Schetley Weekly Blog - Week 9

The past week involved our group designing our final 36-inch bridge for competition this coming week. We had to think of what was going to span that amount, keep our cost down, and still remain strong enough to hold a decent amount of weight. When we did our final design, we kept the same basic design as the 24-inch bridge except extended it to 36 inches, reinforced the middle, and added a structure to the top to help distribute the weight better. This was actually the hardest part of the conversion from a 24-inch span to a 36-inch span. Simply extending the bridge weakens it in the middle, so it requires extra support in the middle, and how to efficiently add that support was a bit challenging. When we tested the bridge in class, it held 35 pounds, and with a cost of $297,000, this gave us a ratio of 8.49, a ratio that I hope ends up being one of the better ratios in the class. Hopefully, when we test the bridge again in class this week, the bridge holds as much weight as it did in our test last class.

Now that the bridge design part of this course has come to an end, I have learned a few things about bridge design itself. First and foremost, I learned about the method of joints for calculating the forces on individual members. I had an idea that the calculations would be very similar to the Physics 101 concept of sum of forces, but I wasn't completely sure. The calculations for member tension and compression are actually a lot simpler than I thought they would be, requiring only basic knowledge of trigonometry. Another thing that was reinforced was the strength of triangles in structures. When initially playing around with the K'Nex, it noticed that squares were a bit weaker and gave more than triangles, so it makes sense that we utilized them in our bridge. Finally, another thing I noticed was that more gusset plates and members doesn't necessarily translate to a better bridge overall. The thing that makes bridges more efficient is the placement of the members and gusset plates to distribute the force on the bridge better, not overloading on one point to make it strong when it might not need to be anyway, as not that much force is applied at that point.