Wind pushes on tall buildings, and they sway a little. Every tall structure sways a little, and engineers watch sway because people on high floors can feel it. Tall, thin buildings sway more, because the larger the height-to-width ratio, the greater the swaying.

Taller buildings face stronger and more complicated wind forces than short ones. Wind has steady pressure and gusty, changing pressure; the changing part can make a tall building sway. Wind swirls around a tall building in an unstable way, creating alternating low-pressure areas called vortices.

Buildings with sharp corners or lopsided faces get uneven wind pressure that can twist them, so designers round corners and taper tops. Engineers test tall buildings with scale models in wind tunnels before building them, as they did for the Burj Khalifa. The Burj Khalifa's Y-shaped plan reduces wind forces, and when wind pushes on one side the opposite arm resists it. Its setbacks spiral upward, which reduces the tower's mass as it rises, and its shape changes as it rises to ease wind pressure.

A building's shape does not always show how it carries load. The Empire State Building's setbacks came from the 1916 Zoning Resolution, not from structural need, while the John Hancock Center's shape is the direct result of how it supports loads.

Fazlur Khan, who designed the tube systems that shaped modern skyscrapers, was born in 1929 in Dhaka, in what is now Bangladesh, and worked in the United States. His idea was to put the strong parts of a skyscraper in its outside walls so that the building acts like a hollow tube. In the 1960s he moved most beams and columns to the outside walls of a tower, creating a stiff tube that stood up to wind better than a normal frame.

Khan found the basic framed tube best for buildings of about 50 to 70 stories, so he developed other systems such as the trussed tube and the bundled tube. The Sears Tower in Chicago, now called the Willis Tower, was built as a bundle of nine tubes. Khan's tubes became standard: his work set structural systems that are fundamental to tall building design today.

A skyscraper core acts like a vertical cantilever fixed at its base, so the core must resist large bending forces from wind. Outriggers are horizontal members that tie the central core to the outer columns, so the whole width of the tower helps resist tipping from wind. A core of concrete or steel linked to the outer columns by outriggers makes tall, thin buildings possible without thick walls, by adding stiffness and cutting the bending stress in the core.

Before steel frames, tall buildings had thick heavy masonry walls, and that limited how high they could go. Because a steel frame carries the weight, the outer wall can have many windows, which stone walls could not.

Steel frames and elevators together made the first skyscraper possible, in Chicago in 1885. The Home Insurance Building in Chicago, 10 stories and 138 feet tall, is called the first skyscraper. The Home Insurance Company wanted a fireproof building, and masonry covered the metal frame to protect it from fire. Historians argue about the first skyscraper: the Home Insurance Building had an iron skeleton with steel floor beams and masonry still carrying part of the load, and Liverpool's Oriel Chambers (1864) already had an iron frame and glass curtain wall.

A tuned mass damper is a heavy weight that is not attached to the building it sits in; as the tower sways, the weight lags behind and pushes against dampers that turn the motion into heat.

Taipei 101 has a huge pendulum at the top that weighs 660 tonnes (as of November 2026). It swings the opposite way from the tower, which helps cancel out its swaying. During Typhoon Soudelor in August 2015, its damper swung 1 meter, and a bumper ring limits its swing to 1.5 meters.

The Citicorp Center in New York was a 59-story tower designed by architect Hugh Stubbins, with plans made in 1970. It was completed in 1977. A church stayed on one corner of its site, so the tower floated above that corner of the church. The tower's columns stood at the middle of each side, not at the corners. A light steel frame made the tower so efficient that it was light and more likely to sway in wind. At the top sat a tuned mass damper, a block of concrete weighing hundreds of tons that floated on oil to reduce sway. The story of Citicorp Center shows what engineers of tall buildings always keep in mind: wind and gravity are the two dominant considerations in the design of tall buildings, and wind forces are among the most critical environmental factors.

Words to know

• cantilever: fixed-end beam
• vortices: air swirls
• masonry: brick or stone
• outriggers: core-to-wall arms