Help Page for the Java-Powered Simulation for Base Isolation

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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 five cases: (i) a conventional structure fixed directly to the ground; (ii) ~ (v) base isolated structures where the isolation system is installed between the structure and the ground to restrict the earthquake energy. Currently base isolation devices which are composed of rubber component and lead plug used for gaining a damping are widely applied. These components have nonlinearlities. Thus the models of base isolation system which is taken account of its nonlinearlities are newly added and the user can compare each reponse. The case (ii) is the model for the linear isolator. This isolator has both linear damping and linear stiffness. (iii) is the model for the nonlinear damping isolator. This case treats a nonlinearlty of a rubber. (iv) and (v) are the models for the hysteretic isolator. These cases deal with the nonlinearlities of lead plug which has elastic and plastic region. The characteristic of the lead plug is described by using Bouc Wen model as case (iv) and bilinear model as case (v). The structure here is modeled as a single-degree-of-freedom linear 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]
Fig. 1 Java Powered Simulation 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) Excitation Signal Frame; (4) 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

Excitation 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 excitation.

Fixed Base, Linear Isolator, Nonlinear Damping, Bouc-Wen Model and Bilinear Model 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:

Excitation 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 signal by the proper selection of the menu.

Response Spectra Plot Frame

This frame, located in the lower left of the simulation window, displays response spectra plots. 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 excitation signal shown in the Excitation Signal Frame. It can show the displacement, velocity or acceleration of the superstructure or base slab, or the shear force of the columns. Besides, not only time reponses but also displacement (or velocity) vs. restoring force (or damping force, or total force) plot can be shown in this frame. Peak response information such as maximum value of each signal, peak reduction (= maximum peak of each 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".

  4. Teb Belytschko, Thomas J.R. Hughes. "Computational Methods for Transient Analysis", North-Holland.

  5. Glen V. Berg. "Elements of Structural Dynamics", Prentice-Hall International.


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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