• Earthquakes and Structures
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• v.19 no.5
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• pp.395-409
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• 2020

With verifications through many relevant researches in the past few decades, adopting the equivalent lateral force procedure for designing seismically isolated structures as a preliminary or even final design approach has become considerably mature and publicly acceptable, especially for seismic isolation systems that mechanically exhibit bilinear hysteretic behavior. During the design procedure, in addition to a given seismic demand, structural designers still need to previously determine three parameters, such as mechanical properties of seismic isolation systems or design parameters and performance indices of seismically isolated structures. However, an arbitrary or improper selection of given parameters might cause diverse or even unacceptable design results, thus troubling structural designers very much. In this study, first, based on the criterion that at least either two design parameters or two performance indices of seismically isolated structures are decided previously, the rationality and applicability of design results obtained from different conditions are examined. Moreover, to consider variations of design parameters of seismically isolated structures attributed to uncertainties of mechanical properties of seismic isolation systems, one of the conditions is adopted to perform bounding analysis for seismic isolation design. The analysis results indicate that with a reasonable equivalent damping ratio designed, considering a specific variation for two design parameters (the effective stiffness and equivalent damping ratio) could present more conservative bounding design results (in terms of isolation displacement and acceleration transmissibility) than considering the same variation but for two mechanical properties (the characteristic strength and post-yield stiffness).

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.247-251
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• 2001

Nowadays, base isolation systems such as lead-rubber bearing, elastomer bearing and sliding bearing have been installed to the various structures to prevent the disaster from seismic. The performance of base isolation system have been well proved by model-scale experiments and numerical analysis. However. the seismic response data measured at real large base-isolated structures is still insufficient. This paper presents a seismic monitoring system, acquiring real-time acceleration signals up to 32 channels, displaying time history and spectrum of the signals, storing the acquired data at a PC hard disk, and replaying the saved data. Moreover, the system can be operated without any limitation for monitoring period by automatic management of stored data file. The developed system has been installed at a real base-isolated building using lead-rubber bearings and we expect its seismic response data with ground motion signal can be well licquired in case of earthquake occurrence.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.7 no.3
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• pp.30-39
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• 2011

URANUS (Ubiquitous, Robust, Accident-forgiving, Non-proliferating, Ultra-lasting and Sustainer) has been developed with 35MWe (100MWth) operating without primary coolant pump, capitalizing on natural circulation capability of lead-bismuth eutectic (LBE) for long-life small and robust power units. To ensure the structural integrity, the large safety margin against Safe Shutdown Earthquake, 0.3g, and furthermore the cost effectiveness for URANUS, three-dimensional seismic base isolation design has been developed. The analytical model has been developed and seismic time history analyses have been carried out. The advantage for using three-dimensional seismic base isolation for URANUS has been discussed.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1997.04a
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• pp.224-231
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• 1997

A study on the seismic responses for a base isolated structure subjected to earthquakes with different frequency characteristics is peformed with time history analyses. Two types of seismic inputs are considered in these analyses, one is short period earthquakes such as El Centro(1940, NS), the other is long period ones such as Mexico(1985). The seismic responses of the base isolated structure depend on seismic input types and isolation frequencies. In this study the 0.5 Hz of isolation frequency for short period earthquakes remarkably reduces the acceleration responses, increases the relative displacements of isolator that are still within the proposed limits of isolator. However higher isolation frequency for long period earthquakes is more adequate to reduce the seismic responses of the base isolated structures; in the study 0.75 Hz is effective to Mexico 1985 earthquake.

• Structural Engineering and Mechanics
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• v.35 no.6
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• pp.759-772
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• 2010

Seismic isolation is a well-known method to mitigate the earthquake effects on structures by increasing their fundamental natural periods at the expense of larger displacements in the structural system. In this paper, the seismic response of isolated and fixed base vertical, cylindrical, liquid storage tanks is investigated using a Finite Element Model (FEM), taking into account fluid-structure interaction effects. Three vertical, cylindrical tanks with different ratios of height to radius (H/R = 2.6, 1.0 and 0.3) are numerically analyzed and the results of response-history analysis, including base shear, overturning moment and free surface displacement are reported for isolated and non-isolated tanks. Isolated tanks equipped by lead rubber bearings isolators and the bearing are modeled by using a non-linear spring in FEM model. It is observed that the seismic isolation of liquid storage tanks is quite effective and the response of isolated tanks is significantly influenced by the system parameters such as their fundamental frequencies and the aspect ratio of the tanks. However, the base isolation does not significantly affect the surface wave height and even it can causes adverse effects on the free surface sloshing motion.

• Journal of the Earthquake Engineering Society of Korea
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• v.17 no.2
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• pp.89-95
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• 2013

Structures in a nuclear power system are designed to be elastic even under an earthquake excitation. However a structural component such as an isolator shows inelastic behavior inherently. For the seismic assessment of nonlinear structures, response history analysis should be performed. In this study, the response of base isolation system was analyzed by response history analysis for the seismic performance assessment. Firstly, several seismic assessment criteria for a nuclear power plant structure were reviewed for the nonlinear response history analysis. Based on these criteria, the spectrum matched ground motion generation method modifying a seed earthquake ground motion time history was adjusted. Using these spectrum matched accelerograms, the distribution of displacement responses of the simplified base isolation system was evaluated. The resulting seismic responses excited by the modified ground motion time histories and the synthesized time history generated by stochastic approach were compared. And the response analysis of the base isolation system considering the different intensities in each orthogonal direction was performed.

• Earthquakes and Structures
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• v.16 no.6
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• pp.743-755
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• 2019

In this paper, a new system of seismic isolation for buildings - called suspended columns - is introduced. In this method, the building columns are placed on the hinged cradle seats instead of direct connection to the foundation. In this system, each of the columns is put on a seat hung from its surrounding area by a number of cables, for which cavities are created inside the foundation around the columns. Inside these cavities, the tensile cables are hung. Because of the flexibility of the cables, the suspended seats vibrate during an earthquake and as a result, there is less acceleration in the structure than the foundation. A Matlab code was written to analyze and investigate the response of the system against the earthquake excitations. The findings showed that if this system is used in a building, it results in a significant reduction in the acceleration applied to the structure. A shear key system was used to control the structure for service and lateral weak loads. Moreover, the effect of vertical acceleration on the seismic behavior of the system was also investigated. Effect of the earthquake characteristic period on the system performance was studied and the optimum length of the suspension cables for a variety of the period ranges was suggested. In addition, measures have been taken for long-term functioning of the system and some practical feasibility features were also discussed. Finally, the advantages and limitations of the system were discussed and compared with the other common methods of seismic isolation.

• Structural Engineering and Mechanics
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• v.61 no.5
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• pp.645-655
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• 2017

To determine the seismic applicability of a long-span railway concrete upper-deck arch bridge with concrete-filled steel-tube (CFST) rigid skeleton ribs, some fundamental principles and seismic approaches for long-span bridges are investigated to update the design methods in the current Code for Seismic Design of Railway Engineering of China. Ductile and mixed isolation design are investigated respectively to compare the structural seismic performances. The flexural moment and plastic rotation demands and capacities are quantified to assess the seismic status of the ductile components. A kind of triple friction pendulum (TFP) system and lead-plug rubber bearing are applied simultaneously to regularize the structural seismic demands. The numerical analysis shows that the current ductile layout with continuous rigid frame approaching spans should be strengthened to satisfy the demands of rare earthquakes. However, the mixed isolation design embodies excellent seismic performances for the continuous girder approaching span of this railway arch bridge.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.10a
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• pp.258-265
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• 1998

Seismic isolation has developed to the point where it may be considered as a viable design alternate for a wide range of building structures. However, it needs to consider various aspects to adopt a suitable isolation system for buildings practically. This report presents the basis for the preliminary design procedure which has been developed for the seismic isolation system using the lead rubber bearings. The design procedures have been developed to ensure that the bearings will safely support the maximum gravity load throughout the life of the structure while they provide a period shift and hysteretic damping during the design earthquake.

• Smart Structures and Systems
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• v.2 no.4
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• pp.329-337
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• 2006

This paper illustrates an analytical investigation of the vibration parameters of buildings on sliding seismic isolation bearings with elastic limiters of the relative displacement. The installation scheme of sliding bearings and elastic limiters for the separate unit of a 4 storey hospital building with brick walls is designed. The analysis of the vibrations of the hospital building is conducted for harmonic base excitation.