World's tallest buildings (part iii): Taipei Tower 101, Burj Dubai & 1-km High Club (projects under construction)

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The Taipei Tower 101, Taiwan, completed in 2003 (1,670 ft - 509.2 m)

The Taipei Tower 101, completed in 2003 took just 4 years to build. It is called the 101 because it has 101 floors (stories) above ground, and 5 below. From ground to tip of spire the Sears Tower is still taller than the Taipei 101, however from ground to top of roof the Taipei does win. The Taipei 101 is the first and currently only habitable building in the world to break the half-kilometer mark in height. However, a tower currently under construction known as "Burj Dubai" is going to do away with any controversy so completely that there will be no doubt as to which is the world's tallest building.

Burj Dubai, United Arab Emirates, to be completed in 2009 (2,684 ft - 818 m)

Construction began in 2004, and the Burj (meaning "tower") is projected to be completed in 2009. As of 12 August 2007, the tower's developers reported that the Burj Dubai's height is 531.3 m (1,743.1 ft), with 145 completed floors. This means that the Burj Dubai is officially taller than the antenna on the Sears Tower at 527 m (1,729 ft), however, until Burj Dubai is officially completed, Taipei 101 continues to hold the title as the world's tallest building.

Height comparison of existing and under construction buildings (click the image above to see at a larger version)

The One Kilometer High Club

Several other mega-projects in various states of planning and construction may vie for the title of "tallest structure". One of Burj Dubai's potential competitors is a proposed tower only 50 kilometers (31 miles ) from the Burj Dubai site. Al Burj ("The Tower"), is being developed by Nakheel Properties who are also keeping the project's final height tightly under wraps. Meed.com recently reported that this tower's projected height would be around 1,200 m (3,937 ft) with at least 200 floors.

Another proposed super tall skyscraper, the Murjan Tower in Manama, Bahrain is planned to be 1,022 m (3,353 ft) tall with 200 floors. The Murjan Tower is being designed by Danish firm Henning Larsens Tegnestue A/S.

Also potentially competing with the Burj Dubai is the proposed 1,001 m (3,284 ft) Mubarak al-Kabir Tower to be erected in Kuwait as part of a massive development project called Madinat al-Hareer ("City of Silk") that also includes an Olympic stadium, residences, hotels, and retail facilities. However, the project may take 25 years to complete.

*Update Nov. 7, 2011*

How The World's Tallest Skyscrapers Work
When the Empire State Building was constructed in 1931, it stood 1,250 feet tall. The famous skyscraper was the world's tallest building — and held that title for more than 40 years. Today the world's tallest building is the Burj Khalifa in Dubai. It stretches more than 1,000 feet above the Empire State Building — 2,717 feet into the air. The Burj Khalifa smashed the record held by Taiwan's Taipei 101, a landmark skyscraper with 101 floors. And at 1,666-feet, Taipei 101 tops the Petronas Towers in Kuala Lumpur by 183 feet.

Designing these massive skyscrapers is a huge challenge for structural engineers. Builders must account for potential natural disasters like earthquakes and hurricanes. They also must take everyday weather occurrences into consideration. Even on a normal day, wind forces can reach more than 100 mph at the very top of very tall buildings. "There are wind currents that when we're down below [on the ground] we don't even notice," says Kate Ascher. "That building, as it rises, interrupts those flows. The larger the building, the greater the wind flows."

Ascher, the former executive vice president of the New York City Economic Development Corp., explores the inner workings of skyscrapers in her new book, The Heights: Anatomy of a Skyscraper. She tells Fresh Air's Terry Gross that engineers purposefully design buildings to sway back and forth in order to alleviate the pressure caused by these high wind flows. "If a building weren't able to move at the top, then various structural elements might be damaged because of the wind pressure," she says. "And some, in earthquake zones, will be designed to move a little bit on their foundations as well — so they don't take as much pressure as they would if they were absolutely static."

Ascher explains that the same principle that allows a building to get taller also accounts for its ability to sway. Joints at the corner of steel beams can expand and contract because of changes in the weather or wind, which allows for slight movements at the very top of buildings. "There's not a precise formula for how much sway a building has, but there is a maximum [amount], which is 1/500 of the building's height," she says. "The minute you get more than that, it's not like the building's going to sway or fall over, but people who are in the buildings themselves will start feeling a little bit queasy."

Some buildings, like the Comcast Center in Philadelphia, are equipped with liquid-filled dampers, which help counteract the sway. The 300,000 gallons of liquid act as a counterweight. China's Shanghai World Financial Center, meanwhile, was built with a hole at the very top of its structure. The aperture is designed to reduce wind pressure by allowing wind to flow freely through it.

In addition to structural concerns, engineers have to worry about the inside of skyscrapers. In a 100-plus story building, circulating clean air and water is not an easy task — particularly when windows don't open. Mechanical areas exist solely to swap inside air with circulating air outside, says Ascher, so you don't have to worry that you're breathing stale air. "It's a constant process," she says, "and it happens around the clock."

And don't worry about flushing a toilet on the 100th floor, either. Engineers have accounted for that, too, she says. "There are very sophisticated bends in the pipes to slow the water as it's moving through," she says. "You don't want to hear it as it's moving through the building, so you need to make sure its sound-proofed as well."

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Original source and photos courtesy of Cool Pics, The Great Pyramid of Cheops (Khufu), Sacred Destinations, and Wikipedia