• Computers and Concrete
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• 제9권3호
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• pp.195-213
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• 2012

This paper presents the investigation of the stochastic responses of seismically isolated bridges subjected to spatially varying earthquake ground motions including incoherence, wave-passage and site-response effects. The incoherence effect is examined by considering Harichandran and Vanmarcke coherency model. The effect of the wave-passage is dealt with various wave velocities in the response analysis. Homogeneous firm, medium and soft soil conditions are selected for considering the site-response effect where the bridge supports are constructed. The ground motion is described by filtered white noise and applied to each support points. For seismic isolation of the bridge, single and double concave friction pendulum bearings are used. Due to presence of friction on the concave surfaces of the isolation systems, the equation of motion of is non-linear. The non-linear equation of motion is solved by using equivalent linearization technique of non-linear stochastic analyses. Solutions obtained from the stochastic analyses of non-isolated and isolated bridges to spatially varying earthquake ground motions compared with each other for the special cases of the ground motion model. It is concluded that friction pendulum systems having single and double concave surfaces have important effects on the stochastic responses of bridges to spatially varying earthquake ground motions.

• Structural Engineering and Mechanics
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• 제59권5호
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• pp.803-820
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• 2016

In this study a direct displacement-based design (DDBD) procedure for a continuous deck bridge isolated with triple friction pendulum bearings (TFPB) has been proposed and the seismic demands of the bridge such as isolator's displacement and drift of piers obtained from this procedure evaluated under two-directional near-field ground motions. The structural model used here are continuous, three-span, castin-place concrete box girder bridge with a 30-degree skew which are isolated with 9 different TFPBs. By comparing the results of DDBD method with those of nonlinear time history analysis (NTHA), it can be concluded that the proposed procedure is able to predict seismic demands of similar isolated bridges with acceptable accuracy. Results of NTHA shows that dispersion of peak resultant responses for a group of ground motions increases by increasing their average value of responses. It needs to be noted that the demands parameters calculated by the DDBD procedure are almost overestimated for stiffer soil condition, but there is some underestimation in results of this method for softer soil condition.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 추계 학술발표회논문집
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• pp.403-410
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• 2003

This paper presents the results of experimental studies on the equipment isolation effect in the nuclear containment. For this purpose, shaking table tests were performed. The isolation system, known as Friction Pendulum System (FPS), combines the concepts of sliding bearings and pendulum motion was selected. Peak ground acceleration, bidirectional motion, effect of vertical motion and frequency contents of selected earthquake motions were considered. Finally, it is presented that the FPS systems are effective for the small equipment isolation. Key word equipment isolation, nuclear containment, shaking table test, Friction Pendulum System (FPS)

• 한국강구조학회 논문집
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• 제17권4호통권77호
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• pp.407-417
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• 2005

원전 주 제어실에 마찰진자 베어링을 이용한 면진시스템을 적용하기 위한 해석 및 실험적 연구를 수행하였다. 마찰진자 베어링을 제작하였으며 동적 물성치 시험을 통하여 이의 성능을 평가하였다. 강재 격자 바닥판, 캐비넷, 4개의 마찰진자로 구성된 주제어실의 부분 면진시스템 모형을 제작하고 진동시험대 실험을 수행함으로써 마찰진자 시스템의 원전 적용성을 평가하였다. 진동대 실험에서는 원전 스펙트럼을 이용한 인공지진파를 사용하였으며 마찰진자 위치 점의 층응답 스펙트럼의 변화를 통하여 면진 성능을 평가하였다. 향후 실험을 통하여 구현하기 어려운 실험변수의 영향을 검토하기 위하여 수치해석 모형을 작성하여 실험 결과 비교 검증하였다.

• 한국운동역학회지
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• 제16권4호
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• pp.147-152
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• 2006

The purpose of this study was to develop the experimental machine for the putting strokes. This experimental machine is called Pendulum Putting Machine(PPM). The height of PPM is 75cm and the mass is 10kg. To make the frame of this machine, 24 and 20 diameters of iron pipes were used. Bottom of the frame(bottom girdle) was made with circle shape and top of the frame(top girdle) was made with rectangular shape. Above the top girdle, iron plate($12{\times}17{\times}0.5cm$) was placed to connect the ball bearing. At the top of the frame two ball bearings with axis were placed for the diverse lies of putters and irons. To verify usefulness of this machine, experiments were executed with the PPM. Two major experimental conditions were hitting points(sweet spot, toe side, heel side) and hitting places(bottom, 3cm before bottom, 3cm after bottom). Eleven different cases were tested. The results showed that the diversity of the ball placement(distance and direction) was acceptable(distance range, 2.70-5.87 standard deviation; direction range, 1.71-4.65 standard deviation). Overall the Pendulum Putting Machine is very useful for the study of putting and driving strokes.

• Structural Engineering and Mechanics
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• 제51권2호
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• pp.277-297
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• 2014

Since the isolation bearings undergo large displacements in base-isolated structures, impact with adjacent structures is inevitable. Therefore, in this investigation, the effect of impact on seismic response of isolated structures mounted on double concave friction pendulum (DCFP) bearings subjected to near field ground motions is considered. A non-linear viscoelastic model of collision is used to simulate structural pounding more accurately. 2-, 4- and 8-story base-isolated buildings adjacent to fixed-base structures are modeled and the coupled differential equations of motion related to these isolated systems are solved in the MATLAB environment using the SIMULINK toolbox. The variation of seismic responses such as base shear, displacement in the isolation system and superstructure (top floor) is computed to study the impact condition. Also, the effects of variation of system parameters: isolation period, superstructure period, size of seismic gap between two structures, radius of curvature of the sliding surface and friction coefficient of isolator are contemplated in this study. It is concluded that the normalized base shear, bearing and top floor displacement increase due to impact with adjacent structure. When the distance between two structures decreases, the base shear and displacement increase comparing to no impact condition. Besides, the increase in friction coefficient difference also causes the normalized base shear and displacement in isolation system and superstructure increase in comparison with bi-linear hysteretic behavior of base isolation system. Totally, the comparison of results indicates that the changes in values of friction coefficient have more significant effects on 2-story building than 4- and 8-story buildings.

• Smart Structures and Systems
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• 제16권4호
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• pp.701-723
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• 2015

Friction isolators are one of the most important types of bearings used to mitigate damages of earthquakes. The adaptive behavior of these isolators allows them to achieve multiple levels of performances and predictable seismic behavior during different earthquake hazard levels. There are three main types of friction isolators. The first generation with one sliding surface is known as Friction Pendulum System (FPS) isolators. The double concave friction pendulum (DCFP) with two sliding surfaces is an advanced form of FPS, and the third one, with fully adaptive behavior, is named as triple concave friction pendulum (TCFP). The current study has been conducted to investigate and compare seismic responses of these three types of isolators. The structure is idealized as a two-dimensional single degree of freedom (SDOF) resting on isolators. The coupled differential equations of motion are derived and solved using state space formulation. Seismic responses of isolated structures using each one of these isolators are investigated under seven near fault earthquake motions. The peak values of bearing displacement and base shear are studied employing the variation of essential parameters such as superstructure period, effective isolation period and effective damping of isolator. The results demonstrate a more efficient seismic behavior of TCFP isolator comparing to the other types of isolators. This efficiency depends on the selected effective isolation period as well as effective isolation damping. The investigation shows that increasing the effective isolation period or decreasing the effective isolation damping improves the seismic behavior of TCFP compared to the other isolators. The maximum difference in seismic responses, the base shear and the bearing displacement, for the TCFP isolator are calculated 26.8 and 13.4 percent less than the DCFP and FPS in effective isolation damping equal to10%, respectively.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2000
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• pp.407-414
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• 2000

The friction pendulum type seismic isolation system (FPS) has been developed to provide a simple and effective way to achieve earthquake resistance for buildings . The major advantages are: the isolation frequency can be easily achieved by designing a curvature of the surface and does not depend on the supported weight of a structure. The function of carrying vertical load is separated to the function of providing horizontal stiffness. Next the friction provides sufficient energy dissipation to protect the structure from earthquake response and resistance to the weak external disturbances such as wind load and ground vibrations due to traffic. In this paper, the friction coefficients are evaluated from number of experiments on the FPS test specimens. The relations between friction coefficient and the test waveform, velocity, and pressure are reviewed and further works are discussed.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2001년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Fall 2001
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• pp.356-363
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• 2001

The friction pendulum type seismic isolation system (FPS) using the PTFE based materials has been developed to provide a simple and effective way to achieve earthquake resistance for buildings. PTFE matrials are soft and apt to be deformed easily after a few working cycles. Instead of the usual PTFE materials, the Polyimide material was used in this research. Polyimide is harder than PTFE, but has smaller friction coefficient and longer duration fur usage. In this paper, various kinds of PTFE materials were tested to define the frictional characteristics compared with the Polyimide material. FPS was manufactured with fine surface roughness and used with Polyimide material to show the seismic isolation efficiency, and life duration when applied to a rigid mass model and a 5 stole frame model.

• Structural Engineering and Mechanics
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• 제53권2호
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• pp.227-248
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• 2015

A CFPBS (Cone-type Friction Pendulum Bearing System) was developed to control the acceleration delivered to a structure to prevent the damage and degradation of critical communication equipment during earthquakes. This study evaluated the isolation performance of the CFPBS by numerical analysis. The CFPBS was manufactured in the shape of a cone differenced with the existing FPS (Friction Pendulum System), and a pattern was engraved on the friction surface. The natural frequencies of the CFPBS were evaluated from a free-vibration test with a seismic isolator system consisting of 4 CFPBS. To confirm the earthquake-resistant performance, a numerical analysis program was prepared using the equation of the CFPBS induced from the equations of motion. The equation reported by Tsai for the rolling-type seismic isolation bearings was proposed to design the equation of the CFPBS. Artificial seismic waves that satisfy the maximum earthquake scale of the Korean Building Code-Structural (KBC-2005) were created and verified to review the earthquake-resistant performance of the CFPBS by numerical analysis. The superstructural mass of the CFPBS and the skew angle of friction surface were considered for numerical analysis with El Centro NS, Kobe NS and artificial seismic waves. The CFPBS isolation performance evaluation was based on the numerical analysis results, and comparative analysis was performed between the results from numerical analysis and simplified theoretical equation under the same conditions. The validity of numerical analysis was verified from the shaking table test.