BUILDING STATISTICS PART 1:

Building Name:  35 West 21st Street

Building Location:  35 West 21st Street, New York, NY

Building Height:  15 stories with a total height of 150 feet

Square Footage:  162,000 sq. ft.

 
Building Occupant:  Retail tenant unknown

Occupancy:  Retail and Residential

Project Team:

Construction Dates:
Construction began on January 2, 2007 and the topping out ceremony was on December 15, 2007.  The interior of the building is still under construction.

Cost:  Overall building cost is $20,000,000

Project Delivery method:  Design-bid-build

Architecture – Design and Functional Components:
35 West 21st Street is shaped by the surrounding buildings and it’s site.  With adjacent 4-12 story buildings, the plan takes on a T-shape to maximize the footprint.  The stem of the T-shape is an eight story residential tower facing the north with studio, one bedroom, and two bedroom apartments.  The top of the T-shape is a fifteen story tower facing the south with retail space on the ground floor and residential apartments comprised of studio, one bedroom, and two bedrooms on the second through fifteenth floor. 

Applicable codes:  New York City Building Code (2003)

Zoning and Historical Requirements:
Zoning is governed by the New York City Department of City Planning.  35 West 21st Street is located in the Flatiron District within the Ladies’ Mile Historic District.  The area is zoned as C6-4A which allows for commercial, light manufacturing, and residential construction.  The predominant historical requirements of Ladies’ Mile consist of street walls a minimum of 60 feet tall that are in character with the surrounding area.  Therefore, the building is has a classic stone façade with infill glass windows.

Building Envelope:
The building is clad in a mix of precast concrete panels with different finishes and punch windows with aluminum frames.  Precast concrete panels have a cast stone finish, a 5/8” brick veneer finish, or a cast in granite finish.  The panels and windows are arranged to form a street wall the matches the character of the surrounding buildings.
Roof construction consists of 4” of gravel on 4” thick rigid insulation with a sheet reinforced hot applied waterproof liquid membrane.

BUILDING STATISTICS PART 2:

Structural Systems:

Floor System

35 West 21st Street is a typical reinforced concrete residential structure.   The floor system is a two way flat plate slab without drop panels or beams.  Typical residential floors are 8 inches thick.  The bottom is typically reinforced with #5 deformed bars at 12 inches on center each way.  Middle strips are typically reinforced with #5 deformed bars at 12 inches on center at the top of the slab, while column strip top bars vary according to span lengths which range from 13’ to 18’.  In areas of high shear, slab supports also have studrails to help prevent punch through shear.  Typical columns are gravity only, and run the entire height of the building without transfers.  On the fifteenth floor, columns lining the exterior balconies are transferred to the 14” slab and then transferred to nearby columns that go down to the foundations.  Typical columns are 16”x18” with 8-#7 longitudinal bars and #3 ties at 12 inches on center.   Minimum concrete compressive strength is 5 ksi for slabs above ground, and 5.95 ksi for columns.  The slab also provides a two hour fire rating.

Basement

The basement floor is a slab on grade reinforced with 6” WWF 6x6 – W2.0xW2.0.  Typical slab on grade thickness is 6”.

Roof system

The roof slab is 12 inches thick with typical reinforcing like that on all the residential floors.  Cooling towers sit on dunnage that consists of 16”x16” concrete piers and galvanized W10x33 steel beams.  The remaining mechanical equipment including elevator machines are housed in the bulkhead which consists of shear wall 16 and three transfer columns.  The concrete piers and columns are transferred through the 12” slab and into columns below that continue to the foundation. 

Lateral System

The lateral system of 35 West 21st Street is comprised of shear walls in both the North-South and East-West directions of the building.  The two towers of the building are built integrally with each other through the two way slab at the basement, ground and second floor.  However, at the second floor, the 15 story south tower steps back to allow for an outdoor courtyard, thus breaking the connection between the two towers.  Because the connection of the two towers only exists on the first two floors, the towers’ lateral systems were designed separately from each other.  It is assumed that the two buildings act separately, and thus do not transfer any torsional moment between the two lateral systems.  Typical shear walls are 1’-0” wide and longitudinal reinforcement ranges from #10 at 12” on center at the base of the shear walls to #4 at 12” on center at the top of the building.  Horizontal shear reinforcement typically consists of #4 at 12” on center closed loop bars.

Foundation 

 The foundation system consists of spread footings for typical concrete columns and large mat foundations for shear walls.  On the east side of the building, 240 ton caissons spread loads from the footings to the bedrock below.  The caissons are at a minimum drilled 9’-0” into bedrock and are typically 12 inches in diameter.

Information regarding mechanical, electrical, construction, and fire protection systems is currently unavailable.