Photo by: Shutterstock


This World-Famous Chicago Skyscraper Can Sway Up to 3 Feet in the Wind

By: Reuben Westmaas

Constructing this tower was a major feat of engineering.

August 01, 2019

From the day it opened in 1973 until it was eclipsed by Malaysia's Petronas Towers in 1998, the Willis Tower (Maiden name: Sears Tower) was the tallest building in the world. Constructing it was a major feat of engineering, because once you get a building that far off the ground, the wind can really start to mess with its structural integrity. And Chicago isn't called the Windy City for nothing.

Swaying In the Sky

Picture a piece of uncooked spaghetti inserted vertically into the ground so that it stands straight up, with a couple of inches of "foundation" underneath. Imagine giving the spaghetti a little slap. Most likely, it'll break. Now, picture the same piece of spaghetti, cooked and dangling from your fingertips. This time, you can slap the spaghetti all you want, but it will just flop around, never break.

The lesson? You gotta bend if you don't want to break. That's one of the principles behind the design of the Willis Tower. We've already told you about how the design broke engineering barriers, but there's one feature of the structure that we left out. The Willis Tower is designed to withstand the heavy winds coming off Lake Michigan, and that means that if you're standing at the top, you can feel it sway up to 3 feet (about 1 meter) in both directions before you should start to feel worried. Even on a calm day, the tower generally sways about 6 inches (15 centimeters) in both directions. For comparison, the Empire State Building is supposed to move about an inch and change even in the face of 100 mile-per-hour (160 kilometer-per-hour) winds.

But forget about being worried — you probably wouldn't even notice. Just search for videos of the Willis Tower swaying. You'll mostly find the interiors of offices, where hapless workers suddenly realize they're moving back and forth because their blinds are swaying and their water is moving on its own.

A New Way to Build

The tower's height and flexibility are all thanks to structural engineer Fazlur Rahman Khan's innovative tube design, which cut way back on the necessary material and made the entire building much lighter than anything of comparable size. Khan built the structure as a hollow steel tube instead of a solid column, an innovation that would guide skyscraper architecture for years afterward.

Winds aren't the only reason to build a hollow building. Architects all over the world have taken Khan's flexible principles to heart, allowing their skyscrapers to shift and sway and keep on standing even during severe earthquakes. In fact, many experts even think that modern skyscrapers could be the safest place to be during a major quake. It all just goes to show how a little outside-the-box thinking allows great things to happen.

This article first appeared on

Next Up

How to Build the 7 Different Campfires You'll Need This Summer

Learn how to master the flame with one of these fires.

Every Year, Thousands of Glass Orbs Are Hidden on This Oregon Beach

When you think of treasure hunters, it's typically Pirates of the Caribbean and Indiana Jones that come to mind. But modern-day treasure hunters do exist. In the coastal town of Lincoln City, Oregon, beachcombers flock to the sand in hopes of finding one very specific treasure: glass fishing floats.

This Tanzanian Lake is a Vision in Red- And You Can Visit

This picturesque lake in northern Tanzania is harsh enough to burn anything that touches it. Unless, of course, you're one of the select few species adapted to thrive in it.

Is This Mars-like Desert the World’s Best Spot to Watch the Stars?

Forget Chile’s Atacama Desert, or Hawaii’s Mauna Kea. A petrified forest in Colombia is where you want to go for the best stargazing on the planet.

This Little-Known Hiking Path Explores One of the Deepest Gorges in the World

A trek through China's Tiger Leaping Gorge is a journey into the country's most ethnically diverse region, where beauty and fear hang intoxicatingly in the air.

Meet the First 6 Awardees of The Explorers Club Discovery Expedition Grant Program

Today, The Explorers Club, a non-profit world leader in exploration, and Discovery Channel announced the first class of awardees to receive approximately a quarter of a million dollars collectively to fund their expeditions. Let’s meet The Explorers Club Discovery Grant awardees.

Andros, Bahamas Has More Than 200 "Blue Holes" — And They're Mostly Unexplored

Learn about the more than 200 underwater cave systems that make Andros a scuba diving mecca at

New Year, New Adventures: What the World has to Offer

With a new year comes new opportunities, and there’s no time like the present to start learning more about parts of the world you’ve never dreamed of before. Please review and follow all state and local guidelines while traveling. Updated December 17, 2021