Despite how it may sound, architectural engineers are not Don Quixote. Wind can be one of the largest enemies when designing the framework of a skyscraper, considering that they often reach hundreds of feet into the air. In Florida, these buildings must be built in accordance with the Florida building code, which specifies that they need to be able to withstand winds of nearly 200 miles per hour in areas like Miami-Dade county. While we don’t see 200-mile per hour winds every day, engineering for the worst conditions ensures that the building will be more than sufficient to stand up to everyday wind gusts, and will last for many years to come.
Vortex Shedding
Vortex Shedding is the natural enemy of the structural engineer. When wind passes around a tall, thin object (such as a skyscraper) it passes to the other side after splitting around the building. Where the wind meets on the other side it can cause a large amount of turbulence and displacement of pressure, meaning that the building will tend to move towards the low-pressure area. Even worse, this turbulence can create oscillation within the building, causing it to vibrate or shake. Interestingly, this is the same phenomenon used to make airplanes fly – if you ever take a look at an airplane wing, the arched surface of the top of the wing displaces more air than the flat bottom side, creating lower pressure on the top of the wing than the bottom and creating lift.
Turning a Problem Into an Opportunity
We don’t want our buildings to operate like airplanes, and that’s why they’re designed to impede the movement of air around the building. You’ve likely already seen many of the measures taken to strengthen skyscrapers against the wind, and considered them to be merely aesthetic choices. The Burj Khalifa for example utilizes several features that reduce vortex shedding, such as its taper towards the top of the building which does not allow vortexes to form by differentiating where the wind is displaced, or concave sides that do not allow wind to wrap around the sides of the building.
Engineers may also make use of dampers, which are massive weights suspended inside the building that essentially act as counterweights to the movement of the building. These dampers can weigh several hundreds of tons and can be made of either metal or giant tanks of water which moves in the opposite direction of the building sway to reduce the amount of movement felt on higher floors.
Wind gusts are just one of the many challenges that structural engineers face when they design structures, and the team at DDA Engineers, P.A. has the skills necessary to tackle any other challenges your next building project poses. Give us a call at (305) 666-0711 to see what we can do for you.
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