A stunning new residential tower on Manhattan’s far west side, 15 Hudson Yards is turning heads with its eye-popping shape and features. But reaching this milestone required some creative approaches to the structural engineering of the building.

As the structural engineer of record, WSP USA was responsible for delivering the structural design of the 918-foot-tall skyscraper, now one of the tallest residential buildings in New York City and the latest property to open its doors at Hudson Yards.

“The geometric form of the building is somewhat unique for New York City,” said Cillian Calpin, WSP vice president who was responsible for delivering the 15 Hudson Yards project. “There is a lot going on at this particular portion of the Hudson Yards development.”

Located in the Southwest corner of the development, 15 Hudson Yards was constructed above the new No. 7 Subway extension line, as well as a recently built Amtrak tunnel, designed by WSP in anticipation of future use. On the east side of the tower is The Culture Shed, a dramatic performing arts space that docks with the new tower. To the south side of the tower is the active High Line elevated park.

“There were a lot of adjacent complexities surrounding this building that had to be negotiated, and some unusual design considerations had to be made before the tower could be built,” Calpin said.

With 965,000 square feet of total space, 15 Hudson Yards features a two-story glass lobby and a quatrefoil design as it climbs, providing amazing views of the Hudson River on one side, and downtown Manhattan on the other. It is part of the Hudson Yards Redevelopment Project, a joint venture by the New York City Department of City Planning and Metropolitan Transportation Authority, the largest private real estate development in U.S. history by square footage. The property is being developed by Related Properties and Oxford Properties.

While the tower cuts a distinct silhouette in a New York City skyline crowded with hard hewn edges, Calpin said it is at the lowest levels where the building’s most unusual manifestation is revealed.

The Culture Shed, an avant-garde performing arts center adjacent to 15 Hudson Yards, exacts its influence by undercutting the tower above with a giant horizontal “V” cut, creating the space for the retractable roof of the culture shed to dock with the tower. The Culture Shed’s motorized roof slides back and forth to create versatile indoor/outdoor performance spaces. This dramatic shift in geometry required the tower width to be reduced from 92 feet at its widest point, to 51 feet at the apex of the “V” cut.

“This was a counterintuitive thing for a building of this size, especially since it was not due to an unavoidable encroachment from an existing neighboring property, but rather a fundamental construct of the building’s conceptual design that required us to plan around it,” Calpin said.

After creating several possible options, the designers favored a system of reinforced concrete sloping elements, diaphragm slabs and transfer systems carefully arranged to direct the tower loads around the culture shed and ultimately to Manhattan bedrock.

This design, which Calpin called a “K-wall” system due to its shape, was considered the optimum solution to accommodate The Culture Shed’s retractable roof. This decision was reached after careful analysis and close collaboration with the buildings architects.

“We used 3D modeling to validate the feasibility of our ideas,” Calpin said. “Collaborating with the construction contractor, Cross Country Construction, during the design phase was instrumental in our ability to deliver a complex building like this. We’d tell the contractor what we were thinking of doing, they’d come back with ideas and what they felt could comfortably work in the field. They were incredible to work with.”

In specific locations, structural steel nodes are embedded in the concrete to allow multiple heavily reinforced elements to criss cross and coalesce. Six-story mockups of the nodes and reinforcement were assembled by the contractor offsite as a means to troubleshoot the installation in advance of the concrete pour. This approach allowed the contractor to identify potential installation issues and course correct before final installation at the site.

The Hudson Yards development is built on a platform above active rail yards used by the Long Island Rail Road for commuter rail train storage. Reinforced concrete was used to thread support around adjacent infrastructure complexities, including the No. 7 subway extension, 11th Avenue bridge to the west, the High Line elevated linear park to the south, and the currently inactive Amtrak tunnel directly underneath the tower to the north. The north tower columns are supported on a reinforced concrete transfer system over the tunnel.

“The Amtrak tunnel was built in anticipation of future needs, and designed to take approximately one-third of the load of the tower,” Calpin said. “So once the tunnel was completed, it was already prepared for structural columns that support the tower.”

Surrounding the base of the tower are 14 acres of public parks, including the High Line. The new tower becomes one of the 16 buildings that will create the Hudson Yards neighborhood, which will feature residential, office, retail, and public open space, and is anticipated to contribute a $19 billion economic boost to New York City when completed in 2025.

Finding solutions that create livable and sustainable urban space in an area where it would have previously been unthinkable is part of WSP’s commitment to creating a world that is Future Ready™—thinking beyond the conventional to help organizations prepare for the changes and challenges the world will face, and improving the overall quality of life through visualization of environmentally beneficial opportunities where none previously existed.

With tenants now moving into their new homes in the tower following its March 15 grand opening, and with The Culture Shed hosting events since April, Calpin looks back fondly at the experience of playing a role with a signature New York City skyscraper.

“It was a complex project delivered successfully by a team operating at the highest levels across the spectrum from design to construction,” Calpin said. “As an expert practice in high rise building design, WSP Building Structures provided a guiding hand through every complexity ultimately delivering Related’s ambitious vision and adding yet another brush stroke to our iconic New York skyline.”

The team included Silvian Marcus as principal-in-charge, Fatih Yalniz as senior vice president and analysis manager, Charles Guerrero as vice president and CAD manager, and Stephen Rys as project manager.