By Lee Snyder
At 3.1 million square feet, SoFi Stadium is one of the largest, most expensive stadiums in professional football history. The stadium sits on the former site of the legendary Hollywood Park racetrack, an iconic fixture in Inglewood, California’s history. From opening in 1938 to its last race in 2013, the track was a hot spot that endured shut down during World War II, a renovation in the 90s and shortly after, a devastating fire. In 2014, the Hollywood Park Racetrack was purchased by a new owner with big plans for what would become SoFi Stadium.
LOD 400 Constructible Model Ensures Accuracy in Complex Design
SoFi stadium is the centerpiece of a 298-acre mixed-use development that includes retail, commercial office space, a hotel and residential units, and parks, and sits on a site 3.5 times the size of Disneyland. The stadium was designed by HKS Architects, the firm behind the $1.3 billion retractable roof at AT&T Stadium in Arlington and $1 billion U.S. Bank Stadium in Minneapolis.
SoFi Stadium’s architecture reflects Southern California’s industry, lifestyle, geography, and landscape. Its roof and underground cisterns collect and store rainwater, providing all of the development’s irrigation needs. The stadium’s aerodynamic shape and permeable flanks were designed to pull the ocean breeze into the seating bowl, giving fans the feeling of being in an outside venue. Situated three miles from LAX, FAA height restrictions required the seating bowl to sit 100 feet below the existing grade. This challenge ended up as one of the project’s most prominent features – indoor/outdoor paths that guide fans through landscaped environments leading to amenities throughout the stadium.
SoFi Stadium also raises the bar with an Ethylene Tetrafluoroethylene (ETFE) roof comprised of 302 unique picture frames, each varying between 30,000 to 70,000 pounds in weight, that broadcasts live football and visuals. The roof is supported by a 1,450-ton, 75,000-foot-long double cable net system.
Construction design and detailing firm DBM Vircon used Tekla Structures, Trimble’s BIM solution, to model and detail the roof’s complex steelwork and extensive on-site temporary steelwork that would support preassembly of large elements. “With the weight and geometry of the structure, the ability to model to a high level of detail in Tekla Structures was critical in making sure everything would fit together,” said Tim Rachow, senior project manager at DBM Vircon. “We modeled to LOD 400, down to nuts and bolts, of which there were thousands. Everything came together extremely well and that’s a testament to the planning and detail and accuracy of the Tekla model.”
Challenging Connections and Seismic Considerations
The project’s roof design required a plated boxed compression ring with large bi-directional tensioned cables that crossed high above the field below and supported the stadium’s 2.2 million-pound circular video screen.
DBM Vircon and Schuff Steel worked closely with the project’s structural engineer of record, Walter P Moore to account for deflection and ensure the roof could structurally respond to seismic forces independently of the bowl structure. Walter P Moore worked entirely in 3D, using a shared Tekla model created by DBM Vircon. “The compression ring at the inner edge of the roof had a series of very complicated connections,” said Mark Waggoner, principal and lead roof designer at Walter P Moore. “We modeled the connections and created our drawings from the Tekla model. At the same time, we provided the portion of the model with those complex connections to DBM Vircon to plug into their model as they populated the rest of the connections on the project. Pretty much everything we did lived in the Tekla model in one way or the other.”
Waggoner credits this continuous flow of data with eliminating the chance for error. “There’s basically no possibility for misinterpreting the data when we keep it in the model from the very early stages of design and share the same data with the detailer and fabricator, Schuff Steel, throughout the connection modeling and fabrication process,” he said. “It’s this continuity of data that makes us confident that nothing will go wrong, especially with a geometrically complex project like SoFi Stadium.”
Walter P Moore also modeled the structure to support the stadium’s video screen, a dual-sided, center hung 70,000 square foot digital LED display. “The support was woven into the roof and cable net design,” said Waggoner. “A series of modular trusses were prefabricated and brought to the site where they were stacked on the playing field. The cable net was complete so we used strand jacks to lift the display 32 feet off the ground until the cladding and electrical work were finished and the display could be lifted to its permanent home 122 feet above the field.”
Cross-team Collaboration for the Win
A project of this magnitude and complexity requires tight collaboration. At the beginning of the project, Schuff Steel and DBM Vircon met with the design team daily, using the data-rich Tekla model to visualize both the big picture and key details. “As challenging as this project was, it was collaboration across teams that really made it work,” said Christopher Pfeiff, global GM at DBM Vircon. “Every decision made impacted multiple teams. Through the power of Tekla Structures, everyone from the design team and our group doing the detailing and modeling, to the erector and fabricator, could visualize the project at an extreme level of detail to make critically important decisions. It was exciting to come together to bring this project to life.”
Lee Snyder is Product Manager for Steel at Trimble, Structures Division.