• Steel and Composite Structures
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• 제29권1호
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• pp.77-90
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• 2018

This paper presents a combined numerical, experimental, and theoretical study on the behavior of the concrete-filled double circular steel tubular (CFDT) stub columns under axial compressive loading. Four groups of stub column specimens were tested in this study to find out the effects of the concrete strength, steel ratio and diameter ratio on the mechanical behavior of CFDT stub columns. Nonlinear finite element (FE) models were also established to study the stresses of different components in the CFDT stub columns. The change of axial and transverse stresses in the internal and external steel tubes, as well as the change of axial stress in the concrete sandwich and concrete core, respectively, was thoroughly investigated for different CFDT stub columns with the same steel ratio. The influence of inner-to-outer diameter ratio and steel ratio on the ultimate bearing capacity of CFDT stub columns was identified, and a reasonable section configuration with proper inner-to-outer diameter ratio and steel ratio was proposed. Furthermore, a practical formula for predicting the ultimate bearing capacity was proposed based on the ultimate equilibrium principle. The predicted results showed satisfactory agreement with both experimental and numerical results, indicating that the proposed formula is applicable for design purposes.

• Geomechanics and Engineering
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• 제14권6호
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• pp.563-570
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• 2018

Ballast layer has an important role in vertical stiffness and stability of railway track. In most of the Middle East countries and some of the Asian ones, significant parts of railway lines pass through desert areas where the track (particularly ballast layer) is contaminated with sands. Despite considerable number of derailments reported in the sand contaminated tracks, there is a lack of sufficient studies on the influences of sand contamination on the ballast vertical stiffness as the main indicator of track stability. Addressing this limitation, the effects of sand contamination on the mechanical behavior of ballast were experimentally investigated. For this purpose, laboratory tests (plate load test) on ballast samples with different levels of sand contamination were carried out. The results obtained were analyzed leading to derive mathematical expressions for the strain modulus ($E_V$) as a function of the ballast level of contamination. The $E_V$ was used as an index for evaluation of the load-deformation characteristics and bearing capacity of track substructure. The critical limit of sand contamination, after which the $E_V$ of the ballast reduces drastically, was obtained. It was shown that the obtained research results improve the current track maintenance approach by providing key guides for the optimization of ballast maintenance planning (the timing of ballast cleaning or renewal).

• 대한기계학회논문집A
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• 제24권10호
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• pp.2502-2512
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• 2000

Truss structures are widely used in many space structures, such as large antenna systems, space stations, precision segmented telescopes because they are light in weight and amenable in assembly or deployment. But, due to the low damping capacity, they remain excited for a long time once disturbed. These structural vibrations can reduce life of the structures and cause unstable dynamic characteristics. In this research, vibration suppression experiment has carried out with a three-dimensional 15-member truss structure using two piezoelectric actuators. Piezoelectric actuators which consist of stacks of thin piezoelectric material disks are directly inserted to the truss structure collocated with the strain sensors. Each actuator is controlled digitally in decentralized manner, based on local integral and proportional feedback. The optimal positions of the actuators are determined by the modal damping ratio and the control force. Numerical simulation has carried out to determine optimal position of each actuator.

• Journal of Construction Engineering and Project Management
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• 제5권2호
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• pp.16-23
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• 2015

In this paper, a survey related to excavation construction activities among national and international construction companies was conducted to evaluate site productivity in construction industry. To analyze the respective productivity levels of each construction company, a benchmarking measures analysis that featured calculations of the performance ratio (PR) and performance management index (PMI) was performed. As a result of these analyses, it has been found that the work performed by local companies was marked by lower productivity and that of international companies was characterized by good productivity. Further analysis of construction workforce resources P% revealed that a construction company's productivity is largely dependent on production capacity and consumption resources, which means that the retention of skilled workers and utilization of high-quality resources yields the highest level of productivity. These results suggest that for a local construction company to be competitive in the construction work market, it must retrain skilled craftspeople, foremen, engineers, and project managers, and strengthen its building capability by leveraging new equipment and technologies.

• Structural Engineering and Mechanics
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• 제68권6호
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• pp.677-689
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• 2018

Residual deformation is a crucial index that should be paid special attention in the performance-based seismic analyses of reinforced concrete (RC) structures. Owing to their superior re-centering capacity under earthquake excitations, the post-tensioned self-centering (PTSC) RC frames have been proposed and developed for engineering application during the past few decades. This paper presents a comprehensive assessment on the seismic fragility of a PTSC frame by simultaneously considering maximum and residual deformations. Bivariate limit states are defined according to the pushover analyses for maximum deformations and empirical judgments for residual deformations. Incremental Dynamic Analyses (IDA) are conducted to derive the probability of exceeding predefined limit states at specific ground motion intensities. Seismic performance of the PTSC frame is compared with that of a conventional monolithic RC frame. The results show that, taking a synthetical consideration of maximum and residual deformations, the PTSC frame surpasses the monolithic frame in resisting most damage states, but is more vulnerable to ground motions with large intensities.

• 한국전문물리치료학회지
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• 제29권3호
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• pp.200-207
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• 2022

Background: The oxygen uptake efficiency slope (OUES) is the most important index for accurately measuring cardiopulmonary function in patients with acute ischemic heart disease. However, the relationship between the OUES variables and important cardiopulmonary function parameters remain unelucidated for patients with acute ischemic heart disease, which accounts for the largest proportion of heart disease. Objects: The present cross sectional clinical study aimed to determine the multiple relationships among the cardiopulmonary function variables mentioned above in adults with acute ischemic heart disease. Methods: A convenience sample of 110 adult inpatients with ischemic heart disease (age: 57.4 ± 11.3 y; 95 males, 15 females) was enrolled at the hospital cardiac rehabilitation center. The correlation between the important cardiopulmonary function indicators including peak oxygen uptake (VO₂ peak), minute ventilation (VE)/carbon dioxide production (VCO₂) slope, heart rate recovery (HRR), and ejection fraction (EF) and OUES was confirmed. Results: This study showed that OUES was highly correlated with VO₂ peak, VE/VCO₂ slope, and HRR parameters. Conclusion: The OUES can be used as an accurate indicator for cardiopulmonary function. There are other factors that influence aerobic capacity besides EF, so there is no correlation with EF. Effective cardiopulmonary rehabilitation programs can be designed based on OUES during submaximal exercise in patients with acute ischemic heart disease.

• 기술혁신연구
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• 제25권4호
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• pp.263-284
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• 2017

본 연구는 에너지 인력양성사업을 중심으로 국가의 R&D 사업의 성과를 분석하고, 성과지표 개선방안을 찾는 데 주목적이 있다. 주요 분석대상은 2010년 이래 지원된 86개 에너지인력양성사업이다. 에너지인력양성사업의 성과지표는 연구역량이나 배출인원, 산학연계 정도, 고용창출 등과 관련되어 있는데 KPI index로 지칭되는 11개 항목의 인력양성 성과지표를 많이 활용해 분석하였다. 과제별로 제시된 목표치의 달성 수준을 분석한 결과 평균적으로 달성도가 가장 높은 지수는 기업연계율이며, 달성도가 가장 낮은 지수는 참여기업 취업인원인 것으로 나타났다. 기업연계활동의 핵심 고용창출효과를 살펴본 결과 인턴십의 횟수가 많을수록 에너지 분야 고용창출효과가 큰 것으로 나타났으며, 전문가강의의 수가 많을수록 참여기업 취업인원이 증가하는 것으로 나타났다. 이상의 분석결과는 다음과 같은 시사점을 제시하고 있다. 첫째, 사업운영 과정에 대한 지표인 기업연계 활동 자체보다 이를 통해 나타나는 취업 등 핵심 성과에 더 초점을 맞춘 성과지표 재설계와 관리가 필요하다. 둘째, 사업의 질적 성과를 표현할 수 있는 지표와 실제적인 기업연계를 표현할 수 있는 성과지표를 추가하는 방안을 고려할 필요가 있다. 셋째, 정책적 성과목표 및 주요 목표 집단 등에 따라 차별화된 성과관리가 필요하다. 마지막으로 성과지표의 정비와 더불어 정보입력 및 축적 시스템 개선이 필요하다.

• Transactions on Electrical and Electronic Materials
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• 제18권2호
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• pp.111-118
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• 2017

The increased diversity of different types of energy sources requires moving towards smart distribution networks. This paper proposes a probabilistic DG (distributed generation) units planning model to determine technology type, capacity and location of DG units while simultaneously allocating ESS (energy storage systems) based on pre-determined capacities. This problem is studied in a wind integrated power system considering loads, prices and wind power generation uncertainties. A suitable method for DG unit planning will reduce costs and improve reliability concerns. Objective function is a cost function that minimizes DG investment and operational cost, purchased energy costs from upstream networks, the defined cost to reliability index, energy losses and the investment and degradation costs of ESS. Electrical load is a time variable and the model simulates a typical radial network successfully. The proposed model was solved using the DICOPT solver under GAMS optimization software.

• 한국작물학회지
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• 제54권2호
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• pp.198-202
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• 2009

The starch properties of two chinese yams were evaluated in this study. Amylose content ranged 13.5% to 19.3%. The swelling power of starches varied 10.98% to 11.43%. Water binding capacity in chinese yam starches ranged 93.46% to 107.21%, high WBC was observed in Ma 1. The onset temperature (To) of two chinese yam starches ranged 62.9 to $75.0^{\circ}C$, peak temperature (Tp) ranged 76.2 to $84.7^{\circ}C$. The PHI(peak height index) was about 4-fold higher in Anwon cultivar than in Ma 1 cultivar. SEM revealed that starches has a presence of large oval or spherical to small irregular-shape granules. Starch granule size ranged 15.23 to 15.52 ${\mu}m$, showing a typical C-type X-ray pattern.

• 한국멀티미디어학회논문지
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• 제8권12호
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• pp.1572-1580
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• 2005

The common requirements for watermarking are usually invisibility, robustness, and capacity. We proposed the watermarking for 3D mesh model based on projection onto convex sets for invisibility and robustness among requirements. As such, a 3D mesh model is projected alternatively onto two convex sets until it converge a point. The robustness convex set is designed to be able to embed watermark into the distance distribution of vertices. The invisibility convex set is designed for the watermark to be invisible based on the limit range of vertex movement. The watermark can be extracted using the decision values and index that the watermark was embedded with. Experimental results verify that the watermarked mesh model has both robustness against mesh simplification, cropping, affine transformations, and vertex randomization and invisibility.