Help Page for the Java-Powered Simulation for Base Isolation


Table of Contents

Go to the Japanese version of this page.
Page created by Yoshinori Sato
Modified by Richard Christenson and Erik A. Johnson

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Welcome to the help page of the Java-Powered Simulation for Base Isolation.

Base isolation is an important strategy for protecting structures from earthquake excitations. Base isolation attempts to isolate a structure from the external ground excitations, not by trying to dissipate the energy of the earthquake within the structure, rather by not allowing this energy to even enter the structure. As a testament to this strategy, buildings in the Kansai region of Japan with base isolation devices survived the devastating 1995 Kobe Earthquake with little or no damage. This event has prompted great interest in the viability of base isolation for seismic protection of Civil structures.

This simulation considers two cases: (i) a conventional structure fixed directly to the ground; and (ii) a base isolated structure where the isolation system is installed between the structure and the ground to restrict the earthquake energy. The structure here is modeled as a single-degree-of-freedom system.

The user can vary the properties of the structure, the isolation system and the earthquake motion, allowing for insight into the influence of various parameters on the responses of the system. Animation of the user designed systems facilitates visualization of parameter effects. The base isolation simulation is intended to be used to increase understanding and provide a conceptual "feel" for various parameter changes on the performance of base isolated systems.

This document offers a description of how to operate and use the Java-Powered Simulation for Base Isolation, a picture of which is shown below. In addition, technical background, including the formulation of the equations of motion and important definitions, is given, a number of "homework" problems (or exercises) are suggested, and references are provided.

[picture of java applet]


How to Use the Simulation

There are five components of the simulator that can be modified by the user to obtain specific and unique conditions for base isolation: (1) Control Panel; (2) Animation Frame; (3) Earthquake Signal Frame; (4) Bode Plot & Response Spectra Plot Frame; and (5) Time Response Frame. These are each identified on the above picture of the simulation page.

Control Panel

Located on the far right of the simulator, this panel is used to enter specific data for the structure, base isolation system and earthquake. This panel also contains the buttons to recalculate the system parameters, animate the system and perform additional functions.

Structural Parameters

Isolation System Parameters

[diagram showing seismic gap]

Earthquake Input Parameter

Check Boxes

Response Window Zooming

Number of Spectra Data Point

Action Buttons

Animation Frame

The animation frame, located in the upper left portion of the simulation window, shows a simulation of the structural system undergoing the earthquake excitation.

Fixed or base isolated structures can be animated by the appropriate selection in the left menu of this frame.

The user can also choose to animate absolute or relative motion of the structure:

Earthquake Signal Frame

Located in the top center of the simulation window, the earthquake signal frame shows the current earthquake signal. Four historical earthquake records are available for simulation:

The user can choose to display the displacement or the acceleration of the earthquake signal by the proper selection of the menu.

Bode Plot & Response Spectra Plot Frame

This frame, located in the lower left of the simulation window, displays Bode plots and response spectra plots. The Bode plots are for the transfer function from ground acceleration to the displacement, velocity or acceleration of the superstructure or base slab, or the shear force of the columns. The particular transfer function displayed corresponds to the response shown in the Time Response Frame. The possible response spectra plots consist of displacement, velocity and acceleration.

Time Response Frame

The time response frame, located in the bottom center of the simulation window, displays the system's response due to the earthquake signal shown in the Earthquake Signal Frame. It can show the displacement, velocity or acceleration of the superstructure or base slab, or the shear force of the columns. Peak response information such as maximum value of each signal, peak reduction (= maximum peak of isolated case / maximum peak of fixed case * 100 (%) ) or base shear is displayed in the lower portion of this frame.


Technical Background

Definition of the Primary Parameters

Mathematical Model

Other Definitions



  1. Change the natural frequency of the superstructure to 0.5, 1.0 and 2.0 Hz and calculate the responses.

  2. Change the natural frequency of isolation layer to 0.1, 0.5 and 1.0 Hz and calculate the responses.

  3. Change the mass ratio to 0.1, 1.0 and 10.0 and calculate the responses.

  4. Change the damping ratio of isolation layer to 0.1, 0.2 and 0.4 and calculate the responses.

  5. Compare the responses of the system to each of the earthquakes having the same maximum acceleration (enter the same number in the text field of the Max Amplitude).

  6. Consider the reason that when using base isolation (the case of isolated base) with default values, the peak or natural frequency of the superstructure in the Bode diagram doesn't appear the same frequency as that of fixed base.

  7. Design an isolation device which can protect the structure against the four earthquake excitations, provided that the parameters of the isolation layer satisfy following restrictions.

    • Natural Frequency: 0.25 ~ 1 Hz
    • Damping Ratio: 0.01 ~ 0.40
    • Seismic Gap: ~ 0.50 m



  1. Skinner, R. I., Robinson, W. H., McVerry, G. H. (1993). "An Introduction to Seismic Isolation", Wiley.

  2. Kelly, James M. (1997). "Earthquake-Resistant Design with Rubber", Springer.

  3. Structural Engineering Design Provisions. "1997 Uniform Building Code".



The support of the National Science Foundation under Grant No. CMS 95-28083 (Dr. S.C. Liu, program director), and the support of the Multidisciplinary Center for Earthquake Engineering Research (MCEER) are gratefully acknowledged. In addition, we would like to thank Prof. Yozo Fujino of the University of Tokyo for his help in securing the Kobe and Hachinohe earthquake records.


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