The viewing attraction called Tilt will tip outward 30 degrees from the building envelope so that visitors feel as though their center of gravity is moving outside of the building. Courtesy of Pixel Pool
A new observation platform on the 94th floor of the John Hancock Center, in Chicago, will incline outward 30 degrees to provide visitors with unprecedented downward views of the city.
April 8, 2014—Chicago’s newest observation attraction may have some visitors holding on with a white-knuckle grip. Christened 360 Chicago, the observatory located near the top of the John Hancock Center, will unveil a new observation platform this spring that will tip outward 30 degrees from the face of the skyscraper to provide visitors with unprecedented downward—and some may say unnerving—views of the city. As unique as the attraction will be, so too are the engineering challenges associated with ensuring that the platform and the mechanical system responsible for its movement are incorporated effectively into the skyscraper’s existing structure.
Appropriately dubbed Tilt, the platform will be part of 360 Chicago on the 94th floor of the John Hancock Center, a 1,127 ft tall skyscraper located in the heart of the Magnificent Mile, the city’s famed shopping and entertainment district. When closed, the platform will appear to be a traditional observation deck with eight viewing windows. But once visitors are in place in front of the windows and the attraction’s mechanical system is engaged, the platform will slowly incline outward to suspend visitors more than 1,000 ft above Michigan Avenue. “Tilt takes patrons and tips them 30 degrees outside of the building envelope so that they feel as though their center of gravity is moving outside of the building,” explains John Peronto, S.E., P.E., SECB, LEED-AP, M.ASCE, a senior associate in the Chicago office of Thornton Tomasetti, Inc., the firm providing structural and mechanical engineering on the project.
The project is part of a larger effort by the owners of 360 Chicago to attract more people to the observatory. Montparnasse 56 Group, a firm based in Paris that operates observation decks in Europe, acquired what was then known as the John Hancock Observatory in 2012. The firm renamed the observatory 360 Chicago because the space offers panoramic views of Chicago and, on very clear days, beyond to four states: Illinois, Indiana, Michigan, and Wisconsin. “We had a vision for elevating the experience and providing memories for guests that will last a lifetime,” said Patrick Abisseror, the chief executive officers of Montparnasse 56 Group, in a March 14 press release.
The steel-framed mechanism and actuator system will tie into the
skyscraper’s 94th- and 95th-floor framing. Courtesy of Pixel Pool
Following the acquisition, Montparnasse 56 Group announced plans to renovate the observatory so that it could compete with Skydeck, another popular observatory located several blocks away on the 103 floor of the Willis Tower in Chicago’s financial district. The firm worked with a consultant to develop a concept for an attraction to rival the Ledge—a set of balconies at Skydeck made entirely of glass. The idea for Tilt emerged from that collaboration. The firm then hired Thornton Tomasetti to examine the John Hancock Center’s existing floor framing and develop a retrofit framing design for the platform, and eventually the engineering firm was retained to design the entire platform in a way that was sympathetic to the existing structure.
Like the John Hancock Center itself, the platform will be framed in steel. Laminated and tempered glass panels—chosen for their durability—will encapsulate the front, top, and sides of the platform to maximize views. “The patron will initially see what almost looks like a window-wall system, but it’s not,” Peronto says. “It’s an operable steel mechanism, and between all of the frames is glass that will be above you and in front of you and ’round the sides.” Three hydraulic actuators will power the platform, moving it in and out of the building. Even though the tower’s existing framing system is robust, additional framing will be incorporated into the floors to tie the new platform and actuator system into the structure. “The platform itself and the gravity loads are supported by the tower’s 94th-floor framing, and the actuation system framing ties back to both the 94th and 95th floors,” Peronto says. “There has been some additional framing installed between the existing structure to tie everything together.”
When closed, the Tilt will look like a traditional observation
platform with eight viewing windows. Courtesy of Pixel Pool
The platform’s elevated location in the skyscraper and the city’s infamous wind made wind tunnel testing a priority for the project. Wind tunnel tests were performed at the Boundary Layer Wind Tunnel Laboratory, in London, Ontario, Canada, to determine how the platform and building would perform under anticipated wind loads. “The challenge for the wind loads are one, addressing the design and making sure you have identified the wind speed associated with being so high in the John Hancock, and two, making sure that we address the occupant comfort and serviceability criteria,” Peronto explains. “We did a wind tunnel test of the upper portion of the John Hancock, looking at how the device in both the open and closed position will interact with the building, what the design loads are, and what the wind speeds are at this height of the building.”
Tilt is currently under construction and is expected to open to the public as early as May. Cupples, Inc., a St. Louis firm specializing in building facade design, is responsible for fabricating and installing the attraction, and Turner Special Projects, an arm of New York City-based Turner Construction Company, is the general contractor on the project. Gensler, an architecture firm headquartered in San Francisco, is the architect of record. Once the project is completed, visitors have an opportunity to see Chicago in a way that few probably ever imagined before. “They will get a view that is unmatchable,” Peronto says. “It will be both a thrill and very unique.”