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Proceedings of the Intel-national Conference on
Advances and New Challenges in Earthquake
Engineering Research, Hong Kong Volume
EFFECTIVENESS OF SMART BASE ISOLATION SYSTEM WITH
MR DAMPERS IN PROTECTING STRUCTURES
IN NEAR-FAULT EARTHQUAKES
Satish Nagarajaiah 1 , Sanjay Sahasrabudhe 2 and Yuqing Mao 2
1.Associate Professor, Civil & Env. Eng. , Rice University, Houston, TX
2 Engineer, McDermott, Houston, TX, Formerly, Graduate Research Assistant, Rice University
Abstract
This paper presents an analytical study of smart base isolated structures with vanable MR dampers,
which extends the results of prior analytical and experimental studies by the authors. New analytical models
of the nonlinear base isolated structures with MR dampers are developed. A Lyapunov based controller is
developed and used to perform simulations. Numerical simulations and parametric studies are performed
using several near-fault ground motions. The computed results are verified using shake table test results of
scaled base isolated structural model with MR dampers. It is demonstrated that base isolated structures with
MR dampers are more effective than base isolated structures with passive nonlinear dampers, in reducing
the response in wide range of near-fault earthquakes.
Introduction
Base isolation systems are effective in protecting structures in strong earthquakes. Recent studies have
shown that base isolated structures tend to have larger base displacements in near-fault long period earthquakes.
This may lead to large isolation gap or in cases—with insufficient isolation gap—pounding against
the retaining wall of the building, and damage to the superstructure. Nonlinear passive dampers have been
implemented in base isolated buildings to counter some of the effects of near-fault earthquakes (Taylor et
al. 2001). Although supplemental nonlinear passive dampers can limit base displacements, the isolation
forces, superstructure drifts and accelerations will be higher. Several researchers have recently studied the
capability of Magneto-rheological (MR) dampers and other variable dampers in effectively countering such
limitations (Gavin et al. 2001, Madden et al. 2000, Nagarajaiah et al. 2000, Spencer et al. 2000, Yang et
al 2002, and Yoshika et al. 2002). MR clampers, which can be used to vary the nonlinear damping in the
isolation systems, can reduce base displacements in near-fault earthquakes, further than passive nonlinear
dampers, while maintaining the same or lower level of isolation forces, superstructure drifts and accelerations,
as compared to passive nonlinear dampers (Sahasrabudhe et al. 2000,2001). Spencer et al. (2000)
and Yoshioka et al (2002) have shown the effectiveness of base isolated structures with MR dampers in
both moderate/strong and in near/far-fault earthquakes by analytical and experimental studies. This paper
presents an analytical study of smart base isolated structures with variable MR dampers, which extends the
results of prior analytical and experimental studies by the authors (Sahasrabudhe et al. 2000, 2001). It is
demonstrated that base isolated structures with MR dampers are more effective than base isolated structures
with passive nonlinear clampers, in reducing the response in wide range of near-fault earthquakes.
Analytical Model of Smart Base Isolated Structure with MR Dampers
The equations of motion for the smart base isolated structure shown in Figure 1 are as follows
M C U C + C C U C + K C U C + F c = B E u s (1)
c
f U \ ("