June 15, 2014
June 15, 2014
June 18, 2014
K-12 & Pre-College Engineering
24.347.1 - 24.347.3
Curriculum Exchange: Cantilever Bridging Submitted for the “Curriculum Exchange” category of the K-12 and Pre-College Engineering Division program.The purpose of the “Cantilever Bridging” activity is to provide an inductive, experientialintroduction to the concept of static equilibrium and its application in structural engineering.From a broader perspective, this activity demonstrates the value of science as a tool in theengineering design process. The activity is best conducted outdoors or in a gymnasium—andthus can be used very effectively to provide a change of pace from traditional indoor classroomactivities.The activity proceeds as follows: • Participants are organized into teams of 4 to 10 students each. • The teams are oriented to the “construction site.” For each team, two bridge abutments (wooden boxes measuring 1 foot wide by 1foot tall by 3 feet long) are placed 9 feet apart, on opposite sides of a simulated river. The simulated river is marked off with tape and is “off limits” to participants. On the near “shore” are two 8-foot-long wooden planks, as well as enough hard hats and work gloves for all team members. • The teams are presented with the problem—to get all members of the team and both planks safely across the river in the shortest possible time. • The teams are briefed on the rules of the game and then are given five minutes to organize themselves and plan their problem-solving strategies. • Construction is begun with “On your mark…get set…build!” The first team to cross all of its members and both planks without any person or plank touching the “river” is declared the winner. • The students are then led on a discussion of the activity and the underlying principles of engineering mechanics that served as the basis for their empirical solution to the bridging problem. The activity concludes with a demonstration of how the basic components used in the bridging activity can be used to model a real-world structure, like the great Firth of Forth cantilever bridge in Scotland. • Following this discussion, the teams are given the opportunity to repeat the exercise— and on this second iteration, the team with the greatest improvement in crossing time is declared the winner. Armed with knowledge of the underlying principles (and with the benefit of having already practiced the task once), the teams’ performance on this second iteration invariably improves substantially.Because the river is 9 feet wide and each plank is only 8 feet long, the only feasible way to solvethis problem is to build a cantilever bridge (see below), with the anchor span extending onlyabout half-way across the river and one or more students standing on its near end to provide acounterweight. Once all but the final team member have crossed, the cantilever configurationmust be reversed in order to get the final student across the river and recover the planks. Thestudent teams rarely recognize this potential solution in their planning, but rather discover itthrough trial and error—as well as observation of the other competing teams. Their improvedperformance on the second iteration serves as the basis for a final discussion on the value ofscience as a tool in engineering design.This activity has been used successfully with students from Grades 4 through 10. For students inthe higher grades, the level of rigor used in the discussion of static equilibrium can be raised.At the Curriculum Exchange session, the authors will demonstrate this activity with a small-scalemodel and with photos of students participating in both indoor and outdoor venues.
Ressler, S. J., & Bale, C. E. (2014, June), Curriculum Exchange: Cantilever Bridging Paper presented at 2014 ASEE Annual Conference & Exposition, Indianapolis, Indiana. 10.18260/1-2--20238
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