How Can Buildings Sway Without Braking (Video)

“Hi, my name is Greg Batista here to answer another question from the internet.

Bubblwatson asks: How can tall towers sway several feet in the wind and not crack?

High-rises are designed to move — and that flexibility keeps them standing. In South Florida, codes require towers to resist hurricane winds of up to 175 mph. Instead of making a building perfectly rigid, engineers design it to bend and sway. A 50-story tower might move a foot or two at the top during strong gusts. To control this, some towers use tuned mass dampers — giant counterweights — or specially shaped façades to reduce wind pressure. If skyscrapers didn’t sway, they’d crack under stress. This controlled motion is also designed to be slow enough that residents rarely feel it. For example, engineers generally limit acceleration so people don’t experience motion sickness. The next time you’re in a Miami high-rise during a storm and feel a gentle movement, that’s not failure — that’s engineering saving the building.

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Authoritative references: American Society of Civil Engineers (ASCE 7 – Minimum Design Loads for Buildings); FEMA Hurricane Design Guidelines.

The author, Greg Batista, PE, CGC, SI is the owner of G. Batista Engineering & Construction and is a nationally-recognized engineer and contractor with more than 35 years of experience and offices in Fort Lauderdale, Florida.