Prototypes

 

http://en.academic.ru/pictures/enwiki/72/Hell_Gate_Bridge_by_Dave_Frieder.jpg
http://www.minimalisti.com/wp-content/uploads/2012/06/Alamillo-Bridge-modern-architecture.jpg
b1.png
b2.png
http://www.westernwoodstructures.com/wp-content/uploads/2012/12/_bowstring_truss_timber_bridge.jpg
b3.png