What it shows
Large parts of India lie in seismic zones, and building codes require earthquake-resistant design. A low-cost shake table moves a model building side to side at chosen frequencies. The project finds the natural frequency of tall and short models, shows resonance and tests a rolling base isolator.
The science
Every structure has a natural frequency that depends on its mass and stiffness, roughly lower for taller and heavier structures. When the ground shakes at a frequency near this natural one, resonance makes the motion grow large. Base isolation puts a flexible layer under the building to lengthen its natural period, so the ground motion is not passed on at the same strength.
Materials
Cost: under Rs 5,000. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A 40 x 40 cm plywood platform on linear rails made from drawer slides
- A 12 V geared DC motor with a crank and connecting rod for a stroke of 1 to 2 cm
- A PWM motor driver and a 12 V sealed supply
- Model buildings from balsa or ice-cream sticks: a 3-storey and a 6-storey frame with weights as floors
- An MPU6050 accelerometer and Arduino, or a phone accelerometer app
- Marbles between two plates for a base isolator
- A phone for slow-motion video
Safety
For this project: Keep clear of the moving platform and clamp the base to the table. Use a battery or sealed 12 V adapter only. An adult must supervise, especially when the model sways strongly.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
11 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Build the table so that the platform slides freely along the rails and is driven by the crank, and check that stroke is about 1.5 cm.
Use PWM to change the motor speed and calibrate the frequency from video or accelerometer data.
Attach one MPU6050 to the platform and another to the roof of the model and log accelerations at 100 Hz.
Build the 3-storey and 6-storey models with the same plan and identical floors.
Find the natural frequency of each model by tapping and recording the free vibration, then calculating the frequency from the peaks.
Run a frequency sweep on the table from 1 to 8 Hz and record the roof acceleration at each step.
Plot the amplification (roof divided by base acceleration) against frequency and mark the resonance peaks.
Compare the peaks with the natural frequencies found in the tap test and check which model resonates at the lower frequency.
Place the model on the rolling marble isolator and repeat the sweep.
Compute the reduction in peak acceleration and the sideways displacement of the isolator.
Write the report with the shake table design, graphs, comparison, and relation to the Indian seismic zone map.
What you should see
Both models show a clear resonance peak, with the taller model peaking at a lower frequency. The isolated model shows much smaller roof acceleration near resonance, with a large slide at the base that the report points out as a design issue.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is resonance?
A large response when the driving frequency equals a natural frequency of the system.
2Why do tall buildings have lower natural frequencies?
They are more flexible and have more mass at height.
3How does base isolation work?
A flexible layer lengthens the building’s period so that less of the ground motion passes into it.
4What is a seismic zone?
A region classified by the expected earthquake intensity, used in the building code.
Take it further
Add diagonal bracing to the 6-storey model and show how it raises the natural frequency and lowers the sway.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
Free ebooks for this project
Science projects
Mini and Major Project Guide
For diploma and BTech students: choose, plan, build, document and present