NEW YORK | 111 W 57th St | 1,428 FT | 85 FLOORS

[CCs77]

Moving Up in the World
Structural gymnastics help ultrathin, ultra-tall residential towers for the ultrarich make their mark on the Manhattan skyline.

By James S. Russell, FAIA
http://archrecord.construction.com/tech/techFeatures/2014/1404-Moving-Up-in-the-World.asp

In New York City these days, residential towers cannot be too slim or too tall. The improbably slender form of One57, now fully enclosed, is the furthest along of a new crop of super-thin, supertall, super-luxe residential towers. Designed by Atelier Christian de Portzamparc for Extell Development Company, with glass panels of blue, pewter, and silver, it rises 1,004 feet, hundreds higher than even its tallest neighbors.

Nearby, SHoP Architects is still refining its design for the 1,350-foot-tall building planned for 111 West 57th Street. So far, it is the slimmest of about a dozen super-skinny, supertall towers planned or under construction in New York. The ultrathin buildings are intended to lure buyers willing to plunk down as much as $95 million for a home perched high in the sky

Codes define a slender building as one that is more than seven times as high as the narrowest side at its base. In the Skyscraper Museum's recent show Sky High and the Logic of Luxury, Willis exhibited towers she calls super-slender—those with at least a 1:12 ratio. The slenderness ratio of 111 West 57th is a startling 1:24.

Core Principles

The simplest tactic to combat those forces is to add weight, especially at the top of the building, but Marcus says that's just a first step. The engineer must engage the building's entire structural system by strengthening the connection of the core to the perimeter columns and shear walls. To stiffen 111 West 57th Street, WSP thickened the shear walls that run the full length of the east and west exterior walls to as much as 3 feet, and linked them to the core with deep beams.

The building's 15½-foot floor-to-floor heights left plenty of space above the ceilings to conceal the stiffening beams. The dimension not only suited the engineer's purpose: the floor-to-floor height also coincides with the maximum code-permitted run of the exit stairs. That allows the floor space given over to the core to be minimized, especially as the two required exit routes are nested atop each other in a “scissor” configuration. The generosity of the resulting 12-foot-high finished ceiling has become a selling point.

Before people panic, please note that it says 1300 ft aproximately, it is not that they reduced the height, in the text of the article you can see that still says 1350 ft.
So please don't begin to ask if they reduced the height, they didn't