In this project, I was tasked to build a truss out of balsa wood and wood glue. The goal was to create a truss to be tested, and I sketched out several possible designs before choosing one often called a K-truss. Once I made a statically determinate design, I solved the truss using a computer program called MD Solids, assuming 100 lbs of force was being evenly applied to the top. Then I constructed the truss by measuring out each stick to the predetermined lengths I had decided on in MD Solids, and gluing them together. It is 8 inches tall and 14 inches wide at the widest point, the bottom. The truss is two dimensional, and is made of less than 10 whole sticks of wood. I added paper gussets to the design after the glue had dried to help keep it together and support as much weight and possible. I predicted that the two outermost diagonal beams in the twin triangles will break first because they have the highest force being applied to them as calculated by MD Solids. Below are pictures of the truss once built, the computer image with solved values from the computer program MD Solids, and the page I used to document this project in my engineering notebook.
Testing Actual Strength of Bridge
The bridge did not break in the place I predicted it would. It broke on the middle beam instead of the two sides, where I calculated the most force would be. I believe this was because there was still a fair amount of force predicted to be on the middle beam, and the machine tester ended up twisting most people's bridges instead of just applying a consistent force, and it didn't seem like the force was equally distributed to all of the members. If the testing machine worked more like it was supposed to, I believe my calculations would have been correct.