Hi!
I would like to design a bridge which will hold as much weight as possible. The bridge will be made of balsa wood, with wood 180 inches long, 1/8 inch wide and 1/8 inch thick, and with a piece of balsa wood that is 1/16 inches thick, 3 inches wide, and 12 inches long. The bridge must have a length of exactly 11 3/8 inches and a width of 1 5/8 inches, the length must be between 2 to 4 inches. Even if all of this wood is used to build the bridge, the bridge will not weigh more than 18 grams. The weight the bridge will hold will be focused on the center of the bridge. Please give input on what type of bridge I should design, and any other architectural hints you can give about designing and building this bridge. I am currently considering building an arch bridge with triangular structures n the length of the bridge.

Gor&co

An arch is not an efficient shape to resist a single point load; this is one reason arches went out of fashion in the nineteenth century when trains became the worst load for bridge design.
I think it would be unfair to your competitors just to tell you the best shape. However, if you ask again, I could offer some clues

As well as the shape of the bridge, a key issue is how your bridge is supported. Will it sit on a smooth surface (e.g. a table), so that its ends can slide; or will it be fixed to the surface e.g. with pins or sticky tape?
This makes a huge difference to the type of bridge that is best. Again, in real life, traditional arch bridges were generally located only where there were very firm foundations.