Week 7: Bridge Results

This past week in lab we got to test the 2 feet bridges we built. Our bridge had a fairly simple design, following a concept I learned from the WPBD; Simple is better. It was a basic X truss across the sides that included an under truss. The idea behind the under truss was that It would help disperse the weight to the outside members. The under truss worked exactly as I expected. Our bridge broke right where the under truss ended. Our bridge only held 20 lbs. I was disappointed with our bridges performance but I was proud that it did not cost an extraneous amount, only $320,000. Another thing I noticed was that many of the bridges experienced the same failures. The Knex gussets are the weakest point on the bridge and through much testing I noticed that the arrangement of the gussets on the bridge mattered and could affect the failure point by several pounds. All the gussets alternated sides starting from the center covering the weaker point

I truly liked our final design but I knew deep down that it just wasn’t going to hold a lot of weight. I spent many hours testing a building bridges but it was hard to do without knowing where the compression and tension forces were and their magnitude. When working with WPBD one could look at the numbers given in the tension and compression columns and deduce where changes could be made to make the bridge strong and where beams were not being utilized at all.  This information can easily be found using trig. I know a main factor in tension and compression calculations are the angle in the triangles. So I would assume in the calculations the angles would be essential. Other than that I am not completely sure and can’t wait to learn Wednesday!

Melissa Mercado