AOL TIME WARNER CENTER
The iconic structure at Columbus Circle in New York City contains approximately 2.1 million square feet spread over 54 floors. Extending 748 feet above the street, the building consists of two towers rising above a podium base. The multifunctional structure is composed of virtually seven “stacked buildings”, one on top of the other. Considering that each stacked building is independently owned and designed by a different architect, the structural system was selected to provide the maximum flexibility for its users, a criterion also reflected in the construction material selections.
The two towers of the structure sit on a “podium” base. The south tower’s 30 residential floors and the north tower’s 18 hotel and 18 residential floors are each crowned by a 60-foot tall lantern. Both are constructed of conventional cast-in-place concrete. The podium below the towers, built with conventional structural steel and concrete floors on metal deck, consists of 17 floors on the north side and 24 floors on the south side and houses a theater, large span studios, CNN broadcasting facilities, a spa, offices retail spaces, restaurants and parking.
In selecting the lateral system, the primary consideration was to find a system that would be totally independent of the supporting columns. This independence would permit the columns to “adapt” to the specific requirements of each of the stacked buildings. The solution, two concrete cores located under each tower, pierce the podium and extend from the ground up to the transfer trusses located at the top of the podium. The cores house the elevators, stairs, and mechanical rooms and act as a double backbone resisting all of the lateral and torsional forces.
There is no single column or shear wall that is continuous throughout the height of the structure. The concrete columns and even the shear walls within the residential/hotel towers are all picked up at the mechanical levels located at the top of the podium by two directional steel trusses encased in concrete. In addition to carrying the weight of the buildings above, the trusses support a variety of hung columns that in turn support the 11 office floors below. These hanging columns, located at the perimeter of the 45-foot clear span of the offices directly below the trusses, could not be extended downward due to the 60-foot clear span required at the studio levels beneath.
The columns permitted to penetrate the floors below and supporting the trusses, also known as “boomers”, carry up to 25,000 Kips, and consist of a built up steel core encased in 66 inch square reinforced concrete columns. There are 20 boomers in the entire project.
To further complicate matters, the developers below the studios had different column requirements for their retail spaces. The boomers had to be sloped or split into an “A” shape in order to provide maximum space usage. The strong lateral forces that resulted from these transfers were passed to the shear walls by steel plates incorporated in the slab system. The same slab system, acting as a “diaphragm”, transfers the horizontal forces created by the ten story high post-tensioned cable atrium wall. In addition, at the southeast corner of the podium, there is a nine story high cantilevered glass box called “the prow”. This feature receives added support from the floors transferring the loads to the shear walls.
Nestled in the center of the podium is “Jazz at Lincoln Center”, a 1200 seat multi-purpose concert hall. For this entertainment venue, high quality noise and vibration insulation was a critical necessity. The structural solution resulted in the construction of a completely separate “box” resting on seven inch thick neoprene pads that provide vertical and horizontal support while acoustically isolating it from the rest of the building.
The AOL Time Warner Center is a symphony of logistics involving a wide spectrum of participants and creative achievements. Every element of its dynamic structural system was calculated to obtain a harmonious blending of the enormous variety of requirements associated with the project. The result of this collective effort will be a monument to all those involved in its creation and a new jewel in the crown of New York City.