• Steel and Composite Structures
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• 제37권2호
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• pp.117-136
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• 2020

Curved steel-concrete composite box girder has been widely adopted in urban overpasses and ramp bridges. In order to investigate its mechanical behavior under complicated and combined bending, shear and torsion load, two large-curvature composite box girders with interior angles of 25° and 45° were tested under static hogging moment. Based on the strain and deflection measurement on critical cross-sections during the static loading test, the failure mode, cracking behavior, load-displacement relationship, and strain distribution in the steel plate and rebar were investigated in detail. The test result showed the large-curvature composite box girders exhibited notable shear lag in the concrete slab and steel girder. Also, the constraint torsion and distortion effect caused the stress measured at the inner side of the composite beam to be notably higher than that of the outer side. The strain distribution in the steel web was approximately linear; therefore, the assumption that the plane section remains plane was approximately validated based on strain measurement at steel web. Furthermore, the full-process non-linear elaborate finite element (FE) models of the two specimens were developed based on commercial FE software MSC.MARC. The modeling scheme and constitutive model were illustrated in detail. Based on the comparison between the FE model and test results, the FE model effectively simulated the failure mode, the load-displacement curve, and the strain development of longitudinal rebar and steel girder with sufficient accuracy. The comparison between the FE model and the test result validated the accuracy of the developed FE model.

• Geomechanics and Engineering
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• 제21권2호
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• pp.95-102
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• 2020

Population concentration in urban areas has led traffic management a central issue. To mitigate traffic congestions, the government has planned to construct large-cross-section tunnels deep underground. This study focuses on estimating the damage caused to frame structures owing to tunnel excavation. When constructing a tunnel network deep underground, it is necessary to divide the main tunnel and connect the divergence tunnel to the ground surface. Ground settlement is caused by excavation of the adjacent divergence tunnel. Therefore, predicting ground settlement using diverse variables is necessary before performing damage estimation. We used the volume loss and cover-tunnel diameter ratio as the variables in this study. Applying the ground settlement values to the settlement induction device, we measured the extent of damage to frame structures due to displacement at specific points. The vertical and horizontal displacements that occur at these points were measured using preattached LVDT (Linear variable differential transformer), and the lateral strain and angular distortion were calculated using these displacements. The lateral strain and angular distortion are key parameters for structural damage estimation. A damage assessment chart comprises the "Negligible", "Very Slight Damage", "Slight Damage", "Moderate to Severe Damage", and "Severe to Very Severe Damage" categories was developed. This table was applied to steel frame and concrete frame structures for comparison.

• Structural Engineering and Mechanics
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• 제86권4호
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• pp.461-472
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• 2023

This paper proposes a novel method for increasing the distortional frame rigidity of off-rail box girder bridges for cranes by reinforcing the diaphragm with staggered truss. The study starts by using the Matrix Displacement Method to determine the shear angle of the staggered truss diaphragm under two assumptions: hinge joint and rigid joint. To obtain closed-form solutions for the transversal and longitudinal deformations and warping stress of the crane girder, the study employs the Initial Parameter Method and considers the compatibility of shear deformation at joints between the diaphragms and the girder. The theoretical solutions are validated through finite element analysis, which also confirms that the hinge-joint assumption accurately represents the shear angle of the staggered truss diaphragm in girder distortion. Additionally, the study conducts extensive parameter analyses to examine the impact of staggered truss dimensions on distortional stress and deformation. Furthermore, the study compares the distortional warping stresses of crane girders reinforced with staggered truss diaphragms and those reinforced with perforated ones, emphasizing the importance of incorporating stagger truss in diaphragms. Overall, this paper provides a thorough evaluation of the proposed approach's effectiveness in enhancing the distortional frame rigidity of off-rail box girder bridges for cranes. The findings offer valuable insights into the design and reinforcement of diaphragms using staggered truss to enhance the structural performance of crane girders.

• 한국구조물진단유지관리공학회 논문집
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• 제28권3호
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• pp.1-9
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• 2024

본 연구는 대기외란 조건에서 비전센서를 활용하여 구조물의 동적 변위 측정을 위하여 멀티스케일 템플릿 매칭 기법 (TMI: Template Matching with Image pyramids)을 제안하고 제안기법의 변위 측정 성능을 조사하기 위해 진행되었다. 촬영거리에 따른 변위 측정 성능을 평가하기 위해 3층 전단 구조물을 설계하였으며, FHD(1920×1080)급 카메라를 준비하여 변위 계측에 사용하였다. 최초 촬영거리를 10m로 설정하였고, 10m씩 멀어지면서 최대 40m까지 변위 측정 실험을 진행하였다. 실내 조도 조건(450lux)에서 발열 기구를 활용하여 대기외란을 발생시켰으며, 대기외란으로 이미지를 왜곡시켰다. 사전실험을 통해 대기외란시 특징점 기반 변위 측정 방법과 제안기법의 변위 측정 타당성을 비교 검증하였으며, 검증 결과 제안기법의 낮은 측정 에러율을 나타냈다. 대기외란 환경에서 변위 측정 성능평가 결과, 인공 타겟을 활용한 TMI는 대기외란 유무에 따라 변위 측정 성능에 큰 차이가 없었다. 하지만 자연 타겟을 활용하였을 때, 20m 이상의 촬영거리에서 RMSE가 크게 상승하여 제안기법의 운용 한계를 보여줬다. 이는 촬영거리 증가에 따라 자연 타겟의 해상도가 저하되며, 대기외란으로 인한 이미지 왜곡이 템플릿 이미지 추정에 오류가 발생 되어 변위 측정 오차가 높게 발생하는 경향을 나타냈다.

• 대한기계학회논문집B
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• 제35권11호
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• pp.1147-1156
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• 2011

CLECDiS 는 면적변화형 정전용량 센서의 단점을 극복하고 나노미터 수준의 분해능으로 밀리미터 이상의 큰 변위를 측정하도록 개발된 접촉식 변위센서이다. 그러나 접촉구동 특성으로 인하여 표면평탄도와 마찰에 의해 작은 접촉상태의 변화에도 출력 신호는 크게 왜곡될 수 있어 실제 이를 활용하기 위해서는 전극간 접촉상태를 안정적으로 유지하는 것이 중요하다. 이에 본 연구에서는 전극간 접촉상태의 변화에 따른 신호의 왜곡 특성을 실제 출력 신호와 비교하여 분석하고, 접촉면 내 압력 분포와 센서의 운동 오차 측정을 통해 접촉상태의 변화를 파악하였다. 이를 통하여 센서의 운동 오차와 마찰력의 영향을 최소화하기 위한 접촉 유지 기구를 설계하고 제작하였으며 이를 이용한 구동실험을 통해 보다 안정적인 센서 출력 신호를 획득하였다.

• Structural Engineering and Mechanics
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• 제80권6호
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• pp.749-765
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• 2021

Suspension bridges bear large eccentric live loads in rush hours when most vehicles travel in one direction on the left or right side of the bridge. With the increasing number and weight of vehicles and the girder widening, the eccentric live load effect on the bridge behavior, including bending and distortion of the main girder, gets more pronounced, even jeopardizing bridge safety. This study proposes an analytical algorithm based on multi-catenary theory for predicting the suspension bridge responses to eccentric live load via the nonlinear generalized reduced gradient method. A set of governing equations is derived to solve the following unknown values: the girder rigid-body displacement in the longitudinal direction; the horizontal projection lengths of main cable's segments; the parameters of catenary equations and horizontal forces of the side span cable segments and the leftmost segments of middle span cables; the suspender tensions and the bearing reactions. Then girder's responses, including rigid-body displacement in the longitudinal direction, deflections, and torsion angles; suspenders' responses, including the suspender tensions and the hanging point displacements; main cables' responses, including the horizontal forces of each segment; and the longitudinal displacement of the pylons' tower top under eccentric load can be calculated. The response of an exemplar suspension bridge with three spans of 168, 548, and 168 m is calculated by the proposed analytical method and the finite element method in two eccentric live load cases, and their results prove the former's feasibility. The nonuniform distribution of the live load in the lateral direction is shown to impose a greater threat to suspension bridge safety than that in the longitudinal direction, while some other specific features revealed by the proposed method are discussed in detail.

• 치과방사선
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• 제29권2호
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• pp.417-422
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• 1999

Purpose : The aim of this study was to assess the validity of standard deviation of gray scale histogram in digital subtraction radiography as a test parameter for superimposition error. Materials and Methods : Twenty periapical radiographs were used as baseline images and they were copied to exclude the influence of exposure geomety and contrast differences. These subsequent images were linearly displaced by 0.1-0.5 mm in the x-. y- and xy-directions, rotated by 0.5-3° and distorted by angular contraction of 1-5° in x- and y-axis before subtraction. The standard deviations of gray levels in the subtraction images were obtained and paired t-tests were performed. Pearson correlation coefficients(r) were calculated between the standard deviations and the superimposition errors. Results : Linear displacement showed high correlation coefficients of 0.997, 0.997 and 0.995 in x-. y- and xy-axis respectively. Statistically significant different standard deviation existed among all linearly displaced groups(p<0.05). Distortion showed relatively low correlation coefficients of 0.982 and 0.959 in x- and y-axis. The standard deviations between the two distortion groups were statistically significant different(p<0.05). Conclusion : Standard deviation of gray level distribution in digital subtraction images is satisfactory but not perfect similarity measure to assess the superimposition errors.

• 한국음향학회지
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• 제14권5호
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• pp.29-35
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• 1995

진동판 변위의 비선형적 운동에 의해 발생하는 스피커의 비선형왜곡은 음질을 열화시킨다. 이러한 비선형왜곡은 저주파 대역의 경우 주로 스피커의 지지부의 강성과 force factor의 비선형 특성에 의해 발생한다. 본 논문에서는 진동판 변위에 따라 변화하는 스피커의 비선형 강성과 비선형 force factor를 2차함수로 모델링하고 각각의 계수를 결정하는 방법에 대해 연구하였다. 진동판에 질량을 부가하여 동작점을 이동시키는 기계적인 방법을 사용하여 강성과 force factor 간의 커플링을 배제하였으며, 여러 동작점에서의 공진주파수를 측정함으로써 비선형 강성의 계수를 추출하였다. 비선형 force factor의 계수는 공진주파수에서 스피커에의 입력전압, 입력전류, 그리고 진동판 변위를 측정하여 얻은 그래프를 curve fitting 함으로써 구하였다.

• 비파괴검사학회지
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• 제30권3호
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• pp.181-193
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• 2010

The paper presents an alternative way to classical stereocorrelation. First, 2D image processing of random patterns is described. Sub-pixel displacements are determined using phase analysis. Then distortion evaluation is presented. The distortion is identified without any assumption on the lens model because of the use of a grid technique approach. Last, shape measurement and shape variation is caught by fringe projection. Analysis is based on two pin-hole assumptions for the video-projector and the camera. Then, fringe projection is coupled to in-plane displacement to give rise to 3D measurement set-up. Metrological characterization shows a resolution comparable to classical (stereo) correlation technique ($1/100^{th}$ pixel). Spatial resolution seems to be an advantage of the method, because of the use of temporal phase stepping (shape measurement, 1 pixel) and windowed Fourier transform (in plane displacements measurement, 9 pixels). Two examples are given. First one is the study of skin properties; second one is a study on leather fabric. In both cases, results are convincing, and have been exploited to give mechanical interpretation.

• 대한한의학회지
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• 제40권3호
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• pp.198-223
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• 2019

Objectives: The purpose of this study was to investigate the effect of Korean medicine treatment on facial asymmetric treatment in 5 cases of facial asymmetry correction by non - surgical treatment such as acupucture, chuna treatment, FCST (Functional cerebrospinal technique) and cranial osteopathy. Methods: We analyzed the initial charts of 5 patients who had undergone facial asymmetry in a Korean medicine clinic and measured the position and distance using the photograph, lateral cephalograms, and whole body radiograms. The results were as follows. Results: To quantify both soft and hard tissues to confirm the results of Korean medicine treatment of facial asymmetry, soft tissues quantitatively measure the displacement of the face, the slope of the left and right eyes, and the slope of the lip in order to grasp the positional displacement of the mandible. As a result, on the average, the correction effect as measured by the angle difference between A and C is $1.8{\pm}0.57$, the correction effect as measured by the angle difference between B and C is $1.4{\pm}0.89$, and the angle difference between D and the horizontal plane is $1.9{\pm}0.89$, and the angle difference between E and the horizontal plane is $1.9{\pm}0.89$. The result of reduced angle difference between A and C means that the head position shifted from the center of the body to the unilateral side was shifted to the center. The decrease in the angle difference between B and C means the restoration of the maxillary distortion relative to the mandible. In hard tissues, numerical values were measured based on the skull standard. The average distortion of the skull was $1.9{\pm}0.67$, and the distortion of the lower eye was $1.4{\pm}0.41$. Conclusion: General studies on facial asymmetric treatment are limited to treatments such as surgery and orthodontics. However, this study confirmed the possibility that facial asymmetry could be corrected by Korean medical treatment consisting of reversible non-surgical treatment rather than irreversible treatment such as surgery or orthodontic treatment. In particular, Korean medicine treatment is effective for muscular asymmetry, soft asymmetry, functional asymmetry, etc. The facial asymmetric treatment of Korean medicine is not limited to the face-centered correction, but the asymmetry of the whole body may be corrected as well.