Low-rise
Frequencies without isolation
fₙ = 2.0 Hz · T = 0.5 s
0.0 cmDeformation: roof relative to baseWhy does this building sway?
The same ground motion. Three different responses. Find the frequency that makes each model sway the most.
Educational model. It does not assess the safety of buildings or homes.
Synthetic input · sine wave
0.0 s
All three models receive identical ground motion.
Mid-rise
Frequencies without isolation
fₙ = 1.0 Hz · T = 1.0 s
0.0 cmDeformation: roof relative to baseHigh-rise
Frequencies without isolation
fₙ = 0.5 Hz · T = 2.0 s
0.0 cmDeformation: roof relative to basePeak since startMotion is enlarged equally for every model; building heights are illustrative.
Earthquake laboratory
Each model has a different mass and stiffness, giving it its own natural rhythm. Move the frequency slider or choose one of the three starting points. Drawing height helps identify the models — it does not determine the behavior of a real building on its own.
Find the structure’s rhythm
When the driving frequency approaches a model’s natural frequency, successive ground movements can increase its response. This is resonance. The sway takes several cycles to develop.
Damping removes energy
Increase structural damping to limit the buildup of motion near resonance. The slider specifies a percentage of critical damping in the model, not a percentage improvement in safety.
Let the base move
Simplified isolation adds a flexible, damped layer beneath the structure. It changes natural frequencies and can reduce building deformation at the cost of greater base movement. It does not help at every frequency — near the new resonance, the response can increase.
How does the experiment relate to real buildings?
This lab explores how frequency, damping and base isolation affect structural motion. The guide below explains these concepts and the information a specialist needs to analyse a real building and earthquake.
From period to frequency
The natural period T₁ is the time taken for one complete cycle of structural vibration. The converter calculates f₁ = 1/T₁ and sets that as the experiment’s ground-motion frequency. The three fictional buildings keep their properties: entering your home’s natural period does not reproduce its behaviour.
s→ 0.67 Hz
Converter range: 0.34–5.00 s. This changes the driving frequency, not the building properties.- Convert a known period: f₁ = 1/T₁. Example: T₁ = 1.5 s gives about 0.67 Hz.
- Set that ground-motion frequency. Compare the three models, then try lower and higher frequencies.
- If damping is unknown, treat 5% only as a teaching value.
- Leave amplitude illustrative and compare responses relatively. The sine-wave centimetres are neither PGA nor the amplitude of a specific record.
Enable base isolation to compare two model configurations under the same input. This illustrates the mechanism; real isolation devices have properties specified in the building’s documentation.
1. Find the building properties
The fundamental period T₁, estimated damping and information about base isolation or dampers are most useful. Real analysis also needs storey masses and stiffnesses, the structural system and the building's condition.
Ask the owner or manager, designer or structural engineer for structural calculations, a seismic diagnosis or time-history analysis. If the period is not documented, an engineer can estimate it from a model or vibration measurements.
2. Find an earthquake record
You need an acceleration time history — an accelerogram from a representative station and the appropriate component. Magnitude, JMA intensity or one PGA value does not describe frequency content or duration.
NIED publishes Japanese records through K-NET and KiK-net; waveform downloads require registration. JMA provides selected records but prohibits redistributing data published there, so we link to the source instead of copying files.
3. Check the site conditions
An exact location lets you inspect AVS30, geomorphologic classification and surface amplification. They help judge whether a station record represents the site, but cannot reconstruct motion at the building by themselves.
In J-SHIS, select Site Amp., zoom to the address and open point information. A building analysis may require local boreholes, an S-wave velocity profile and the site's geotechnical report.
| Information | Where to find it | How it works here |
|---|---|---|
| Period T₁ / frequency f₁ | Structural documents or engineering measurement | The converter sets the ground-motion frequency; the buildings remain fictional models |
| Damping | Model, analysis or measurement | Set the slider; 5% is only an example |
| Accelerogram | K-NET / KiK-net or JMA | The experiment uses a generated sine wave, without importing earthquake records |
| AVS30 and site amplification | J-SHIS or geotechnical documents | Local ground information; these are not parameters of this experiment |
If the question is “is my building safe?”, a qualified structural engineer must assess it. This module can help explain such an analysis, but cannot replace one.
Parameters of the fictional structures
Without isolation, u is roof displacement relative to the ground, m is mass, c is the damping coefficient, k is stiffness and a_g is ground acceleration. u′ denotes velocity and u″ denotes acceleration. With isolation, we solve two coupled equations of motion: one for the structure and one for the base.
| Natural frequency | Low-rise | Mid-rise | High-rise |
|---|---|---|---|
| fₙ / T | 2.0 Hz / 0.5 s | 1.0 Hz / 1.0 s | 0.5 Hz / 2.0 s |
| Mass | 100 t | 300 t | 800 t |
| Stiffness | 15.79 MN/m | 11.84 MN/m | 7.90 MN/m |
| Structural damping | ζ = 5% | ||
| Damping coefficient | 125.7 kN·s/m | 188.5 kN·s/m | 251.3 kN·s/m |
| Base isolation | fᵢ = 0.25 Hz · ζᵢ = 20% · mᵦ = 0.25 m | ||
The base mass is 25% of the structure’s mass. The isolation parameters — 0.25 Hz and 20% of critical damping — are chosen for the combined base and structure mass, treating the structure as rigid. The actual natural frequencies of the coupled two-mass model differ.
m·u″ + c·u′ + k·u = −m·ag · k = m·(2πfₙ)² · c = 2ζ√(km)
What does this experiment show?
These are linear models with illustrative masses, stiffnesses, natural frequencies and damping. The structure has one degree of freedom without isolation and two with isolation. We omit effects such as twisting, multiple vibration modes, damage and complex soil–foundation interaction. The input is a generated sine wave with a gradual ramp, not a historical earthquake recording. Neither AVS30 nor a soil amplification factor is sufficient to reproduce a particular building’s response. The drawing does not predict damage, provide a structural assessment or serve as an EEW warning system.
Original JISHINDESU model and illustrations. The input is generated mathematically; the listed sources explain the model’s foundations.
Model foundations and sources: USGS · FEMA · Fujitani et al. (2012)