Like trees, tall buildings must be able to sway in the wind. If they didn't, the wind would literally push them over. Still, you don't want to let the building sway too much. The motion might make people who work inside sick! The concrete in the Petronas Towers makes the frame stiff enough to minimize swaying. And the reinforcing steel helps the building resist the wind's bending force. But the building still moves in a strong wind. Hungspruke won't say how much. But, in the United States, tall buildings are allowed to sway 1/500th of their height. That means that if the Petronas Towers were built here, the tops of the buildings could sway about one full meter (3 feet) in each direction!