Charles Pringle (Mechanical Engineering Technology)
Faculty at Central Washington University proposed a challenge to mechanical engineering students that could be accomplished in an in-home setting. The goal was to create a balsa wood bridge, weighing no more than 85 grams, that can support a load over an open span and raise above its resting position by means of a mechanical system. To produce a successful solution to the problem, a vertical lift bridge was created consisting of two lifting towers and a load bearing bridge. Using equations of static equilibrium and strength of materials, the required width for each member was determined. Project requirements were accounted for with multiple supporting analysis on various parts in the design. The contents of each structure were limited strictly to balsa wood and glue, by evaluating both the tensile and shearing strength of each, stress concentrations were identified and mitigated. The construction of the device was achieved by setting up multiple fixtures to manufacture and join each component of the assembly. Testing is achieved with multiple nondestructive procedures first, followed by a final load bearing test. The device when tested can successfully raise and lower through use of the articulating components. When at rest the device can support the static testing load of 20kg and meets the weight requirement at 84.4 grams.
Keywords: Materials, Mechanics, statics