How SFO earthquake-proofed a terminal using steel balls

How it works: The ball would rest in a concave base connected to the ground and serve as a friction pendulum seismic isolator by allowing the terminal's 267 columns to sway back and forth within the base, separate from the motion of the ground in the case of an earthquake.

• Once the earthquake was over, the columns would return to the center of their bases due to gravity.
• The innovative design meant the terminal structure could, in theory, withstand a magnitude 8.0 earthquake.

Zoom in: The concave surface provides a three-second isolated period, which reduces the earthquake force's "demands on the building" by 70%, according to a 1999 article published in the American Institute of Steel Construction's journal Modern Steel Construction.

• "The bearings are designed to accommodate 508mm (20") of lateral displacement and dissipate energy from peak earthquake ground motions."

The big picture: The construction for the terminal, which broke ground in October 1995, was the largest public works project in California at the time.

• It opened on Dec. 10, 2000, and has since served over 200 million passengers from around the world.