Tallbridgeguy mentioned this before me, but I had planned to feature it here anyway.
ArchDaily has a very interesting post with text and images of the American architect Paolo Soleri's bridge designs. Only one of his bridges has ever been built, a horrible footbridge at Scottsdale, and judging from the many other examples showcased, that may be no bad thing.
Sometimes, this lack of embedment within a discipline can result in a design which shatters hidebound preconception and reminds us quite how trapped we often are within the habits of tradition. Many of Soleri's designs look lovely on paper, science fiction fantasies of what a bridge might be unconstrained by gravity or cost.
I'm reminded that there are many histories of structural engineering yet to be written. Those few that do exist are partial and often hamstrung by linguistic limitations: the likes of Musmeci are rarely featured in books on bridge engineering. Beyond the bridge world and considering wider structural engineering, the English-speaking world often seems largely ignorant and unappreciative of great designers like Heinz Hossdorf, Ulrich Müther or Eladio Dieste.
If a history of the unknown would be welcome, a history of the unbuilt and unbuildable would be equally so, and Soleri's bridges would certainly merit inclusion.