For the tallest buildings in the world, gravity is not the hardest problem. Wind is. A skyscraper is essentially a very tall cantilever sticking out of the ground, and it must resist powerful sideways forces every day of its life.
Buildings are meant to sway
Tall towers are designed to move slightly in strong winds. The top of a very tall building can drift by a noticeable amount during a storm. The structure is perfectly safe, but if the motion is too fast, occupants on upper floors can feel uncomfortable or even seasick.
Confusing the wind
As wind flows around a building, it sheds swirling vortices from alternating sides, which can make the tower oscillate. Engineers reduce this by changing the shape: tapering the tower, twisting it as it rises, rounding or notching the corners, or adding openings near the top. These shapes break up the vortices so they do not build a rhythm.
Tuned mass dampers
Some towers contain a huge weight, often a steel ball or a block of concrete, suspended near the top. When the building sways one way, the damper lags behind and moves the other way, absorbing energy and reducing the motion. A few of these dampers are even displayed to visitors as attractions.
Testing before building
Before construction begins, scale models of the tower and its surrounding neighbourhood are tested in wind tunnels. Nearby buildings can funnel and accelerate wind, so the whole urban context matters, not just the tower itself.