• Earthquakes and Structures
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• 제18권2호
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• pp.215-222
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• 2020

In this paper, slit steel rubber bearing is presented as an innovative seismic isolator device. In this type of isolator, slit steel damper is an energy dissipation device. Its advantages in comparison with that of the lead rubber bearing are its simplicity in manufacturing process and replacement of its yielding parts. Also, slit steel rubber bearing has the same ability to dissipate energy with smaller value of displacement. Using finite element method in ABAQUS software, a parametric study is done on the performance of this bearing. Three different kinds of isolator with three different values of strut width, 9, 12 and 15 mm, three values of thickness, 4, 6 and 8 mm and two steel types with different yield stress are assessed. Effects of these parameters on the performance characteristics of slit steel rubber bearing are studied. It is shown that by decreasing the thickness and strut width and by selecting the material with lower yield stress, values of effective stiffness, energy dissipation capacity and lateral force in the isolator reduce but equivalent viscous damping is not affected significantly. Thus, by choosing appropriate values for thickness, strut width and slit steel damper yield stress, an isolator with the desired behavior can be achieved. Finally, the performance of an 8-storey frame with the proposed isolator is compared with the same frame equipped with LRB. Results show that SSRB is successful in base shear reduction of structure in a different way from LRB.

• 대한토목학회논문집
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• 제36권3호
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• pp.361-374
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• 2016

이 연구는 대표적인 면진장치인 납고무베어링(LRB)의 유한요소모델의 신뢰성을 향상시키기 위하여 주재료인 고무의 재료특성에 대하여 연구하였다. 고무는 일반적인 탄성재료와는 달리 대변형, 비선형특성을 가지는 초탄성 재료이다. 본 연구에서는 고무를 초탄성 재료로 가정하고 그의 재료특성을 변형률에너지함수로 표현하여 LRB의 유한요소모델을 개발하였다. 연구를 위하여 여러 변형률에너지함수 중 몇 가지를 선별하고 이를 이용하여 고무의 재료특성을 예측하였다. 변형률에너지함수를 이용하여 결정된 고무의 재료특성과 표준적인 납의 재료특성을 이용하여 LRB의 유한요소모델을 개발하고, 수평방향과 수직방향의 힘-변위 관계를 해석하였다. LRB의 유한요소모델을 통하여 해석으로 예측한 수평과 수직방향 강성을 실험결과와 비교함으로써 개발된 유한요소모델의 적합성을 검증하였다.

• Earthquakes and Structures
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• 제5권1호
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• pp.23-48
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• 2013

In this study, the effect of flexibility of superstructures and nonlinear characteristics of LRB (Lead Rubber Bearing) isolator on inelastic response of base isolated structures is investigated. To demonstrate the intensity of damage in superstructures, demand response modification factor without the consideration of damping reduction factor, demand RI, is used and the N2 method is applied to compute this factor. To evaluate the influence of superstructure flexibility on inelastic response of base isolated structures, different steel intermediate moment resisting frames with different heights have been investigated. In lead rubber bearing, the rubber provides flexibility and the lead is the source of damping; variations of aforementioned characteristics are also investigated on inelastic response of superstructures. It is observed that an increase in height of superstructure leads to higher value of demand RI till 4-story frame but afterward this factor remains constant; in other words, an increase in height until 4-story frame causes more damage in the superstructure but after that superstructure's damage is equal to the 4-story frame's. The results demonstrate that the low value of second stiffness (rubber stiffness in LRBs) tends to show a significant decrease in demand RI. Increase in value of characteristic strength (yield strength of the lead in LRBs) leads to decrease in the demand RI.

• 대한토목학회논문집
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• 제26권1A호
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• pp.155-162
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• 2006

본 연구에서는 납면진받침(LRB)이 설치된 중경간 엑스트라도즈드교에서 교각의 파손, 상부구조의 이동변위, 그리고 케이블의 항복에 대한 지진위험도를 평가하였다. 지진위험도는 다수의 지진자료를 이용하여 지진에 대한 구조적 취약성을 평가한 지진취약도와 지진재해지도를 이용하여 해당지역에서의 지진재해도를 산정하여, 이들을 조합함으로써 평가할 수 있었다. 지진시 교각에서 소성힌지의 발생을 고려하기 위해 SAP2000을 사용하여 비선형 지진해석을 수행하였다. 지진자료는 암반노두에서 설계응답스펙트럼을 만족하는 인공지진을 작성한 후, SHAKE91을 사용하여 해당지역의 지반증폭효과를 고려하여 지진 가속도 시간이력을 구하여 사용하였다. 교각의 비선형 응답은 연성도를 사용하여 나타내었고, 2선형 직선의 모멘트-곡률 곡선으로 작성하였다. 본 연구에서는 대수정규분포함수로 지진취약도를 표현하였으며, 한반도를 대상으로 작성된 지진재해지도를 이용하여 지진재해도를 산정하였다. 해석결과 엑스트라도즈드교에서는 케이블과 거더보다는 교각하단에서 면진장치가 더 효과적인 것을 알 수 있었다.

• Earthquakes and Structures
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• 제13권4호
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• pp.353-363
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• 2017

The present study considers a multi-span continuous bridge, isolated by lead rubber bearing (LRB). Dynamic soilstructure interaction (SSI) is modelled with the help of a simplified, sway-rocking model for different types of soil. It is well understood from the literature that SSI influences the structural responses and the isolator performance. However, the abovementioned effect of SSI also depends on the earthquake ground motion properties. It is very important to understand how the interaction between soil and structure varies with the earthquake ground motion characteristics but, as far as the knowledge of the authors go, no study has been carried out to investigate this effect. Therefore, the objectives of the present study are to investigate the influence of earthquake ground motion characteristics on: (a) the responses of a multi span bridge (isolated and non-isolated), (b) the performance of the isolator and, most importantly, (c) the soil-structure interaction. Statistical analyses are conducted by considering 14 earthquakes which are selected in such a way that they can be categorized into three frequency content groups according to their peak ground acceleration to peak ground velocity (PGA/PGV) ratio. Lumped mass model of the bridge is developed and time history analyses are carried out by solving the governing equations of motion in the state space form. The performance of the isolator is studied by comparing the responses of the bridge with those of the corresponding uncontrolled bridge (i.e., non-isolated bridge). On studying the effect of earthquake motions, it is observed that the earthquake ground motion characteristics affect the interaction between soil and structure in such a way that the responses decrease with increase in frequency content of the earthquake for all the types of soil considered. The reverse phenomenon is observed in case of the isolator performance where the control efficiencies increase with frequency content of earthquake.

• Structural Engineering and Mechanics
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• 제29권6호
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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.

• 한국지진공학회논문집
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• 제19권4호
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• pp.161-171
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• 2015

A series of tests was conducted for full-scale single-pylon asymmetric cable-stayed bridges using a system of multiple shaking tables. The 2-span bridge length was 28 m, and the pylon height was 10.2 m. 4 different base conditions were considered: the fixed condition, RB (rubber bearings), LRB (lead rubber bearings), and HDRB (high damping rubber bearings). Based on investigation of the seismic response, the accelerations and displacements in the axial direction of the isolated bridge were increased compared to non-isolated case. However, the strain of the pylon was decreased, because the major mode of the structure was changed to translation for the axial direction due to the dynamic mass. The response of the cable bridge could differ from the desired response according to the locations and characteristics of the seismic isolator. Therefore, caution is required in the design and prediction in regard to the location and behavior of the seismic isolator.

• 대한토목학회논문집
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• 제13권2호
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• pp.85-93
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• 1993

구조물의 진동을 제어하기 위하여 널리 활용되고 있는 기초분리시스템(base isolation system)는 대상구조물에 경제적이며 효율적으로 적용할 수 있는 장점을 가지고 있다. 본 연구에서는 가장 널리 쓰이고 있는 적층(積層)고무받침(laminated rubber bearing) 방식의 기초분리장치(base isolator)를 제작하여 이에 대한 정적 및 동적 특성실험을 수행하였다. 실험으로부터 얻어진 결과를 통하여 제작된 기초분리 장치의 정적 및 동적특성을 분석하였으며 실제 구조물에 대한 기초분리장치로서의 적용가능성을 고찰하였다. 최종적으로 기초분리장치에서 나타나는 비선형 힘-변위 이력곡선을 수치적으로 이상화하여 실험결과와 비교하였다.