I wasted half a day playing with West Point Bridge Designer 2011, a free game released as part of a contest each year by West Point. I have been unable to get to the contest web page for more details that what is incorporated into the game software. So far as I can tell, the contest is for middle school and high school students to design a bridge that meets load limitation requirements for the lowest possible cost. The cost model is simple, but tricky, as it includes costs for both the weight of the different sorts of steels and the number of different dimensions of tubes that are needed, as well as the number of connectors. The costs of excavation, fill, and abutments are also estimated.
Each year West Point releases a new version of the software with a new bridge-design challenge, and with various upgrades to the software. Older versions of the software ran only on Windows, but the 2011 version runs on Mac OS X as well, and there is some talk in the documentation that they might support Linux in future (if there is demand).
Sample designs are given, but they are ridiculously overbuilt—much more expensive than even my first try at building a bridge, when I didn’t even know the cost model, but was just building a bridge that looked pretty and making the beams thicker until it held up. I suppose they were included to make kids feel good about their design skills fairly quickly.
The software gives templates for some standard trusses (Howe, Warren, and Pratt), which helps particularly in creating arch bridges. I’ve not played around much with other sorts of bridges, but I managed to make several different arch bridges for about $167k (with the symmetric load—it took me about $170k for the asymmetric load). For all of them, I modified a Pratt truss, as it seemed to be the cheapest for the needed strength. Tweaking got me something between a Pratt and a Warren truss.
In the animation, the bridges flex rather alarmingly, because the vertical deflection is exaggerated, unless you turn that feature off in the animation controls.