• Structural Engineering and Mechanics
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• 제50권2호
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• pp.241-255
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• 2014

The girder of self-anchored suspension bridge is subjected to large compression force applied by main cables. So, serious damage of the girder due to breakage of hangers may cause collapse of the whole bridge. With the time increasing, the hangers may break suddenly for their resistance capacities decrease due to corrosion. Using nonlinear static and dynamic analysis methods and adopting 3D finite element model, the responses of a concrete self-anchored suspension bridge to sudden breakage of hangers are studied in this paper. The results show that the sudden breakage of a hanger has significant effects on tensions of the hangers next to the broken hanger, bending and torsion moments of the girder, moments of the towers and reaction forces of the bearings. The results obtained from dynamic analysis method are very different from those obtained from static analysis method. The maximum tension of hanger produced by breakage of a hanger exceeds 2.2 times of its initial value, the maximum dynamic amplification factor reaches 2.54, which is larger than the value of 2.0 recommended for cable-stayed bridge in PTI codes. If two adjacent hangers on the same side of bridge break one after another, the maximum tension of other hangers exceeds 3.0 times of its initial value. If the safety factor adopted to design hanger is too small, or the hangers have been exposed to corrosion, the bridge may collapse due to breakage of two adjacent hangers.

• Steel and Composite Structures
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• 제21권3호
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• pp.589-604
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• 2016

Kenya has recently experienced worrying collapse of buildings during construction largely attributable to the poor quality of in-situ concrete and poor workmanship. The situation in the country is further compounded by rapid deterioration of infrastructure, hence necessitating the development of alternative structural systems such as concrete filled unplasticized poly vinyl chloride (UPVC) tubes as columns. The work herein adds on to the very limited and scanty work on use of UPVC tubes in construction. This study presents the findings of experimental and analytical work which investigated the structural response of composite concrete filled UPVC tubes under compressive load regime. UPVC pipes are cheaper than steel tubes and can be used as formwork during construction and thereafter as an integral part of column. Key variables in this study included the strength of infill concrete, the length to diameter ratio (L/D) of the plastic tube, as well as the diameter to thickness ratio (D/2t) of the plastic tube. Plastic tubes having varying diameters and heights were used to confine concrete of different strengths. Results obtained in the study clearly demonstrate the effectiveness of UPVC tubes as a confining medium for infill concrete, attributable to enhanced composite interaction between the UPVC tube and infill concrete medium. It was determined that compressive strength of the composite column specimens increased with increased concrete strength while the same decreased with increased column height, albeit by a small margin since all the columns considered were short columns. Most importantly, the experimental confined concrete strength increased significantly when compared to unconfined concrete strength; the strength increased between 1.18 to 3.65 times the unconfined strength. It was noted that lower strength infill concrete had the highest confined strength possibly due to enhanced composite interaction with the confining UPVC tube. The study further proposes an analytical model for the determination of confined strength of concrete.

• Steel and Composite Structures
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• 제16권5호
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• pp.491-506
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• 2014

Buckling-restrained braces (BRBs) have excellent hysteretic behavior while buckling-restrained braced frames (BRBFs) are susceptible to residual lateral deformations. To address this drawback, a novel self-centering (SC) BRB with Basalt fiber reinforced polymer (BFRP) composite tendons is presented in this work. The configuration and mechanics of proposed BFRP-SC-BRBs are first discussed. Then an 1840-mm-long BFRP-SC-BRB specimen is fabricated and tested to verify its hysteric and self-centering performance. The tested specimen has an expected flag-shaped hysteresis character, showing a distinct self-centering tendency. During the test, the residual deformation of the specimen is only about 0.6 mm. The gap between anchorage plates and welding ends of bracing tubes performs as expected with the maximum opening value 6 mm when brace is in compression. The OpenSEES software is employed to conduct numerical analysis. Experiment results are used to validate the modeling methodology. Then the proposed numerical model is used to evaluate the influence of initial prestress, tendon diameter and core plate thickness on the performance of BFRP-SC-BRBs. Results show that both the increase of initial prestress and tendon diameters can obviously improve the self-centering effect of BFRP-SC-BRBs. With the increase of core plate thickness, the energy dissipation is improved while the residual deformation is generated when the core plate strength exceeds initial prestress force.

• Smart Structures and Systems
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• 제19권3호
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• pp.269-277
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• 2017

Recently, there has been significant interest in structural health monitoring for civil engineering applications. In this research, a specially designed tendon, proposed by embedding FBG sensors into the center king cable of a 7-wire strand tendon, was applied for long-term health monitoring of tensile forces on a ground anchor. To make temperature independent sensors, the effective temperature compensation of FBG sensors must be considered. The temperature sensitivity coefficient ${\beta}^{\prime}$ of the FBG sensors embedded tendon was successfully determined to be $2.0{\times}10^{-5}^{\circ}C^{-1}$ through calibrated tests in both a model rock body and a laboratory heat chamber. Furthermore, the obtained result for ${\beta}^{\prime}$ was formally verified through the ground temperature measurement test, expectedly. As a result, the ground temperature measured by a thermometer showed good agreement compared to that measured by the proposed FBG sensor, which was calibrated considering to the temperature sensitivity coefficient ${\beta}^{\prime}$. Finally, four prototype ground anchors including two tension ground anchors and two compression ground anchors made by replacing a tendon with the proposed smart tendon were installed into an actual slope at the Yeosu site. Tensile forces, after temperature compensation was taken into account using the verified temperature sensitivity coefficient ${\beta}^{\prime}$ and ground temperature obtained from the Korean Meteorological Administration (KMA) have been monitored for over one year, and the results were very consistent to those measured from the load cell, interestingly.

• Computers and Concrete
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• 제22권1호
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• pp.123-132
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• 2018

Reinforced concrete (RC) columns which are the main vertical structural members are exposed to several static and dynamic effects such as earthquake and wind. However, impact loading that is sudden impulsive dynamic one is the most effective loading type acting on the RC columns. Impact load is a kind of impulsive dynamic load which is ignored in the design process of RC columns like other structural members. The behavior of reinforced concrete columns under impact loading is an area of research that is still not well understood; however, work in this area continues to be motivated by a broad range of applications. Examples include reinforced concrete structures designed to resist accidental loading scenarios such as falling rock impact; vehicle or ship collisions with buildings, bridges, or offshore facilities; and structures that are used in high-threat or high-hazard applications, such as military fortification structures or nuclear facilities. In this study, free weight falling test setup is developed to investigate the behavior effects on RC columns under impact loading. For this purpose, eight RC column test specimens with 1/3 scale are manufactured. While drop height and mass of the striker are constant, application point of impact loading, stirrup spacing and concrete compression strength are the experimental variables. The time-history of the impact force, the accelerations of two points and the displacement of columns were measured. The crack patterns of RC columns are also observed. In the light of experimental results, low-velocity impact behavior of RC columns were determined and interpreted. Besides, the finite element models of RC columns are generated using ABAQUS software. It is found out that proposed finite element model could be used for evaluation of dynamic responses of RC columns subjected to low-velocity impact load.

• 대한전자공학회논문지SP
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• 제49권4호
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• pp.111-119
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• 2012

Time Stretched Pulse (TSP)는 공간적으로 임펄스(Impulse)를 효율적으로 전달하고 분석하기 위해서 사용되어 진다. 하지만 발신기와 수신기의 전달함수를 포함시키지 않으면, 시간 영역에서의 분석은 직, 간접 신호의 중첩으로 공간의 자유음장 특성을 파악하기 불가능하다. 일반적으로 공간의 자유음장(Free Field)은 표준 ISO 3745 Annex A에 의해서 평가되고 있는데, 일정 주파수 간격의 1/3 옥타브 밴드 신호를 연속적으로 발신 및 수신하여 거리별 신호 감소를 역자승 법칙(Inverse Square Law)을 적용하여 판단하고 있다. 본 논문은 자유음장 분석에서 TSP 신호를 적용하여 일반적인 ISO 3745의 1/3 옥타브 밴드 신호와 비교하였다. 역자승 모델 값과의 차이점을 분석한 결과 TSP 신호 또한 1/3 옥타브 밴드 신호와 유사한 결과를 보이고 있으며, 측정 시간 및 확장성에 대해서는 우수하게 판단되었다. 본 실험에서는 ISO 3745에 의해서 제한된 주파수 범위에서 자유음장과 반자유음장(Hemi-free Field)을 검증 받은 무향실을 사용하였다.

• 설비공학논문집
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• 제18권6호
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• pp.501-508
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• 2006

MPCM (Microencapsulated Phase Change Material) slurries show several advantages over the sensible heat transportation system. In this study, a numerical model for a vapor compression refrigeration system using MPCM slurries as a secondary fluid through an evaporator was developed, and the system performance was compared with that using water. Generally, the MPCM system showed higher performance than the water system. The COP of the MPCM system was higher by 16.6 to 18.6% than that of the water system at all conditions. The MPCM slurry yields better performance in the aspect of heat transfer and heat transportation comparing to the sensible heat transfer medium such as water.

• 한국산업융합학회 논문집
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• 제21권2호
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• pp.87-93
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• 2018

This Study Propose A New Approach To Impliment A Intelligent Robot Control Based on Voice Recognition For Smart Factory Automation Since human usually communicate each other by voices, it is very convenient if voice is used to command humanoid robots or the other type robot system. A lot of researches has been performed about voice recognition systems for this purpose. Hidden Markov Model is a robust statistical methodology for efficient voice recognition in noise environments. It has being tested in a wide range of applications. A prediction approach traditionally applied for the text compression and coding, Prediction by Partial Matching which is a finite-context statistical modeling technique and can predict the next characters based on the context, has shown a great potential in developing novel solutions to several language modeling problems in speech recognition. It was illustrated the reliability of voice recognition by experiments for humanoid robot with 26 joints as the purpose of application to the manufacturing process.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제9권6호
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• pp.2271-2288
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• 2015

The emerging high efficiency video coding (HEVC) standard adopts the quadtree-structured transform unit (TU) in the residual quadtree (RQT) coding. Each TU allows to be split into four equal sub-TUs recursively. The RQT coding is performed for all the possible transform depth levels to achieve the highest coding efficiency, but it requires a very high computational complexity for HEVC encoders. In order to reduce the computational complexity requested by the RQT coding, in this paper, we propose a fast TU size decision method incorporating an adaptive maximum transform depth determination (AMTD) algorithm and a full check skipping - early termination (FCS-ET) algorithm. Because the optimal transform depth level is highly content-dependent, it is not necessary to perform the RQT coding at all transform depth levels. By the AMTD algorithm, the maximum transform depth level is determined for current treeblock to skip those transform depth levels rarely used by its spatially adjacent treeblocks. Additionally, the FCS-ET algorithm is introduced to exploit the correlations of transform depth level between four sub-CUs generated by one coding unit (CU) quadtree partitioning. Experimental results demonstrate that the proposed overall algorithm significantly reduces on average 21% computational complexity while maintaining almost the same rate distortion (RD) performance as the HEVC test model reference software, HM 13.0.

• 전자공학회논문지CI
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• 제40권3호
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• pp.156-163
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• 2003

워터마킹 기술 중에 공간 영역을 주파수 영역으로 변환하여 워터마크 신호를 삽입하는 이유는 워터마크를 삭제하려는 악의적인 공격에 대해 살아 남을 수 있고 인간이 삽입되는 워터마크 신호를 쉽게 인지할 수 없는 주파수 대역을 고려할 수 있기 때문이다. 그러나 3차원 데이터의 비정규성(irregularity)으로 인하여 공간영역의 3차원 데이터를 주파수 영역으로 자연스럽게 변환한다는 것은 쉽지 않다. 본 논문에서는 3차원 메쉬(mesh) 데이터를 주파수 영역으로 변환하여 수행하는 새로운 워터마킹 방법을 제안한다. 이를 위해 우선 3차원 모델을 운행(traversing)하여 삼각형 스트립을 생성하고, 각 스트립에 속한 꼭지점 좌표들을 각 좌표축에 따라 독립적으로 1차원 DCT 변환한다. 그리고 쉽게 인지되지 않으면서도 불법적인 공격으로부터 워터마크 신호가 살아남기 위해 AC 계수의 중간 주파수 대역에 워터마크 신호를 삽입한다. 마지막으로, 컴퓨터 실험을 통해 제안한 3차원 데이터 워터마킹 방법은 무작위 잡음 첨가 공격이나 Affine 변환, 그리고 MPEG-4 SNHC의 표준 기하 압축에 강인하다는 것을 보였다.