• 한국지진공학회논문집
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• 제8권2호
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• pp.35-44
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• 2004

탄성응답스펙트럼을 사용하는 능력스펙트럼법은 비선형 시스템을 등가의 선형시스템으로 치환하여 주어진 지진 하중에 대한 구조물의 최대 비선형 거동을 예측한다. 본 연구의 목적은 이러한 능력스펙트럼법들의 정확성을 검증하고, 예측 특성을 비교하는 것이다. 이를 위해, ATC-40, G lkan, Kowalsky, 그리고 Iwan이 제시한 방법을 이용하여 등가주기와 등가감쇠비를 산정한 후, ATC-40에서 제시한 절차B에 따라 성능점을 산정 하였다. 전반적으로 ATC-40 방범은 구조물의 응답을 과소 평가하여 안전하지 못한 설계결과를 가져 올 수 있으며, G lkan과 Kowalsky의 방법은 과대 평가하는 경향을 가지고 있다. Iwan이 제시한 방법은 ATC-40 방법과 G lkan과 Kowalsky 방법의 중간 값을 예측함으로써, 비교적 정확한 값에 가까운 최대 변위를 산출하였다. 그리고, Kowalsky 방법은 항복 후 강성비에 따라 등가감쇠비를 음수로 산정함으로써 예측 값을 제시하지 못하는 경우가 있음을 확인하였다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 춘계 학술발표회 논문집
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• pp.359-366
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• 2002

Direct Integration method(D.I) and Mode Superposition method(M.S) are used widely in dynamic analysis method for structure with isolation devices. D.I is used firstly because it is consider to nonlinearity of isolation device. M.S is applied in elastic region, but it is difficult to apply M.S because coincidence with othogonality condition in the case of adding the damping of isolation device. In this study, the method for calculation of damping ratio of isolated structure is proposed, and proposed method is verified with analysis for example structure.

• Earthquakes and Structures
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• 제13권2호
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• pp.119-130
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• 2017

This paper presents a numerical investigation on the seismic behavior of isolated bridges with supplemental viscous damping. Usually very large displacements make seismic isolation an unfeasible solution due to boundary conditions, especially in case of existing bridges or high risk seismic regions. First, a suggested optimal design procedure is introduced, then seismic performance of three real bridges with different isolation systems and damping levels is investigated. Each bridge is studied in four different configurations: simply supported (SSB), isolated with 10% damping (IB), isolated with 30% damping (LRB) and isolated with optimal supplemental damping ratio (IDB). Two of the case studies are investigated under spectrum compatible far-field ground motions, while the third one is subjected to near-fault strong motions. With respect to different design strategies proposed by other authors, results of the analysis demonstrated that an isolated bridge equipped with HDLRBs and a total equivalent damping ratio of 70% represents a very effective design solution. Thanks to confirmed effective performance in terms of base shear mitigation and displacement reduction under both far field and near fault ground motions, as well as for both simply supported and continuous bridges, the suggested control system provides robustness and reliability in terms of seismic performance also resulting cost effective.

• Structural Engineering and Mechanics
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• 제56권4호
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• pp.569-588
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• 2015

A comprehensive methodology is proposed for design of metallic dampers in seismic retrofit of earthquake-damaged frame structures. It is assumed that the metallic dampers remain elastic and only provide stiffness during frequent earthquake (i.e., earthquake with a 63% probability of exceedance in 50-year service period), while in precautionary earthquake (i.e., earthquake with a 10% probability of exceedance in 50-year service period), the metallic dampers yield before the main frame and dissipate most of the seismic energy to either prevent or minimize structural damages. Therefore by converting multi-story frame to an equivalent single-degree-of-freedom system, the added stiffness provided by metallic dampers is designed to control elastic story drifts within code-based demand under frequent earthquake, and the added damping with the combination of added stiffness influences is obtained to control structural stress within performance-based target under precautionary earthquake. With the equivalent added damping ratio, the expected damping forces provided by metallic dampers can be calculated to carry out the configuration and design of metallic dampers along with supporting braces. Based on a detailed example for retrofit of an earthquake-damaged reinforced concrete frame by using metallic dampers, the proposed design procedure is demonstrated to be simple and practical, which can not only meet current China's design codes but also be used in retrofit design of earthquake-damaged frame with metallic damper for reaching desirable performance objective.

• Wind and Structures
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• 제7권4호
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• pp.235-250
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• 2004

The current study reports the results of an experimental program conducted on a structure fitted with a liquid damper (TLD) and subjected to harmonic excitation. Screens were placed inside the TLD to achieve the required inherent damping. In the first part of the study, reduced scale models of the building-TLD systems were tested under two levels of excitation. The efficiency of the damper was assessed by evaluating the effective damping provided to the structure and comparing it to the optimum effective damping value, provided by a linear tuned mass damper (TMD). An extensive parametric study was then conducted for one of the three models by varying both the excitation amplitude and the tuning ratio, defined as the ratio of the TLD sloshing frequency to the natural frequency of the structure. The effectiveness and robustness of a TLD with screens were assessed. Results indicate that the TLD can be tuned to achieve a robust performance and that its efficiency is not significantly affected by the level of excitation. Finally, the equivalent amplitude dependent TMD model, developed in the companion paper is validated using the system test results.

• Geomechanics and Engineering
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• 제24권1호
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• pp.15-28
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• 2021

Digging well foundation has been widely used in railway bridges due to its good economy and reliability. In other instances, bridges with digging well foundation still have damage risks during earthquakes. However, there is still a lack of knowledge of lateral behavior of digging well foundation considering the soil-foundation interaction. In this study, scaled models of bridge pier-digging well foundation system are constructed for quasi-static test to investigate their lateral behaviors. The failure mechanism and responses of the soil-foundation-pier interaction system are analyzed. The testing results indicate that the digging foundations tend to rotate as a rigid body under cyclic lateral load. Moreover, the depth-width ratio of digging well foundation has a significant influence on the failure mode of the interaction system, especially on the distribution of foundation displacement and the failure of pier. The energy dissipation capacity of the interaction system is discussed by using index of the equivalent viscous damping ratio. The damping varies with the depth-width ratio changing. The equivalent stiffness of soil-digging well foundation-pier interaction system decreases with the increase of loading displacement in a nonlinear manner. The absolute values of the interaction system stiffness are significantly influenced by the depth-width ratio of the foundation.

• 한국지진공학회논문집
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• 제12권3호
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• pp.11-20
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• 2008

본 연구에서는 저경도 고감쇠 고무받침 시험체의 다양한 특성실험을 통하여 저경도 고감쇠 고무받침의 특성을 파악하였다. 고무받침의 파악하고자 하는 특성은 압축강성, 전단강성, 등가감쇠비, 전단특성의 변형율 의존성, 전단특성의 면압 의존성, 전단특성의 주파수 의존성, 전단특성의 온도 의존성, 극한전단특성 등이다. 특성실험은 ISO 22762-1에 따라 수행하였으며, ISO 2276-3에 따라 평가하였다. 특성실험결과 전단강성은 전단변형율과 온도 의존성이 큰 것으로 나타났고, 등가감쇠비는 면압 의존성이 큰 것으로 나타났다. 전단특성의 주파수 의존성 실험결과 0.1Hz를 기준으로 경향이 나뉘는 것으로 나타났다. 0.1Hz 이상에서는 전단특성의 변화가 적었지만, 0.1Hz 이하에서는 전단강성과 등가감쇠비 모두 급격히 감소하는 것으로 나타났다. 추가적으로 크리프실험과 극한전단특성실험을 수행하였고, 실험결과는 ISO 22762-3의 요구사항을 만족하는 것으로 나타났다.

• Earthquakes and Structures
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• 제3권6호
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• pp.821-838
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• 2012

This paper proposes a new three-layer pillar-type hysteretic damper system for residential houses. The proposed vibration control system has braces, upper and lower frames and a damper unit including hysteretic dampers. The proposed vibration control system supplements the weaknesses of the previously proposed post-tensioning vibration control system in the damping efficiency and cumbersomeness of introducing a post-tension. The structural variables employed in the damper design are the stiffness ratio ${\kappa}$, the ductility ratio ${\mu}_a$, and the ratio ${\beta}$ of the damper's shear force to the maximum resistance. The hysteretic dampers are designed so that they exhibit the targeted damping capacity at a specified response amplitude. Element tests of hysteretic dampers are carried out to examine the mechanical property and to compare its restoring-force characteristic with that of the analytical model. Analytical studies using an equivalent linearization method and time-history response analysis are performed to investigate the damping performance of the proposed vibration control system. Free vibration tests using a full-scale model are conducted in order to verify the damping capacity and reliability of the proposed vibration control system. In this paper, the damping capacity of the proposed system is estimated by the logarithmic decrement method for the response amplitudes. The accuracy of the analytical models is evaluated through the comparison of the test results with those of analytical studies.

• Earthquakes and Structures
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• 제25권3호
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• pp.161-175
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• 2023

High-damping rubber bearings (HDRB) are commonly used as seismic isolation devices to protect civil engineering structures from earthquakes. However, the nonlinear hysteresis characteristics of the HDRB, such as their dependence on material properties and hardening phenomena, make predicting their behavior during earthquakes difficult. This study proposes a hysteretic model that can accurately predicts the behavior of shear deformation considering the nonlinearity when designing the seismic isolation structures using HDR bearings. To model the hysteretic characteristics of the HDR, dynamic loading tests were performed by applying sinusoidal and random waves on scaled-down specimens. The test results show that the nonlinear characteristics of the HDR strongly correlate with the shear strain experienced in the past. Furthermore, when shear deformation occurred above a certain level, the hardening phenomenon, wherein the stiffness increased rapidly, was confirmed. Based on the experimental results, the dynamic characteristics of the HDR, equivalent stiffness, equivalent damping ratio, and strain energy were quantitatively evaluated and analyzed. In this study, an improved bilinear HDR model that can reproduce the dependence on shear deformation and hardening phenomena was developed. Additionally, by proposing an objective parameter-setting procedure based on the experimental results, the model was devised such that similar parameters could be set by anyone. Further, an actual dynamic analysis could be performed by modeling with minimal parameters. The proposed model corresponded with the experimental results and successfully reproduced the mechanical characteristics evaluated from experimental results within an error margin of 10%.

• 전력전자학회논문지
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• 제20권3호
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• pp.239-246
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• 2015

A novel control method of a three-phase PWM inverter with LC filter is proposed. The transfer function of LC filter is the same as that of second-order low pass filter(LPF), which has a zero damping ratio. A simple method of implementing second-order LPF with damping ratio is to add a resistor in an LC circuit. However, in a real power system, adopting damping resistors is impractical because it results in losses proportional to the square of the current flowing through the resistors. Instead of inserting resistors, the proposed control strategy utilizes the measured capacitor voltages to control the oscillation of LC circuit. The overall transfer function of the proposed method is the same as a second-order LPF, and its damping ratio is controllable via control variables. The current controller can have overshoots caused by LC filter. Improved current controller is implemented by an equivalent second-order of LC filter. A 7.5 kVA PWM converter and a PWM inverter with a 5.5 kW induction motor are set up to verify the proposed control algorithm. Test waveforms are also presented to verify the proposed LC filter control algorithm.