[hunser]

http://www.crainsnewyork.com/article...skyscrapers-go

How tall can NYC's skyscrapers go?

As towers surpass 1,400 feet, one structural engineer predicts 2,000-foot spires are around the corner—and maybe even half-mile-tall spires will follow suit.

The growing list of super-tall, ultra-skinny towers—reaching higher than 1,400 feet—has raised the question of just how far New York City developers will dare venture into the sky.

Although it may be difficult to predict what materials and engineering advances will permit, one structural engineer who has worked on several soaring buildings, including 220 Central Park South and a spire planned at the site of the Park Lane Hotel, said it won't be long before 2,000 feet or even a half-mile high will be possible.

According to Stephen DeSimone, who operates his own firm, DeSimone Consulting Engineers, cement and steel have doubled in strength in the past 10 years and already make structures up to 2,000 feet possible. Mr. DeSimone expects those materials to become 50% stronger in the next five to 10 years, allowing developers to build even higher structures with less bulk.

"The whole point of going high is to have big windows to enjoy the view," Mr. DeSimone said. "If you have thick concrete supports and structural elements everywhere, it impedes that. But that's changing."

The last major roadblock to building upward has been creating sophisticated dampening mechanisms to reduce the natural sway that gigantic towers experience from wind.

"People who buy $90 million penthouse apartments don't want to feel like they're in a boat," Mr. DeSimone said. "Right now, engineers and builders are exploring the idea of advanced dampening systems that will anticipate the motion of a building and counteract it before it even sways. This is the last hurdle in building taller than we are already."

New buildings like 432 Park Ave. use an internal pendulum—a gigantic pile of steel plates hung on cables inside the top of the tower—to stabilize the building during gusts of wind. As the tower moves, the pendulum stays put and counteracts the shifting. The building at 220 Central Park South, which is even more pencil-like than the 1,400-foot tall 432 Park Ave., has a 1,000-ton dampening pendulum on its unoccupied top floors, according to Mr. DeSimone.

But those systems are reactive, Mr. DeSimone said: They resist movement once it happens, but don't anticipate it with sensors that detect wind and building sway in time to offset it. Towers that soar even higher than those properties will need such technology because structural movement becomes more pronounced at extreme heights of 2,000 feet and beyond.

"Systems are being developed where a building's interior pendulum can be controlled to move ahead of time," Mr. DeSimone said.

I say it's about damn time NYC gets its first 2,000 footer!