Cameron Week 9

Over the course of this term, I have learned many things about the bridge design process.  One thing that I had already known, but gained more of an understanding of is the fact that triangles are the most structurally sound shape.  I knew that this was the case, but was not sure of the reasoning behind it.  It makes sense because the triangle is the only shape that can not change unless the lengths of each side is changed. 

Another element of bridge design which I learned through this course is that there is a point where too much structure begins to counteract the intent of the design.  In simpler terms, if a bridge is incredibly tall, the benefit of the extra support from above is far less than if the bridge was shorter.  Yes, increasing the height of some bridge designs will make them more structurally sound, but there is a point where this benefit is reduced.  This point is why there were so many designs from the 1900s because bridge designers tried so many different ideas not knowing what the best proportion was/is.

Last week in class, we worked on perfecting the bridge that we had began creating in week 8.  We started class by testing what we had built during the previous week, which included a secondary truss component above the main portion of the truss.  When first tested the bridge held about 20 pounds.  For our second test, we removed the secondary upper truss and tested just the main truss.  This dramatically reduced the cost while keeping the weight relatively stable; thus lowering the ratio of cost to weight.  Having enough extra time for a third test, we decided to test the bridge using a secondary lower truss which spanned almost 8 inches more than the previously tested upper truss.  This lower truss added to the cost of the initially tested bridge, but held significantly more weight (33.6 pounds).  After computing all three ratios, we found that the bridge with the lower truss proved to hold the most weight per dollar. 

After conducting our three tests, we then began to consider the effects of filling all of the gaps in our outermost gusset plates.  We noticed that all three of our proposed designs failed at the outer gusset plates.  We added the small white members to each available space to increase the force needed for a member to pull out of the newly-filled gusset plates.

In the coming week, we hope to test our final design.  We expect it to fail in a similar fashion as our proposed designs did.  After testing we will complete a more in depth analysis as to why the bridge failed.