At a total height of 1,421 feet, and a small footprint of 11,400 sf, 111W57 achieves a record slenderness ratio of 1:24, making it the slenderest high-rise building in the history of humankind. 111W57 is the composition of two separate projects: the renovation of the existing landmarked Steinway building, and the construction of a new super-tall tower, partially rising from within the Steinway building.

The 95-story new development is composed of an 85-story concrete superstructure crowned by a 10-story steel bulkhead atop. Because of its extreme slenderness, several atypical structural systems had to be deployed. Amongst these are the introduction of outriggers, wind break floors, tuned mass damper (TMD) and a study of the mass distribution that resulted in floor slabs as thick as 72”.

The structural system is composed of two walls running in the long direction of the building, linked by core and link beams with encased steel elements. As a result of the very large forces that the building elements must resist, the thickness of these elements range from 12” to 42” in thickness. Even with such a variety of dimensions, the stresses distribution required the use of high strength concrete mixes up to an f’c of 14,000 psi. To free up spaces for architectural use, only two columns were introduced at the north face of the building, where most of the gravity loads accumulate due to the setbacks at the south face. The floors are composed of flat plate slabs with a thickness of 12”.

Due to the large number of rebar that had to be used to reinforce the walls, self-consolidating concrete mixes with high quantities of slag cement were used. These concrete mixes performed exceptional during construction and almost no segregation through the project was observed, resulting in a particularly smooth finish.