Visionary artists often come up with bridge designs to illustrate their ideas and/or philosophies. Sometimes their bridges are built during their lifetimes, or after they're gone, but usually they remain tantalizing ideas that only exist in books. The architect Paolo Soleri
believed that humans were migratory creatures and wanted to design high density cities (to minimize their impact on the environment) where they could stop between their travels. He built Arcosanti in the Sonoran Desert to test his ideas. His 'Beast' bridge (shown above) was designed to help carry his imagined tribal societies on their journey. It's a continuous concrete structure with the superstructure folded upward at midspan and folded downward at the supports. It actually looks a lot like Frank Lloyd Wright's 'Butterfly' bridge, which isn't surprising since they worked together at Taliesen in the 1940s. Most likely, they influenced each others designs. This bridge was in 'The Architecture of Bridges
," a book that The Happy Pontist rated highly in a blog last week.
Buckminster Fuller developed a philosophy of tensegrity with structures composed of prestressed tension cables (on the outside) and isolated compression struts (in the middle). These truss-like structures are composed of elements loaded axially without any bending, shear, or torsion. Although a tensegrity bridge was never built in Buckminster Fuller's lifetime, the Kurilpa Bridge in Brisbane, Australia is said to have been designed (by Cox Rayner Architects and Ove Arup Engineers) using tensegrity principles.
Frank Gehry's structures are easily identifiable because of their undulating stainless steel surfaces. The BP (Millennium Park) Pedestrian Bridge in Chicago is a long steel box girder bridge (designed by SOM) that supports Frank Gehry's design. To help in the design and construction of his structures, Gehry's uses Grasshopper programming software, which is good at creating intricately folded surfaces. If you are a famous architect, most cities are happy to own your bridge (although even Gehry had to go through many iterations before his design was finally accepted).