Reinforced concrete -- the compressive strength of which has tripled in the past 40 years, "allowing concrete structures to be thinner, lighter and far, far taller" -- provides the skeleton for the world's tallest building. Dubai's Burj Khalifa beats the steel-frame Taipei 101 by 1,050 feet, representing a true technological feat, writes Blaine Brownell an assistant professor at the University of Minnesota School of Architecture.

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