Fighting “plug and chug” structural design through
effective and experiential demonstrations

Abstract

Structural engineering students are prone to conflating structural design with the ability to “plug-and-chug” prescriptive specification equations or to be “able with the table.” But this relegates structural design to simply being familiar with specification documents. Of course, experienced structural engineers know that a solid conceptual understanding of the underlying structural mechanics and behavior are far more useful, where engineering judgment must be used alongside design specifications. This is especially true for the ever increasing amount of automation offered by structural analysis and design software packages. New engineering grads who learn only to “plug and chug” specification equations for textbook problems will be less creative and will be ill-prepared to interpret computer results and make important decisions with the aid of computer generated designs.

It can be difficult to steer students away from this habit. One way to convince students that behavior is important is to demonstrate structural behaviors in ways that are easily relatable to the applicable specification equations. When coupled with “thoughtful explanations and comparisons, even simple ad hoc activities may trigger “ooooooh moments” and encourage stronger conceptual connections between the equations and structural behavior.

This short paper summarizes many experiential demonstrations along with explanations and important implementation details that may help an instructor teach structural design with a focus on important concepts, linking structural behavior and mechanics to specification equations and design philosophy. A range of engaging student-active demonstrations are presented, from grabbing some coffee stir sticks on the way to class to building an interactive shear wall and diaphragm model for use in the classroom.

Since readers likely have their own ideas for experiential demonstrations, this paper will remain active “on the cloud.” The authors invite future contributions thereby making it a living repository. Since it will remain active on the internet, other media can also be easily added, such as videos and links to augmented reality/VR applications or other applications utilizing future technologies.

Link to this Living Collaborative Paper Containing A Database of Demonstrations: http://bit.ly/structural-demos 

“Plug and Chug” of specification equations is not design. Letting students have this impression is doing them a huge disservice.

Teaching is tricky business. How one teaches structural design has some particularly impactful consequences. Students expect to learn the specifications (or codes) but over emphasizing the code may leave students without a deeper understanding of the mechanics and structural behaviors involved in structural design. There must be a balance between teaching the code and behavior because many students likely have become programmed, trudging through many math and science courses, to solve problems in a very methodical fashion of reading a prompt, recognizing the method or formula to use, and arriving at the single correct answer.

For structural design this is “plugging and chugging” where little meaningful understanding of the underlying engineering concepts has been gained, and students are trained calculator and code operators. Being “able with the table,” a cousin to “plug and chug,” refers to the simplistic skill of knowing how to use published tables to “design” members (such as the AISC Manual Design Aids [AISC 360-16] or joist catalogs). Although these are without question important items for students to be exposed to, they certainly should not be the priority and focus. This relegates structural design to simply comparing a few numbers and selecting a “design.” Without a good physical comprehension of the design concepts, “plug and chug” “skills” will be “crammed and flushed” after the exam (Bella 2003).

There’s a time and place for number crunching, detailed design calculations, and utilizing design aids. Students will encounter many different problems in their career, but a few design courses in college certainly cannot expose students to every scenario, much less effectively teach them how to solve each problem. Further, the purpose of our design courses should not be to simply “teach the code” (Hines 2012). This is sure to reinforce the impression that design is cranking through equations and picking sizes from tables - a practice that can limit creativity.

“The creative structural engineer must be able to anticipate how a structure responds to applied loads and other external influences, and in turn is able to visualise structural forms which are appropriate for given conditions.”
(Teng, et al 2004)

Experienced structural engineers know that detailed calculations are not the most important nor the majority of the work performed in their day-to-day life (Hoit 2012). For several decades software has done the heavy computational lifting, and in the past few decades design can also be automated. But, effective use of structural analysis software requires qualitative understanding of how structures behave, as has been noted since the dawn of personal computers (Jennings and Gilbert, 1988; Brohn, 1992).

How can we fight “plug and chug”?

If we want students’ structural analysis and design skills to extend beyond the surface of a problem statement, then we must grab their attention and show them structural design directly uses structural behaviors they can understand (and often they already do without knowing it). It may be easy for students to lose sight of this fact, making a space for “plug and chug” to thrive. Our job as instructors is to highlight and tie those behaviors to the specification equations, giving them relatable context, in order to encourage a lasting connection in the mind of the student.

Therefore, the main goal of this paper is provide instructors with an organized set of easy-to-implement demos and activities aimed at supporting an engaging concept-driven lecture style for structural design (Lanning 2018). This is part of an ongoing effort by the authors, which includes growing a collaborative effort to reform teaching of structural design. The intent here is to facilitate instructors to make an explicit effort towards emphasizing concepts in almost every lecture in an easy and effective way. This may help students begin to think like experts.

Creating expert-like thinking about structural problems and design.

Perhaps the best way to prepare students for their career is to allow them to develop a strong conceptual framework upon which every problem can become a variation of a few crucial themes (Hines 2012). Using a strong conceptual understanding (of structures) is how experts (experienced structural engineers) operate in their fields, after all!

“When solving problems, experts in physics often pause to draw a simple qualitative diagram—they do not simply attempt to plug numbers into a formula. The diagram is often elaborated as the expert seeks to find a workable solution path. (National Academy Press 2000)

Therefore, undergraduate design courses should focus on connecting the theory, mechanics, and structural behavior to the real world application (using design specifications), and not trudging through a plethora of textbook style homework problems. Showing students that many structural behaviors are similar in concept can extend to and facilitate their grouping of specification procedures and design philosophies into tractable categories and to begin thinking like experts.

Further, experiential demonstrations requiring partners or group discussions foster an engaging learning community. When students work together to understand or make the demonstrations work, they are participating in peer instruction. When it is time to perform example calculations, students may be more likely to discuss amongst themselves and to speak up and ask questions.

I think most students already get it, why waste time having students do such simple activities? Don’t give in to expert blindness! Your students will appreciate it.

An instructor is likely an expert. But, with experience comes “expert blindness”, or “expert blind spots” (Nickerson 1999), which is the expert’s inability to relate with a novice on mistakes and misconceptions, trouble visualizing, and synthesizing ideas. To correct for this phenomenon, instructors must constantly remind themselves that students are novices and they do not see things through the lens of experience. From the authors’ observations, students often do not understand things that we, as experts, see as fundamental and basic. That is not to say students are lazy or have not studied enough. Rather, students are students and they are still learning. They have a very small fraction of the instructor’s experience on which to build new knowledge. So, although simple demonstrations may feel drastically prerequisite to the expert, they may be just the type of experiential learning to make all the difference to the novice student.

Students who already have an intuitive understanding of structural mechanisms and behaviors may not view the activities as worthwhile. These students will still benefit from improved confidence and may build a better connection by physically feeling or seeing the concept in real life (Felder and Silverman 1988). However, students who have not yet developed a strong intuition may dramatically benefit from seeing firsthand the simplicity of the behaviors being discussed “in theory” and in real life. Spending time to ensure that students are making quality conceptual connections is certainly not time wasted and if a few are bored for 10 minutes then that is a worthwhile cost.

Several of the experiential demonstrations discussed in this paper were conducted in the most recent (2018) offering of structural steel design by one of the authors. Of 65 students responding to the course survey, only one commented that this type of activity was not very useful. Conversely, there were eight comments that explicitly reflected positively on the use of demonstration and activities to learn concepts.

Further, the value of class demonstrations is shown by comparing the most recent course (2018) with the previous course (2017). The 2017 offering of the course did not use classroom demonstrations (to any significant extent). Comparing 2017 to 2018, there was a 93% increase in the response rate for comments positively mentioning demonstrations and an 81% increase in the rate of comments exclaiming that the lectures were engaging (Figure 1a). It is important to note that, except for classroom demonstrations, the course content was essentially the same with lectures in both offerings being heavy on discussion of concepts. This is supported by an essentially constant percentage of comments mentioning “concepts” as the focus of the class in the 2017 and 2018 offerings (Figure 1a).

The 2017 course was fairly successful from the standpoint of the student course evaluation ratings (where students assign the instructor a “grade” of A through F, shown in Figure 1b). But, with the 2018 course and the injection of demos and activities there was a 10% increase response rate in A-grades given by the students in response to “Explanations of concepts were clear”. This was accompanied by a 16% increase in A-grades give by students for the overall rating of the course.

A few activities described later in this paper were recently carried out in class. Informal and anonymous polls were taken to gauge their effectiveness (Figure 2). Large majorities of students agreed that the demonstrations were helpful.

Okay, I want to do some simple demonstrations. What do I do? I don’t have a lot of time.

The format herein is intended to be less formal and is provided in a quick-reference style for instructors to quickly gather many ideas for direct implementation in their classrooms. Therefore, the following sections present many experiential activities grouped by structural topics and behaviors and assigned an approximate level of required preparation.

Learn by doing and by sharing.

Finally, this paper is intended to be a collaborative living repository of demonstrations. Readers are highly encouraged to add items by requesting access to the shared document.

Link to this Living Collaborative Paper Containing A Database of Demonstrations: http://bit.ly/structural-demos 

Living Table of Contents

*Indicates activities that require partners

Flow of forces        9

Gravity Framing        9

Metal Decking - Supplies: paper (prep time: 0-10 mins)        9

One-Way Slab - Supplies: paper, rubber bands, and tape (prep time: 0-10 mins)        9

Lateral Framing        10

Shear Walls and Diaphragms - Supplies: wood, silicone sheets, and spring scales (prep time: 4-6 hours)        10

Tension Members / Connections        10

Weld Transfer of Tension in Connections via Shear - Supplies: paper and tape (prep time: 5 mins)        10

Bolt Bearing and Tear-Out - Supplies: silicone pot holder (prep time: 5 mins)        11

Tension Distribution in a Plate from Bolt in Bearing - Supplies: silicone pot holder (prep time: 5 mins)        11

Shear Lag - Supplies: paper (prep time: 0 mins)        12

Columns        12

Elastic Flexural Buckling        12

Weak-Axis versus Strong-Axis and Column Bracing - Supplies: coffee stir stick and/or Pasco Superflex I-Beam (prep time: 0 mins)        12

Beams        12

Torsional Stiffness of Rectangular Beams - Supplies: coffee stir stick and/or Pasco Superflex I-Beam (prep time: 0 mins)        13

Strong & Weak Axis Bending and Lateral Torsional Buckling - Supplies: coffee stir stick (prep time: 0 mins)        13

Strain Variation and Lateral Torsional Buckling - Supplies: foam beam (prep time 5 mins)        14

LTB Bracing (partners) - Supplies: coffee stir stick (prep time: 0 mins)        14

Composite Beams        15

Composite Action        15

Non-Composite Action - Supplies: coffee stir stick (prep time: 0 mins)        15

Composite Steel Beams        15

Shear Studs and Concrete Slab Effective Width - Supplies: Pasco Super-Flex I-Beam, cardboard, and push pins (prep time: 5-10 mins)        15

Increased/Lower Bound Stiffness and LTB Resistance - Supplies: Pasco Super-Flex I-Beam, cardboard, and push pins (5-10 mins)        16

Combined Loading        17

P/M Interaction and Second Order Effects/Analysis        17

Comparing 1st and 2nd Order Analyses - Supplies: coffee stir stick (prep time: 0 mins)        17

Destabilizing Effects of Gravity Loads on a Frames and P-Δ - Supplies: coffee stir stick, textbook (prep time: 0 mins)        18

Advanced Topics        19

Shear Buckling and Tension Field Action - Supplies: silicone pot holder (prep time: 5 mins)        19

Flow of forces

Gravity Framing

• Metal Decking - Supplies: paper (prep time: 0-10 mins)

Have students corrugate paper into the same cross-sectional shape as corrugated metal decking. To help them make the correct shape, it is advised to print a set of parallel lines where folds are to be placed along with arrows to indicate the fold direction.

• One-Way Slab - Supplies: paper, rubber bands, and tape (prep time: 0-10 mins)

Using a plain piece of paper, some cut rubber bands, and tape, students can quickly make a model of a one-way slab and directly experience how the longitudinal reinforcement (rubber bands) allow the slab to span in only one direction. Although not pictured here, it is very easy to see why the slab is assumed not to span the other direction. This could be extended to two-way slabs as well.

Lateral Framing

• Shear Walls and Diaphragms - Supplies: wood, silicone sheets, and spring scales (prep time: 4-6 hours)

Under Construction - check out the living version of the paper at http://bit.ly/structural-demos  for updates on this model and other additions by future collaborators.

(Contributions Sought - Please submit your idea)

Tension Members / Connections

• Weld Transfer of Tension in Connections via Shear - Supplies: paper and tape (prep time: 5 mins)

The shear transfer by welds can be shown using two pieces of paper and some tape. Loosely tape a folded piece of paper to another, and draw a few lines (as shown below). Upon applying the loads shown, students will feel and see the shearing effect. This could then be extended to show how welds behave when loaded perpendicular to their length.

(Contributions Sought - Please submit your idea)

• Bolt Bearing and Tear-Out - Supplies: silicone pot holder (prep time: 5 mins)

An ordinary silicone pot holder, with a strategically located hole, can provide students a direct experience with what bearing and tear-out failure look like and how the bolt hole deforms (to an exaggerated scale, of course).

• Tension Distribution in a Plate from Bolt in Bearing - Supplies: silicone pot holder (prep time: 5 mins)

The same pot holder can mimic a gusset plate and let students directly experience the Whitmore section. They can also wiggle the potholder while under tension and directly see the ineffective area.

• Shear Lag - Supplies: Paper (prep time: 0 mins)

Students can make their own paper model of a steel L-shape with bolts connecting one leg (drawing the bolts as shown below). Using a partner, students then engage the angle in tension and then estimate the path of the flow of tension force and the effective net section. To identify the effective area, it is helpful to flick the leg that is not attached along the length of the member.

Columns

Elastic Flexural Buckling

• Weak-Axis versus Strong-Axis and Column Bracing - Supplies: coffee stir stick and/or Pasco Superflex I-Beam (prep time: 0 mins)

Heavy outlined red arrows are the forces that are intentional. Light, translucent, gray arrows are those which may “coach” the demonstration prop into displaying the desired behavior. Of course, the bracing shown (middle) with the stir stick can also be accomplished with the Pasco beam (Pasco 2019).

(Contributions Sought - Please submit your idea)

Beams

• Torsional Stiffness of Rectangular Beams - Supplies: coffee stir stick and/or Pasco Superflex I-Beam (prep time: 0 mins)

Students can directly feel and see the flexibility of rectangular and I-shaped members in torsion.

• Strong & Weak Axis Bending and Lateral Torsional Buckling - Supplies: coffee stir stick (prep time: 0 mins)

• Strain Variation and Lateral Torsional Buckling - Supplies: foam beam (prep time 5 mins)

Instructors use many variations of a beam prop that demonstrates the strain variation over the cross section of a loaded beam (see part a of the figure below). If the beam is proportioned just right, a bending load will allow students to see and feel lateral-torsional buckling (figure part b). The beam shown in these figures was created by cutting foam padding to size (donated by a furniture manufacturer) and drawing on the grid with a permanent marker. Enough beams were produced so that each student in class could use one for the demonstration.

   (a)                                                     (b)

A foam beam (a) in bending showing strain variation and (b) demonstrating lateral-torsional buckling.

• LTB Bracing (partners) - Supplies: coffee stir stick (prep time: 0 mins)

Coffee stir sticks can be used to demonstrate increased beam resistance to moment with decreased unbraced length (e.g., with beam bracing). One student bends the stick about the major axis and causes LTB to occur. The student applies moment again while another braces the compression face of the beam. The student applying moment will notice a significant increase in the amount of applied moment that is required to cause LTB. The photo to the right shows bracing in just one direction, so care must be taken by the instructor to explain that bracing should be able to apply a transverse force in either direction.

Composite Beams

Composite Action

• Non-Composite Action - Supplies: coffee stir stick (prep time: 0 mins)

This simple demonstration is an easy way to have students directly feel the multiple cross sections slipping relative to one another. The activity is suggested to supplement simply drawing or showing a figure of the behavior. When students feel the slip it seems they immediately realize that shear compatibility between the cross sections is required to obtain composite action. Together with this, the instructor can ask for estimates of the moment of inertia of this “beam.”

Composite Steel Beams

• Shear Studs and Concrete Slab Effective Width - Supplies: Pasco Super-Flex I-Beam, cardboard, and push pins (prep time: 5-10 mins)

Adding a small piece of cardboard (this was taken out of an old 3-ring binder) to the Pasco I-beam can demonstrate composite steel beams, with push pins acting as headed steel studs (they even have a similar appearance to aid in visualization). To help explain that the concrete slab has a certain effective width, the instructor can draw the approximate stress distribution directly on the added slab and explain that is why the cardboard is cut to the length provided. (See figure below)

(Contributions Sought - Please submit your idea)

• Increased/Lower Bound Stiffness and LTB Resistance - Supplies: Pasco Super-Flex I-Beam, cardboard, and push pins (5-10 mins)

With part of the beam acting compositely and the other remaining bare, students can:

• Feel the difference in stiffness.
• See the push pins rotate slightly upon bending of the beam, which indicates to them the shearing action acting on the steel headed studs.
• Experience the resistance to LTB of the composite section compared to the non-composite section.

Overall, having a small physical model of the composite beam is helpful to explain the system.

Combined Loading

P/M Interaction and Second Order Effects/Analysis

• Comparing 1st and 2nd Order Analyses - Supplies: coffee stir stick (prep time: 0 mins)

Having students apply moment and axial forces sequentially, they can directly experience the combined effect of these forces. With a moment applied, ask the students to draw the moment diagram. With the applied moment remaining on the stir stick, have their partner apply an axial force and again ask them to draw the moment diagram. Students will either struggle to account for the increased moment they experience, or they will realize that equilibrium must be taken on the deformed shape. Either outcome drives home the fact that axial force has an effect on the moment, but the only way to obtain that effect in analysis is to consider equilibrium on the deformed shape (i.e., perform a 2nd order analysis).

(Contributions Sought - Please submit your idea)

• Destabilizing Effects of Gravity Loads on a Frames and P-Δ - Supplies: coffee stir stick, textbook (prep time: 0 mins)

When teaching system-level stability it is difficult to explain with words or pictures the destabilizing effect of gravity loads. Using coffee stir sticks as fixed-pinned columns and a textbook as a floor gravity load, students can work as a team (some must hold the sticks straight up and down, with the proper end conditions, some will place the book on top, and some may provide “emergency” stability of the book) and  to demonstrate the destabilizing effect. Of course, this activity opens up the options of instructor to discuss P-Δ, story-level buckling capacity, and lateral bracing among other topics.

(Contributions Sought - Please submit your idea)

Advanced Topics

• Shear Buckling and Tension Field Action - Supplies: silicone pot holder (prep time: 5 mins)

An ordinary silicone pot holder can mimic a plate girder web and demonstrate shear buckling which can be difficult to describe and difficult for students to visualize.

This is another opportunity to engage the class using partners (not shown) to constrain the pot holder web segment, where the top and bottom hands (students) need to simulate the flanges while the hands on the sides apply the transverse shear in the beam. The instructor must explain that the pot holder will “pop” slightly, and that’s how they know they achieved the buckling behavior. It might be tricky to get the restraints and applied forces just right. It will require a little practice but the students will pick it up quickly.

Shear buckling and Tension Field Action

(Contributions Sought - Please submit your idea)

REFERENCES

AISC 360-16. (2016). Specifications for Structural Steel Buildings, American Institute of

Steel Construction, Chicago, IL.

AISC  Educator Workshop (2018). AISC Educator Workshop Materials, American Institute of Steel Construction, Chicago, IL., 2018. AISC Educator Workshop, June 2018 Dallas, TX.

Bella, D. (2003) “Plug and chug, cram and flush” J. of Prof. Issues in Eng. Edu. and Practice, 129(1): 32-39.

Brohn, D. M. (1992). New paradigm for structural engineering. Structural Engineer, 70(13), 239-242.

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https://www.structuremag.org/wp-content/uploads/D-EdIssues-Hines-Aug121.pdf 

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https://www.structuremag.org/wp-content/uploads/2014/08/C-EducationIssues-Hoit-Jan101.pdf

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https://www.structuremag.org/wp-content/uploads/2018/06/C-ProfessionalIssues-Dong-Jul18.pdf 

Jennings, A., Gilbert, S. (1988) “Where now with the teaching of structures?”. Structural Engineer. 66(1), 3-7.

Lanning, J. (2018) “Developing an Effective and Engaging Concept-driven Approach to Teaching Structural Design

National Academy Press (2000) How People Learn: Brain, Mind, Experience, and School: Expanded Edition, Washington D.C

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Pasco (2019) Super-flex I-Beam, Pasco, Roseville, CA

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https://www.structuremag.org/wp-content/uploads/2014/08/C-StructuralForum-Powell-Nov081.pdf 

Richards, P., (2012) Build with Steel - A Companion to the AISC Manual, CreateSpace Independent Publishing Platform

Teng, J.G., Song, C.Y., Yuan, X. F. (2004) “Fostering creativity in students in the teaching of structural analysis” International Journal of Engineering Education, 20(1), 96-102.