This 27-story, 357,000 square-foot luxury “green” high-rise residential building is located on North End Avenue overlooking Tear Drop Park in Battery Park City in lower Manhattan. The $75 million tower, designed by renowned architect Robert A. M. Sterns of New York City, contains 270 condominium units, ground floor retail spaces, a business center, cellar level mechanical, electrical and plumbing (MEP) facilities, a basement level garage, and a vegetated “green” roof.
Designed to comply with both the New York State and Battery Park City Authority “Green Building” Program, the project achieved LEED® Silver compliant status. As such, Tribeca Green attempts to offer a fresh opportunity to lead a healthier, more eco-friendly lifestyle. Energy efficiency measures abound throughout the project, and consequently the building offers a host of environmentally-friendly features including energy-producing photovoltaic solar panels, a cogeneration system and a microturbine that will supply clean energy for a portion of the building needs.
Tribeca Green is a reinforced concrete flat plate structure designed by the structural engineering office of DeSimone Consulting Engineers of New York City. Selecting concrete not only provided an innovative means by which to achieve green, but also provided a versatile structure to meet the project’s architectural requirements and lateral load demands.
Situated on fill created by excavation of the former World Trade Center, and adjacent to the Hudson River, the site hosts very poor soil conditions. The location posed many challenges for design and construction. To accommodate the situation, numerous 12-inch diameter 200-ton compression piles were extended through the landfill to bear directly on the bedrock below. The building’s lowest level is a 12-inch thick structural pressure slab, which enables the building to resist the site’s aggressive hydrostatic pressures.
The building’s superstructure is 255-feet tall. Concrete strengths vary depending upon location requirements. Basement pressure slabs, black water walls and slabs and pile caps all utilize 5,950 psi concrete. Exterior foundation walls use 4,000 psi. Columns, shear walls and transfer mat slabs use 8,000-psi concrete with silica fume for added strength. To meet LEED ratings, the structure’s concrete mix utilized a high percentage of slag. In the 8,000-psi mix, slag replaced approximately 47 percent of the cement, and in the 5,950-psi mix, slag replaced exactly 50 percent of the cement.
Because a network of beam elements was too difficult to achieve, transfer slabs were utilized at two floor levels. At the 15th floor, concrete columns were discontinued and again transferred to accommodate the roof garden setback and the new architectural layouts. A 28-inch mat slab was used to handle the shifted loads. At the 25th floor, columns were discontinued and transferred using a 14-inch mat slab.
In general, the design also accommodates heavier loads than normally found in residential design. The sidewalk slab was designed for superimposed dead loads of 150 pounds per square foot (psf) and live loads of 600 psf. At the 15th floor, superimposed dead loads of 200 psf were used to accommodate the roof garden. Black water tanks required a live load of 650 psf, and a storm water tank required a live load of 450 psf. The bulkhead roof slab, was designed to support a water tank weighing in excess of 127,000 pounds. In addition, the concrete structure was also designed to support solar panels attached to the facade of the building. Already penalized by a terrible site coefficient, this added superimposed dead load contributed greatly to the high seismic forces.
The structure’s lateral support is comprised primarily of interconnected shear walls and “link” beams. Thicknesses vary from 12- to 16-inches, and in some instances are fortified with three layers of vertical reinforcement to accommodate tension forces generated by the high seismic loads.
To aid the project’s fast paced construction schedule, 8-inches thick reinforced concrete flat plates were used with studrails to augment punching shear capacity were used extensively throughout the building to. These studrails help alleviate the congestion of reinforcing steel around columns while preventing punching shear distress caused by many adjacent mechanical openings.
A key advantage of conventional flat slab systems is the reduction of floor to floor heights which significantly reduced the cost of formwork and building frame. The flat-slab lends itself to the use of conventional plywood construction while the lower floor to floor heights allow for the use of conventional stick shoring. Building each floor on a two-day cycle is facilitated by selecting this floor system with the simplified formwork it offers. While an aggressive construction schedule, the two-day cycle is the preferred method of construction in New York City. This trend was set in the late 1960s and made possible by the moderate spans and lower floor to floor heights common in residential hi-rise flat-plate construction. Unprecedented in residential building construction, the two-day cycle reduced the floor completion schedule by 50 percent compared to an equivalent structural steel floor system.
Related Companies, New York, New York
Battery Park City Authority, New York, New York
Bovis Lend Lease, New York, New York
Robert A. M. Stern, New York, New York
DeSimone Consulting Engineers, New York, New York
Concrete Hi-Rise Contactor:
Superstructure Concrete Supplier:
Quadrozzi Corporation Foundation, Arverne, New York
JCivetta & Sons, Bronx, New York
Foundation Concrete Supplier:
NYCON Supply Corporation, Long Island, New York