Analysis for ME 14
Bridge Competition (Learning from Failure)
Jefferson Cam and Xinghao Huang
The second midterm of ME 14 statics was the bridge competition. Two people would form a team and use balsawood to build a bridge that was 40 cm long, 10 cm wide, and 21 cm tall (maximum dimension). The bridge also had a 25 cm gap between its two main supports and 10 cm clearance. Only Elmer's glue was allowed to use at the joint, and no spacer allowed to enhance joint. The team that had the highest load to weight ratio would win.
The 40-hour effort input didn't make us win, but learn a lesson... |
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I and my roommate Jeff Cam formed the team and built our bridge. We used a software developed by Pre-Engineering Inc. called ModelSmart3D, which can simulate balsawood in different structures. Below are two designs we made and their simulation at the breaking force.
We eventually chose the triangular shaped design. We chose it because:
We started building its sections. We printed out the cross sections of the bridge on paper and and used it as a reference template to build the side first. We then built the two triangle bases. |
The two sides were connected by horizontal beams. When gluing, we had to lie it down on its side and put load on it.
Finished:
FailureOn the test day, Professor Kirk used a compression actuator to put a load on our bridge. The peak load would be recorded to calculate our final score.
When it was our turn, our bridge only hold around 50 lbs of load and only last 5 seconds. But before that, we got 1080 newton in our simulation. Why the simulation is so different from the actual situation? |
There are three reasons we failed:
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So, never trust simulation and glue. Trust the structure. It would be better if we can build one more prototype and test it.