A1 - Lester

     My goal for this design was to create the most stable bridge possible. After finding designs that were sturdy, I worked on making them less expensive to build. I went through many trials, testing various shapes like X's, backwards and forwards V's, and single or double level trusses. I began with trusses build below the road, but switched to above the road support. There was no significant difference between above and below supported trusses except the beams had a tendency to overstretch on the bottom while they overcompressed on the top. An X structure bridge, which is what I call a bridge that has crossed beams instead of stand-alone triangles as support, was my first design. Although it is very stable, it costs more to build because there are double the amount of beams needed as compared to a simple triangle structure. The equilateral triangle V's on a slope was the most stable of all my trials, according to the Compression Force/Strength Analysis column in the load test results report. The angled slope of the bridge as it goes from the beginning to the middle cuts costs, since the beams are more compact and, therefore, cost less money (since beam are priced by size). Tubes are included in the most structurally sound locations to cut costs as well. Using tubes in a few places cut the cost of this bridge by almost $100,000. This bridge costs $620,984.96 altogether.
     I learned a lot about the Westpoint Bridge Designer program, like shortcuts and stress test features. I got a feel for what a correctly build bridge should look like. Symmetry and simplicity were both extremely important factors in keeping the bridge stable while limiting building materials to keep costs low. I also learned that designing a stable bridge is not nearly as easy as I'd thought. Shapes that seem stable actually collapse at unexpected places, like a horizontal support beam in the first half of the bridge, or a vertical beam in the center. Also, despite my partial skepticism, I found that simple triangles are in fact the strongest support.
     Next week, our group will compare our final designs and discuss which we want to continue modifying and what features can be taken from each design to make our bridge the most stable and cost efficient.

Belinda Lester