The building owner's representative, the architect and the contractor reached out to Schnitta in hopes of persuading the residents to continue the project. But the noises, which included the gunshot-like bangs, were so bad they were ready to abandon their plans and move out. They planned to build their dream home there, living in a rented apartment two floors down while they oversaw the construction. In the first pencil tower Schnitta consulted on, a couple had purchased an entire floor of the building, empty except for the exterior walls and elevator shaft. "The flexibility goes up exponentially with an aspect ratio being so thin," he said. Still, Ochsendorf expects most pencil towers probably move more than traditional buildings of a similar height. Pencil towers are built from materials stiffer than those in traditional buildings to compensate for their increased tendency to sway. These towers owe their existence to recent advances in materials and engineering, as well as space constraints that compel developers to build up rather than out. A less extreme pencil tower, 432 Park Avenue, is 15 times taller than it is wide. That's still fatter than New York's 1,428-foot-tall Steinway Tower. Now imagine taking three of those cardboard tubes and stacking them on top of each other. The Empire State Building, for example, is about seven-and-a-half times taller than its thinnest side, counting the spire seen edge-on, it has about the same shape as the cardboard tube in a paper towel roll. Classic skyscrapers don't move much because they are relatively squat. In general, the taller and skinnier the building, the more it sways. Sometimes it can be as small as just the metal stud slipping from one thread of the screw to the next," said Adam Wells, an acoustical engineer at CDM Stravitec in New York, who was not involved in the project. "These movements are usually very, very small, the ones that create these noises. Such parts may rub and strain where they connect to the rest of the architecture. Instead, they're caused by things like pipes, ducts and internal walls - components that aren't responsible for holding the building up. Residents of skyscrapers may be reassured to know that most of the noise isn't caused by the support structures, which are designed to flex and move as a single system, said Brügger. The other way building movements can bother occupants is by creating noise. "If you would just now lie down in your office building and close your eyes, you'd suddenly feel the floor move." "You may be in an office building all day that actually moves 10 times as much as your home," said Brügger. Similar illusions can occur in buildings, especially when people are trying to sleep. For example, when planes take off, there is usually a moment when the acceleration slows, and passengers may feel like the plane is falling. People tend to feel changes in acceleration more than movement itself, so what a person feels isn't always what's happening. Carleton Strength of Materials Laboratory at Columbia University, who was not involved in the project. When people do feel movements, it's a comfort problem, not a safety problem, said Adrian Brügger, director of the Robert A. "The whole trick is to design the buildings so that the building occupants never feel the movement." "They can't not sway," said John Ochsendorf, a structural engineer at MIT who was not involved in the project. The key, she said, is that everything must be flexible enough to move when the wind makes the whole structure sway and twist. In November, at a meeting of the Acoustical Society of America in Seattle, Schnitta presented what she and her team have learned from solving sound problems in slender skyscrapers. The buildings are perfectly safe, said Schnitta, but such noises can disturb and frighten residents. It was loud creaking and then a 'Pop! Pop! Pop!' So I called it snap, crackle, pop," said Bonnie Schnitta, founder and CEO of the New York-based acoustical consulting firm SoundSense, recalling what she heard in the first "pencil tower" she worked on in 2016. "On a windy day, there were literally these sounds almost like guns going off. Apparently, many of them sound like it, too. (Inside Science) - In recent years, major cities like New York have sprouted a new breed of skyscraper so tall and thin they look like they should topple in a breeze.
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