Curtain wall systems cover the outer walls of buildings but are not structural. They keep out the weather. Since they are not structural, they can save construction costs. Curtain wall systems can incorporate curved steel to create curved curtain walls.
For example, the Sprint Arena in Kansas City, Missouri, has an elaborate curtain wall system that curves in both plan and elevation to create a structure that looks a little like a crystal bowl. Curved 16 inch diameter pipe runs both vertically and horizontally.
The Kimmel Center in Philadelphia, Pennsylvania, has a half-barrel vault covering comprised of glass and 5 inch square tubing curved 45 degrees off axis. 
And Central Washington University Music Education Building in Ellensburg, Washington has a curved curtain wall made of steel tubing curved in plan view.
All of these structures use curved curtain wall not merely to keep out the weather but to create strikingly beautiful structures.
