My sister Quinn, and I built this bridge for a competition at her school. I made a similar one four or five years ago for the same competition. It wasn't this nice, though. It also had different requirements for design.
She's required to break it since we can't be bothered to make another. I think it'll hold lots of weight though; at least 80 lbs.
The loading point (above).
Almost all the joints are lap joints of some type. There are very few butt-joints. We notched them using a scalpel, needle files, and a jeweler's saw. It's hard to tell all the work that went into it, because you can't tell a lap joint from a butt joint by looking at it from only one side.
Above is a picture of the loading surface, as seen from above. The 3/8" rods go though the bottom of the bridge to connect to the weights on the left and right of the 'canoe.' The loading plate only goes on one side, not both at once.