• 국제강구조저널
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• 제18권5호
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• pp.1741-1753
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• 2018

Metallic dampers are sacrificial devices (fuses) that dissipate significant energy during earthquakes while protecting other parts of structures from possible damage. In addition to numerous implementation opportunities of other base isolation systems, U-shaped dampers (UD) are one of the widely investigated and used devices in practice especially in Japan. The present study focuses on enhancing seismic performance of these types of dampers by changing their geometric properties. UDs with perforated (i.e. with holes) and/or nonparallel arms are developed for this purpose. For a better comparison, the criterion of equal material volume (or mass) has been utilized. Three dimensional finite element models of the new type of UDs are formed and investigated numerically under selected displacement histories. Based on the obtained hysteretic curves; dissipated energy intensities, effective stiffness ratios, reaction forces, effective damping ratios are evaluated in this parametric study. It is found that both damper types have merits in use of seismic applications and that the selection of the damper configuration is dependent on the design specific issues.

• Structural Engineering and Mechanics
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• 제41권3호
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• pp.349-363
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• 2012

Fuzzy logic based control has recently been proposed for regulating the properties of magnetorheological (MR) dampers in an effort to reduce vibrations of structures subjected to seismic excitations. So far, most studies showing the effectiveness of these algorithms have focused on the use of a single MR damper. Because multiple dampers would be needed in practical applications, this study aims to evaluate the effects of multiple individually tuned fuzzy-controlled MR dampers in reducing responses of a multi-degree-of-freedom structure subjected to seismic motions. Two different fuzzy-control algorithms are considered, a traditional controller where all parameters are kept constant, and a gain-scheduling control strategy. Different damper placement configurations are also considered, as are different numbers of MR dampers. To determine the robustness of the fuzzy controllers developed to changes in ground excitation, the structure selected is subjected to different earthquake records. Responses analyzed include peak and root mean square displacements, accelerations, and interstory drifts. Results obtained with the fuzzy-based control schemes are compared to passive control strategies.

• 한국안전학회지
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• 제8권1호
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• pp.80-87
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• 1993

본 논문은 에너지 분산 장치의 일종인 점탄성 감쇠기를 설치한 건물의 거동에 관한 실험 및 해석적 연구를 다루고자 한다. 지진 모형 실험 장치를 이용하여 감쇠기를 설치한 건물의 구조응답을 구하고. 이를 감쇠기를 설치하지 않은 건물에 대하여 행해진 비탄성 해석 결과와 비교한다. 결론적으로 말하면. 점탄성 감쇠기는 강지진 하중에 의하여 건물에 발생한 과도한 진동을 감소시키는데 효과적이다 일반적으로 점탄성 감쇠기를 건물에 설치함으로써 감쇠비와 함께 강성도가 증가하여 지진 응답을 감소시키는데 기여하나, 대부분은 감쇠기의 역할에 의해 증가된 감쇠비의 영향인 것으로 밝혀졌다. 모드 변형에너지법을 이용하여 감쇠기에 의해 증가된 등가구조 감쇠를 성공적으로 예측할 수 있으며 따라서 점탄성 감쇠기를 설치한 건물의 지진 응답이 일반적인 모드 해석 기법을 이용한 수치모형해석에 의해 정확히 예측된다.

• Earthquakes and Structures
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• 제13권2호
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• pp.151-164
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• 2017

This article aims to investigate the possible retrofitting of a deficient building with soft story failure mode by connecting it to an adjacent building which is designed based on current code with friction dampers at all floors. Low cost and high performance reliability along with significant energy dissipation pertaining to stable hysteretic loops may be considered in order to choose the proper damper for connecting adjacent buildings. After connecting two neighbouring floors by friction dampers, the sliding forces of dampers at various stories are set in two arrangements: uniform sliding force and then variable sliding force. In order to account for the stochastic nature of the seismic events, incremental dynamic analyses are employed prior and after the installation of the friction dampers at the various floors. Based on these results, fragility curves and mean annual rate of exceedance of serviceability and ultimate limit states are obtained. The results of this study show that the collapse mode of the deficient building can affect the optimum arrangement of sliding forces of friction dampers at Collapse Prevention (CP) performance level. In particular, the Immediate Occupancy (IO) performance level is not tangible to the sliding force arrangement and it depends solely on sliding force value. Generally it can be claimed that this rehabilitation scheme can turn the challenge of pounding two adjacent buildings into the opportunity of dissipating a large amount of the seismic input energy by the friction dampers, thus improving significantly the poor seismic performance of the deficient structure.

• 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.

• 토지주택연구
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• 제1권1호
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• pp.43-50
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• 2010

본 연구에서는 RC골조의 내진보강을 위해 K형브레이스로 지지되는 강재댐퍼 설치방식을 제안하고 강재댐퍼에 의한 RC골조의 내진보강효과를 실험 및 설계식의 비교를 통해 검증하였다. 강재댐퍼로 보강된 RC골조의 성능은 RC골조 및 강재댐퍼의 강도-변형 관계를 각각 산정한 후 조합하여 산정하였다. 강재댐퍼 지지부재의 강성이 충분히 크지 않을 경우 댐퍼의 성능이 제대로 발휘될 수 없으므로 댐퍼의 지지부재인 브레이스의 강성 고려하여 강재댐퍼의 성능을 산정 하였다. 강재댐퍼 보강 RC골조의 내진보강효과를 확인하기 위한 실험은 비보강 RC골조를 기준 실험체로 하고 K형브레이스로 지지되는 강재 댐퍼의 설치 방법을 변수로 하여 횡력에 대한 실험체의 강도, 강성, 이력특성 등의 항목에 대해 평가하였다. 강재댐퍼 보강 RC골조는 강도, 강성, 에너지소산능력이 비보강 RC골조에 비해 우수한 것으로 나타나 강재댐퍼에 의한 보강효과를 확인할 수 있었다. 강재댐퍼 보강 RC골조의 실험결과와 설계식에 의한 성능을 비교한 결과 설계식이 강재댐퍼 보강 RC골조의 성능을 비교적 유사하게 나타낼 수 있는 것으로 검증되었다.

• Earthquakes and Structures
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• 제14권3호
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• pp.215-227
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• 2018

Supplemental passive control devices are widely considered as an important tool to mitigate the dynamic response of a building under seismic excitation. Nevertheless, a systematic method for strategically placing dampers in the buildings is not prescribed in building codes and guidelines. Many deterministic and stochastic methods have been proposed by previous researchers to investigate the optimum distribution of the viscous dampers in the steel frames. However, the seismic performances of the retrofitted buildings that are under large earthquake intensity levels or near collapse state have not been evaluated by any seismic research. Recent years, an increasing number of studies utilize genetic algorithms (GA) to explore the complex engineering optimization problems. GA interfaced with nonlinear response history (NRH) analysis is considered as one of the most powerful and popular stochastic methods to deal with the nonlinear optimization problem of damper distribution. In this paper, the effectiveness and the efficiency of GA on optimizing damper distribution are first evaluated by strong ground motions associated with the collapse failure. A practical optimization framework using GA and NRH analysis is proposed for optimizing the distribution of the fluid viscous dampers within the moment resisting frames (MRF) regarding the improvements of large drifts under intensive seismic context. Both a 10-storey and a 20-storey building are involved to explore higher mode effect. A far-fault and a near-fault earthquake environment are also considered for the frames under different seismic intensity levels. To evaluate the improvements obtained from the GA optimization regarding the collapse performance of the buildings, Incremental Dynamic Analysis (IDA) is conducted and comparisons are made between the GA damper distribution and stiffness proportional damping distribution on the collapse probability of the retrofitted frames.

• Earthquakes and Structures
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• 제9권1호
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• pp.73-91
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• 2015

The effectiveness of tuned mass dampers (TMDs) in reducing the seismic response of civil structures is still a debated issue. The few studies regarding TMDs on inelastic structures indicate that they would perform well under moderate earthquake loading, when the structure remains linear or weakly nonlinear, while tending to fail under severe ground shaking, when the structure experiences strong nonlinearities. TMD seismic efficiency should be therefore rationally assessed by considering to which extent moderate and severe earthquakes respectively contribute to the expected cost of damages and losses over the lifespan of the structure. In this paper, a method for evaluating, in a life-cycle cost (LCC) perspective, the seismic effectiveness of TMDs on inelastic building structures is presented and exemplified on the SAC LA 9-storey steel moment-resisting frame benchmark building. Results show that the LCC concept may provide an appropriate alternative to traditional performance criteria for the evaluation of the effectiveness of TMDs and that TMD installation on typical existing middle-rise buildings in high seismic hazard regions may significantly reduce building lifetime cost despite the poor control performance observed under the most severe seismic events.

• 한국안전학회지
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• 제37권6호
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• pp.60-70
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• 2022

This paper proposes an optimal design method of a seismic reinforcement system for the seismic performance of adjacent asymmetric-stiffness structures with viscous dampers. The first method considers plan asymmetry for efficient seismic reinforcement, and evaluates the seismic performance of optimal design applied to two cases of modeling: adjacent stiffness-asymmetric structures and adjacent stiffness-symmetric structures. The second method considers the response of asymmetric structures to derive the optimal objective function, and evaluates seismic efficiency of the objective function applied to two cases of responses: horizontal displacement and torsion. Numerical analyses are conducted on 7- and 10-story structures with a uni-asymmetric-stiffness plan using six cases of historic earthquakes, normalized to 0.4g. The results indicate that the seismic performance is excellent as modeled by adjacent asymmetric-stiffness structures and how much horizontal displacement is applied as the objective function.

• Steel and Composite Structures
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• 제43권5호
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• pp.565-579
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• 2022

This study investigated the yielding capacity and performance of seismic dampers constructed with steel ring plates using numerical and analytical approaches. This study aims to provide an analytical relationship for estimating the yielding capacity and initial stiffness of steel ring dampers. Using plastic analysis and considering the mechanism of plastic hinge formation, a relation has been obtained for estimating the yielding capacity of steel ring dampers. Extensive parametric studies have been carried out using a nonlinear finite element method to examine the accuracy of the obtained analytical relationships. The parametric studies include investigating the influence of the length, thickness, and diameter of the ring of steel ring dampers. To this end, comprehensive verification studies are performed by comparing the numerical predictions with several reported experimental results to demonstrate the numerical method's reliability and accuracy. Comparison is made between the hysteresis curves, and failure modes predicted numerically or obtained/observed experimentally. Good agreement is observed between the numerical simulations and the analytical predictions for the yielding force and initial stiffness. The difference between the numerical models' ultimate tensile and compressive capacities was observed that average of about 22%, which stems from the performance of the ring-dampers in the tensile and compression zones. The results show that the steel ring-dampers are exhibited high energy dissipation capacity and ductility. The ductility parameters for steel ring-damper between values were 7.5 to 4.1.