• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.2
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• pp.119-131
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• 2024

Pulse-like ground motion can cause greater damage to structures than nonpulse-like ground motion. Currently, much research is being conducted to determine the presence or absence of velocity pulses and to quantify them from seismic-acceleration records. Existing ground motion is divided into far-field (FF) and near-fault ground motion, based on the distance of the measurement point from the fault. Near-fault ground motion is further classified into near-fault pulse-like (NFP) and near-fault nonpulse-like (NFNP) ground motion by quantifying the presence or absence of velocity pulses. For each ground motion group, 40 FF, 40 NFP, and 40 NFNP ground motions are selected; thus, 120 ground motions are used in the seismic analysis to assess the seismic fragility of sample bridges. Probabilistic seismic demand models (PSDMs) are created by evaluating the seismic responses of two types of sample bridges with lead-rubber and elastomeric rubber bearings using three groups of ground motions. Seismic fragility analysis is performed using the PSDM, and from these results, the effect of the presence or absence of seismic velocity pulses on the seismic fragility is evaluated. From the comparison results of the seismic fragility curve, the seismic fragility of NFP ground motion appears to be approximately three to five times greater than that of NFNP ground motion, according to the presence or absence of a velocity pulse of seismic waves. This means that the damage to the bridge is greater in the case of NFP ground motion than that in the case of NFNP ground motion.

• Journal of the Earthquake Engineering Society of Korea
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• v.8 no.3
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• pp.63-76
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• 2004

This paper presents LRB-based hybrid base isolation systems employing additional active/semiactive control devices for mitigating earthquake-induced vibration of a cable-stayed 29 bridge. Hybrid base isolation systems could improve the control performance compared with the passive type-base isolation system such as LRB-installed bridge system due to multiple control devices are operating. In this paper, the additional response reduction by the two typical additional control devices, such as active type hydraulic actuators controlled by LQG algorithm and semiactive-type magnetorheological dampers controlled by clipped-optimal algorithm, have been evaluated bypreliminarily investigating the slightly modified version of the ASCE phase I benchmark cable-stayed bridge problem (i.e., the installation of LRBs to the nominal cable-stayed bridge model of the problem). It shows from the numerical simulation results that all the LRB based hybrid seismic isolation systems considered are quite effective to mitigate the structural responses. In addition, the numerical results demonstrate that the LRB based hybrid seismic isolation systems employing MR dampers have the robustness to some degree of the stiffness uncertainty of in the structure, whereas the hybrid system employing hydraulic actuators does not. Therefore, the feasibility of the hybrid base isolation systems employing semiactive additional control devices could be more appropriate in realfor full-scale civil infrastructure applications is clearly verified due to their efficacy and robustness.