It’s one factor for an architect to sketch a constructing with a cantilever; it’s one thing else to construct one which’s structurally secure. But structural engineers have a number of methods to make cantilevered buildings a actuality.
Smaller cantilevers can typically be achieved with out a lot particular engineering, mentioned Hezi Mena, a senior vice chairman on the engineering agency WSP, which has labored on quite a few New York towers with cantilevers, together with Era, Central Park Tower, 56 Leonard Street and One West End.
“Up to 15 feet or so, it’s not a huge engineering feat,” Mr. Mena mentioned, noting that a balcony is a good instance of a easy cantilever, the place the ground is robust sufficient to increase a brief distance past the outer wall of a constructing with out resorting to structural gymnastics. Part of the explanation that many buildings have a collection of stepped cantilevers “is to stay within a cost-effective solution,” he mentioned, “trying to minimize the cantilever every time.”
With a challenge like Era, nonetheless, it’s not so easy. There, WSP achieved the cantilevers with massive Vierendeel trusses — trusses with members that kind rectangular reasonably than triangular openings. “The benefit to doing a Vierendeel truss is to have windows with no diagonal members crossing through,” Mr. Mena mentioned.
“It’s not just columns and beams,” mentioned Eran Chen, the founding principal of ODA. “It’s a whole three-dimensional stable structure that holds itself.”
At bedrock, “we have rock anchors that are drilled very deep into the rock, actually anchoring the building through the rock,” Mr. Mena added, “so it doesn’t tilt over or anything crazy like that.”
At Central Park Tower, WSP and Adrian Smith + Gordon Gill Architecture employed a totally different answer by including a muscular switch ground on the backside of the constructing’s cantilever on the 12th ground. “Think of it as a structural platform in the sky,” mentioned architect Gordon Gill, “that’s capturing the load coming down on the east side and then bringing that back into shear walls and the core of the building.”
Greenpoint Landing, Block D, which was designed with DeSimone Consulting Engineers, depends on yet one more answer. Sloped columns run by quite a few flooring to convey a lot of the cantilevered load again into different columns that run to the bottom, whereas further tensioned columns work as hangers beneath these bigger diagonals to carry up decrease flooring. (All of this supporting construction shall be coated when the constructing’s cladding goes on.)
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