When you see a concrete building or a statue made of stone, the first thing that will most likely come to your mind is the sturdy and firm nature of it all. In addition to the aesthetics and the general grandeur of concrete buildings, the height adds another layer of appeal. But do you know that the taller a building is, the more likely it gets swayed by the wind?
Skyscrapers sway in the wind because their height makes them more susceptible. As the strong wind moves around the building, the areas of less pressure on the skyscraper create suction forces that pull at the building and cause it to sway.
The rest of this article will explain a few topics related to this question in great detail, how wind affects skyscrapers, and how these skyscrapers are made to withstand the swaying effect of the wind. So let’s get started.
How Does Wind Affect Skyscrapers?
Wind affects skyscrapers through vortex shedding. This happens when strong winds blow past a high-rise building creating a low-pressure area behind it which in turn causes the structure to vibrate faintly.
Engineers have come up with different methods of overcoming this vortex effect by tweaking the buildings’ designs. Some of these solutions may look aesthetically relevant to the design of the building, but in truth, they are there to reduce the effects of wind action.
Skyscrapers with twisted sides like the Shanghai Tower or tapered pointy tips like the Burj Khalifa all have these distinct features to mitigate the swaying effects of wind.
Today, skyscrapers are constructed taller and higher than ever before, and the farther they get away from the ground, the more susceptible they are to the effects of wind. These buildings can be so tall that they get pushed from side to side by high winds, so much so that they move a few inches to several feet from their center.
The Burj Khalifa stands at 828 m (2716.54’) and sways about 4- 5’ (1.21-1.52 m) due to wind disturbance. Due to how well these buildings are constructed, the sway action caused by high winds can either be damped or manipulated so that residents on these top floors don’t feel the building move.
There have been reports of skyscrapers making creaking sounds at night or during typhoon seasons, all caused by wind.
Residents who live on the top floors of some poorly constructed skyscrapers report experiencing the swaying of the building as it moves from side to side in the wind. The accompanying feeling of nausea is one of the many not-so-fun side effects of this swaying action.
How Concrete and Metal Sway
To understand this, let’s look at how height and length affect the sturdy nature of metals and concrete. A 5” (12.7 cm) metal rod is as firm and unshakable as any metal rod can be, and the same can be said for a concrete pole of the same height and size.
But increase that metal rod to 20” (50.8 cm), and you will begin to notice some attributes like vibrations when the rod is hit on another metal or concrete. Increase that same metal rod to 50” (127 cm), and you would detect more vibrations as you hit the rod, but this time the vibrations last longer and is more noticeable.
Apart from vibrations, if you place one end of the rod on the ground with the other in the air, you would notice it sways at the slightest touch close to the very top. This movement and vibration with an increase in height are the same for concrete buildings, but these buildings are not in inches.
Instead, they are hundreds of meters high.
So the question remains, how do construction engineers make buildings overcome this unavoidable swaying of skyscrapers?
How Skyscrapers Are Made To Withstand This Swaying
To ensure residents of the top floors don’t experience nausea-induced headaches each time the wind blows, architects and engineers have developed some techniques to help reduce the effects of high winds.
One technique is by installing dampers into these skyscrapers to counteract the swaying movement caused by wind.
These dampers are commonly called tuned mass dampers, and they usually consist of an iron ball that weighs about 400 to 700 tons (362,874 to 635,029 kg) depending on the height and thickness of the skyscraper. This damper is usually attached to the middle of the building dangling by springs.
Another type of damper used is the Slosh tank or Slosh damper, which uses tons of water in a specialized tank instead of metal.
How do these dampers stop the effects of wind on skyscrapers?
Well, It will interest you to know that these dampers don’t stop the buildings from swaying, as that would be almost impossible. In truth, they only reduce the swaying effects that would otherwise have been felt.
When a skyscraper is hit by powerful winds and begins to sway in response, these preinstalled dampers, which are either suspended steel balls or tanks of water, reduce the effect. The physics at work here is, the dampers move in the opposite direction to the swaying building and are only a shorter distance compared to the building itself.
This counteracting movement helps reduce the total height the building would have moved and effectively pulls it back to its original position at the center.
It is important to note that these dampers do not contribute to the structural stability of the skyscraper as it is already built and designed to experience and withstand the effects of strong winds. These dampers only serve to reduce the overall effects felt by residents and occupants of these top floors by steadying the building as best they can.
You might be wondering why you’ve never seen any of these dampers when there are so many skyscrapers in your city? Well, believe it or not, a giant metal bell in the middle of an expensive building whose primary purpose is to prevent it from swaying too far isn’t much of a confidence booster.
People like to think their high-rise skyscrapers are 100% sturdy, which is practically impossible in engineering terms, and seeing a camper would only reduce confidence. This is why most architects have dampers hidden from public view inside the upper floors of the building.
The only known exception to the rule is Taipei 101, one of the tallest buildings globally, which has its dam open to the public as a tourist attraction to be viewed by the public.
Conclusion
In conclusion, as sturdy as skyscrapers appear to be, it has been proven that they sway in the wind due to several factors. However, the good news is that engineers and architects have devised different methods of ensuring that these gigantic structures remain safe and habitable.
Sources
- Gizmodo: The Tallest Apartment Building in America Sways 4 to 5 Feet
- Business Insider: The Real Reason Behind Skyscrapers’ Pointy Tips and Gaping Holes
- WSP: Engineering 432 Park Avenue
- Medium: What Keeps Skyscrapers From Moving in the Wind?
- Inquiries Journal: Confusing The Wind: The Burj Khalifa, Mother Nature, and the Modern Skyscraper
- The B1M: How Tall Buildings Tame the Wind
- Wikipedia: Vortex Shedding
- Britannica: Burj Khalifa | Height, Architect, Top Floor, & Facts
- Wikipedia: Tuned Mass Damper
- Wikipedia: Taipei 101
