Just beautiful. The ability of 3D printing, not just to automate a traditional construction process, but to enable radically different designs is going to create a whole new style of architecture. Many of the old constraints don't apply and the human imagination is given a freer reign. There's still that pesky law of gravity that must be respected, but otherwise this offers a remarkable freedom.
An interesting thing that's happening alongside 3d printing is the emergence of visual programming languages specialized for geometry, the most popular being Grasshopper.
If you do a google image search for 'grasshopper geometry' or 'grasshopper architecture', you'll see a lot of buildings designed with grasshopper, including many which have been constructed.
There are other interesting things going on, like automated construction with robots or laser cutters. For example, theverymany builds massive organic structures out of laser-cut metal pieces, and the living (new york) did some interesting things with robotic placement of bricks.
New design tools specialized for automated manufacturing methods.
Check out the grasshopper primer. I haven't read it in a while but I used to claim it was written by programmers for non-programmers. Great getting-started guide. Rhino probably still has a demo available, too. Dynamobim.org is another option if you want to try visual programming without an investment. Dynamo is mostly visible for it's connections to other software, e.g., Revit, but can stand alone as in sandbox mode.
I suspect that the time and cost involved in non-trivial structures will limit any real experimentation with non-traditional designs. It might be trivial to throw away a kilogram of plastic on a failed prototype, but the same doesn't extrapolate up to experiments with bridges.
But that's just the thing, you aren't limited so much by time and cost. The time is proportional to the size of what you're printing, and the cost to the amount of materials and time involved. None of which says much about what the design must look like. You design it on the computer, look at in 3D on the screen as much as you like, and print a scaled model, if you must.
You don't need to print up a full-scale prototype anymore than you would do that with a traditional design and construction technique.
I assume the printing of this bridge didn't go smoothly in one pass, but one advantage of larger-scale metal printing is if something goes wrong you can grind off the failure, reposition the print head (extruder? welder???), and try again.
I suppose you could do that with FDM as well, but the precision required for smaller prints is much greater.
