Campus: Seattle Central College

4. Balsa Wood Bridge Project

Educator: Francois Lepreintre – Faculty Physics, astronomy, computer science, and engineering
Context: Out-of-class; ENGR 214 Statics
Keywords: statics, design process
Student Activity Time: 1 hour

After completing a design build project, students reflected on their design process.

Introducing the Reflection Activity

The engineering design process is very reflective in nature, and in the engineering classroom it is important to ensure that students are reflecting on their processes and decisions as they engage in course projects. An educator implemented an engineering build project into a statics course, had students complete the design process, build and complete theoretical failure analyses for their project. The purpose of this activity was to help students use reflection in authentic engineering problem solving.

In the first class meeting, the term-long project, deadlines, and milestones for the project were introduced. The educator required student teams to submit three designs for a balsa wood bridge that met specific requirements that aligned with content being discussed in the class. Along with their designs, a narrative of why they selected one of the three designs was required. In the next stage, students used a web based analysis software to analyze the force in each member of their proposed bridge design. After using the software, students made necessary changes and revisions to their design and were given building supplies by the educator.

Near the end of the term, the educator facilitated an in-class testing day during which each teams’ bridge was tested for its ability to support a slow increase in weight to failure. The educator also video recorded the bridge testing with a high speed camera to support a post failure analysis.

The final presentation took place two weeks following the testing day. During the presentation, students explained why their bridge failed in the place that it did and under the load that it failed. This also included a comparison with their calculations from the design process and considerations for the building process.

The primary outcome of this activity for students was realizing the connection between engineering design and reflection. Students also demonstrated enhanced mastery and increased meaning of the course material through both the application of the course concepts in the design and building experience, along with the reflective project debrief.

 Recreating the Reflection Activity

Step Description
1 Assign the balsa wood project in the middle of the term and assign students to teams of three.
2 Review students’ initial 3 design choices and provide feedback regarding the quality of the designs, and the analyses performed.
3 Collect and students’ computer analysis of their bridge design.
4 Allow students 2-3 weeks to build their bridge.
5 Facilitate the bridge testing day in class.
6 Provide students 15 minutes in the next class for students to present their design process, the failure analysis, and comparison with the actual failures.
In the words of the Educator: Tips and Inspiration

The feedback loop is essential. This project is successful because we have feedback points at several stages including after the final presentation. It’s a lot like working as an engineer, and that’s what I’m really trying to prepare them for. They need to make sure they realize that the engineering process is not as easy as it looks based on the final project. It might not work right away, and you have to be very precise in every step. During the presentation, I ask a lot of questions to see how they have used the feedback throughout the design process. I really want them to reflect on the quality of their work. Since they present in the last class of the term, I also want to set them up for the next course, dynamics, where they will have a similar project. 

Focus students on explaining their design. On the day that they test the bridge and in the presentation, I ask them to summarize what they did: why they selected the design, where it failed, and why. I try to steer them to be more specific than just using numbers and explain them. They should be able to explain the physics; it’s not just a design project. If the project is well constructed, their analysis can be very good, and that is evident in the way they explain the failures. Also, I ask if the bridge failed where it was supposed to fail, instead of just allowing them to blame it on human error in building the bridge.

What was the inspiration for this activity? Will be added.


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