• Journal of Korean Society of Steel Construction
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• v.22 no.2
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• pp.109-119
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• 2010

There are many restrictions in the application of high-strength HSSs, including yield strength and yield ratio for the 600-MPa steel. The AISC and Canadian codes recommend that the yield strength and yield ratio of HSS members be 360 MPa and 80%, respectively. It is important to understand the true buckling behaviors of HSSs using high-strength steel at the limit states. There are many experimental data regarding the rectangular HSSs, and the circular ones are not enough for high-strength steel. Therefore, this study was conducted to create a better understanding of the buckling behaviors of the 600- and 400-MPa steels based on the results of the finite-element analysis that was done before the experiment. To understand the structural behaviors of the aforementioned steels, the width-to-thickness ratios, the angle of the web members, the yield strength, and the gap of the web members were selected as the main parameters in this study, and ABAQUS, a general finite-element program, was used.As a result, the compression web member reached elastic buckling in the 600-MPa steel and inelastic buckling in the 400-MPa steel. A brittle fracture occurred in the case where the yield ratio was greater than 80%. At the same time, it was found that the limit strength determined via FEM analysis had a higher value compared to the code evaluation with the variation of the width-to-thickness ratio in the main code member. The change in the connection load in high-strength steels was not identified by the other factors.

• Journal of the Korean Wood Science and Technology
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• v.25 no.2
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• pp.88-99
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• 1997

뉴질랜드산(産) 라디아타소나무의 수간(樹幹) 및 지재(枝材)에 발달(發達)되어 있는 압축이상재(壓縮異常材), 대응재(對應材) 및 측면재(側面材)의 해부학적(解剖學的) 특성(特性)을 광학현미경(光學顯微鏡), 주사전자현미경(走射電子顯微鏡) 그리고 투과전자현미경(透過電子顯微鏡)을 이용하여 조직학적(組織學的) 및 구성요소(構成要素)의 수량적(數量的) 측면(側面)에서 비교(比較), 검토(檢討) 하였다. 조직학적(組織學的)인 면(面)에서 볼 때 춘재(春材)로부터 추재(秋材)로의 가도관(假導管) 이행(移行)은 대응재(對應材)나 측면재(側面材)보다 압축이상재(壓縮異常材)가 훨씬 더 점진적(漸進的)이었다. 편심생장(偏心生長)으로 인해 연륜폭(年輪幅)은 압축이상재(壓縮異常材)가 가장 컸고 그 다음이 측면재(側面材) 및 대응재(對應材)의 순이었으며 추재솔(秋材率) 역시 압축이상재(壓縮異常材)가 대응재(對應材) 및 측면재(側面材)보다 컸다. 횡단면상(橫斷面上) 가도관(假導管) 형상면(形狀面)에서 압축이상재(壓縮異常材)가 원형(圓形)을 나타내는 반면 대응재(對應材)와 측면재(側面材)는 각형(角形)을 띠고 있었다. 또한 압축이상재(壓縮異常材)에서만 가도관(假導管)의 세포벽(細胞壁)에 나선강(螺旋腔)과 나선열(螺旋裂) (helical cavity and check), 슬릿(slit)형(形) 벽공구(壁孔口)가 존재(存在)하였으나 $S_3$층(層)이 결여(缺如)되어 있었으며 굴곡(屈曲)된 선단(先端)과 불규칙(不規則)한 형상(形狀)의 가도관(假導管) 및 세포간극(細胞間隙)이 자주 관찰(觀察)되었다. 직교분야(直交分野) 벽공(壁孔)은 압축이상재(壓縮異常材)가 가문비나무형(型) 그리고 대응재(對應材) 및 측면재(側面材)는 소나무형(型) 벽공(壁孔)을 나타냈다. 수량적(數量的) 특성(特性) 면에서 볼 때 가도관(假導管)의 길이는 압축이상재(壓縮異常材)가 가장 짧고 측면재(側面材)가 가장 길었으며 가도관(假導管)의 벽(壁) 두께는 압축이상재(壓縮異常材)가 대응재(對應材)나 측면재(側面材)보다 두꺼웠다. 수직수지구(垂直樹脂溝)는 대응재(對應材)가 그리고 수평수지구(水平樹脂溝)(방추형(紡錐形) 방사조직(放射祖織))는 압축이상재(壓縮異常材)의 쪽이 많았다. 결론적(結論的)으로 보면 라디아타소나무의 압축이상재(壓縮異常材)는 근본적으로 대응재(對應材)나 측면재(側面材)와는 상이(相異)한 특성(特性)을 지녔으나 대응재(對應材)와 측면재(側面材)는 거의 유사(類似)한 특성(特性)을 공유(共有)하는 것으로 밝혀졌다.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.335-343
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• 2003

In the previous experimental study, it is verified that the ultimate strain of concrete (${\varepsilon}$$_{cu}$=0.003) and coefficient of equivalent stress block (${\beta}$$_1$) can be used for the analysis of RC beams under biaxial and uniaxial bending moment. However, the characteristics of stress distribution of non rectangular compressed area in the RC columns are different to those of rectangular compressed area. The properties of compressive stress distribution of concrete have minor effect on the pure bending moment such as beams, but for the columns subjected to combined axial load and biaxial bending moment, the properties of compressive stress distribution are influencing factors. Nevertheless, in ACI 318-99 code, the design tables for columns subjected to axial loads with bidirectional eccentricities are based on the parameters recommended for rectangular stress block(RSB) of rectangular compressed areas. In this study the characteristics of stress distribution through both angle and depth of neutral axis are observed and formulated rationally. And the modified parameters of rectangular stress block(MRSB) for non rectangular compressed area is proposed. And the computer program using MRSB for the biaxial bending analysis of RC columns is developed and the results of MRSB are compared to RSB and experimental results respectively.

• Journal of the Korean Geotechnical Society
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• v.33 no.8
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• pp.5-16
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• 2017

When a lateral load is applied to a short pile whose embedded depth is relatively smaller than its diameter, an overturning failure occurs. To investigate the behavior of laterally loaded short piles, several model tests in laboratory scales had been carried out, however the behavior of large moment carrying piles for electric poles, traffic sign and road lamp, etc. have not been revealed yet. This paper deals with the real-scale load tests for 750 mm diameter short piles. To simulate the actual loading condition, very large moment was mobilized by applying lateral loads to the location 8 m away from the pile head. Three load tests changing the pile embedded lengths to 2.0 m, 2.5 m, and 3.0 m were carried out. The test piles overturned abruptly with very small displacement and rotation before the failures. These brittle failures are in contrast with the ductile failures shown in the former model tests with the relatively smaller moment to lateral load ratio. Comparisons of the test results with three existing methods for the estimation of the ultimate lateral capacity show that the method assuming the rotation point at pile tip matches well when the embedded depth is small, however, as the embedded depth increases the other two methods assuming the inversion of soil pressure with respect to rotation points in pile length match better.

• Journal of the korean academy of Pediatric Dentistry
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• v.29 no.4
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• pp.586-591
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• 2002

Bruxism can be generally regarded as a diurnal clenching or nocturnal teeth grinding or a combination of both. Clenching of the teeth is forceful closure of the opposing dentition in a static relationship of the mandible to the maxilla, whereas grinding of the dentition is forceful closure of the opposing dentition in a dynamic maxillo-mandibular relationship as the mandibular arch moves through various excursive positions. The causes of bruxism are not yet discovered clearly, but most consistently mentioned cause is psychological stress. Bruxism can be also associated with sleep disorders, medication, and disturbances of the central nervous system. There is no permanent treatment method of bruxism, so the objectives for management of bruxism are reduction of psychological stress and treatment of signs and symptoms of bruxism by occlusal adjustment, occlusal splint, systemic medication and physical therapy. These cases report present three cases of children with bruxism. The bruxism was reduced in these patients wearing occlusal splint.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.12
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• pp.237-246
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• 2019

The Electro-Mechanical Brake (EMB) is the next generation braking system for automobiles and railway vehicles. Current brake systems for high-speed trains generate a braking force using a pneumatic cylinder, but EMB systems produce that force through a combination of an electric motor and a gear. In this study, an EMB operation mechanism capable of generating a high braking force was proposed, and structural and vibration analyses of the gears and shafts, which are the core parts of the mechanisms, were performed. Dynamic structural analysis confirmed that the maximum stress in the analysis model was within the yield strength of the material. In addition, the design that maximizes the diameter of the motor shaft was found to be advantageous in strength, and large shear stress could be generated in the bolt fixing the gear and eccentric shaft. In addition, a test apparatus that can reproduce the mechanism of the analytical model was fabricated to measure the strain of the fixed bolt part, which is the most vulnerable part. The strain measurement results showed that the error between the analysis and measurement was within 10%, which could verify the accuracy of the analytical model.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.6
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• pp.531-537
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• 2016

The damage and fracture of machine or structure are caused by the crack happened from the defect existed at the inside of material. The properties of crack propagation and growth characteristic must be considered because there are many cases at which these cracks are densely existed. Therefore, this study investigates the fracture property due to the position of crack and hole inside the standard compact tension (C. T.) specimen. When the concentrated load is applied eccentrically at the standard C. T. specimen, the fracture mechanical behavior due to the existence or non-existence and the position of hole near crack is investigated. As the result of analysis study, model 3 (in case of the distance of 2mm on the horizontal direction between the end part and hole as the specimen model existed with one hole near the crack) has the maximum deformation, stress and deformation energy of the most values among three models. As the distance between the crack and hole inside the specimen becomes nearer, the maximum stress becomes higher in cases of three models. Apart from the number of holes, it is seen that the maximum stress becomes higher near the crack when the hole exists near the crack inside the specimen. If the hole inside the machine or the mechanical structure is punctured by using the result of this study, it is thought that the occurred breakage or breakdown can be prevented by reducing the fracture stress happened at the specimen.

• International Journal of Highway Engineering
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• v.10 no.3
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• pp.171-178
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• 2008

Compressive strength of concrete has been regarded as a very important parameter of the quality control both in new and existing concrete pavement. It has been used a lot as the concrete strength evaluation both in the various-mixture-using laboratory and construction field using the same mixture. An error usually occurs in the test experiments of the strength, even in the test experiments with evenly mixed and compacted specimens of the compressive strength. It is caused by the 'manually operated' compressing testing, or by the specimens preparation with eccentricity. When compressive strength of evenly mixed concrete is investigated by the curing ages at the construction field, there have to be lots of specimens. And it needs much labor and cost. To substitute the endlessly repeated test experiments of compressive strength, presumption of compressive strength, by nondestructive tests, is needed. In this study, elastic waves were used among various nondestructive tests. Compressive strength of concrete was presumed according to the curing ages, by using the shear wave velocity which is not affected by restricted conditions. In the result, shear wave velocity is very closely related to the compressive strength at the evenly mixed concrete.

• Journal of Soil and Groundwater Environment
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• v.11 no.6
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• pp.61-68
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• 2006

Soil washing techniques coupled with high pressure air jet were applied for diesel-contaminated soils sampled by an underground oil reservoir of which the initial total petroleum hydrocarbon (TPH) ($2,828{\pm}206\;mg/kg$) exceeded 5 times of current standard level (500 mg/kg) regulated by the Soil-Environment Conservation Law. Through several tests, we found that the position of impeller has a critical impact for washing efficiencies. The highest washing efficiency was obtained at an oblique angle (30 degree) for the impeller and optimized mixing speed (300 rpm) that could have high shearing forces. Considered economical and feasible aspects, the optimum mixing time was 10 min. Rate constants of TPH removal derived from the first-order equation were not linearly increased as mixing speed increased, indicating that mechanical mixing has some limits to enhance the washing efficiencies. Application of high-pressure air jet in washing process increased the washing efficiency. This increase might be caused by the fact that the surface of micro-air bubbles strongly attached hydrophobic matters of soil particles. As the pressure of air jet increased, the separation efficiencies of TPH-contaminated soil particles increased. In the combined process of high-pressure air jet and mixing by impeller, the optimum mixing speed and air flow-rate were determined to be 60 rpm and $2\;kg/cm^2$, respectively. Consequently, the washing technique coupled with high-pressure air jet could be considered as a feasible application for remediating petroleum-contaminated soils.

• Journal of the Korean Geotechnical Society
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• v.28 no.11
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• pp.17-31
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• 2012

No analytical solution exists for evaluating in-situ hydraulic conductivity of vertical cutoff walls by analyzing slug test results with consideration of transient flow. There is an analytical solution proposed to interpret a slug test performed in a partially penetrated well within an aquifer. However, this analytical solution cannot be directly applied to the cutoff wall because the solution has been developed exclusively for an infinite aquifer instead of a narrow cutoff wall. To consider the cutoff wall boundary conditions (i.e, constant head boundary and no flux boundary condition), the analytical solution has been modified in this study to take into account the narrow boundaries by introducing the imaginary well theory. Type curves are constructed from the currently derived analytical solution and compared with those of a partially penetrated well within an aquifer. The constant head boundary condition provides faster hydraulic head recovery curve than the aquifer case. On the other hand, no flux boundary condition leads to slower hydraulic head recovery. The bigger the shape factor and deviation of the well and the smaller the width of the vertical cutoff wall are, the more effect of boundary condition was observed. The type curves obtained from the analytical solution for a cutoff wall are similar to those made by the numerical method in the literature.