"This is a high-end, upscale condo building," Johansson said. Motion sickness high above San Francisco is not acceptable.
The solution was to build a 50,000-gallon water tank at the top and to equip the tank with devices called tuned liquid dampers, which are screens that move the water and allow the liquid to move in the opposite direction of any building movement, a bit like water sloshing in a bathtub.
The effect of so much water - 50,000 gallons weighs 416,500 pounds - prevents the building from swaying. "It's there to settle the building, " Johansson said.