, according to Reichwein. They started with traditional geodesic sphere patterns, but they didn’t produce the type of repetition the engineers desired.
“So we landed on this geodesic space grid, which is a series of equally spaced latitudes that produce identical rings,” he notes. “And then they’re just literally cut with diagonals, and the diagonals cut out where there’s low utilizations. As you get to the top, it becomes very congested, so members are simply truncated away where they’re not needed anymore. It’s as simple as the topographical analysis gets, because it’s a sphere and you’re just eliminating members where they don’t do anything.”
The indoor venue structure is totally isolated from the outer sphere (with the exterior LED screen) that wants to breathe without restriction. Temperature swings in Las Vegas are quite dramatic—up to 100 degrees Fahrenheit because of the desert climate.
“The structure wants to breathe,” explains Reichwein. “It doesn’t want to be prohibited in any way, which is very key. It’s not attached to anything that’s inside of a thermal envelope. It simply passes through with expansion joints where it needs to. There are some places where you can interact with the exosphere when you’re entering the building. A lot of people take selfies by it, but it’s completely structurally isolated from the venue.”
To further illustrate the exosphere’s thermal expansion, Reichwein explains that it expands radially up to 3 inches, which sounds like a lot, but the exosphere is 500 feet in diameter, so it’s not that much in relative terms. “The public doesn’t perceive it that way,” he notes. “It’s just those engineers who keep everything relative.” Relative is all that matters in the engineering sense.
The Sphere’s dome roof was optimized for pitch and ring count. According to Reichwein, the ring count was an isolated optimization, and the radial count depended on the column grid, which was architecturally driven. The Sphere has 32 pairs of columns around the perimeter as well as 32 radials for the dome, all optimized for pitch at 90 feet.
“The dome roof is a distinct structure in that it’s a roof,” says Reichwein. “It has to function as a roof, but columns offer more restraint than you want them to.
“Where you start to get restraint in the rings, that’s where you start to get distortions and these unusual behaviors in the force flow,” he adds. “A dome roof wants to have a very uniform force flow. We had different-size columns; some of them had more load than others, so you got more restraint at one side vs. another. You start to get distorted shapes in the ring, and you start to get these weird discontinuities in force flow.
“To alleviate that, we essentially put the dome roof on radial sliders,” he explains further. “They’re allowed to basically glide over the columns radially; but circumferentially, they’re locked in. The only circumferential load you’ll pick up is seismic. There’s not much wind that hits the dome because not only is it shielded by the geosphere, it’s also a very aerodynamic shape since it’s just a parabola, more or less.”
The exosphere itself has the LED system tacked to it, but it was generally fairly forgiving because it was strands with fairly wide spacing.
“You’d be surprised when you walk up to it,” says Reichwein. “It’s fairly transparent when you’re in front of it, but you step 100 feet away and it looks like it’s a full screen. So that screen was fairly forgiving, but the media plane inside is a different story. At 16K, that’s the star of the show. It has very, very tight tolerances—definitely under an inch—in fractions of an inch.
“A 400-foot dome roof doesn’t have tight tolerances, so we basically approached it like an onion—a series of layers,” explains Reichwein.
The first layer is the dome roof with the highest tolerance because it’s a large 400-foot span supporting all the concrete and roof activities. The dome generally was designed with a 3-inch tolerance, but when it was built came within an inch of where it was supposed to be. Reichwein credits the excellent steel fabrication and detailing for the better-than-designed output. He also notes that it had about 1,200 members, and they didn’t weld a single one—all were bolted and fit together.
The next layer of the onion was the grillage system, which looks like something just hanging from the dome roof, but it bridges two geometries together. The dome roof is at the center of the Sphere, but the media plane is slightly offset if you’re looking at the seating bowl.
“Trying to hang something with one coordinate system and center point from another one is quite challenging geometrically,” notes Reichwein. “So we use the grillage to marry the two geometries.”
The next layer of the onion is a primary structural system hung from the grillage, which got the structure to within a half-inch tolerance. Little pancake jacks at each hanger were used to adjust elevations before locking them off.
Then there was another layer called the secondary, which had clips attached to the media plane that allowed adjustment up to a quarter inch. And then finally the tiles came in, and they have an eighth-inch tolerance.
“When you factor in deflection and everything, you’re going to use up to the one-quarter inch that you’re allowed to have differential from tile to tile,” he explains. “By the time we layered that all together, we finally got to where we needed to be.”
Separate from the “onion system” is the pedestrian bridge that takes people from the strip into the convention center. Like the exosphere, it requires thermal expansion and was built separate from the internal structures. “An additional building connects the venue to the bridge, but its structural system is isolated from the venue so forces aren’t passing back and forth between the two, because it would act like a podium backstay effect,” explains Reichwein.
Project Launch and Success
The Sphere was launched in two stages. The outside LED screen was turned on July 4, 2023, to “wow everyone and finally tell Las Vegas what we were building,” says Reichwein. “What we were building wasn’t public knowledge yet, so we had to keep it a secret.”
Then on Sept. 29, 2023, Sphere debuted its first concert, where U2 started a residency of shows at the Sphere. The secret was out.
According to Reichwein (the spectator and not the engineer), the audience experience is like nothing he’s ever witnessed before. “It’s just something that you have to be there, you have to experience it,” he adds. “That’s the best I’m going to be able to do with words.”
Author’s Note: Learn more about the specific software and technologies used to design and construct the Sphere as well as some of Reichwein’s advice to fellow engineers embarking on similar projects by watching the full interview at bit.ly/427BFwJ