As you can see i took your advice on using a t-shape for the bottom cord. Which was really cool, cause it gave me a lip for my cross members. I did sandwich the top cord. I glued lap joints and gusset plates, plus pinned the legs to the cords with small wire nails that I cut to size. The model is 19″ long x 2 1/4″ high. The road way deck is 3″ wide. I didn’t weigh it yet. It spans 18″ with 1/2″ end bearings.
Thanks again for all the great info and advice. This project only has to hold 10 lbs. extra credit if it has a 25% or less load capacity percentage. The record in the class on this project is 80 lbs… I’m planning to donate 1$ for every 10 lbs this bridge holds to your web site.