Do skyscrapers sway in the wind?
Yes. Every tall building moves when the wind blows, and its engineers knew exactly how far. Movement is the plan, not a fault in it.
The short answer
A skyscraper leans away from the wind, comes back, and leans again. The cycle takes a few seconds, and the top traces a slow oval instead of a clean back-and-forth line, because wind pushes on one face and pulls on the others at once. The structure is built to do this.
How much does a skyscraper sway?
The usual design target is a deflection at the top of about one five-hundredth of the height. For the 828 m Burj Khalifa that is roughly 1.66 m, and for the 632 mShanghai Tower about 1.26 m. The number is not a safety margin. It is where people inside start to notice, and comfort runs out long before strength does.
Older buildings move much less. The owners of the 381 mEmpire State Building put its deflection at 1.48 inches in a 110 mph wind, under four centimeters on 102 floors, because its riveted frame and masonry infill are stiffer than anything built since the 1960s. Toronto's CN Tower has been measured at 1.07 m in its antenna mast in a 120 km/h wind.
The wind at the top is why the top moves most. Ground friction slows air near the surface, so speed climbs with altitude: a gale reading 60 mph at a weather station can pass 100 mph at 500 m. Pressure rises with the square of speed, which puts the load on the upper third of a supertall in a different class from street level.
Why a stiff building would be worse
A rigid tower sends gust energy straight down into its columns, and every gust arrives as a shock. A flexible tower absorbs that energy by deflecting and returns it on the way back, the way a fishing rod handles a strike. Forces in the members stay lower and the steel stays affordable. Chicago engineers worked this out with the framed tube on the Willis Tower, whose whole perimeter acts as one hollow beam cantilevered out of the ground.
Wind also refuses to stay attached to a tall box. It breaks away in alternating eddies, first from one face and then the other, and each eddy tugs the building crosswise. That is vortex shedding, and when its rhythm matches the building's natural period the tugs add up. Crosswind motion is often larger than the along-wind push.
Shaping the tower so the wind cannot get a grip
The cheapest fix is geometry. The Burj Khalifa steps inward 27 times on the way up, so the cross section changes every few floors and no single vortex rhythm can establish itself. The Shanghai Tower twists about 120 degrees from base to crown, which cut its wind load by roughly a fifth. The Shanghai World Financial Center carries a trapezoid aperture through its crown so crosswind pressure equalizes instead of building on one face. Every supertall now goes through a boundary-layer wind tunnel, and its verdict on setbacks, chamfers and openings reaches the architect as a change to the silhouette.
Tuned mass dampers and liquid dampers
Where shape alone leaves too much motion, engineers add mass that fights the building's rhythm. A tuned mass damper is a weight near the top, tuned to the natural period so it lags behind the structure and pushes against the motion. Taipei 101 has the best-known one: a 660-tonne steel sphere on eight cables, visible between the 88th and 92nd floors, which takes up to 40 percent out of the sway.
A tuned liquid damper does the same work with water. A tank at the top is sized so its sloshing period matches the building's, and the water piles up on the trailing side as the tower leans. Comcast Center in Philadelphia uses a 1,300-ton tank, and water is cheaper than steel.
Can you feel it?
Sometimes, and what you feel is not the distance. The human balance system responds to acceleration, so a slow half-meter drift goes unnoticed while a sharp few centimeters at the wrong frequency makes people queasy. That is why a design brief writes its comfort criterion in milli-g, and why two towers that move the same distance feel different.
The tells are indirect. Water swings in a toilet bowl, a hanging lamp drifts off plumb, a door creeps shut, partitions creak. None of it means trouble: occupants notice motion well before it reaches anything a structural engineer would call significant.
Elevators stop, and why that is reassuring
Elevator service in the top zones is sometimes suspended in high wind. The reason is the hoist ropes and travel cables, which run hundreds of meters down a shaft and can be set swinging by the building's own movement until they slap the walls. Sway sensors slow or park the cars automatically. That is a decision about ride quality and equipment wear, not danger to the building.
At what height does it start?
There is no threshold floor. A two-story house deflects in a storm too, by a fraction of a millimeter nobody will perceive. Movement becomes a design concern around 150 m, and slenderness decides it more than height does: New York's pencil towers on 57th Street pass height-to-width ratios of 20 to 1 and need dampers a squat building would not.
All of it starts in the 1880s Chicago office block, where an iron frame first took the load off the walls. The history of the day covers how that frame arrived, Louis Sullivan what to do with it, and the twelve buildings put the braced tubes next to the setback towers.