Growing up in the bay area, I was always one drive away from large buildings in that dominated the San Francisco skyline. When I first learned that skyscrapers are designed to move in the wind, I was surprised. I was under the assumption that buildings had to stay rigid to maintain strength against natural forces. This question led me to conduct research¹ on why structural engineers design buildings to be flexible and how they do this while maintaining its strength.

Buildings are constantly bombarded with strong winds. Taller buildings especially experience an extremely high force of wind pushing on them because of the higher surface area they have compared to other buildings. Structural engineers had to come up with a design that would make sure buildings do not topple under the forces of winds. They discovered that allowing the building to sway a little allowed for the building to withstand more wind without falling. Flexibility of the building allows for the energy to dissipate evenly across the building, rather than the building absorbing all the energy at once.

Engineers used several tactics to allow for swaying without compromising the building’s integrity, such as strong steel cores, tuned mass dampers, and aerodynamic shaping. Steel cores built into the center of the building act as a spine, keeping the building from contorting and breaking but allowing the outer edges of the building to flex. Some buildings have structures called tuned mass dampers², which act as a counterbalancing weight. When the building sways in one direction, the dampers move in the opposite direction, allowing for the building to regain its vertical position after swaying. Aerodynamic shaping is also integrated into most tall buildings by minimizing the flat surface area that could catch wind.

Swaying is essential for the design of skyscrapers. Without flexibility of buildings, there would need to be significantly more material to keep the building from falling over, making them much more expensive and heavier. Allowing for movements while keeping those movements controlled lets buildings be safe without needing extremely high resources and costs.

Reading about skyscrapers and how they are built to be flexible helped me understand how strength can be achieved in many different ways. Good structural design is not defined by rigid structures that resist all movement. Incorporating flexibility into buildings actually improves stability and safety.

1. https://theskydeck.com/do-skyscrapers-sway/ ↩︎
2. Video on tuned mass dampers: https://www.youtube.com/watch?v=f1U4SAgy60c ↩︎