The performance of nonlinear lead-core-rubber base isolators (LCR) to passively
control highly nonlinear vibrations in two steel buildings and a prestressed concrete
bridge under various ground motion inputs is evaluated. The Bouc and Wen model is
used to predict the behavior of the lead-core component of the LCR base
isolator. Members of the steel buildings that may have yielded are analyzed
according to a highly nonlinear constitutive rule used to model the smooth
stiffness degradation in the damaged members. The previously developed
constitutive rule analyzes kinematically strain-hardened materials under cyclic
conditions. The ability of the LCR to reduce displacement, velocity, and
acceleration demands is demonstrated numerically using an algorithm developed
herein called BISON (base isolation in nonlinear time history analysis). The
performance of the LCR isolation is measured for a two story isolated building
excited by the El Centro ground motion, a nonstationary signal, and the
Northridge ground motion. An eight-story building exhibiting higher-mode
influence is also analyzed, and finally the overpass bridge on Highway 99 in
Selma, CA is modeled, outfitted with LCR isolation, and also analyzed. The
hysteresis of the force-displacement relationships of the structures and the LCR
isolators are analyzed parametrically through two LCR design parameters.
The results indicate that with an appropriate tuning of these parameters,
which affect the inelastic stiffness of the LCR isolator, an appropriate LCR
system may be designed to behave with a stationary-like hysteresis and
that can very adequately reduce the structural demands under the various
excitations.
Keywords
base isolation, passive control, bridge isolation,
lead-core rubber base isolation, higher-mode effects,
plastic analysis, inelastic structures
