• Steel and Composite Structures
• /
• 제18권2호
• /
• pp.497-517
• /
• 2015

This study evaluates behavior of the Y-type perfobond rib shear connector proposed by Kim et al. (2013). In addition, an empirical shear resistance formula is developed based on push-out tests. Various types of the proposed Y-type perfobond rib shear connectors are examined to evaluate the effects of design variables such as concrete strength, number of transverse rebars, and thickness of rib. It is verified that higher concrete strength increases shear resistance but decreases ductility. Placing transverse rebars significantly increases both the shear resistance and ductility. As the thickness of the ribs increases, the shear resistance increases but the ductility decreases. The experimental results indicate that a Y-type perfobond rib shear connector has higher shear resistance and ductility than the conventional stud shear connector. The effects of the end bearing resistance, resistance by transverse rebars, concrete dowel resistance by holes, and concrete dowel resistance by Y-shape ribs on the shear resistance are estimated empirically based on the push-out test results and the additional push-out test results by Kim et al. (2013). An empirical shear resistance formula is suggested to estimate the shear resistance of a Y-type perfobond shear connector for design purposes. The newly developed shear resistance formula is in reasonable agreement with the experimental results because the average ratio of measured shear resistance to estimated shear resistance is 1.024.

• 대한소아치과학회지
• /
• 제46권3호
• /
• pp.328-336
• /
• 2019

이 연구의 목적은 변화하는 사회경제적 환경에 따른 소아치과의 환자 분포와 진료 양상 변화를 파악하는 데 있다. 2008년 1월부터 2017년 12월까지 단국대학교 치과병원 소아치과의 환자분포와 진료 현황에 대한 정보를 분석하였다. 초진 환자 수와 재진 환자 수 모두 증가하였다. 초진 환자의 평균 연령은 감소하는 추세를 보였고, 만 0 - 6세 학령기 전 환아가 다수를 차지했다. 수복치료의 경우 복합레진 수복은 감소하였고, 레진강화형 글라스아이오노머 수복은 증가하였다. 유치에서의 치수절제술 시행 비율은 크게 증가하였으나 치수절단술 시행 비율은 감소하였다. 전신마취, 진정법 하 치과치료 시행 수는 증가하는 추세를 보였다. 진정법의 경우 2014년 이후로 꾸준히 미다졸람 근육주사 하 치과치료가 증가하였다.

• Steel and Composite Structures
• /
• 제30권3호
• /
• pp.281-292
• /
• 2019

In this paper, analysis of critical fluid velocity and heat transfer in the nanocomposite pipes conveying nanofluid is presented. The pipe is reinforced by carbon nanotubes (CNTs) and the fluid is mixed by $AL_2O_3$ nanoparticles. The material properties of the nanocomposite pipe and nanofluid are considered temperature-dependent and the structure is subjected to magnetic field. The forces of fluid viscosity and turbulent pressure are obtained using momentum equations of fluid. Based on energy balance, the convection of inner and outer fluids, conduction of pipe and heat generation are considered. For mathematical modeling of the nanocomposite pipes, the first order shear deformation theory (FSDT) and energy method are used. Utilizing the Lagrange method, the coupled pipe-nanofluid motion equations are derived. Applying a semi-analytical method, the motion equations are solved for obtaining the critical fluid velocity and critical Reynolds and Nusselt numbers. The effects of CNTs volume percent, $AL_2O_3$ nanoparticles volume percent, length to radius ratio of the pipe and shell surface roughness were shown on the critical fluid velocity, critical Reynolds and Nusselt numbers. The results are validated with other published work which shows the accuracy of obtained results of this work. Numerical results indicate that for heat generation of $Q=10MW/m^3$, adding 6% $AL_2O_3$ nanoparticles to the fluid increases 20% the critical fluid velocity and 15% the Nusselt number which can be useful for heat exchangers.

• Composites Research
• /
• 제32권2호
• /
• pp.120-126
• /
• 2019

고성능 직물은 방탄, 방검 등의 개인 보호구뿐만 아니라, 우주보호시스템, 차량방탄 등 다양한 분야에서 활용되고 있다. 또한 고성능 직물의 성능향상을 위한 다양한 종류의 연구가 진행되었고, 동시에 많은 해석 방법들이 개발되어 왔다. 본 연구에서는 고속 및 초고속 충돌, 충격 현상 등에 특화된 상용해석 프로그램인 Autodyn을 사용하여 국산 고성능 직물인 Heracron의 고속 충돌 현상을 최초로 모사하였다. Heracron 직물에 사용된 입력 물성치별 민감도를 확인하는 해석을 수행하였다. 시험의 검증을 위해 2단 경 가스건을 사용하여 직물 1, 3, 5장의 시편을 약 200-500 m/s의 알루미늄 구체의 충돌시켜 전 후 속도를 측정하였다. Autodyn 프로그램을 이용하여 Heracron 직물의 고속 충돌 현상을 성공적으로 구현하였다.

• 한국정보통신학회논문지
• /
• 제22권11호
• /
• pp.1531-1537
• /
• 2018

해운 물류에서 대량의 컨테이너는 선박, 트럭, 철도 등 복합 운송의 형태로 항만을 거쳐 목적지로 이동된다. 선사, 화주와 같은 물류 주체는 화물의 주요 물류 거점에 대한 실시간 반 출입 정보를 필요로 한다. 특히 항만은 해운과 내륙을 연결하는 중요한 공간으로써 물류 주체의 관심이 높다. 본 논문에서는 GPS를 이용한 위치 추적을 점 단위가 아닌 면 단위를 기반으로 동적으로 나타낸다. 즉 어느 항만의 영역 안으로 들어가는지, 나가는지, 또는 통과하는지와 같은 동적인 위치 추적을 나타내고 있다. 이전 연구의 위치 추적 알고리즘을 기반으로 능동형(Active) IP-RFID 기술을 활용한 항만 진출입, 항만 내부에서의 실시간 위치 추적 알고리즘을 제안한다.

• 한국치위생학회지
• /
• 제19권2호
• /
• pp.287-295
• /
• 2019

Objectives: The purpose of this study was to investigate the factors affecting subjective oral symptoms according to the gender of youth from multi-cultural families in Korea using data from the 14th (2018) Korean Youth Health Behavior Survey. Methods: The independent variables used in this study consisted of gender and sweet drink intake. The dependent variable was experience of subjective oral symptoms. Compensation variables consisted of general characteristics of school type, academic performance, economic status, drinking status, smoking status, and number of tooth brushings day before. The subjects of the study were 835 children of multi-cultural families whose parents were foreigners. All statistical analyses were performed by complex samples cross-tabulation analysis and complex samples logistic regression analysis. Statistical analysis was performed using the PASW statistical package 21.0 (Statistical Packages for Social Science Inc., Chicago, IL, USA). A significance level of 0.05 was used for statistical significance. Results: The composite sample logistic regression analysis showed that there was a statistically significant difference between gender and intake of sweet drinks in experience of subjective oral symptoms. Conclusions: These results suggest that factors influence subjective oral symptoms in Korean multi-cultural adolescents. Therefore, I hope that they will be used as basic data for the introduction and development of a customized oral health education program for improving oral health of multi-cultural adolescents.

• Composites Research
• /
• 제32권3호
• /
• pp.163-169
• /
• 2019

본 연구에서 우리는 자유 라디칼 중합에 기반한 열가소성 고분자의 동적 분자동역학 중합 알고리즘을 이용하여 95%의 변환률을 갖는 PMMA의 고분자 모델을 구성하였다. 본 알고리즘에서는 계산 수행에 필요한 시간을 줄이기 위해 PCFF 포텐셜 함수의 결합 항들 TraPPE-UA 포텐셜 함수의 비결합 항을 조합한 united-atom level의 coarse-grained 포텐셜 함수를 도입하였다. 자유 라디칼 중합 시뮬레이션을 통해 생성된 각 사슬을 분석하여 고분자의 분자량 분포와 평균 분자량을 계산하였고, 고분자의 분자량은 초기 상태에 존재하는 개시제 라디칼의 수를 이용하여 조절하였으며, 유리전이온도, 기계적 물성에 미치는 분자량의 효과에 대해 연구되었다.

• 한국지진공학회논문집
• /
• 제23권5호
• /
• pp.239-248
• /
• 2019

In this study, the out-of-plane seismic resistance of lightly-reinforced existing walls strengthened with thick RC jacket was investigated. The thick RC jacket with a thickness of 500 mm was placed at one side of the thin existing wall with a thickness of 150 mm. At the interface between the wall and RC jacket, a tee-shaped steel section with a number of anchor bolts and dowel bars was used as the shear connector. To investigate the connection performance and strengthening effects, the cyclic loading tests of four jacketed wall specimens were performed. The tests showed that the flexural strength of the jacketed walls under out-of-plane loading was significantly increased. During the initial behavior, the tee shear connector transferred forces successfully at the interface without slip. However, as the cracking, spalling, and crushing of the concrete increased in the exiting walls, the connection performance at the interface was significantly degraded and, consequently, the strength of the jacketed walls was significantly decreased. The flexural strength of the jacketed walls with tee shear connector was estimated considering the full and partial composite actions of the tee shear connector.

• Steel and Composite Structures
• /
• 제30권5호
• /
• pp.417-432
• /
• 2019

This paper presents the results of axial compression testing and numerical modeling on reinforced concrete columns (RCC) with normal concrete (NC) and high-strength concrete (HSC), RCC confined by glass-fiber reinforced plastic pipes (GRP) casing as well as carbon fiber reinforced polymer (CFRP), The major parameters evaluated in the experiments were the effects of concrete type, GRP casing and CFRP wrapping, as well as the number of CFRP layers. 12 cylindrical RCC ($150{\times}600mm$) were prepared and divided into two groups, NC and HSC. Each group was divided into two parts; with and without GRP casing. In each part, one column was without CFRP strengthening layer, a column was wrapped with one CFRP layer and another column with two CFRP layers. All columns were tested under concentrated compression load. Numerical modeling was performed using ABAQUS software and the results of which were compared with experimental findings. A good agreement was found between the results. Results indicated that the utilization of CFRP wrapping and GRP casing improved compression capacity and ductility of RCC. The addition of one and two layer-FRP wrapping increased capacity in the NC group to an average of 18.5% and 26.5% and in the HSC group to an average of 10.2% and 24.8%. Meanwhile, the utilization of GRP casing increased the capacity of the columns by 3 times in the NC group and 2.38 times in the HSC group. The results indicated that although both CFRP wrapping and GRP casing increased confinement, the GRP casing gave more increase capacity and ductility of the RCC due to higher confinement. Furthermore, the confinement effect was higher on NC group.

• Steel and Composite Structures
• /
• 제29권6호
• /
• pp.717-734
• /
• 2018

This paper presents the flexural performance of steel beam-to-column joints composed of hollow structural section beams and columns. A finite element (FE) model was developed incorporating geometrical and material nonlinearities to evaluate the behaviour of joints subjected to bending moments. The numerical outcomes were validated with experimental results and compared with EN1993-1-8. The demountability of the structure was discussed based on the tested specimen. A parametric analysis was carried out to investigate the effects of steel yield strength, end-plate thickness, beam thickness, column wall thickness, bolt diameter, number of bolts and location. Consequently, an analytical model was derived based on the component method to predict the moment-rotation relationships for the sub-assemblies with extended end-plates. The accuracy of the proposed model was calibrated by the experimental and numerical results. It is found that the FE model is fairly reliable to predict the initial stiffness and moment capacity of the joints, while EN1993-1-8 overestimates the initial stiffness extensively. The beam-to-column joints are shown to be demountable and reusable with a moment up to 53% of the ultimate moment capacity. The end-plate thickness and column wall thickness have a significant influence on the joint behaviour, and the layout of double bolt-rows in tension is recommended for joints with extended end-plates. The derived analytical model is capable of predicting the moment-rotation relationship of the structure.