• 콘크리트학회논문집
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• 제16권4호
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• pp.565-572
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• 2004

The mechanical behavior of concrete-filled glass fiber reinforced polymer columns is affected by various factors including concrete strength, stiffness of tube, end confinement effect, and slenderness ratio of members. In this research the behavior of slender columns was examined both experimentally and analytically. Experimental works include 1) compression test with 30cm long glass fiber composite columns under different end confinement conditions, 2) uni-axial compression test for 7 slender columns, which have various slenderness ratios. Short-length stocky columns gave high strength and ductility revealing high confinement action of FRP tubes. The strength increment and strain change were examined under different end confinement conditions. With slender columns, failure strengths, confinement effects, and stress-strains relations were examined. Through analytical work, effective length was computed and it was compared with the amount of reduction in column strength, which is required to predict design strength with slender specimens. This study shows the feasibility of slender concrete-filled glass fiber reinforced polymer composite columns.

• 콘크리트학회논문집
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• 제29권4호
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• pp.335-343
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• 2017

본 연구에서는 80 MPa 수준의 압축강도를 갖는 고강도 콘크리트 부재의 휨 강도 특성에 대한 연구를 수행하였다. 실험변수는 SD 400 및 SD 600의 철근 공칭항복강도, 0.98~1.97%의 휨 철근비 및 부재의 전단지간-유효깊이 비(a/d)를 고려하였다. 고강도 콘크리트 보의 하중-처짐 관계, 연성, 휨강도 및 현행 설계코드에 의한 휨강도 예측값을 분석하였다. 고강도 철근의 사용은 부재의 휨강도는 증가시키는 반면에 연성을 감소시킨다. 전단지간-유효깊이 비가 증가함에 따라 연성도는 감소한다. 현행 콘크리트구조기준, Erocode 2 및 도로교설계기준에 의한 휨강도 예측값과 휨강도 측정값을 비교하였다. 고강도 콘크리트 보의 휨강도 예측값은 측정값을 과소평가하고 있으며, 보수적인 설계결과를 나타낸다. 또한, 강도감소계수를 사용하는 콘크리트구조기준에 의한 고강도 콘크리트 보의 휨강도 예측값과 재료계수를 사용하는 Erocode 2 및 도로교설계기준에 의한 휨강도 예측값은 서로 유사하게 나타난다.

• Earthquakes and Structures
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• 제11권3호
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• pp.461-481
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• 2016

The research described in this paper investigates the seismic behaviour of lightly reinforced concrete (RC) bearing sandwich panels, heavily conditioned by shear deformation. A numerical model has been prepared, within an open source finite element (FE) platform, to simulate the experimental response of this emerging structural system, whose squat-type geometry affects performance and failure mode. Calibration of this equivalent mechanical model, consisting of a group of regularly spaced vertical elements in combination with a layer of nonlinear springs, which represent the cyclic behaviour of concrete and steel, has been conducted by means of a series of pseudo-static cyclic tests performed on single full-scale prototypes with or without openings. Both cantilevered and fixed-end shear walls have been analyzed. After validation, this numerical procedure, including cyclic-related mechanisms, such as buckling and subsequent slippage of reinforcing re-bars, as well as concrete crushing at the base of the wall, has been used to assess the capacity of two- and three-dimensional low- to mid-rise box-type buildings and, hence, to estimate their strength reduction factors, on the basis of conventional pushover analyses.

• Geomechanics and Engineering
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• 제25권1호
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• pp.17-30
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• 2021

This paper develops a convenient approach for deterministic and probabilistic evaluations of tunnel face stability using support vector machine classifiers. The proposed method is comprised of two major steps, i.e., construction of the training dataset and determination of instance-based classifiers. In step one, the orthogonal design is utilized to produce representative samples after the ranges and levels of the factors that influence tunnel face stability are specified. The training dataset is then labeled by two-dimensional strength reduction analyses embedded within OptumG2. For any unknown instance, the second step applies the training dataset for classification, which is achieved by an ad hoc Python program. The classification of unknown samples starts with selection of instance-based training samples using the k-nearest neighbors algorithm, followed by the construction of an instance-based SVM-KNN classifier. It eventually provides labels of the unknown instances, avoiding calculate its corresponding performance function. Probabilistic evaluations are performed by Monte Carlo simulation based on the SVM-KNN classifier. The ratio of the number of unstable samples to the total number of simulated samples is computed and is taken as the failure probability, which is validated and compared with the response surface method.

• International Journal of Automotive Technology
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• 제6권3호
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• pp.293-303
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• 2005

Bonded dissimilar materials are being increasingly used in automobiles, aircraft, rolling stocks, electronic devices and engineering structures. Bonded dissimilar materials have several material advantages over homogeneous materials such as high strength, high reliability, light weight and vibration reduction. Due to their increased use it is necessary to understand how these materials behave under stress conditions. One important area is the analysis of the stress intensity factors for interface cracks emanating from circular holes in bonded dissimilar materials. In this study, the bonded scarf joint is selected for analysis using a model which has comprehensive mixed-mode components. The stress intensity factors were determined by using the boundary element method (BEM) on the interface cracks. Variations of scarf angles and crack lengths emanating from a centered circular hole and an edged semicircular hole in the Al/Epoxy bonded scarf joints of dissimilar materials are computed. From these results, the stress intensity factor calculations are verified. In addition, the relationship between scarf angle variation and the effect by crack length and holes are discussed.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.777-782
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• 2007

Displacement amplification factor can be used to estimate inelastic displacement demands from elastic displacement demands, The simple formula for displacement amplification factor considering hysteretic behavior of structural system and earthquake characteristics is proposed. And the effects of several parameters such as displacement ductility, strain hardening ratio, period, characteristics of earthquakes and hysteretic models for the displacement amplification factor are evaluated. Accuracy of the proposed formula is evaluated by comparing the displacement amplification factors estimated by existing and proposed formula with those calculated from inelastic time history analysis. The displacement amplification factors by proposed formulas provide a good agreement with those calculated by inelastic time history analysis.

• 한국주조공학회지
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• 제7권4호
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• pp.366-379
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• 1987

The influences of some factors on the variation of compression strength of $CO_2$ process were investigated with an attention given to use of high $SiO_2\;/Na_2O$ silicate, addition of organics and gassing operation. 1) Higher ratio binder offers faster rates of hardening with lower $CO_2$ consumption requiring more concentration for a good strength development. A mixture containing 4 percent of 2.7:1 ratio silicate produces the strength above $8kg\;/\;cm^2$ after 80 seconds gassing, but 5% and 6% respectively of 3.0:1 and3.3:1 ratio silicate are necessary to achieve equivalent levels of strength. 2) The correct water content in sand mixtures containing higher ratio silicates is necessary for the better strength properties to be obtained. The addition of 1% water to the sand mixtures bonded with 5%,3:1 ratio and 6%,3.3:1 ratio silicates maintains near-maximum strength on extended gassing. 3) When higher ratio silicates with 3:1 and 3.3:1 ratios are used,the addition of organic additives such as oil, sucrose and polyol results in considerable changes in strength. The presence of 1.0 to 1.5 percent of polyol produces a noticiable improvement 4) Gas diluted with air raises the efficiency of gas utilization. When gas contains 50 percent $CO_2$, the efficience is significantly increased with the best strength in the silicates having high ratios of 3:1 and 3.3:1. 5) The strength of molds is liable to change on storage with the reduction in water content. The magnitude of the strength change is determinded with the mole ratio. The presence of polyol in the mixture with 3.3:1 ratio silicate has a pronounced effect on maintaining the gassed strength.

• 대한치과보철학회지
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• 제34권2호
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• pp.266-276
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• 1996

Numerous factors are known to affect the accuracy of elastomeric impression materials. Factor often overlooked is the quality of the bond between putty and wash during corrective reline impression technique. The putty-wash bond strength must be strong enough to over-come the local stress at putty-wash interface. It is not always possible to avoid saliva contamination in making corrective wash impres-sion. And putty preliminary impression material con be used as a template for provisional restoration. Human saliva and the residual monomer of autopolymerizing acrylic resin are thought to affect the bond strength and the failure type. This study examined the effect of contaminants like human saliva, and residual resin monomer on the putty-wash bond strength and the effectiveness of treatment. 1. Of the tested three brands of Vinyl Polysiloxane impession meterial, Express Exhibited the greatest bond strength followed by Eamix and Perfect showed the lowest putty-wah bond strength. 2. Coating the putty substrates with human saliva did not produce decreased failure load in all the breands of Vinyl Polysiloxane impression meterail. 3. Of the three brands of VPS impression material that were exposed to methhylmethacry-late resin(Jet), only the putty-wash bond strength of the Perfect group diminished signifi-cantly. Moreover, all the specimens from group C of Perfect exhibited adhesive failure. 4. Exposing the substrates to ethylmethacrylate resin(SNAP. diminished the putty-wash bond strength significantly. With Perfect and Examix, failure occurred cohesively through the light-body, whereas with Express, failure occurred adhesive-cohesively. 5. Removing approximately 1mm thickness of the contaminated putty interface was the most effective treatment in countering the undesirable effect caused by residual resin monomer. The putty-wash bond strength of the groups that were treated with 1mm even putty reduction was not significantly different from those of control groups. With Perfect and Examix, cleaning the specimens with gauze soaked in 70% isopropyl alcohol increased the putty-wash bond strength, but was not as effective as 1mm even reduction of contaminated putty substrates. With Express, 70% isoproryl alcohol treatment exhibi0ted comparable putty-wash bond strength to that of control group.

• 대한물리의학회지
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• 제7권3호
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• pp.329-337
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• 2012

Purpose : The purpose of this study was to assess more effective exercise prescription for the people with chronic neck pain by comparing stretching exercise and isometric exercise about strength and pain. Method : The research design of the study was that 20 young adults with mild neck disability (5-14 out of 50 in Neck Disability Index) were randomized into 2 groups and underwent stretching exercise(10 peoples) and isometric exercise(10 peoples) at 3 times a week for 5weeks. Measures of pain scale (Visual Analog Scale) and Muscle strength of deep neck flexor (Pressure Biofeedback) were assessed before and after intervention. The pre and post exercise results were compared using paired t-test and the effectiveness of intervention of two groups were compared using Independent t test. Results : The results of this study were that pain reduction was seen after stretching and isometric exercise and significantly difference. There was significantly improvement of cervical flexor strength after stretching and isometric exercise. But, there was no significant difference between stretching and isometric exercise groups. Conclusion : The stretching and isometric exercise for chronic neck pain patients may use according to preference of patient because the effects of treatment was same. Further studies are needed to analyzed psycho social factors, cost effects, group approach.

• 대한토목학회논문집
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• 제36권4호
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• pp.659-665
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• 2016

풋월 비탈면 설계 시 해석시간이 짧고, 간편하여 한계평형법을 주로 이용하였으나, 쟁기형태파괴를 모사하기에는 어려움이 따른다. 따라서, 본 연구에서는 2차원 DEM (Distinct Element Method) 해석프로그램인 UDEC을 이용해 수치해석을 수행하여 풋월 비탈면에서 발생되는 쟁기형태파괴에 미치는 영향인자를 분석하였다. 매개변수분석은 암반절리(층면절리, 공액절리, 비탈면의 하단에 위치한 절리)의 구조 및 암반절리상태 등을 변경하여 수행하였으며, 비탈면의 안전율은 강도감소법(Strength Reduction Method)을 이용하여 산정하였다. 수치해석 결과를 통해 쟁기형태파괴는 공액절리(conjugate joint)의 경사각에 주로 의존하고 있음을 확인할 수 있었으며, 층리의 한계간격 및 슬래브의 한계길이가 공액절리의 경사각에 영향을 받는 것으로 나타났다. 본 연구결과는 비탈면 보강을 포함한 풋월 비탈면의 최적설계 및 시공에 적용될 수 있을 것으로 판단된다.