Precast concrete box culverts provide large-scale underground air duct system for upcoming cutting-edge entertainment venue in Las Vegas.
By Mason Nichols
Las Vegas is anything but ordinary and boasts eclectic architecture that is a visual treat. The MSG Sphere, a $1.66 billion entertainment venue under construction at the Venetian Resort, will be no different when it is completed in 2023. The structure will include approximately 875,000 sq. ft. of interior space, a seating capacity of up to 20,000 and a fully programmable LED exterior. When completed, it will be a one-of-a-kind design, which will offer an immersive sensory experience unlike any other in the world.
While MSG Sphere’s exterior will certainly leave an impression, the work taking place underground is just as technologically advanced. To power the HVAC system for the world’s largest spherical building, they needed a specialized air duct system, and precast was the building material for the job.
Designing with speed
Initial plans specified a fiberglass solution. But according to Keith Stewart, senior project manager for Harris Company, the plumbing, piping and HVAC subcontractor on the job, that approach had issues.
“To get the fiberglass ductwork in the timeframe originally specified wasn’t going to work,” Stewart said. “Additionally, workers were also going to be driving cranes over the ground where this ductwork was going in to keep the project moving and on schedule. The fiberglass couldn’t support this.”
The Harris team quickly pivoted, and the answer was precast concrete. Harris shifted gears and reached out to long-time partner Jensen Precast to begin crafting an entirely new design.
Joshua Myers, vice president of operations and engineering for Jensen, explained the design, production and installation timeline was extremely compressed. Matters were further complicated by the complex engineering required for the new precast system.
In the span of just a couple days, Jensen and Harris went from having an initial conversation to needing a layout design.
Myers added that laying out a project like this in 3D would typically take about 2 or 3 weeks. With only a few days to spare, he connected with his engineering manager and got straight to work on the air duct, which was designed to be the arena’s return air system – similar to what you’d see in a home, but on a massive scale.
Jensen Precast benefitted from an experienced team and multiple locations near the installation site when taking on the complex project. Collaboration between the Jensen teams involved with the work was key to delivering both a successful design and product.
“A big part of this operation was coordination,” said Tyler Haack, P.E., vice president of operations for Jensen. “We had the Las Vegas plant, where the project was located, but we also had the Fontana plant in California involved. There was a great coordination and project management effort employed throughout the entire process.”
The air duct system was engineered using the design-build process, so the collaboration between Jensen and Harris was just as important. The two sides worked together diligently while sharing iterative designs.
“We’d draw a layout, ship it out to Harris, and then Harris would take our structure and insert it into the overall BIM model,” Myers said. “Then, we’d look at it to determine if we had enough clearance and what might need to move. Really, it was a lot of back and forth between us to get this done.”
Ultimately, the two sides chose a precast box culvert solution that employs two different styles to help achieve the airtightness and curvature the air duct system required. Jensen manufactured more than 100 box culvert pieces for the arena, each measuring about 10-feet-high-by-10-feet-wide and weighing approximately 40,000 pounds. Pieces included mono-gasketed, dry-cast culvert structures that were manufactured out of the Fontana plant and match-cast culvert structures, which were primarily produced in Las Vegas. The custom match-cast pieces allowed for the atypical skews and complex joint transitions in the design.
The Jensen team also had to contend with the designed openings to ensure proper airflow.
“Putting large openings in a box completely affects that box’s structural integrity,” Myers said. “We had certain length requirements that we could do. For the gasketed boxes, our lay length was about 8 feet, limiting the type of hole we could put in that piece to about 3-by-3 (feet) or 4-by-4 (feet) without having to completely change the structural walls and massively increase the rebar.
“We had to transition from that type of lay length to a cantilevered wall structure box culvert, which has the capability – because of the design of the structure – to go with bigger openings.”
Achieving major success
Thanks to the precast concrete structures and the open lines of communication among all parties involved, the MSG Sphere’s air duct project was a major success.
“In the case of this project, it was really timeline, timeline, timeline,” Myers said. “The initial need arose out of a supply chain issue relating to the fiberglass, and the contractor simply couldn’t cease operations for several months while they waited for that material to show up.”
Haack referenced not just the manufacturing and installation speed as positives, but the Jensen team’s engineering process as well.
“We were turning around our custom engineering extremely quick for us to meet the ship dates that they needed,” Haack said. “Our ability to change the location and radiuses of what needed to be done to avoid their existing footings and the footings that were going to be installed during the next stage was a big reason that precast ended up being a great success.”
Haack added that they were able to achieve rapid design strengths, which allowed them to ship pieces quickly from both plant locations. This was paramount to staying on schedule.
The project also benefitted from the pre-existing relationship between Jensen and Harris. Because the two firms are so familiar with each other, they were able to quickly power through the design-build process, overcoming obstacles and challenges with efficiency. As Stewart explained, Jensen’s assistance solving the difficulties of converting the air duct design to precast was flawless.
The end result was a precast concrete air duct solution for the MSG Sphere that wasn’t only installed on time, but also capable of supporting the tremendous amount of weight of construction operations both on and surrounding the installation site.
All in on precast
In Las Vegas, everything is about raising the stakes. Pushing the limits of what’s expected isn’t a rare occurrence, it’s the norm. It’s no surprise, then, that the MSG Sphere will revolutionize entertainment when it opens to the public in 2023. And Harris Company and Jensen Precast can stand proud of their efforts, which collectively helped redefine how engineers and designers view box culverts moving forward.
“When we put our minds and talents together – both internally and externally with our partners – we can do some pretty amazing things,” Myers said.
Mason Nichols is a Grand Rapids, Mich.-based writer and editor who has covered the precast concrete industry since 2013.