General Card #3361

Statics Truss Structures: Method of Joints Gallery Walk

Summary

This card presents a way to make the statics method of joints more interactive.

Description

**30-Second Overview**

One-sentence description: A gallery walk reinforces the importance of drawing accurate and complete FBDs for all of the joints in a truss structure.

Course: Statics

Topic: Truss structure analysis

Type: Gallery Walk

Time: 30 minutes

Materials: Large papers and tape or poster boards (one per joint in truss + one for entire truss), markers (suggest 2 per poster), sticky notes (at least two per table or team), truss problem, whiteboard or overhead projector

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Introduction: The free-body diagram is a diagram that shows all the forces acting on a particle or rigid body. For an example of a free-body diagram, in this case for a joint in a truss structure, download the attached .pdf where several sketches can be seen for the different joints of this example.

Setup: Instructor should select a truss problem, preferably one where the joints are already labeled, and divide the class into teams. The number of teams should be equal to the number of joints in the truss plus one. Large paper such as A-17 or poster boards can be taped on the walls or placed around the room. There should be one such paper for each team. For clarity, the paper or poster can be labeled with the name of the joint, such as A, B, etc or "Global/Entire Truss."

Each team will be tasked with a particular joint of the truss, or the entire truss. They will then have 3-5 minutes to draw the appropriate free-body diagram for their particular assignment on the provided sticky note. During this time the instructor can circulate and ask questions if desired. One method for ensuring participation among all group members would be to distribute pens of different colors to each team (for example, if a team has four group members then the instructor may provide them with black, blue, red, and green) and request that all four colors appear on the diagram, without any exchanging of markers.

After the drawing time has elapsed, each team will place their sticky note on the poster or paper in the room corresponding to their assigned joint or structure. Then all students will be directed to take 10-15 minutes to walk through the 'gallery' to look at their fellow classmates' drawings and write comments next to the drawing. In particular, the instructor should focus on asking the students to comment on whether all of the information necessary for generating equilibrium equations is present. The instructor can then lead a discussion on sign conventions and how to homogenize the names of each truss member (for example, one team may call a vector F_AB on their FBD and another may call it T_BA).

Students may then generate a second draft of their drawing and post it. The instructor should check all FBDs for accuracy before proceeding on to the next step.

Then all students rotate to a different team's FBD and are tasked with writing the necessary equilibrium equations from the given FBD, without referencing the original picture. The instructor can check for accuracy and homogeneity of nomenclature as mentioned above, and have the students write their final equations on the whiteboard.

Once all equations are completed, the instructor may then direct the students to solve the equations to find the force in each member of the truss. The problem deliverable would be a complete listing of the support reactions and the force carried by each member of the truss along with appropriate units.

A possible method of assessing the students' retention of the concept may be to provide a different truss problem during the following class session and ask them to draw the FBDs and write the corresponding equilibrium equations again. It is hypothesized that students' drawings will be clearer for the instructor as the students are now accustomed to drawing them for a different audience besides themselves, and that they will avoid common mistakes after the post-gallery-walk discussion. This type of problem would also be likely to appear on a quiz or test in a typical engineering statics course, so a graded assessment would be possible as well.

A possible method of determining the development of an entrepreneurial mindset would be to consider how they might implement a truss structure in a real engineering scenario. Many case studies exist of failing bridge structures (most famously the Tacoma Narrows Bridge), so perhaps students could be directed to consider the costs of a failing bridge vs the cost of additional labor to run simulations and perform analyses prior to the construction of a bridge. Students could see a real-world application of a cost-benefit analysis as it relates to a truss structure.

Creating Value

- Persist through and learn from failure

It is unlikely that students' first attempts at their FBDs will be perfect. Instructors can allow multiple attempts at the drawing with feedback provided for each.

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