Wind and gravity are the two dominant considerations in the design of tall buildings, and wind forces are among the most critical environmental factors. Taller buildings face stronger and more complicated wind forces than short ones. Every tall structure sways a little, and engineers watch sway because people on high floors can feel it. Engineers design aerodynamic shapes to calm wind: curved edges, large openings and tapered tops all help a tall building handle wind forces. Wind pushes on tall buildings, and they sway a little.

In the 1960s Fazlur Khan 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. The first tube building was the DeWitt-Chestnut Apartments in Chicago, finished in the 1960s, which used closely spaced exterior columns and open floors. Khan's tube design could cut the steel in a tower by nearly half, lower building costs and open up the inside by moving the structure to the outer wall.

The John Hancock Center in Chicago is a 100-story tower with a 344-meter trussed tube structure that topped out on May 6, 1968. Khan's tubes became standard: his work set structural systems that are fundamental to tall building design today.

The inside of a tower works with the outside. A building's core is a tube in the middle that holds the elevators, stairs and pipes. The core resists wind and earthquake forces because its concrete walls, called shear walls, are far stiffer than the outer frame. 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.

The Burj Khalifa shows how shape can calm the wind. Its plan is Y-shaped, with three wings that hold each other up around a six-sided center. The 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. Engineers test tall buildings with scale models in wind tunnels before building them, as they did for the Burj Khalifa.

A building has a foundation, the part that goes down into the ground and holds the building up. Where the ground near the surface is too weak, builders use deep foundations that carry the load down to stronger layers. Piles are long, slender columns of steel, concrete or sometimes timber that are put deep into the ground.

The ground can also be the problem. To keep the Leaning Tower of Pisa from leaning more, engineers laid lead weights on a concrete ring on its north side. To straighten it, they slowly removed soil from beneath its high north side through boreholes. They used an inclined drill, and the cavities it made closed gently under the weight of soil above. Cable stays could be tightened one at a time to stop any movement in an unwanted direction.

Earthquakes ask for a different answer. Shaking is the main cause of damage to buildings, and a building built straight on the ground moves with the shaking. A base isolator is a flexible bearing of rubber, steel and lead under a building, so the building moves less when the ground shakes. A gap around the building is needed so it can move during an earthquake.

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 stood on one corner of the site, so the tower floated above that corner, with its support columns at the middle of each side instead of 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.

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), and it swings the opposite way from the tower. During Typhoon Soudelor in August 2015, the damper swung 1 meter, and a bumper ring limits its swing to 1.5 meters. A tuned mass damper is a heavy moving weight tied to a building through springs or pistons, and it is commonly used to reduce vibrations in tall buildings.

Words to know

• outriggers: core-to-wall arms
• damper: motion calmer
• isolator: shake blocker
• setbacks: stepped-in sections