Hello everybody my name is First Timer and I had to make a balsa wood bridge with theses specs: 40.5 cm long, 11-12 cm wide 13-25 cm high, must have a span of 26 cm, peek of the span must be at least 9 cm, and this bridge could weigh no more than 16 grams.
With all the rules in my head and absolutely no idea where to begin, I searched model bridge designs on google. It came up with Garrett’s Bridges and that’s where I started learning everything I know about bridges. First I looked at the trusses and came up with a K-Truss to modify and build a bridge from. My first design was relatively good although I never got around to testing it an engineer said it would hold 35 pounds (maximum). For a first bridge I thought this would be decent but I wanted to win the competition so I modified my K-Truss Arch, and came up with the bridge design pictured. It’s my first bridge so please give me a break. I know it’s rough and sloppy but it took me 3 hours to make.
This bridge weighed 19 grams, so I could not use this for my competition. I plan on reworking the design to make it under weight and hold a higher load. After testing this bridge using the Textbook method (it held 7 textbooks which each weighed 4.5 lbs), I calculated an efficiency at 752. It could be my way of finding efficiency but that stinks so now I have set the bar (very low) and I hope to get an efficiency of 1500 off of this project.