Architect: Ismael Leyva Architects, New York, NY
Design Architect: Ten Arquitectos
Structural Engineer: Rosenwasser/Grossman Consulting Engineers, P.C.
Construction Management: Two Trees Management, Brooklyn, NY
Concrete Contractor: SBF Construction Inc., Hackensack, NJ
Total Project Size: 500,000+ sq ft
Award: 2016 CRSI Award Winner – Residential Building Category
The 32-story rental tower BAM South will have 379 apartments in all, 76 apartments (20%) of which will be affordable housing. The 500,000 plus square foot mixed-use building sits on a triangular plot of land (bordered by Ashland Place, Lafayette Avenue, and Flatbush Avenue) adjacent to Atlantic Terminal in Fort Greene, Brooklyn, NY. The building’s base will give way to 50,000 square feet of community and cultural space including a four screen BAM Cinemas, a dance studio for 651 Arts, a new branch of the Brooklyn Public Library, 43,000sf of retail space and a 10,000 square foot public plaza design by Grain Collective.
STRUCTURAL FRAMING SYSTEM
The ordinary concrete moment frame and shear wall interaction system is comprised of an outdoor multi-level plaza, joined with a three story podium that borders a uniquely faceted oblong 32-story tower standing just over 436 feet tall. Fully surrounded by underground transit structures at the perimeter, numerous design obstacles littered the “Support of Excavation” (S.O.E.) and foundation, thus dividing the base footprint into two areas regarding the zone of influence. In order to best accommodate the inherent site conditions, various foundation components were utilized, creating a hybrid conglomerate consisting of friction piles within the zone of influence, a 60 inch mass concrete mat to support the tower, and traditional spread footings integrated with an eight inch slab on grade beneath the podium. Unable to utilize a traditional tie back system, the soldier pile wall was forced to rely to on three levels of interior diagonal rakers integrated with soil supported concrete heel blocks staged with the excavation to mitigate lateral earth pressure deflection. To maximize efficiency, the concrete mat was constructed in two phases to coincide with the foundation schedule and S.O.E. design. Immediately after the first stage of soil removal, the mat area outside the zone of influence was constructed and designed to receive the temporary diagonal rakers. Poured in the dead heat of summer, engineering control of mass concrete proved necessary, as the peak internal core temperature of a test specimen was recorded at more than 190ª F. With further modification to the concrete mix design and the addition of ice; temperatures of mass concrete were properly maintained.
The outdoor plaza is an amalgamation of undulations and urban landscape that wraps around the northern end of the tower to the western face, where it steps up to join the podium at the second floor. Due to the numerous design elevations, integrated planters, and a column layout governed by the ramp geometry at the sub-cellar; the framed area of the multi-level plaza was achieved through the use of two diagonally sloped girders integrated with required slab folds, pickups, and cantilevered beams. At the southern triangular apex, a one of kind steel moment frame bolsters full height sloping glass IGU panels to create a high-end column free retail space with spans reaching 80 feet and ceiling heights of 36 feet. Along the western face of building within the 55,000 square feet of cultural space, four cantilevered rectangular volumes housing film theaters, dance studios, and concessions protrude up to 20 feet from the façade to provide exclusive architectural anomalies through a simplified structural solution. Spanning an elevation of four floors, these spaces are supported through the use of a mid-level full height cantilevered walls integrated with tower shear walls and columns. Using small concrete columns at the corners of each volume, the lower floors were suspended below, while the floors above were picked up in a traditional manner. Moving up the building program to the mechanical floor at five, nine massive downturn/upturn concrete pickup beams, measuring up to 6′-0″x6′-0″ transfer a total of twelve tower columns. To maximize operations and the overall utilization, a reinforced concrete deck was incorporated to create an accessible raised “mezzanine” above the upturn transfers.
UNIQUE STRUCTURAL AND/OR ARCHITECTURAL DESIGN FEATURES
The facade aesthetic of the 32-story slender tower is described as an articulation of a central circulation spine and two flanking volumes. Non-symmetrical starburst facets in the eastern and western faces caused completely unique floor plates at each story, which lead to a decision by the developer to utilize exterior sloping columns to maximize residential floor area. With a total of 46 tower columns, 18 are sloped to follow the cross sectional trapezoidal shape of the façade. Reaching slopes up to seven degrees in varying directions, the eccentric column geometry was not the only the design hurdle. The ingrained trapezoidal shapes caused lateral thrust at each column-floor joint, maximized at slope differentials that were resolved through the design of a hairpin reinforcing details. Made up of “U” bars Integrated with continuous edge and flexural reinforcing, the “hairpin” detail mitigated lateral thrust and increased joint ductility. In addition to the analytical obstacles, construction tolerance and installation was a major concern for these columns.
Probing the minds of numerous contractors, it became apparent that column coordinates were needed for every instance at all associated floors located on the underside of the slab to coincide with formwork. The required level of coordination to construct the sloping columns properly drove engineering to new innovations with Building Information Modeling (BIM) technology. Through the use of customized column families, BIM add-ins, and visual basic programming, this predominate feature of the project was completely automated; allowing for the harmonious execution with the respective design teams.