Double-Deck Elevators Rise as Tallest Towers Test LimitsTim Catts
Otis Elevator Co.’s quest to carry people up skyscrapers twice as tall as the Empire State Building hearkens back to a pivotal innovation by its founder: ensuring that riders won’t plummet back to earth if something goes awry.
The United Technologies Corp. unit has to go beyond the braking mechanism Elisha Otis demonstrated with a rope and saber at the 1854 World’s Fair. It’s working on systems able to stop 16 metric tons (35,274 pounds) of elevator and cable falling from the top of a kilometer-tall tower -- equal to a half-full tractor trailer driven off a cliff.
With high-rises in China and Saudi Arabia poised to surpass Dubai’s record 2,717-foot (828-meter) Burj Khalifa, the race to outfit the next generation of super-tall buildings is spurring engineering leaps at Otis, Kone Oyj and their elevator-making competitors in a market valued at $66 billion in 2010.
“We’re reinvesting in the skyscraper because the buildings on the drawing board right now are just different,” President Pedro Baranda said in an interview at Otis’s headquarters in Farmington, Connecticut. “Understanding the elevatoring of a very high-rise building can often give you insights into what you can do better at the lower end.”
Skyscraper construction is rebounding as the global economy regains its footing after the worst slump since the Great Depression. As many as 24 skyscrapers approaching 1,000 feet may be completed in 2013, compared with nine in 2012, according to the Council on Tall Buildings and Urban Habitat, and a new round of even loftier structures is on the drawing board.
They include Sky City, a 2,750-foot mixed-use high-rise in Changsha, China, whose builder says it would use prefabricated panels to cut construction time to 90 days, and Kingdom Tower, a proposed kilometer-high skyscraper in Jeddah, Saudi Arabia, that would soar at least 20 percent higher than Burj Khalifa.
Elevators used in smaller structures aren’t up to the task of moving people that high. Engineers are responding by double-decking cars to serve two floors at once and coordinating elevator traffic with computers, council Chairman Antony Wood said.
“Advances in elevators in the past 20 years are probably the greatest advances we’ve seen in tall buildings,” Wood said in a telephone interview from Chicago.
The recovery in skyscraper demand is good news for companies such as Otis. Cleveland-based researcher Freedonia Group estimates the global elevator market will grow 6.4 percent annually to $90 billion for five years ended in 2015.
For Burj Khalifa, completed in 2010 for $1.5 billion, Otis designed a system using double-deck cars, computerized dispatch and its compact Gen2 lifts, which replace steel ropes with polyurethane-coated belts and bulky motors with smaller gearless drives, eliminating the need for a large engine room.
To reach even higher, Otis is looking for ways to improve its braking systems. It’s familiar territory for the company.
Elisha Otis, its founder and namesake, pioneered the so-called safety elevator more than 150 years ago at a time when lifts were seen as too unsafe. He devised a spring-loaded mechanism that activated to catch the platform if the hoisting rope failed.
Otis teamed with circus founder and showman P.T. Barnum to demonstrate his invention at the 1854 World’s Fair in New York, according to the U.S. Library of Congress. Wielding a sword, Otis cut the rope and his safety device activated, arresting the platform’s fall.
The modern version of such a system relies on more advanced technology, and the complexities only increase with the height of the building, Daryl Marvin, director of innovation at Otis, said in a telephone interview.
A plummeting elevator car and its hundreds of feet of supporting steel cable can fall as fast as 45 miles per hour. Stopping that much weight moving so quickly generates a lot of heat -- as much as 300 degrees Celsius (572 degrees Fahrenheit), Marvin said.
So to start preparing for next-generation elevators, Otis had to strengthen its 383-foot test tower rising from an office park in suburban Bristol, Connecticut, about 100 miles northeast of New York.
“We need to be able to test a system for a kilometer-high building before a kilometer-high building is built,” Marvin said. “It’s a bit of a challenge to set it up in such a way that it doesn’t destroy our test tower if it doesn’t completely work the way we expect it to.”
Technology developed for super-high-rises can eventually reach more-modest buildings. One example: Otis’s intelligent-dispatch software, which lets riders enter a destination on a keypad or touch screen in a building lobby before being directed to the appropriate elevator, Marvin said.
Since the $36 million contract for Burj Khalifa’s 57 elevators and eight escalators would represent only 0.4 percent of Otis’s revenue in 2005, the year it was awarded, applying expensive R&D from the project to a broader swath of products is important.
Kone, which has its elevators in Saudi Arabia’s 1,970-foot Makkah Clock Royal Tower and the 1,700-foot Taipei 101 tower in Taiwan, the world’s second- and third-tallest buildings, decided to go the other direction with its test tower.
Instead of building up, the Finnish company built more than 1,000 feet down into a limestone mine in the town of Lohja, about 30 miles from its Espoo headquarters.
The facility allows for testing elevators at the breakneck speeds super-tall buildings require, said Johannes de Jong, Kone’s director of projects and technology.
“The goal was to develop the technology needed for super-and mega-high-rise buildings,” de Jong said in a telephone interview. “This is the only test tower in the world where you can test speeds of 2,000 feet per minute up to 3,500 feet per minute. Others have to rely on simulators, so it’s an advantage.”
Kone is also using the facility to test the optimal speed for fans that control air pressure inside its cars, which can descend in a mega-high rise building faster than a landing commercial airplane, de Jong said. While jets may have 30 minutes to reduce cabin pressure as they approach the airport, elevators in the tallest buildings may have just 30 seconds to depressurize, he said.
Both Otis and Kone said they will compete to put elevators in Saudi Arabia’s proposed kilometer-high Kingdom Tower.
“We are definitely verging on technology that will allow buildings to be higher,” de Jong said.