X-bracing

X-bracing is a structural engineering practice where the lateral load on a building is reduced by transferring the load into the exterior columns.

The John Hancock Tower has visible X-bracing on its exterior

X-bracing was used in the construction of the 1908 Singer Building, then the tallest building in the world.^[1]

Some skyscrapers by engineer Fazlur Khan, such as the 1969 John Hancock Center, have a distinctive X-bracing exterior, allowing for both higher performance from tall structures and the ability to open up the inside floorplan (and usable floor space) if the architect desires.^[2]