[NYguy]

A little more on the design and construction...

http://www.asce.org/CEMagazine/Artic...id=23622322774

“Angled” Tower Breaks Ground in New York City





The 895 ft tall tower will taper in an east-west direction, creating the visual appearance of leaning toward the city.
The groundbreaking for a 47-story concrete, “angled” tower in Manhattan—part of the new 26-acre Hudson Yards development—took place in December.

January 8, 2013
By Catherine A. Cardno, Ph.D.

A new 47-story, 1.8 million sq ft tower, boasting a 15-story-tall atrium located midway up its height, will join the Manhattan skyline by 2015. To be built entirely of concrete rather than of the city’s more typical steel, the building will be one of a pair of towers that appear to lean away from one another—one toward the Hudson River and one toward Manhattan. Tower C, the southernmost of these two commercial towers, is the first portion of the 26-acre Hudson Yards project—owned and operated by Related Companies and Oxford Properties Group, both of New York City—to break ground.

Tower C will be 895 ft tall, tapering in an east-west direction from approximately 225 ft at the base to 140 ft at the top, creating different floor areas at each level and the visual appearance of leaning toward the city. The exterior of the tower will boast floor-to-ceiling glass and two large outdoor terraces—one on the 32nd floor, and the other on the 47th floor.

Concrete is the building material of choice for the tower despite the fact that buildings in Manhattan are more typically built from steel, because of the “great efficiency” that it would bring to the tower, according to Joanna Rose, the vice president of Related Companies.

The tower will feature a cast-in-place concrete frame with a concrete core; large, flexible floor plates; and extensive column-free spaces, according to Aine M. Brazil, P.E., LEED AP, M.ASCE, the vice chairman of Thornton Tomasetti’s New York office, who wrote in response to written questions posed by Civil Engineering online. The floor framing will comprise one-way slabs spanning to posttensioned beams supported by lines of columns spaced 30 ft apart on center. Thornton Tomasetti is serving as the structural engineer for Tower C and for two glass-and-cable walls that form portions of the building’s skin.

A large portion of the building is being leased by the global fashion firm Coach Inc., which will make the space its world headquarters. An internal atrium will visually tie together Coach’s headquarters by extending upward from the 6th floor to the 21st floor, encompassing the entire space being leased by the firm. The cable-and-glass façade at this location comprises 10 ft by 4 ft 6 in. glass panels spanning nearly 200 by 60 ft, “creating a dramatic portal overlooking the High Line and southern Manhattan,” Brazil said.

The glass panels will be supported by 1 5/8 in. diameter cables that will be pretensioned from trusses and concrete walls located at the 5th and 21st floors, according to Brazil. To reduce the required amount of pretensioning, architecturally expressed steel spandrels will be located at alternating floors, she noted. These will also provide pathways for the heating elements.

The foundations are typical large-capacity caissons weighing up to 7,500 tons, Brazil said. Piles will be used in some locations in which loads are lower, she noted.