• 한국지진공학회논문집
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• 제12권6호
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• pp.35-45
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• 2008

구조물의 응답에 대한 잔류변위의 영향을 평가하기 위하여, 초기 잔류변형이 있는 상태에서 작용하는 설계지진에 대한 좌굴방지 가새골조(BRBF)와 특수 모멘트골조(SMRF)의 응답을 평가하였다. 초기 잔류변형은 구조물에 두 가지 방법으로 적용하였다. 첫 번째 방법은 첫 지진에 대하여 구조물이 정지 상태에 도달한 이후 같은 크기의 지진을 적용하는 것이다. 두 번째 방법은 소요 잔류층간 변형이 발생할 때까지 일방향으로 가력한 다음 지진하중을 적용하였다. 해석결과에 따르면 초기 잔류층간변위는 BRBF와 SMRF의 응답에 큰 영향을 주었다. SMRF 시스템보다 BRBF의 응답이 초기 잔류변형에 크게 의존하였다. 그러므로 지진발생 이후 보수비용을 최소화하기 위하여 잔류층간변위를 줄이는 것이 필요하다.

• 한국통신학회논문지
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• 제31권5C호
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• pp.519-533
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• 2006

IEEE 802.15.4 저속 무선 개인망 표준에서 기술하고 있는 채널의 숫자는 같은 지역 내에서 많은 수의 개인망을 동시에 운용하기에는 매우 부족하다. 이러한 제한을 해결하기 위해서, 우리는 많은 개인망이 공존하는 경우 가용한 채널의 숫자를 늘릴 수 있는 가상 채널(Virtual Channel)이라는 개념을 소개한다. 기본적으로 가상 채널은 이미 다른 개인망에 의해 점유된 논리적 채널 속에의 비활성 구간 속에 슈퍼 프레임을 위치시키는 방법을 통해 새롭게 만들어 지는 채널을 가리킨다. 이러한 가상 채널을 사용하여 하나의 채널 내에 공존하는 개인망들의 공존능력을 최대화하기 위하여 이 논문에서는 충돌 수퍼프레임 스케줄러(Least Collision-Scheduler)와 복잡도가 줄어든 휴리스틱 알고리즘을 제안한다. 그리고 다수의 채널이 주어졌을 경우, 주어진 채널을 효율적으로 관리하는 가상채널 선택기(Virtual Channel Selector)를 제안한다. 부가적으로, 공존하는 많은 개인망들 간의 비동기화 문제를 해결하기 위한 간단하고 실제적인 동기화 기술을 고안한다. 우리는 컴퓨터 시뮬레이션을 통해서 이러한 가상 채널 기법을 사용할 경우 개인망의 공존 능력에 있어 획기적인 개선을 이룰 수 있음을 확인하였다.

• 한국지진공학회논문집
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• 제12권4호
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• pp.35-44
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• 2008

최근 새로운 지진하중 저항시스템으로 셀프센터링(SCED) 가새 시스템이 개발되었다. 진보된 가새 시스템인 비좌굴 가새(BRB) 시스템과는 달리 큰 지진이 발생한 후 구조물의 잔류 변형을 줄이거나 없앨 수 있는 셀프센터링 능력은 SCED 가새 시스템의 장점이다. 본 논문에서는 SCED 가새와 BRB 가새 시스템의 거동에 비틀림의 영향을 조사하기 위하여 세 가지 다른 편심을 가진 3차원 구조물의 응답을 비선형 동적해석을 수행하여 비교하였다. 해석결과에 따르면 층간변위의 높이방향의 변화는 비정형성에 관계없이 SCED 가새골조의 응답이 BRB 가새골조보다 일정하였으며, 잔류 층간변위와 잔류 회전 응답은 비정형성이 증가함에 따라 감소하였다. 중층 구조물에서 SCED 가새골조의 변형집중계수(DCF)는 BRB 가새골조보다 작은 것으로 나타났다. 이것은 SCED 가새골조가 건물 높이에 따라 보다 일정하게 변형함을 의미한다. DCF의 크기에 대한 비틀림 비정형의 효과는 작았다.

• Structural Engineering and Mechanics
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• 제58권6호
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• pp.1045-1075
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• 2016

Shallow footings are one of the most common types of foundations used to support mid-rise buildings in high risk seismic zones. Recent findings have revealed that the dynamic interaction between the soil, foundation, and the superstructure can influence the seismic response of the building during earthquakes. Accordingly, the properties of a foundation can alter the dynamic characteristics (natural frequency and damping) of the soil-foundation-structure system. In this paper the influence that shallow foundations have on the seismic response of a mid-rise moment resisting building is investigated. For this purpose, a fifteen storey moment resisting frame sitting on shallow footings with different sizes was simulated numerically using ABAQUS software. By adopting a direct calculation method, the numerical model can perform a fully nonlinear time history dynamic analysis to realistically simulate the dynamic behaviour of soil, foundation, and structure under seismic excitations. This three-dimensional numerical model accounts for the nonlinear behaviour of the soil medium and structural elements. Infinite boundary conditions were assigned to the numerical model to simulate free field boundaries, and appropriate contact elements capable of modelling sliding and separation between the foundation and soil elements are also considered. The influence of foundation size on the natural frequency of the system and structural response spectrum was also studied. The numerical results for cases of soil-foundation-structure systems with different sized foundations and fixed base conditions (excluding soil-foundation-structure interaction) in terms of lateral deformations, inter-storey drifts, rocking, and shear force distribution of the structure were then compared. Due to natural period lengthening, there was a significant reduction in the base shears when the size of the foundation was reduced. It was concluded that the size of a shallow foundation influences the dynamic characteristics and the seismic response of the building due to interaction between the soil, foundation, and structure, and therefore design engineer should carefully consider these parameters in order to ensure a safe and cost effective seismic design.

• Structural Engineering and Mechanics
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• 제46권6호
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• pp.755-773
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• 2013

One of the main requirements of the seismic design codes must be its easy application by structural engineers. The use of practically-applicable models or simplified models as single-degree-of-freedom (SDOF) systems is a good alternative to achieve this condition. In this study, deterministic and probabilistic response transformation factors are obtained to evaluate the response in terms of maximum ductility and maximum interstory drifts of multi-degree-of-freedom (MDOF) systems based on the response of equivalent SDOF systems. For this aim, five steel frames designed with the Mexican City Building Code (MCBC) as well as their corresponding equivalent SDOF systems (which represent the characteristics of the frames) are analyzed. Both structural systems are subjected to ground motions records. For the MDOF and the simplified systems, incremental dynamic analyses IDAs are developed in first place, then, structural demand hazard curves are obtained. The ratio between the IDAs curves corresponding to the MDOF systems and the curves corresponding to the simplified models are used to obtain deterministic response transformation factors. On the other hand, demand hazard curves are used to calculate probabilistic response transformation factors. It was found that both approaches give place to similar results.

• Earthquakes and Structures
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• 제18권3호
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• pp.349-365
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• 2020

Since the peak seismic response of a base-isolated building strongly depends on the characteristics of the imposed seismic ground motion, the behavior of a base-isolated building under different seismic ground motions is studied, in order to better assess their effects on its peak seismic response. Specifically, the behavior of a typical steel building is examined as base-isolated with elastomeric bearings, while the effect of near-fault ground motions is studied by imposing 7 pairs of near- and 7 pairs of far-fault seismic records, from the same 7 earthquake events, to the building, under 3 different loading combinations, through three-dimensional (3D) nonlinear dynamic analyses, conducted with SAP2000. The results indicate that near-fault seismic components are more likely to increase the building's peak seismic response than the corresponding far-fault components. Furthermore, the direction of the imposed earthquake excitations is also varied by rotating the imposed pairs of seismic records from 0◦ to 360◦, with respect to the major construction axes. It is observed that the peak seismic responses along the critical incident angles, which in general differ from the major horizontal construction axes of the building, are significantly higher. Moreover, the influence of 5% and 10% accidental mass eccentricities is also studied, revealing that when considering accidental mass eccentricities the peak relative displacements of the base isolated building at the isolation level are substantially increased, while the peak floor accelerations and interstory drifts of its superstructure are only slightly affected.

• Structural Engineering and Mechanics
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• 제51권3호
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• pp.487-502
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• 2014

In buildings structures, the flexural stiffness reduction of beams and columns due to concrete cracking plays an important role in the nonlinear load-deformation response of reinforced concrete structures under service loads. Most Seismic Design Codes do not precise effective stiffness to be used in seismic analysis for structures of reinforced concrete elements, therefore uncracked section properties are usually considered in computing structural stiffness. But, uncracked stiffness will never be fully recovered during or after seismic response. In the present study, the effect of concrete cracking on the lateral response of structure has been taken into account. Totally 120 cases of 3 Dimensional Dynamic Analysis which considers the real and accidental torsional effects are performed using ETABS to determine the effective structural system across the height, which ensures the performance and the economic dimensions that achieve the saving in concrete and steel amounts thus achieve lower cost. The result findings exhibits that the dual system was the most efficient lateral load resisting system based on deflection criterion, as they yielded the least values of lateral displacements and inter-storey drifts. The shear wall system was the most economical lateral load resisting compared to moment resisting frame and dual system but they yielded the large values of lateral displacements in top storeys. Wall systems executes tremendous stiffness at the lower levels of the building, while moment frames typically restrain considerable deformations and provide significant energy dissipation under inelastic deformations at the upper levels. Cracking found to be more impact over moment resisting frames compared to the Shear wall systems. The behavior of various lateral load resisting systems with respect to time period, mode shapes, storey drift etc. are discussed in detail.

• 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.

• Smart Structures and Systems
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• 제21권3호
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• pp.359-371
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• 2018

Strong seismic events commonly cause large drift and deformation, and functionality failures in the superstructures. One way to prevent functionality failures is to design structures which are ductile and flexible through yielding when subjected to strong ground excitations. By developing forces that assist motion as "negative stiffness forces", yielding can be achieved. In this paper, we adopt the weakening and damping method to achieve a new approach to reduce all of the structural responses by further adjusting damping phase. A semi-active control system is adopted to perform the experiments. In this adaptation, negative stiffness forces through certain devices are used in weakening phase to reduce structural strength. Magneto-rheological (MR) dampers are then added to preserve stability of the structure. To adjust the voltage in MR dampers, an inverse model is employed in the control system to command MR dampers and generate the desired control forces, where a velocity control algorithm produces initial required control force. An extensive numerical study is conducted to evaluate proposed methodology by using the smart base-isolated benchmark building. Totally, nine control systems are examined to study proposed strategy. Based on the numerical results of seven earthquakes, the use of proposed strategy not only reduces base displacements, base accelerations and base shear but also leads to reduction of accelerations and inter story drifts of the superstructure. Numerical results shows that the usage of inverse model produces the desired regulated damping, thus improving the stability of the structure.

• 한국구조물진단유지관리공학회 논문집
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• 제17권1호
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• pp.27-36
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• 2013

본 연구에서는 등대 구조물을 대상으로 한 면진기술 적용방안을 제시함으로써 지진에 대해 무방비상태에 놓여 있는 등대구조물의 지진안전도 확보방안을 제시하였다. 또한, 제안된 면진기술 적용방안을 활용하여 내진설계 이전에 지어진 등대를 대상으로 등대전체를 면진하였을 경우와 등대 렌즈만을 면진하였을 경우에 대하여 면진효과를 분석해 보았다. 해석결과, 등대 전체를 면진화하였을 경우 최대응답가속도와 층전단력 측면에서 충분한 면진효과를 얻은 반면, 등대 렌즈만을 면진화한 경우에는 렌즈부의 면진효과는 유효한 것으로 나타났으나 등대 자체의 안전이 확보되지 못한 상황에서는 등대의 파괴가 선행될 가능성이 있음에 주의할 필요가 있는 것으로 나타났다. 또한 등대전체와 렌즈를 동시에 면진화한 경우 비 면진구조 대비 유효한 면진효과는 나타내었지만, 최대응답가속도가 등대전체를 면진화한 경우보다 증가하는 경향을 나타내었으며, 렌즈의 면진화로 인한 층전단력의 감소가 미소함으로 이중면진의 적용으로 인한 실효성은 그 효과가 크지 않은 것으로 나타났다.