Application and design of lead-core base isolation for reducing structural demands in short stiff and tall steel buildings and highway bridges subjected to near-field ground motions

Abstract

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.