• Computers and Concrete
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• 제14권2호
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• pp.109-125
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• 2014

The force transfer mechanism in positive moment continuity details for prestressed concrete girder bridges is investigated in this paper using a three-dimensional detailed finite element model. Positive moment reinforcement in the form of hairpin bars as recommended by the National Cooperative Highway Research Program Report No 519 is incorporated in the model. The cold construction joint that develops at the interface between girder ends and continuity diaphragms is also simulated via contact elements. The model is then subjected to the positive moment and corresponding shear forces that would develop over the service life of the bridge. The stress distribution in the continuity diaphragm and the axial force distribution in the hairpin bars are presented. It was found that due to the asymmetric configuration of the hairpin bars, asymmetric stress distribution develops at the continuity diaphragm, which can be exacerbated by other asymmetric factors such as skewed bridge configurations. It was also observed that when the joint is subjected to a positive moment, the tensile force is transferred from the girder end to the continuity diaphragm only through the hairpin bars due to the lack of contact between the both members at the construction joint. As a result, the stress distribution at girder ends was found to be concentrated around the hairpin bars influence area, rather than be resisted by the entire girder composite section. Finally, the results are used to develop an approach for estimating the cracking moment capacity at girder ends based on a proposed effective moment of inertia.

• Computers and Concrete
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• 제13권1호
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• pp.49-70
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• 2014

Steel fiber-reinforced concrete (SFRC) is known as one of the efficient modern composites that can greatly enhance the material performance of cracked concrete in tension. Such improved tensile resistance mechanism at crack interfaces in SFRC members can be heavily influenced by methodologies of treatments of crack direction. While most existing studies have focused on developing the numerical analysis model with the rotating-angle theory, there are only few studies on finite element analysis models with the fixed-angle model approach. According to many existing experimental studies, the direction of principal stress rotated after the formation of initial fixed-cracks, but it was also observed that new cracks with completely different angles relative to the initial crack direction very rarely occurred. Therefore, this study introduced the direct tension force transfer model (DTFTM), in which tensile resistance of the fibers at the crack interface can be easily estimated, to the nonlinear finite element analysis algorithm with the fixed-angle theory, and the proposed model was also verified by comparing the analysis results to the SFRC shear panel test results. The secant modulus method adopted in this study for iterative calculations in nonlinear finite element analysis showed highly stable and fast convergence capability when it was applied to the fixed-angle theory. The deviation angle between the principal stress direction and the fixed-crack direction significantly increased as the tensile stresses in the steel fibers at crack interfaces increased, which implies that the deviation angle is very important in the estimation of the shear behavior of SFRC members.

• Structural Engineering and Mechanics
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• 제83권6호
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• pp.789-798
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• 2022

The stud shear connector is the main force transfer member in the steel-concrete composite member, and the mechanical behavior is very complicated in the concrete. The concrete around the stud is subjected to the pry-out local pressure concentration of the stud, which can easily produce splitting mirco-cracks. In order to solve the problem of pry-out local splitting of stud shear connector, a kind of stud shear connector with constraint measure is proposed in this paper. Through the push-out test, the interface shear behavior of the new stud shear connector between steel and concrete flange plate was studied, and the difference between the new stud shear connector and the traditional stud connector was compared. The results show that the stud shear connector with constraint measure can effectively avoid the adverse effect of local pressure splitting by relying on its own constraint measure. The shear stiffness of the interface between steel and concrete flange plates is greatly improved, which provides a theoretical basis for the design of strong connection coefficient of steel-concrete composite structures.

• Structural Engineering and Mechanics
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• 제38권4호
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• pp.385-403
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• 2011

Continuous deep girders which transmit the gravity load from the upper wall to the lower columns have frequently long end shear spans between the boundary of the upper wall and the face of the lower column. This paper presents the results of tests and analyses performed on three 1:2.5 scale specimens with long end shear spans, (the ratios of shear-span/total depth: 1.8 < a/h < 2.5): one designed by the conventional approach using the beam theory and two by the strut-and-tie approach. The conclusions are as follows: (1) the yielding strength of the continuous RC deep girders is controlled by the tensile yielding of the bottom longitudinal reinforcements, being much larger than the nominal strength predicted by using the section analysis of the girder section only or using the strut-and-tie model based on elastic-analysis stress distribution. (2) The ultimate strengths are 22% to 26% larger than the yielding strength. This additional strength derives from the strain hardening of yielded reinforcements and the shear resistance due to continuity with the adjacent span. (3) The pattern of shear force flow and failure mode in shear zone varies depending on the amount of vertical shear reinforcement. And (4) it is necessary to take into account the existence of the upper wall in the analysis and design of the deep continuous transfer girders that support the upper wall with a long end shear span.

• 대한토목학회논문집
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• 제6권1호
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• pp.25-33
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• 1986

일반적(一般的)으로 대규모(大規模) 하천(河川)은 저수로(低水路)와 고수부지(高水敷地)를 갖는 복단면수로(複斷面水路)로 되어있다. 복단면(複斷面) 수로(修路)에 대한 일반적인 해석방법은 저수로(低水路)에서 고수부지(高水敷地)로의 운동량(運動量) 전달(傳達)을 무시하였기 때문에 소통능력을 과대하게 평가(評價)하는 경향을 보여왔다. 따라서 본(本) 연구(硏究)에서는 운동량(運動量) 전달(傳達)을 고려하여 비대칭 고수부지(高水敷地)를 갖는 구형단면(矩形斷面)의 실험수로(實驗水路)에서 실험(實驗)하였으며, 단면의 여러 점에서 유속(流速)을 측정(測定)하고 유속분포(流速分布)로부터 경계층의 전단응력을 계산하여 윤변을 따라 이를 적분(積分)하여 겉보기 전단력을 구한다. 그리고 복단면(複斷面) 수로(水路)에서의 수리학적(水理學的) 특성(特性)을 실험단면(實驗斷面)의 유속분포(流速分布), 경계층의 전단응력(剪斷應力), 그리고 겉보기 전단력 등의 여러 가지 관계로부터 규명하였다.

• 한국건설순환자원학회논문집
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• 제9권3호
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• pp.348-355
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• 2021

도로 포장에 널리 사용되는 아스팔트는 도로가 노출되는 환경에 따라 요구되는 물리적 특성이 상이하다. 이에 따라 첨가제의 배합에 따라 아스팔트가 어떤 물리적 특성을 나타내는지 평가하고 도로의 교통, 기후 환경에 맞추어 적절한 배합을 선택하는 것이 아스팔트 도로의 수명을 확보하기 위해 필수적이다. 아스팔트의 다양한 물리적 특성 중 소성변형에 대한 저항성을 측정하기 위해서는 Dynamic shear rheometer(DSR) 테스트를 주로 사용한다. 하지만 DSR 테스트는 실험 세팅에 따라 결과가 상이하고 특정 온도 범위 내에만 측정이 가능한 단점이 있다. 따라서 본 연구에서는 DSR 테스트의 단점을 극복하고자, Atomic force microscopy로부터 수집된 이미지를 학습하여 레올로지적 특성을 예측하고자 했다. 딥러닝 아키텍처 중 하나인 EfficientNet을 통해 이미지를 학습하였고 딥러닝 모델의 한계인 많은 데이터를 요구한다는 점을 극복하기 위해 전이학습을 이용하여 학습을 진행하였다. 학습된 모델은 이종의 첨가제를 사용하였음에도 높은 정확도로 아스팔트 바인더의 레올로지적 특성을 예측하였다. 특히, 전이학습을 사용하지 않았을 때와 비교하여 빠르게 학습이 가능했다.

• 한국소음진동공학회논문집
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• 제12권2호
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• pp.161-169
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• 2002

Based on the analytic expression for the elasto-dynamic behavior of rotating shaft, the transfer matrix is formulated for the shaft element with uniform cross-section. Timoshenko beam theory is Introduced for modeling the behavior of shaft. Complex variables representing the displacement, slope, moment and shear force are used for deriving the transfer matrix between both ends of the shaft element. Simulation result obtained by applying the transfer matrix to a general rotor model is compared with the reference result and proved to be exact. Natural frequencies and the corresponding modes are analyzed with varying the bearing: stiffness. The generally used bearings are considered for discussions. and the bearing stiffness is shown to affect the vibration characteristics of rotor.

• 대한기계학회논문집B
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• 제27권1호
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• pp.17-24
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• 2003

A mathematical model of the hydrodynamic and heat transfer performances of two-phase flow (gas-liquid) in thin film region of micro channel is proposed. For the formulation of modeling, the flow of the vapor phase and the shear stress at the liquid-vapor interface are considered. In this work, disjoining pressure and capillary force which drive the liquid flow at the liquid-vapor interface in thin film region are adopted also. Using the model, the effects of the variations of channel height and heat flux on the flow and heat transfer characteristics are investigated. Results show that the influence of variation of vapor pressure on the liquid film flow is not negligible. The heat flux in thin-film region is the most important operation factor of micro cooler system.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 가을 학술발표회 논문집
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• pp.569-574
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• 1997

This research has improved composite joint system of R/C column and steel beam developed at previous study. In this system, the shear force occurred at beam is transmitted by bearing resistance of stiffness and moment is resisted by tension capacity of coupling members. As the preliminary step of stress transfer tests of this system, welding performance test of coupling member such as round bar or square bar which has a role of moment transfer has been carried out. From the test, this element has a good welding performance and enough resistance capacity compared to design force.

• Steel and Composite Structures
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• 제3권1호
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• pp.33-46
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• 2003

This study focuses on the influence of a composite external strengthening on the natural frequencies of a steel beam with open cracks. In a first step, the leading parameters associated with the effect of the composite strengthening are experimentally identified. An analytical model is developed in order to quantify the importance of the force transfer within the resin interface. In a second step, the analytical model of a cracked beam with composite external strengthening is compared to experiments.