Project Title

Balsa Wood Drawbridge

Document Type

Undergraduate Project

Date of Degree Completion

Spring 2021

Degree Name

Bachelor of Science


Mechanical Engineering Technology

Committee Chair

Craig Johnson

Second Committee Member

Roger Beardsley

Third Committee Member

Charles Pringle


Which truss design is best suited to a drawbridge when precision equipment is unavailable for the construction process and what design is suitable for the articulation system? To address this problem, several different designs were considered for a truss made of balsa wood. Initially a warren truss, a k-truss, and a bowstring truss were considered. The designs were evaluated using a decision matrix, the winning design was produced and tested. The testing methods used were a mass limit of the bridge, a minimum length requirement, loading requirements, and a minimum height for the roadway to reach when raised. Various other smaller tests were conducted but they had little to no impact on the design of the bridge. The design was evaluated during the testing phase using a pass-fail system for each of the requirements. The warren truss design was able to sustain the twenty-kilogram loading, span the four-hundred millimeters between the abutments, and the final mass of the bridge was fifty-four grams without the articulation system attached, which was less than the maximum allowable weight of eighty-five grams. During the articulation process the bridge was lifted with the center of the roadway reaching a height greater than fourteen centimeters from the resting position. The bridge was also able to maintain this position without assistance for the ten second required before being lowered.