• Journal of the Earthquake Engineering Society of Korea
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• v.24 no.4
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• pp.157-167
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• 2020

In this study, a field bridge test was conducted to find the dynamic properties of cable supported bridges with resilient-friction base isolation systems (R-FBI). Various ambient vibration tests were performed to estimate dynamic properties of a test bridge using trucks in a non-transportation state before opening of the bridge and by ordinary traffic loadings about one year later after opening of the bridge. The dynamic properties found from the results of the tests were compared with an analysis model. From the result of the ambient vibration tests of the cable supported bridge with R-FBI, it was confirmed that the dynamic properties were sensitive to the stiffness of the R-FBI in the bridge, and the seismic analysis model of the test bridge using the effective stiffness of the R-FBI was insufficient for reflecting the dynamic behavior of the bridge. In the case of cable supported bridges, the seismic design must follow the "Korean Highway Bridge Design Code (Limit State Design) for Cable supported bridges." Therefore, in order to reflect the actual behavior characteristics of the R-FBI installed on cable-supported bridges, an improved seismic design procedure should be proposed.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.975-982
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• 2005

Scientific community agrees about the fact that base Isolation provides interesting solutions to minimize the seismic risk. Reliability of such a technique is nowadays proofed by a large number of applications like public buildings, nuclear plants, bridges, etc. This paper reports the results of performance verification tests of the base isolated RC building with the laminated rubber bearings which is manufactured by enterprise in Korea. The shaking table tests were performed using a three story model scaled to 1/3 of the prototype RC apartment building. Several major earthquake records were scaled to different peak ground accelerations and used as input base excitations. Especially in this study, effect of earthquake characteristics on response reduction and effect of the intensity of excitations are studied. Through the verification tests, the validity of the applied base isolaion device and the response reduction effect against earthquakes are confirmed.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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• pp.391-398
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• 2000

To evaluate the seismic performance of a base isolated building accurate analytical model should be selected. The analytical results such as reduced accelerations member forces and relative displacements of the superstructure of the base isolated building are only meaningful when the analytical model is close enough to the real structure. Real size one bay-two story steel frame and two kinds of seismic isolators(laminated elastomeric bearing and lead-rubber bearing) are designed. manufactured and constructed in the laboratory. Free vibration tests using fuse bars were conducted to evaluate the change of dynamic characteristics(period and damping) before and after base isolation of the steel frame. The experimental results of free vibration tests were also used as a bench mark for adjusting the selected analytical modeling to real base isolated steel frame.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.10a
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• pp.167-175
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• 2000

Seismic analyses of structures can`t be performed without considering the effect of soil-structure interaction and seismic responses of a structure taking into account the stiffnesses of a foundation-soil system show a significant difference from those with a rigid base. However, current seismic analyses of apartment building structures were carried out assuming a rigid base and ignoring the characteristics of a foundation and the properties of the underlying soil. In this study, seismic analyses of apartment buildings of a particular wall-slab structural type were carried out comparing seismic response spectra of a flexible base with those of a rigid base and UBC-97. Wall-slab type low-rise or mid-height apartment buildings built on the deep soil layer showed a rigid body motion with the reduced seismic responses due to the base isolation effect, indicating that it is too safe but uneconomical to utilize the design spectra of UBC-97 for the seismic analysis of a wall-slab type apartment buildings due to the too conservative design.

• Structural Engineering and Mechanics
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• v.53 no.1
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• pp.57-71
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• 2015

This study investigates the feasibility of retrofitting an existing building by connecting the existing building to a new building using connecting dampers. The new building is base-isolated and viscoelastic dampers are assigned as connecting dampers. Scaled models are tested under three different earthquake records using a shaking table. The existing building and the new building are 9 and 8 stories respectively. The existing building model shows more than 3% increase in damping ratio. The maximum dynamic responses and the root mean square responses of the existing building model to earthquakes are substantially reduced by at least 20% and 59% respectively. Further, numerical models are developed by conducting time-history analysis to predict the performance of the proposed seismic mitigation system. The predictions agree well with the test results. Numerical simulations are carried out to optimize the properties of connecting dampers and base isolators. It is demonstrated that more than 50% of the peak responses can be reduced by properly adjusting the properties of connecting dampers and base isolators.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.5
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• pp.377-388
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• 2016

This study is aimed to evaluate the embedment effect of foundation as compared to the surface foundation on the response of a base-isolated nuclear power plant structure. For this purpose, the boundary reaction method (BRM), which is a two-step frequency domain and time domain technique, is used for the nonlinear SSI analysis considering nonlinear behavior of base isolators. The numerical model of the BRM is verified by comparing the numerical results obtained by the BRM and the conventional frequency-domain SSI analysis for an equivalent linear SSI system. Finally, the displacement response of the base isolation and the horizontal response of the structure obtained by the nonlinear SSI analysis using the moat foundation model are compared with those using the surface foundation model. The comparison showed that the displacement response of the base isolation can be reduced by considering the embedment effect of foundation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.5
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• pp.1025-1037
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• 2015

Flexible base isolation bearings that separate superstructure from ground have been widely used in the construction field because they make a significant contribution to increasing the fundamental period of the structure, thereby decreasing response acceleration transmitted into the superstructure. However, the established bearing devices installed to uphold the whole building give rise to some problems involved with failure and collapse due to lack of the capacity as modern structures are getting more massive and higher. Therefore, this study suggests new isolation bearings assembled with additional restrainers enabled to reinforcing and recentering, and then evaluates their performance to withstand the seismic load. The superelastic shape memory alloy (SMA) bars are installed into the conventional lead-rubber bearing (LRB) devices in order to provide recentering forces. These new systems are modeled as component spring models for the purpose of conducting nonlinear dynamic analyses with near fault ground motion data. The LRB devices with steel bars are also designed and analyzed to compare their responses with those of new systems. After numerical analyses, ultimate strength, maximum displacement, permanent deformation, and recentering ratio are compared to each model with an aim to investigate which base isolation models are superior. It can be shown that LRB models with superelastic SMA bars are superior to other models compared to each other in terms of seismic resistance and recentering effect.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.2 s.42
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• pp.37-46
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• 2005

To date, many viable smart base isolation systems have been proposed and investigated. In this study, a novel friction pendulum system (FPS) and an MR damper are employed as the isolator and supplemental damping device, respectively, of the smart base isolation system. A fuzzy logic controller (FLC) is used to modulate the MR damper because the FLC has an inherent robustness and ability to handle non linearities and uncertainties. A genetic algorithm (GA) is used for optimization of the FLC. The main purpose of employing a GA is to determine appropriate fuzzy control rules as well to adjust parameters of the membership functions. To this end, a GA with a local improvement mechanism is applied. This method is efficient in improving local portions of chromosomes. Neuro fuzzy models are used to represent dynamic behavior of the MR damper and FPS. Effectiveness of the proposed method for optimal design of the FLC is judged based on computed responses to several historical earthquakes. It has been shown that the proposed method can find optimal fuzzy rules and the GA optimized FLC outperforms not only a passive control strategy but also a human designed FLC and a conventional semi active control algorithm.

• Journal of Korean Association for Spatial Structures
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• v.10 no.3
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• pp.49-56
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• 2010

In this study, the control performance of a smart top-story isolation system for tall buildings subjected to wind excitation was investigated. To this end, a 77-story tall building structure was employed and wind loads obtained from wind tunnel test were used for numerical simulations. The top-story of an example structure is separated from the main structure by a smart base isolation system composed of friction pendulum systems (FPS) and MR dampers. The primary purpose of the smart top-story isolation system is to mitigate the dynamic responses of the main structure, but the excessive movement of the isolated top story may cause the unstableness of the building structure. Therefore, the skyhook control algorithm was used to effectively reduce both responses of the isolated top story and the main structure. The control performance of the proposed smart top-story isolation system was investigated in comparison with that of the passive top-story isolation system. It has been shown from numerical simulation results that the smart top-story isolation system can effectively reduce wind-induced responses of the example building structure compared to the passive top-story isolation system with reduction of the top-story movement.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.3
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• pp.65-74
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• 2019

This study presents the optimal isolation period according to the number of vertically expended stories in order to provide the basic data for the application of the seismic isolation system in the vertically expended remodeling of the aged apartment. As a result of the structural analysis, the isolation period should be at least twice the primary structure in three-story vertical expansion, three times in two-story expansion, and four times in one-story expansion for the effective application of the isolation system. On the basis of the result, the efficacy of an isolation system for the actual apartment structure, which is three-story vertically expended, was analytically verified. The maximal acceleration response on the top floor reduced by 70% and 65% of the non-isolated structure in the X and Y directions respectively. Additionally, the base shear force decreased by 30% in the both directions, compared to the non-isolated structure.