The final project for ENGS 33, Solid Mechanics during Fall 2017 was to build
a cantilever bridge and predict how it would fail. We were also supposed to
optimize its strength to weight ratio.
A cantilever bridge is supported only one side, and for this class, we had
a number of other restrictions. The bridge had to attach to a standardized
mount, and we could only use 1/8 in or 1/4 in laser cut plywood, as well as
guitar strings. Also, the bridge had to be roughly statically determinate.
I worked with two other students to design the bridge. We decided to design
a simple beam bridge supported by two guitar strings. We picked this design
because we thought the guitar strings would have a high strength to weight
ratio, significantly higher than wood.
We modeled the bridge in SolidWorks, and predicted the strength of the bridge
using a simplified structural model as well as with finite element analysis
We wanted the guitar strings to break before the deck, so we ended up making
the deck significantly stronger than was necessary. We were not confident
in our calculations, so we designed our bridge conservatively. This meant we
did not have a high strength to weight ratio, but we successfully predicted
the failure location and came fairly close to the predicting the breaking load.