Makers+Shakers

To view the figures and tables associated with this article, please refer to the flipbook above.

You’re the structural engineer designing a new multi-story condominium on the Pacific coast. The architect wants clear, unobstructed views of the ocean, high ceilings, and a rooftop pool. The developer wants to maximize the number of sellable units and minimize costs. Your design needs to support the architect’s vision at a cost that works for the developer. And, of course, you need to design the building to withstand an earthquake.

Does this sound familiar? This is essentially the problem statement Schaefer team members give students in junior high school participating in the firm’s Makers+Shakers program. Students use K’nex to design their condo towers and test them on a homemade shake table. They get exposed to load path, resonance, torsional irregularities, and mass and stiffness irregularities. They learn to design with constraints and deal with competing objectives. But most importantly, they get exposure to the structural engineers leading the program, and the creativity + technical acumen necessary in our industry.

Makers+Shakers taps into the tangible aspects of ‘build and break’ structural engineering projects that students love and adds a dynamic component more engaging than static load tests.

There is a sizable gap between the expected demand for civil engineers and the number of civil engineers entering the workforce. The U.S. Bureau of Labor Statistics is projecting nearly 23,000 civil engineer job openings each year on average for the rest of this decade. But, according to the National Center for Education Statistics, only 15,051 bachelor’s degrees in civil engineering were awarded in 2021.

How do we bridge the gap? The team at Schaefer believes we can make a difference by sharing our passion with students and introducing a potential career path they may not be familiar with. Age matters – our program is built for seventh and eighth graders for a reason. Many undergraduate engineering programs have math and science prerequisites beyond high school graduation requirements, so we need to meet students when they still have time to plan their high school courses accordingly.

If students don’t see civil or structural engineering as a potential accessible and rewarding profession before high school, they may not have sufficient exposure to the math and science classes required to even apply to a college engineering program.

Makers+Shakers is an intentionally brief but intensive introduction to structural engineering concepts that can be done as part of a career day activity, within a junior high STEM or engineering class, or as an activity for a club. The entire program can typically be completed in one or two classroom sessions, about one to three hours.

While Makers+Shakers can serve as a launching point to supplement larger scale outreach programs such as Future City or any of the outreach projects that NCSEA promotes on their stem-outreach page, the goal of Makers+Shakers is to grab students’ attention and get them engaged quickly. We’re not lecturing students about engineering—they’re actually doing it. We ask them to solve a real-world problem that we, as structural engineering professionals, work through every day.

This small-scale, intensive, one- to two-session approach also makes it easy for facilitators. We’re all busy, so having an impactful outreach activity that can be accomplished in a few hours makes it easier to find volunteers willing and interested in participating.

Schaefer has had great success with our Makers+Shakers program in Cincinnati and Columbus, Ohio, and we’d like to see our partners, peers, and friends participate as well. That’s why we’re publishing all the resources needed to create your own Makers+Shakers program, including building your own shake table.

Following is a high-level overview of the resources and directions; you can find full materials for a prototype shake table on our website.

You can build a homemade shake table for $200-$400.

The 2-dimensional shake table design enhances visibility of mechanical components while remaining cost-effective. Accessibility and visibility are intentional. This build reinforces the creative “maker” attributes of engineers, it allows the students to intuitively understand how the table works, and by making the tables out of off-the-shelf components (plywood, skateboard parts and servo motor), the build doesn’t seem out of reach for the students themselves.

The prototype shake table consists of a plywood base with stacked plywood cutouts forming shallow foundations and pedestals (Fig. 1). The center pedestal secures the servo motor holding a rotating gear. The two outside pedestals support the roller skate wheels. A pegboard, attached to a wooden block with an interlocking chain, rests on these wheels. During operation, the motor's rotation moves the pegboard horizontally along the chain's length. Our current build of the table replaces the pegboard with a plexiglass board and incorporates the plywood base into a wooden case to make it easy to transport.

The table, controlled by a Raspberry Pi, can simulate ground motions from actual earthquake records! The movement is generated by the servo motor. The large gear and chain convert the rotational velocity of the motor to linear translational velocity of the table. Typical servo motors only have one speed (e.g. they operate at a constant rotational velocity). Our servo operates at 50 Hz, and we provide a pulse every 20 milliseconds (ms). Pulse length within this 20ms interval determines the motor's rotation degree (0.5ms = 0˚, 1.5ms = 90˚, and 2.5ms = 180˚). The motor rotates to the specified rotation degree at the motors default rotational velocity. By using small timestep data and displacement scale, we can control when the servo stops, starts, and reverses to control speed and acceleration.

The Raspberry Pi serves as the control center, running Python code that directs the servo's movement timing and magnitude. Excel files store the timestep and displacement data. The Python code converts this data into appropriate pulse widths and translates it into a format readable by the Raspberry Pi. The Raspberry Pi transfers the translated data through a series of electrical components (ribbon, GPIO Extender, breadboard) to the servo motor. The breadboard is wired with push buttons and an LCD display to facilitate user interaction.

We’ve developed three primary demonstrations for Makers+Shakers:

Each demonstration illuminates the competing demands of architect and engineer and sets the stage for a classroom competition activity.

The initial demonstration utilizes sinusoidal motions rather than historical seismic records. This simulation pairs with three "lollipop-shaped" building models of varying heights—a single-story structure (house), a mid-rise building (hotel), and a high-rise tower (Fig. 2). Each sinusoidal frequency corresponds to the natural frequency of one of the lollipop models, demonstrating to students that every structure possesses a unique resonant frequency that must be incorporated into design considerations.

The second demonstration contrasts the seismic performance of two four-story K'nex structures: a braced frame and a moment frame (Fig. 3). This comparison reveals how different structural systems respond to identical forces, highlighting the relationship between framing methods and building behavior. The demonstration sparks discussions about practical trade-offs, including construction efficiency, material costs, and architectural implications such as window placement and the aesthetic potential of structural bracing.

The final demonstration examines mass influence through identical structures, with one bearing additional weight (Fig. 4). Students observe how the heavier structure exhibits more pronounced responses to seismic forces. This leads to meaningful discussions about real-world design elements that add mass—like rooftop pools, green roofs, solar installations—and their associated cost implications and engineering challenges.

Collectively, these demonstrations effectively bridge structural dynamics principles with industry realities and serve as hints and tips for the classroom competition activity.

After participating in the demonstrations, students are put into teams and tasked with designing and building a tower that meets specific project goals including withstanding an earthquake. A combination of incentives and costs are considered by each team in order to optimize their design. They are given a construction budget, and each K’nex piece has a cost associated with it. The winning structure is the building that creates the most value, at the lowest budget, and survives an earthquake.

Rooftop gardens and pools increase the value of the tower but add mass (bean bag) to the roof, increasing seismic loads and overturning. First-floor amenity spaces with a taller floor-to-floor height also create additional value but could create a soft story. Avoiding braces on the ocean-facing side of the tower makes for better views for the tenants but also impacts building stiffness and could create a torsional irregularity.

Facilitators can adjust the accompanying scorecard and activity instructions based upon age of the students and time available for the program. The most important part is that the kids are engaged and excited about engineering.

All of the intellectual resources are publicly available in hopes that various ASCE local chapters, student organizations, or outreach minded engineering firms will be interested in building their own tables and engaging with their community schools to inspire the next generation of structural engineers. The Makers+Shakers program goal is to expand students' understanding of engineering's inherent complexities and uncertainties, while fostering appreciation for creative problem-solving in structural design.

Scan the QR code for build instructions for a prototype table. You’ll find parts lists, approximate prices, wiring diagrams and python code to make your own table. In addition, you’ll find the classroom program and score sheets as well as sample demonstrations. Everything is open source. Let us know how it’s going, either through our webpage and/or with the hashtag #MakersandShakers and share what modifications or improvements you’ve made to the table or the program. We’ll add it to the Makers+Shakers website for others to try. ■

About the Author

Tara Flaherty is an EIT in Schaefer’s Cincinnati office where in addition to serving as a project engineer, she leads Schaefer’s Makers+Shakers outreach program.
(tara.flaherty@schaefer-inc.com)

References

NCSEA Outreach Programs

U.S. Bureau of Labor Statistics

https://www.bls.gov/ooh/architecture-and-engineering/civil-engineers.htm

National Center for Education Statistics: Table 325.47

https://nces.ed.gov/programs/digest/d22/tables/dt22_325.47.asp

Schaefer Inc

Makers + Shakers | Schaefer Structural Engineers