Pisa Tower vs Willis Tower

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The Leaning Tower of Pisa (Italian: Torre pendente di Pisa) or simply the Tower of Pisa (Torre di Pisa [?torre di ?pi?za]) is the campanile, or freestanding bell tower, of the cathedral of this Italian city of Pisa, known globally for its almost four-degree lean, the result of an unstable foundation. The tower is situated behind the Pisa Cathedral and is the third-oldest structure in the city's Cathedral Square (Piazza del Duomo), following the palace and the Pisa Baptistry. The height of this tower is 55.86 metres (183.27 feet) from the ground on the low side and 56.67 metres (185.93 feet) on the high side.

The width of the walls at the base is 2.44 m (8 feet 0.06 in). Its weight is estimated at 14,500 metric tons (16,000 short tons). The tower has 296 or 294 steps; the seventh floor has two fewer steps on the north-facing staircase. The tower began to lean during construction in the 12th century, due to soft ground which could not properly support the structure's weight, and it worsened through the completion of building in the 14th century. By 1990, the tilt had reached 5.5 degrees. The structure was stabilized by remedial work between 1993 and 2001, which decreased the tilt to 3.97 degrees.

Source: Wikipedia

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The Willis Tower (formerly and informally: Sears Tower, its title until 2009) is a 110-story, 1,450-foot (442.1 m) skyscraper in Chicago. At completion in 1973, it surpassed the World Trade Center in New York City to become the tallest building in the world, a title that it held for nearly 25 years; it was also the tallest building in the Western Hemisphere for 41 years, before the new One World Trade Center surpassed it in 2013. While it held the title of'Tallest Office Building' before 2013, it dropped the title of'Tallest Man-Made Construction' after only 3 decades. The CN Tower in Toronto, which functions as a communications tower, took over the title in 1976. The Willis Tower is considered a seminal accomplishment for engineer Fazlur Rahman Khan. It is currently the third-tallest construction in the USA and the Western hemisphere -- and the 23rd-tallest in the world. Annually, several million people visit its observation deck, the highest in the USA, which makes it one of Chicago's most popular tourist destinations. The arrangement was renamed in 2009 by the Willis Group as a term of its lease. As of April 2018, the building's largest tenant is United Airlines, which moved its corporate headquarters in 77 West Wacker Drive (then the United Building) in 2012, occupying around 20 flooring. Other major tenants include the building's namesake Willis Towers Watson and law firms Schiff Hardin and Seyfarth Shaw. Morgan Stanley plans to move into the construction in 2019 and become its fourth-largest tenant by 2020.

Source: Wikipedia