Schetley Weekly Blog - Week 7

Within the past week we got our first formal test of our bridge that we designed last week, and it actually held a lot of weight for it's shape and cost. The bridge held a weight of 39.1 pounds for only $133,000 worth of materials, resulting in a cost to weight ratio of 3.40 thousand dollars for every pound of sand held by the bridge, the lowest ratio in the class. I believe our bridge performed well because we had a feeling where the most weight and pressure would be on the bridge, so we put more members in those places to account for that. We also refrained from using grooved gusset plates. These gusset plates are weaker because as opposed to snapping in place like the other plates, one part simply slides into another, making these pieces (once again) weaker, but more expensive. In the next week I hope to learn about the ways of calculating stress and weight placed on the gussets and members in class, and I feel like that will be useful in attempting to improve our bridge.

The software we used before (West Point Bridge Design) gave us all the data we needed to analyze our bridge. It gave us compression and tension data automatically without having to turn on any special settings or run some ridiculous and tedious simulation to get the data, we just had to simply place a member, then run the general simulation to get the data. Unfortunately, using the K'Nex pieces don't readily give us any kind of data of how much weight is on each member when sand is loaded into the apparatus. That being said some of the data I would like to see for our design is firstly how much weight is on each member when sand is being loaded into the bucket. I know there is a way to calculate that number, but I'm not sure of how to do that yet, if it is possible at all. Another calculation I want to know is the breaking point of each gusset plate and I feel like that is something we are going to learn in class this week. It probably has something to do with the basic sum of forces concept we learned in Physics I, but I once again I suspect we will learn that in class this week. Finally, if this is even possible, I wonder if there is a way to see the amount of wear and tear is on some of the pieces from previous tests. While they don't break at the slightest amount of weight, these K'Nex pieces are still under a pretty decent amount of stress when these tests are administered. Each time a test is run the pieces get weaker and weaker, and if that has a significant impact on our bridge strength within a couple tests, I would like to know to be able to swap out those pieces.