Building a bridge was trial and error. This is not something you can do over night. When building the bridge I have to focus on the structure, details and actually putting it together right.
The structure of my frame I made with the thicker wood, but it should have been placed different. Looking at the data from testing other bridges, the bridges who double bonded their wood at the bottom last a lot longer that the one piece of wood. My bridge failed when one of the connecter beams became unattached to the beam. Also with the structure you have to be very careful how you glue your beams together and making sure they are cut perfectly. The structure will be messed up if the measurements are not exact and precise. To make the structure stronger you have to make sure each sides of your bridge are equal. I found when building my bridge the sides were uneven on the structure causing more weight onto one side of the bridge than the other. If I would have made the sides equal and checked by putting them next to each other, my bridge would have been more evenly distributed on weight. Also when building your bridge I learned that you need to put cross beams across the top because eventually the bridge will start to twist and that prevents it. Next on the structure of the bridge to keep more of the pressure from breaking the bridge make more of the beams straight up and down and have supporting beams. I think for the next structure of my bridge I will keep it the same but make slight modifications. I will double beam my bottom frame and make the height of my bridge smaller. I think that the smaller and more compact and solid something is the harder it would be for something to break it.
Details of the bridge go down to the glue you use, how exact you measure, your bridge plan, and amount of glue you use. When making my bridge this time I thought that the more glue you use the more stable it would be,...