Even on a calm day, the tower sways around 6 inches (15 cm) in both directions. In comparison, the Empire State Building is designed to move only an inch and change even in gusts of up to 100 miles per hour (160 kilometers per hour).
The Willis Tower's ability to sway comes from its being built on top of an other building. Because it is not as solid ground-wise as the original Sears Tower, it has more space for the wind to move around inside the structure.
In addition, the Willis Tower uses magnetic levitation technology instead of traditional foundations. This means that there are no holes in the ground where water could pool or soil could be damaged.
Finally, the Willis Tower is made of steel and concrete, which are both strong materials. So the idea that it would collapse under its own weight due to overloading is false. However, since 1963, when the Sears Tower was first built, many buildings have been built that are taller than it is. So it may be possible for the Willis Tower to sway enough to damage itself over time.
In conclusion, the Willis Tower can sway considerably because it is built on top of another building.
According to Discovery, the Empire State Building in New York City, with a roof height of 1,250 feet, is intended to shift one inch in high winds. The Willis Tower in Chicago, with a roof height of 1,450 feet, has an average wobble of six inches off its "true center," yet is only supposed to shift three feet. The PGW Building in Philadelphia, with a roof height of 1,000 feet, exhibits strong vibrations when winds exceed 25 miles per hour.
These are just some of the many questions that have been raised about the stability of skyscrapers that have been built over the past 100 years or so. While the science of structural engineering has come a long way since the first skyscraper was built in 1913, new technologies have continued to be developed that have pushed the limits of what engineers can do.
In fact, research has shown that even very tall buildings may not be completely stable. A study conducted by researchers at MIT found that large buildings create their own windstorms that can cause damage or destruction if they reach critical levels. The study also revealed that larger is not always better when it comes to building stability. There appears to be some kind of limit beyond which further increases in size will not make buildings more stable but instead may result in sudden and catastrophic collapse.
In the wind, the tower sways around six to seven cm (2-3 inches). Its amplitude increases with the wind speed and it takes about three seconds for the tower to fully swing back and forth.
Its average daily wind speed is about 20 km/h (12 mph), but peaks at about 40 km/h (25 mph). The wind comes from all directions, but it is strongest at ground level on the leeward side of the building.
The tower is designed to sway in the wind without falling over. If it did fall over, it would be because there was no one up there to catch it.
It was built as a luxury hotel called the Grand Hotel de Paris, which opened its doors in 1889. It was later became a military hospital and then a science museum before being converted into a casino in 1995. Today, it is again used as a hotel.
You can visit the top of the tower for $18. They offer great views of Paris!
According to consulting engineers Rowan Williams Davies and Irwin, a 1,000-foot-tall structure may shift a few of inches on an average windy day. A 50-mile-per-hour wind blows in roughly once a year, pushing a tower of this size about half a foot. If the wind is blowing in the opposite direction, the tower will sway more than half a foot.
The highest building currently under construction is the Shanghai Tower (1,551 feet), which was completed in 2016. The previous record holder, the Petronas Towers (1,453 feet), were built in 1998.
The first skyscraper in America was the Singer Building (233 feet), built in 1892 near Chicago's central business district. The tallest building in America as of today is the Willis Tower (2,722 feet) in Chicago, which was completed in 1974.
An average-size house in San Francisco or New York City can be found in areas where there are no historical building standards. Houses in these cities can be any height, as long as they're not taller than what's permitted by local laws. For example, in New York City, houses can't be taller than 14 stories (or 29 meters).
In general, older urban centers have many low-rise buildings, while newer ones tend to have more high-rise buildings.