• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.7_spc
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• pp.453-460
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• 2016

The Gyeong-Ju earthquake in the magnitude of 5.8 on the Richter scaleoccurred in September 12, 2016. Because there are many nuclear power plants (NPP) near the epicenter of the Gyeong-Ju earthquake, the seismic stability of nuclear power plants is becoming a social problem. In order to evaluate the safety of seismically isolated NPP, the seismic response of a NPP subjected to the Gyeong-Ju earthquake was compared with those of 30 sets of artificial earthquakes corresponding to the nuclear standard design spectrum (NSDS). A 2-node model and a simple beam-stick model were used for the seismic analysis of seismically isolated NPP structures. Using 2-node model, the effect of internal temperature rise, decrease of shear stiffness, increase of lateral displacement and decrease of vertical stiffness according to nonlinear behavior of lead-rubber bearing (LRB) were evaluated. The displacement response, the acceleration response, and the shear force response of the seismically isolated nuclear containment structure were evaluated using the simple beam-stick model. It can be observed that the seismic responses of the isolated nuclear structure subjected to Gyeong-Ju earthquake is significantly less than those to the artificial earthquakes corresponding to NSDS.

• Earthquakes and Structures
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• v.26 no.6
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• pp.463-475
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• 2024

The study aims to investigate the pounding that occurs between the isolator's ring and slider of isolated structures resulting from excessive seismic excitation, while considering soil-structure interaction. The dynamic responses and poundings of structures subjected a series seismic records were comparatively analyzed for three different soil types and fixed-base structures. A series of parametric studies were conducted to thoroughly discuss the effects of the impact displacement ratio, the FPB friction coefficient ratio, and the radius ratio on the structural dynamic response when considering impact and SSI. It was found that the pounding is extremely brief, with an exceptionally large pounding force generated by impact, resulting in significant acceleration pulse. The acceleration and inter-story shear force of the structure experiencing pounding were greater than those without considering pounding. Sudden changes in the inter-story shear force between the first and second floors of the structure were also observed. The dynamic response of structures in soft ground was significantly lower than that of structures in other ground conditions under the same conditions, regardless of the earthquake wave exciting the structure. When the structure is influenced by pulse-type earthquake records, its dynamic response exhibits a trend of first intensifying and then weakening as the equivalent radius ratio and friction coefficient ratio increase. However, it increases with an increase in the pounding displacement ratio, equivalent radius ratio, friction coefficient ratio, and displacement ratio when the structures are subjected to non-pulse-type seismic record.

• Journal of the Earthquake Engineering Society of Korea
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• v.3 no.4
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• pp.11-22
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• 1999

In this study, the validity of the currently used seismic regulations for seismic isolated building structures is investigated, and a new formula for vertical distribution of seismic load is proposed. The distribution formula in UBC-91 did not provide sufficient safety, and thus revised in 1994. However it is pointed out that the revised formula overestimates the seismic load because of its similarity to that of the fixed-base structure. Therefore, in the proposed approach, it is intended to satisfy safety, economy, and applicability by combining the mode shapes of the seismic isolated structure idealized as two degrees of freedom system and those of fixed-base structure. For verification of the proposed formula, both a moment resisting frame and a shear wall system are analyzed. The results obtained from the proposed method turn out to be close to the results from a dynamic analysis.

• Journal of the Earthquake Engineering Society of Korea
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• v.1 no.4
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• pp.45-58
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• 1997

This paper describes a series of shaking table and pseudodynamic tests for evaluation of seismic performance of base-isolated structures subjected to various seismic earthquake inputs. The main objectives of this study are : (1) evaluation of the effectiveness of base-isolation systems for low-rise structures against severe seismic loads through shaking table tests, (2) verification of the substructuring pseudodynamic test method for the base-isolated structures in comparison with the shaking table test results. In the shaking table test, a quarter scaled three-story structure base-isolated by laminated rubber bearings is tested. In the pseudodynamic test, only the laminated rubber bearing s are tested using the substructuring technique, while the concurrent seismic responses of the superstructure are computed using on-line numerical integration. Comparison with the shaking table test results indicates that the substructuring pseudodynamic test method is very effective for determining the dynamic responses of the base-isolated structure.

• Structural Engineering and Mechanics
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• v.46 no.5
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• pp.645-672
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• 2013

The differential settlements and rotations among footings cannot be avoided when the frame-footing-soil system is subjected to seismic/dynamic loading. Also, there may be a situation where column(s) of a building are located near adjoining property line causes eccentric loading on foundation system. The strap beams may be provided to control the rotation of the footings within permissible limits caused due to such eccentric loading. In the present work, the seismic interaction analysis of a three-bay three-storey, space frame-footing-strap beam-soil system is carried out to investigate the interaction behavior using finite element software (ANSYS). The RCC structure and their foundation are assumed to behave in linear manner while the supporting soil mass is treated as nonlinear elastic material. The seismic interaction analyses of space frame-isolated footing-soil and space frame-strap footing-soil systems are carried out to evaluate the forces in the columns. The results indicate that the bending moments of very high magnitude are induced at column bases resting on eccentric footing of frame-isolated footing-soil interaction system. However, use of strap beams controls these moments quite effectively. The soil-structure interaction effect causes significant redistribution of column forces compared to non-interaction analysis. The axial forces in the columns are distributed more uniformly when the interaction effects are considered in the analysis.

• Structural Engineering and Mechanics
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• v.29 no.6
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• pp.689-707
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• 2008

This study presents a method to evaluate the seismic risk of an extradosed bridge with seismic isolators of lead rubber bearings (LRBs), and also to show the effectiveness of the LRB isolators on the extradosed bridge, which is one of the relatively flexible and lightly damped structures in terms of seismic risk. Initially, the seismic vulnerability of a structure is evaluated, and then the seismic hazard of a specific site is rated using an earthquake data set and seismic hazard maps in Korea. Then, the seismic risk of the structure is assessed. The nonlinear seismic analyses are carried out to consider plastic deformation of bridge columns and the nonlinear characteristics of soil foundation. To describe the nonlinear behaviour of a column, the ductility demand is adopted, and the moment-curvature relation of a column is assumed to be bilinear hysteretic. The fragility curves are represented as a log-normal distribution function for column damage, movement of superstructure, and cable yielding. And the seismic hazard at a specific site is estimated using the available seismic hazard maps. The results show that in seismically-isolated extradosed bridges under earthquakes, the effectiveness of the isolators is much more noticeable in the columns than the cables and girders.

• Earthquakes and Structures
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• v.23 no.6
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• pp.517-526
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• 2022

Previous studies have shown that pile-soil interactions have significant influences on the isolation efficiency of an isolated structure. However, most of the existing tests were carried out using a 1-g shaking table, which cannot reproduce the soil stresses resulting in distortion of the simulated pile-soil interactions. In this study, a centrifuge shaking table modelling of the seismic responses of a friction pendulum bearing isolated structure with a pile foundation under earthquakes were conducted. The pile foundation structure was designed and constructed with a scale factor of 1:100. Two layers of the foundation soil, i.e., the bottom layer was made of plaster and the upper layer was normal soil, were carefully prepared to meet the similitude requirement. Seismic responses, including strains, displacement, acceleration, and soil pressure were collected. The settlement of the soil, sliding of the isolator, dynamic amplification factor and bending moment of the piles were analysed to reveal the influence of the soil structure interaction on the seismic performance of the structure. It is found that the soil rotates significantly under earthquake motions and the peak rotation is about 0.021 degree under 24.0 g motions. The isolator cannot return to the initial position after the tests because of the unrecoverable deformation of the soil and the friction between the curved surface of the slider and the concave plate.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.10a
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• pp.561-568
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• 2001

For obtaining the time history nodal responses of reactor building, a lumped-mass beam model composed of two sticks for the reactor building and the reactor support structure is developed. The time history responses for the non-isolated and isolated reactor buildings are calculated under an artificial time history, generated using the seismic spectrum curve of US NRC RG1.60. The analysis results show that the horizontal accelerations of the isolated building are dramatically decreased to one-tenths of the non-isolated one, but the vertical responses are increased by about 40%.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.11
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• pp.1743-1750
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• 2001

This paper presents an analysis of nonlinear response of the seismically isolated structure against earthquake excitation to evaluate isolation performances of a rubber bearing. In the analysis of the vibration of building, the building is modeled by lumped mass system where the restoring force is considered as linear, bilinear and trilinear. Fundamental equations of motion are derived for the base isolated structure, and hysteretic and nonlinear-elastic characteristics are considered for a numerical calculation. The excitation levels are magnified fur the recorded strong earthquake motions in order to examine dynamic stability of the structure. Seismic responses (of the building are compared fur the each restoring force type. As a result, it is shown that the effect of the motion by the nonlinear response of the building is comparatively not so large from a seismic design standpoint. The responses of the isolated structures reduce sufficiently and controled the motion of the building well in a practical range. By increasing the acceleration of the earthquake, the yielding of the farce was occurred in the concrete and steel frame, which shows the necessity of the exact nonlinear dynamic analysis.

• Structural Engineering and Mechanics
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• v.77 no.4
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• pp.481-493
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• 2021

Low rise masonry structures are relatively inexpensive and easier to construct compared to other types of structures such as steel and reinforced concrete buildings. However, masonry structures are relatively heavier and less ductile and more vulnerable to damages in earthquakes. In this research, a new innovative low-cost seismic isolator using steel rings (SISR) is employed to reduce the seismic vulnerability of masonry structures. FEA of a masonry structure, made of concrete blocks is used to evaluate the effect of the proposed SISR on the seismic response of the structure. Two systems, fixed base and isolated from the base with the proposed SISRs, are considered. Micro-element approach and ABAQUS software are used for structural modeling. The nonlinear structural parameters of the SISRs, extracted from a recent experimental study by the authors, are used in numerical modeling. The masonry structure is studied in two separate modes, fixed base and isolated base with the proposed SISRs, under Erzincan and Imperial Valley-06 earthquakes. The accelerated response at the roof level, as well as the deformation in the masonry walls, are the parameters to assess the effect of the proposed SISRs. The results show a highly improved performance of the masonry structure with the SISRs.