Supporting design flexibility for a world-leading architect
New York by Gehry (8 Spruce Street) is a celebrated addition to lower Manhattan, praised by the Times’s architecture critic as the finest skyscraper to rise in New York in nearly half a century. At 76 stories, it is also the tallest residential tower in the Americas.
We were brought onto the design team at an early stage of the project, when the building’s distinctive façades (described by a critic as “stainless steel that undulates like quicksilver running down the sides in slow motion”) had not yet been finalized. Our first task was to develop an accurate understanding of wind loads on the building to allow the structural engineer to design an efficient, high-performing structure and foundation. If it were an ordinary building, this task would be reasonably straightforward--but 8 Spruce Street was not ordinary.
First, the building’s 870-foot height and slender profile meant that wind loads needed particular attention during the design process. We anticipated that cross-wind vibration would be a significant issue. If the building’s resonant response to vortex shedding became great enough during a windstorm, the structure’s movement could become uncomfortable for its occupants. Even more significant was the fact that the architect, Frank Gehry, needed the flexibility to iterate his design before selecting the final exterior form. We had to meet the immediate needs of the structural engineer without constraining the architect’s choices. As the project advanced, we would deliver a series of wind-engineering solutions that maximized design flexibility for the entire team-- engineers and architects alike--all while sticking to a fast-paced design schedule and helping the team control costs.
One way to keep Gehry’s options open while delivering the necessary wind-load information for the structural engineers would be to conduct preliminary wind-tunnel testing, and build a conservative “buffer” into our analysis to account for the uncertainty in the final form of the design. But this inelegant solution would mean unnecessary construction costs.
Instead, RWDI carried out detailed consultations with both the structural engineer and the architect, helping everyone involved with the project to understand which of their own design choices would be most significant in determining wind-load effects on the structure. Drawing on our experiences with many supertall structures around the world, we established that if building massing and the shapes of the corners were frozen early on, the form of the undulating panels closer to the centre of each façade could be modified throughout the design process with limited impact on overall structural wind loads. Equipped with this information, the architect finalized the overall massing of the tower as well corner shapes early in the process, reducing uncertainty for the structural engineers and enabling them to produce an efficient, high-performance structural system. With this matter resolved, Gehry was free to iterate and experiment, eventually arriving at the stunning exterior that would come to define 8 Spruce Street in the eyes of New Yorkers.
As the design process proceeded, we continued to deliver valuable intelligence to support both the architect’s and structural engineer’s work. One approach that increased the whole team’s opportunities for exploration and refinement was our use of the high-frequency-force-balance (HFFB) technique to determine the structural wind responses of the tower. The HFFB technique enabled us to conduct wind-tunnel testing early in the process, generating a core of data about the structure’s response to wind loading, which we could then repeatedly (and economically) analyze and reanalyze, determining the wind loads for different iterations of the design as both the skin and structural skeleton of the building evolved. We later refined estimates from these tests with an aeroelastic model study, comparing the predicted motions of the building against published guidelines for wind-induced building acceleration to ensure that the building would be comfortable for occupants and meet all relevant standards. The last phase of our work was the cladding wind tunnel study, the final testing process to understand the wind loads on the envelope of the building with the exterior form finalized. In conducting this study we maximized design freedom for the project team by using a rapid prototyping technique called SLA printing. This 3D printing technique enabled us to quickly generate and test wind tunnel models that were faithful to the complex geometry of Gehry’s design.
New York by Gehry was completed in 2011 and has been celebrated as “majestic” and “one of the most beautiful towers downtown.” The New York Times review of the building called it an expression of Gehry’s desire “to celebrate the joy that can come out of creative freedom.” We’re proud that our technical capabilities and years of experience with tall buildings made some of that freedom possible.