Week 9 - Yilei Jiang

       During the last week, we worked on building our three foot span bridge. we didn't change our design a lot because we thought that is the most serviceable way to build. The bridge we had based on the tension and suspension measured by "Method of Joints", also depended on the predicted price. We then tested the bridge using the parameters we will be using in the next week for the official testing of the bridges. It was able to hold decent amount of weight on the first try (about 25 lbs) so we decided to reduce its cost by removing some of the members connecting the two sides of the bridge. We tested it again but the amount of weight it held dropped significantly. So our plan for next week is to re-design the final bridge that can hold decent amount of weight without failing which we will be test during week 9. The only accomplishment this week was to test the same design with different number of members connecting the two sides of the bridge which gave us an idea on how much the connecting pieces contribute to its weight holding capacity.

      We have completed almost 9 weeks of the bridge module which has brought many new things into my perspective. I learned quite a few things from the bridge design tools such as WPBD, Knex, truss analysis etc. that we utilized throughout the term. One of techniques I learned in designing a bridge when our goal is to have the lowest cost is that you can analyze the compression and tension forces using WPBD and try to reach the ratio of 1. This can be done by using different variations throughout the bridge which include changing the member size, material and length etc. while reaching a ‘functioning’ bridge. However, in real world, the bridge would be undergoing a lot of external forces such as wind turbulence etc. The amount of force applied by the vehicles travelling over the bridge would also vary constantly. So to ensure the safety, the bridge would have to be designed such that it can withstand the maximum amount of force. Every members and gusset plates would have to be analyzed in great detail to ensure that they wouldn’t give up under the normally expected force. In this case, the safety would be the first priority, not the overall cost of the bridge.