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When the observatory at 1 World Trade Center (1 WTC) opens May 29 in lower Manhattan, visitors will be treated to a spectacular 360-degree view of New York City and the surrounding area from nearly390 meters above its bustling streets. All that’s needed to travel to the upper reaches of the building, also known as the “Freedom Tower,” is a 60-second ride in the Western Hemisphere’s fastest elevator system.

The 104-story 1 WTC—which opened for tenants in November—has 71 elevators, five of which will be express elevators with a top speed of more than 36.5 kilometers per hour. They are not the fastest in the world—Taiwan’s Taipei 101 skyscraper elevators race to the top of that 508-meter-tall tower at up to about 60 kilometers per hour—but they are still a full 25-percent faster than the express elevators in 1 WTC’s predecessor, the Twin Towers.

Eight 2.3-ton electric motors installed on 1 WTC’s roof power the high-speed elevators. Each elevator operates using a pulleylike system that consists of a cab and counterweights connected by a cable. Together, 1 WTC’s elevators use about 454,000 kilograms of counterweight to ascend and descend the building’s hoistways, or shafts.

In addition to being speedy, the elevators serving 1 WTC—the tallest building in the Americas—feature several advanced technologies designed to improve ride quality, safety and logistics. Although some of these features are already used in other “supertall” buildings around the world, a closer look at 1 WTC’s lift system reveals just how far elevator technology has advanced since the first Otis Brothers and Co. passenger elevator lifted shoppers from the ground floor of a New York City department store in 1857.

Future elevators are expected to function without cables, but these are years away as engineers develop the means to dead-lift elevator cabs—which weigh upward of 4,500 kilograms apiece—without any help from counterweights. One approach that several elevator companies have pursued over the years is the development of cable-free cars that use electromagnetic levitation to move in any direction.

An elevator needs more than just powerful motors to travel at high speeds. Like bullet trains, fast-moving elevators also require incredibly smooth rails and rail joints to move swiftly. “Over time, train rails have gotten longer in order to cut down on the number of joints a train must pass over and create a smoother ride,” says John Koshak, owner of Elevator Safety Solutions, a Collierville, Tenn.–based elevator and escalator consulting firm. The vertical positioning of elevator rails, however, limits their length to about 4.9 meters, which means any skyscraper requires a large number of rail joints.

Elevators must also account for minute changes in the distance between guide rails that occur as changes in temperature, wind and other conditions cause skyscrapers to sway slightly throughout the course of a day. “These factors mean that you can’t ever have a perfect plane for an elevator to travel in very tall buildings,” Koshak observes.

At 1 WTC, engineers are minimizing elevator car jostling using what is known as an “active roller guide” system. Roller guides keep an elevator’s wheels, known as rollers, in contact with the guide rails as the car ascends and descends. The rollers used at 1 WTC are made of polyurethane so they can absorb slight imperfections in the rail joints and are controlled by a system that pushes and pulls against the rails to prevent any misalignments or imperfections from interfering with a smooth ride, according to Alpharetta Ga.

Air pressure is also a concern when designing and building high-speed elevator systems that can scale supertall skyscrapers, which by definition exceed 300 meters. Engineers, architects and builders must take into account how changes in air pressure impact not just the elevator cars and their passengers but the floors they pass as well. As a typical 4,500-kilogram car with a 7,300-kilogram counterweight rushes up its hoistway, it creates a massive air displacement. “With an area of high pressure above the car and low pressure below it, you’re creating a situation where the hoistway doors above the car want to blow out into the hallway and the hoistway doors below the car want to suck into the hoistway,” Koshak explains.

They placed aerodynamic aluminum shrouds around the tops of the elevators in 1 WTC to reduce air resistance, drag and wind noise in a way that minimizes air displacement. The idea behind this creative airflow design is that air pressure between the elevator doors and the hoistway doors remain neutral—minimal “whooshing” sound or door rattling when an express elevator passes by a floor without stopping, Koshak says. Air pressure changes that affect people inside the car are more difficult to mitigate, however.Their approach at 1 WTC is to provide extra air pressure inside the cars to compensate for pressure drops, then slowly releasing it to keep passengers’ ears from popping.

An elevator can ascend as fast as the technology will allow without creating any passenger discomfort caused by changes in pressure. Elevators generally do not descend faster than 36 kilometers per hour, however, because anything faster can lead to ear-popping.

One of the main structural differences between the Twin Towers—built in the late 1960s and early 1970s—and 1 WTC is that the former were held together by a steel exoskeleton, whose vulnerability was revealed on September 11, 2001.

The new building has a hollow concrete core that serves as a structural backbone for the building. The elevator hoistways run through this core, protected by a one-meter-thick concrete wall.

The 530-meter-tall CTF Finance Center in Guangzhou, China, is expected to have elevators that ascend at speeds up to72 kilometers per hour

Fl - Scientific American.

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