22 Structure and Equipment Isolation Y.B. Yang

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National Taiwan University L.Y. Lu

National Kaohsiung First University

of Science and Technology J.D. Yau

Tamkang University

22.1 Introduction ........................................................................ 22-2

22.2 Mechanisms of Base-Isolated Systems .............................. 22-4

Elastomeric Isolation System † Sliding Isolation System †

Sliding Isolation System with Resilient Mechanism †

Electricite de France System † Concluding Remarks

22.3 Structure – Equipment Systems with Elastomeric

Bearings ............................................................................... 22-9

Formulation of Base Isolation Systems with Elastic

Bearing † Free Vibration Analysis † Dynamics of

Structure – Equipment Isolation Systems to Harmonic

Excitations † Illustrative Example † Concluding

Remarks

22.4 Sliding Isolation Systems ................................................... 22-17

Mathematical Modeling and Formulation † Methods for

Numerical Analysis † Simulation Results for Sliding

Isolated Systems † Concluding Remarks

22.5 Sliding Isolation Systems with Resilient

Mechanism .......................................................................... 22-36

Mathematical Modeling and Formulation † Methods for

Numerical Analysis † Simulation Results for Sliding

Isolation with Resilient Mechanism † Concluding

Remarks

22.6 Issues Related to Seismic Isolation Design ....................... 22-50

Design Methods † Static Analysis † Dynamic

Analysis † Concluding Remarks

Summary

In this chapter, a brief review will be given of the concept of isolation for suppressing the vibrations in structures and

equipment subjected either to harmonic or seismic ground excitations. The mechanism of various isolation devices,

including the elastomeric bearing, sliding bearing, resilient-friction base isolator, and Electricite de France system,

will first be described in Section 22.2, together with their mathematical models. In Section 22.3, a closed form

solution will be derived for the dynamic response of a structure – equipment system isolated by bearings of the

elastomeric type, subjected to harmonic motions. Such a solution enables us to interpret the various behaviors of the

structure and equipment under excitation. The elastomeric bearings can help increase the fundamental period of

the structure, thereby, reducing the accelerations transmitted to the superstructure. In Section 22.4 and Section 22.5,

the seismic behavior of a structure – equipment system isolated by a sliding support, with and without resilient force,

will be studied using a state-space incremental-integration approach. With the introduction of a frictional sliding

interface, the motion of the structure – equipment system will be uncoupled from the ground excitation, and the

influence of the latter will be mitigated. The residual base displacement caused by the sliding isolator can be reduced

22-1

© 2005 by Taylor & Francis Group, LLC

through inclusion of a resilient mechanism in the isolator. Nevertheless, the resilient mechanism can make the

system more sensitive to the low-frequency components of excitation. In Section 22.6, issues related to design of base

isolators will be discussed, along with the concepts underlying some design codes and guidelines. The notation used

is listed at the end of the chapter.

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