The crashworthiness characteristics of rectangular tubes made from a carbon-fiber reinforced hybrid-polymeric matrix (CHMC) composite were investigated using quasistatic and impact crush tests. The hybrid matrix formulation of the CHMC was created by combining an epoxy-based thermosetting polymer with a lightly crosslinked polyurea elastomer at various cure-time intervals and volumetric ratios. The load-displacement responses of both CHMC and carbon-fiber reinforced epoxy (CF/epoxy) specimens were obtained under various crushing speeds; and crashworthiness parameters, such as the average crushing force and specific energy absorption (SEA), were calculated using subsequent load-displacement relationships. The CHMC maintained a high level of structural integrity and post-crush performance, relative to traditional CF/epoxy. The influence of the curing time and volumetric ratios of the polyurea/ epoxy dual-hybridized matrix system on the crashworthiness parameters was also investigated. The results reveal that the load carrying capacity and total energy absorption tend to increase with greater polyurea thickness and lower elapsed reaction curing time of the epoxy although this is typically a function of the loading rate. Finally, the mechanism by which the CHMC provides increased damage tolerance was also investigated using scanning electron microscopy (SEM).

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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.

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