Vegas' City Center Unveils McLaren's "Tree House" Sculpture

The Tree House at City Center

When the innovative Sobella Retail space of The Crystals at City Center in Las Vegas opened yesterday, the public got its first look at the Tree House, the sculptural centerpiece of the new retail area.

This Tree House, however, is not some rickety structure thrown together by a group of 12-year-olds from scrap lumber in dad’s garage. Nor is it a pre-fabricated tree house kit with a slide, fire pole, and rope swing like those sold in Wal-Mart. No, this is altogether different.

“The Tree House” is a two-story, free form, wood clad structure that seems to defy gravity, sitting precariously on a narrow base, spreading out to envelope part of the mezzanine floor, and then reaching away from its support to the skylight above. It appears to be made from horizontal and vertical slices of curved wood, and contains illuminated faces. The upper “oculus” allows light to shine inside the encapsulated bar, which bulbs out from the mezzanine.

McLaren provided complete structural engineering for the Tree House down to the main floor, the bulbed-out mezzanine floor, and support from the roof. The firm’s design team considered weights of steel, wood cladding, lighting, electrical wiring, sprinklers, and pendant lighting. It also considered earthquakes. The irregular member size and form made the design process extremely challenging – their orientations were based on aesthetics, not structural efficiency – and the system behaves like a large, 3-D moment frame.

In addition, each structural member and connection experiences unique stresses, so each had to be analyzed individually. The connections of the secondary “ring” members to the primary “vertical” members were accomplished with bolts inside tapped holes, hiding the connection from view. Connections consist of four, six, eight, or ten bolts; connections with excessive forces required field welds. The shallow connection geometry (5” deep holes spaced only 2½” apart vertically) required stiffener plates to span across the primary members inside the joint, further complicating fabrication. Electrical wiring, recessed lighting units, and sprinkler pipes had to be installed along and through members without affecting the clean finished profiles, further complicating member intersections.

The cantilevered “oculus” needed to be supported from wire ropes at the roof in order to make the framing work within the size constraints. There are four splayed wire ropes with turnbuckles, attached via ball joints to the roof truss members and via swivel hoist rings to the Tree House.

The main floor structure was reinforced to support the Tree House’s weight. The mezzanine floor was framed with steel beams and a lightweight concrete slab that receives the upper primary members and delivers these loads onto the mezzanine floor framing. These connections involved severely curved members bolted via thick base plates onto receiving beams.

The Tree House is a very ambitious design in which each piece affects every other piece, and no two pieces are alike. The fabricator produced precise steel and wood elements that fit perfectly when assembled on site, and the result is a one-of-a-kind sculptural assembly of “wood” elements that defies gravity.

Please click here to look inside The Crystals.