In our week 6 lab we load tested our 2' span bridges. Before the test we made a few minor modifications that helped with our cost. In the load test, our bridge exceeded our expectations. It was able to hold 48 pounds of sand, including the bucket, before ultimately failing. The bridge failed at one of the gusset plates near the middle of the bridge. We had actually predicted that it would fail in this area, so it was not a surprise to us. We plan to keep this in mind in our next design.
For the 2nd bridge design, we must fabricate a 3' span bridge that is hollow in the middle so a roadway can be placed through it. This will pose a little more of a challenge for us, because we will not be able to add cross bracing in the middle of the bridge, something that greatly increases the rigidness of the structure.
One thing that I believe would greatly help in the Knex design process would be the ability to see all of the forces acting on the bridge. If a script was generated that could hook up to a bridge and record the changing forces on the bridge, it would be very difficult to test without again. The ability to see all of the forces in the bridge allows one to have a better idea of what parts are weak and failing or what parts are holding strong. This is unfathomable for a small scale Knex project though, because a machine capable of all that would take a large sum of time and money to create. This would be unnecessary for a small scale project like this one because of the time and money involved in something like that would make our design too expensive
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