10 Strange Structural Engineering Marvels

Capital Gate
No, really. It's supposed to lean. © Jumana El Heloueh/Reuters/Corbis

Most engineers don't want their skyscrapers to lean. In fact, a building that begins to list after construction almost always indicates a failure of design. The Leaning Tower of Pisa, for example, was built on weak, unstable soil, which caused the foundation to sink on one side. As a result, the famous tower pitches almost four degrees off-center.

Then you get crazy engineers who decide to make their structures lean on purpose. That's the case with Capital Gate, a 35-story skyscraper situated on the island city of Abu Dhabi, United Arab Emirates. By design, the structure leans westward a full 18 degrees -- more than four times greater than Pisa's famous tower. To pull this off, engineers drilled 490 piles almost 100 feet (30 meters) into the ground and built a solid foundation consisting of a dense mesh of reinforced steel [source: Salmi]. Then they erected what's known as a pre-cambered core -- a steel-reinforced concrete spine with a case of scoliosis. Because the core curves, the whole building curves with it. Workers had to cut the diamond-shaped panels to slightly different dimensions because each one fit at a unique angle.

In 2010, Guinness World Records designated Capital Gate as the Farthest Man-made Leaning Building. Not to be confused with the Farthest Man-made Leaning Tower, which, unlike a building, doesn't have usable floor space.