Students will be able to observe two ways engineers counter seismic accelerations on high-rise strucutres on order to make them safe. This demonstration will need to be made age-appropriate by the lesson that is built around it. Several suggestions are below.
The introduction to the lesson will develop the path your lesson takes. This demonstration could be used in lessons on pendulums (and all related principles such as waves, resonance, frequency, period, force, gravitational acceleration, and mass relationships), inertia, system equilibrium, earthquakes (ground motions and wave types), earthquake interactions with structures, earthquakes, structural or general engineering career fields, and damped harmonic oscillators.
Earthquake Engineering Component
Structural earthquake engineering is an iterative process that strives to improve structural response to earthquake-induced forces. Earthquakes can cause walls to crack, foundations to move or settle, utilities to rupture and even entire buildings to collapse. In an effort to protect the public and avoid structural damage engineers incorporate into their structural designs techniques that withstand these incredible forces. Some examples include cross bracing, tapered profiles, base isolation and tuned mass damping. In all cases engineers contrive an idea, test it, and then, based on its performance, re-engineer the structure until the desired outcome is achieved.
Learning Objectives and Standards
Links to the National Science Standards and to individual State Science Standards are available by using this link:
- Recognize that objects in motion have kinetic energy and objects at rest have potential energy. 2010 Indiana Academic Standard of Science: 6.1.4
- Discuss how the earthquake transfers kinetic energy into the structure, the structure transfers kinetic energy into the pendulum, and the pendulum oscillates between potential and kinetic energy. 2010 Indiana Academic Standard of Science: 6.4.3,
- Describe and investigate how forces act by means of direct contact between the ground and the structure or system. 2010 Indiana Academic Standard of Science: 7.1.5
- Use the model structures and shake table to demonstrate how an earthquake’s applied force acts upon it and changes its speed and direction. Explain that earthquake engineers strive to produce a structure that can resist or deflect those forces. 2010 Indiana Academic Standard of Science: 7.1.7
- Discuss how earthquakes are generated (through convection currents in the mantle and lithospheric plate movement). 2010 Indiana Academic Standard of Science: 7.2.4
- Follow the precise multistep procedure for the following experiment. 2010 Indiana Academic Standard of Science: 6-8.RS.3
- Learn important terms related to earthquakes and earthquake engineering, such as waves, energy, pendulum and force. 2010 Indiana Academic Standard of Science: 6-8.RS.4
- Identify some of the factors that help make buildings earthquake-proof including cross bracing and tuned mass dampers. Use technology, including the internet, to write about relationships between these systems. 2010 Indiana Academic Standard of Science: 6-8.WS.6, 6-8.WS.8
- Conduct research to answer: Why is it important for engineers to understand earthquakes? 2010 Indiana Academic Standard of Science: 6-8.WS.7
- Identify cause-effect relationships between earthquakes and structures. 2010 Indiana Academic Standard of Science: 6-8.WS.6
- Discuss methods to improve and re-engineer the structure they have created.
- Read and write for a variety of purposes and audiences. 2010 Indiana Academic Standard of Science: 6-8.RS.4
- Maintain a journal as a record of observations and conclusions.
- K’nex toys (or other building materials as desired)
- 1 inch iron plumbing elbow (weight used to replicate a simplified tuned mass damper)
- 18 inches of 1/4 inch nylon rope (used to dangle the tuned mass damper; see photos)
- OPTIONAL: Accelerometer from Quake Catcher Network (QCN) linked to a computer and QCN software (see link to QCN below).
See instructions at nees.org/education [update this with exact address once available] on how to assemble a shake table for the following activity. Construct and shake the structure(s):
- Build structures replicating bridges or buildings, as desired from the K’nex (or other materials; see photos).
- Attach the structure(s) to the shake table and apply lateral motion to the shake table emulating an earthquake.
- Suggestion: if possible, use two identically built structures for the demonstration. This way the students are able to observe the structure with and without the engineered correction in a side-by-side comparison.
- First, shake alone the structure with no earthquake engineering built into it. The students will quickly observe the amplitude of the building’s movement as it sways freely. Next, add the second structure that includes the pendulum tuned mass damper. Shake them side by side. Take caution to shake at the frequency of the tuned mass damper. It will be apparent that you’ve found its frequency when it sways freely while the building moves very slightly. Finally, add cross bracing stiffeners to the structure that does not have the pendulum. Now shake the structures once again showing that both are now resistant to the earthquake shaking.
- OPTIONAL: Attach the QCN accelerometer to the shake table for students to observe the accelerations being applied to the structures. Explain that earthquakes don’t apply forces to the buildings; they apply accelerations, which when combined with the mass of the building produce forces.
- Further explanation: Care must be taken to shake the table such that the frequency and amplitudes allow for the pendulum to counteract the swaying of the building. Engineers strive to design TMDs whose frequency and amplitude match that of their corresponding structures such that every time the building is accelerated by some external system, such as wind or earthquakes, the pendulum pushes back equally and in the opposite direction. For the scope of this demonstration the TMD is not scientifically “tuned” so the demonstrator will need to shake in such a way as to show how the TMD steadies the structure when it is tuned to its frequency.
- Base Isolation – a collection of structural elements that work to decouple a structure from its foundation resting on a shaking ground, thereby protecting it from damage.
- Cross Bracing – a system used to reinforce structures with diagonal supports.
- Earthquake Engineering – study of the behavior of buildings and other structures subject to seismic loading.
- Frequency – the number of times a structure or system goes through one complete cycle of vibration in one second (1/period, Hz).
- Inertia – the resistance of a structure or system to change its state of motion or rest.
- Period – the length of time it takes a structure or system to go through one complete cycle of vibration (1/frequency, s).
- Resonance Vibration – the tendency of a structure or system to oscillate with larger amplitudes at some frequencies than at other frequencies. Seismic Loading – earthquake generated excitation to a structure.
- System Equilibrium – a condition in which all acting influences are canceled by others, resulting in a stable, balanced, or unchanging system.
- Tuned Mass Damping – the use of a tuned mass damper to reduce the vibration of a structure or system and stabilize it against violent motion caused by resonance vibration.
Links and Resources
- NEES Academy: http://nees.org/education/for-teachers/k12-teachers
- Quake Catcher Network: http://qcn.stanford.edu
- Teach Engineering: http://teachengineering.com
Pre Activity Assessment
- Compare and contrast differences in each model: have students write their observations before either building is shaken.
- Have students make predictions based on their preliminary observations and write them in a notebook.
Activity Embedded Assessment
- Compare and contrast differences in each model during and after each shaking activity: have students write their observations.
- Invite students to comment on what they are observing, draw conclusions, and innovate with new ideas that might have similar effects on the structures. You may choose to test the innovative ideas to see how well they work, or don’t work.
Post Activity Assessment
- Compare and contract what was observed before and after the engineered corrections were applied to the structures.
- Invite students to comment on why these applications are important. Have them record their reflections in a notebook.
- This activity could be extended by having the students construct their own buildings and holding a competition where each building is shaken to see which holds up best. Attaching some kind of weight to the top floor (or multiple floors) of the structure (pennies or washers, etc.) will generate larger forces and make the design more difficult.
- Additionally, USGS, Center for Engineering Strong Motion Data (www.strongmotioncenter.org), EERI, NEHRP, and NEES are excellent inquiry sources for the students to explore answers to questions, current global seismic activity, or other as desired. Then have students write reports on their findings and draw connections and relationships between their findings and their observations in this experiment. 2010 Indiana Academic Standard of Science: 6-8.WS.6, 6-8.WS.7, 6-8.WS.8
- This activity could be accomplished with several types of materials, see this link for a similar demonstration using foam and wood blocks http://nees.org/resources/430 .
- This demonstration can be tailored to the learning level of the students by the complexity of the principles drawn upon for discussion and reflection (i.e. harmonic oscillators vs. forces).
- This demonstration is easily made more difficult and interactive by making it a competition between student teams with provided constraints and performance requirements.
Cite this work
Researchers should cite this work as follows: