(MTE 219) Balsa Wood Bridge

Project Summary

This project involved designing and constructing a full 3-dimensional truss bridge was with balsa wood with the overall goal of maximizing strength-to-weight ratio (PV), where: \begin{equation} PV = \frac{\text{Max applied load}}{\text{Mass of the truss}} \end{equation} The truss was suspended across a gap, with a hook on one side and a platform on the other. Design constraints included dimensional constraints (40cm × 8cm × 10cm), as well as material constraints (amount of balsa wood and hardwood dowel). Various concepts were evaluated based on design criteria, such as load capacity, material efficiency, and construction-related considerations. After these concepts were evaluated, the final design was chosen and calculations were done, with a theoretical PV of 258.6. The final design was realized with three iterations; an initial iteration to test the design and identify weaknesses, a second iteration with minor tweaks to address these weaknesses, and a third iteration prepared for the official competition. The official bridge evaluated at the competition had a mass of 15.9g and was able to hold 5kg (failing due to link tearing when 5.5kg was loaded), resulting in a PV of 314.4; this result is reasonably close to our theoretical calculations and preliminary tests.