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Cantilever Bridge

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 18 in or 14 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 within SolidWorks.

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.