Architect: Kohn Pedersen Fox Associates PC
Engineer: WSP USA
General Contractor: Gilbane Building Co.
Concrete Contractor: Cross Country
Total Project Cost: $300,000,000
Total Project Size: 1,300,000 sf
STRUCTURAL FRAMING SYSTEM
55 Hudson Yards is a 51-story reinforced and post-tensioned concrete office tower reaching 760 feet in height and encompassing 1.3 million square feet of space. It is situated above an existing Metro Transit Authority (MTA) infrastructure. The site constraints due to the infrastructure as well as a need for column free space required innovative design strategies and construction sequence planning. As the result of the architectural intent, the structural solution of 55 Hudson Yards was envisioned through a central reinforced concrete core comprised of orthogonally arranged shear walls, an exterior moment frame, and a partial outrigger towards the top of the tower.
UNIQUE DESIGN FEATURES
This building utilizes three types of post tensioning to achieve the lightest possible structure. First, the thickness of typical floor spanning 40 to 50 feet was reduced to only nine inches using postensioned slabs. The weight of the floors was further decreased with the use of 130-pcf lightweight concrete, a somewhat unconventional practice for postensioned floor slabs.To allow for future floor layout modifications, the tendons were banded together creating rather ample tendon-free zones where tenants may create new floor openings. The second implementation was the provision of bonded postensioned tendons draped over a 39 feet tall transfer wall located in ninth and 10th floors to redirect a portion of the vertical load of the central core to the perimeter (Figure 2). Finally, at the change in geometry between the tower and the podium, walking columns were used to transfer vertical loads to the perimeter columns. This solution resulted in significantly large compression and tension forces within the 10th and 9th floors, respectively. The latter were carried by straight postensioned tendons.
REASONS FOR CHOOSING REINFORCED CONCRETE
Changes in project ownership and project requirements during the construction of the MTA infrastructure below changed the original project economics , the original steel-based structural solution became less attractive in financial terms, and an alternate concrete-based solution was explored even when a concrete structure of comparable height to the original design would typically be heavier.