• Geomechanics and Engineering
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• 제20권5호
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• pp.399-410
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• 2020

Cavities often develop behind the vault during the construction of double-arch tunnels, generally in the form of various defects. The study evaluates the impact of cavities behind the vault on the mechanical and failure behaviors of double-arch tunnels. Cavities of the same sizes are introduced at the vault and the shoulder close to the central wall of double-arch tunnels. Physical model tests are performed to investigate the liner stress variation, the earth pressure distribution and the process of progressive failure. Results reveal that the presence of cavities behind the liner causes the re-distribution of the earth pressure and induces stress concentration near the boundaries of cavities, which results in the bending moments in the liner inside the cavity to reverse sign from compression to tension. The liner near the invert becomes the weak region and stress concentration points are created in the outer fiber of the liner at the bottom of the sidewall and central wall. It is suggested that grouting into the foundation soils and backfilling injection should be carried out to ensure the tunnel safety. Changes in the location of cavities significantly impact the failure pattern of the liner close to the vault, e.g., cracks appear in the outer fiber of the liner inside the cavity when a cavity is located at the shoulder close to the central wall, which is different from the case that the cavity locates at the vault, whereas changes in the location of cavities have a little influence on the liner at the bottom of the double-arch tunnels.

• 토지주택연구
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• 제7권4호
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• pp.281-289
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• 2016

압축 부재인 PHC 말뚝(직경 600mm)도 강선의 부착력을 높이면 83.6~91.6tonf의 극한 인장력에 대해 구조적으로 저항할 수 있는 것으로 실험결과 나타났다. 이러한 시험결과에 안전율을 고려하여 적절한 허용값을 제시하면 부상방지 앵커를 대체하거나 절감시킬 수 있는 것으로 기대되었다. 이를 위해서는 구조적 인장성능과 함께 실제 지반에 시공된 매입말뚝의 인발저항 거동이 규명되어야 한다. 본 연구에서는 현장에 시공된 실제 매입말뚝의 인발거동 특성을 파악하기 위하여 정적 인발재하시험을 실시하여 주면마찰력 산정식과 비교하였다. 또한, 간편하게 인발저항력을 평가하기 위하여 PDA를 이용한 동재하시험을 실시하여 정적 인발재하시험 결과와 비교하였다. 그 결과, 매입말뚝의 시멘트풀이 충분히 경화한 후인 15일 후에는 LH 주면마찰력 산정식의 마찰력과 정적인발재하시험결과가 잘 일치하였고 동재하시험에서 구한 마찰력과도 비교적 잘 일치하는 것으로 나타났다.

• 콘크리트학회지
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• 제11권1호
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• pp.231-242
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• 1999

면외 바닥하중과 토압과 수압에 의한 면내 압축력을 받는, 깊은 지하구조에 사용되는 플랫플레이트 슬래브에 대한 수치해석연구를 실시하였다. 비선형 유한요서해석을 위하여 재료와 기하학적 비선형효과를 고려한 수치해석프로그램을 개발하였으며, 이 수치해석방법은 4 변이 단순지지된 플레이트에 대한 실험결과와 비교에 의하여 검증되었다. 해석모델로서 국내 콘크리트계산규준의 직접설계법에 의하여 설계된 플랫플레이트 슬래브가 사용되었다. 하중조합과 하중순서에 대한 연구를 통하여 플랫플레이트 슬래브의 강도를 지배하는 하중조건을 연구하였으며, 이 지배하중을 받는 슬래브에 대한 변수연구를 통하여 철근비, 형상비, 콘크리트강도, 세장비에 따를 슬래브의 강도변화를 연구하였다. 이 연구결과를 바탕으로 바닥하중증대법을 제시하였다.

• Journal of Preventive Medicine and Public Health
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• 제33권2호
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• pp.184-192
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• 2000

Objectives : To inquire the prevalence and the risk factors for myofascial pain syndrome (MPS) on young boys in order to use these results as the fundamental data for the prevention of their MPS. Methods : For 7 days in May 1999, this research was taken on 489 male students ranging from 6th to 12th grade. We randomly selected a class for every group and from these classes we operated physical examinations, self-reported questionnaires and from a rehabilitation doctor, MPS test was taken. Thoracic kyphosis and lumbar lordosis were also taken by using the inclinometer. We defined MPS as a regional pain complaint, palpable taut band that is painful on compression. Results : The shoulder MPS prevalence of the subjects were 29.7 persons/100 persons. The statistics revealed that as grades went up, the percentage significantly increased in the MPS prevalence. As of case-control study, 145 students who were tested postive in all aspects were placed as cases, and 176 students who were perfectly normal as controls on risk factors. As a result of comparing the student groups who were stisfied with their chairs to the student groups were not satisfied, the taller showed a significantly higher odds ratio (p<0.01). By the multiple logistic regression test, we concluded that the MPS disease was prevailed far more in the students in the higher grades (Odds ratio: 1.16, 95% C.I.: 1.03-1.31), and also those who were dissatisfied with their chairs than in the ones who were satisfied (Odds ratio: 1.92, 95% C.I.: 1.17-3.17). Conclusions : Significant correlations showed between the MPS diagnosed group and the students who are dissatisfied with their chairs. As a result, more research and observation has to be made concerning this disease, and the desks and chairs should be adjusted to suit the student's physical standards.

• 한국자동차공학회논문집
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• 제17권3호
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• pp.81-89
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• 2009

In this experimental study, the effects of clean alternative fuels compatible with diesel combustion on nano-sized particle emission characteristics were investigated in a 0.5L auto-ignited single-cylinder engine with a compression ratio of 15. Because the number concentration of nano-sized particles emitted by automotive engine, that are suspected of being hazardous to human health and environment, might increase with engine fuel considerably and recently attracted attention. So a ultra-low sulfur diesel(ULSD), BD100(100% bio-diesel) and Di-Methyl Ether(DME) fuels used for this study. And, as a particle measuring instrument, a fast-response particle spectrometer (DMS 500) with heated sample line was used for continuous measurement of the particle size and number distribution in the size range of 5 to 1000nm (aerodynamic diameter). As this research results, we found that this measurements involving the large proportion of particles under size order of 300nm and number concentration of $4{\times}10^9$ allowed a single or bi-modal distribution to be found at different engine load conditions. Also the influence of oxygen content in fuel and the catalyst could be a dominant factor in controlling the nano-sized particle emissions in auto-ignited engine.

• Elastomers and Composites
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• 제46권3호
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• pp.186-194
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• 2011

셀룰로오스계 천연섬유인 kenaf를 천연고무와 함께 균일하게 배합한 후 압축성형 방법을 사용하여 천연섬유/천연고무 복합재료를 제조하였으며, 이들의 가황거동, 경도, 인장특성, 인열강도 및 정적, 동적 특성에 미치는 kenaf 섬유함량의 영향을 조사하였다. 복합재료를 구성하는 천연섬유의 함량은 천연고무 및 배합제 대비 0, 5, 10, 15, 20 phr이었다. 실험결과 천연고무의 여러 가지 특성이 kenaf 섬유의 함량에 의존한다는 것을 나타내었다. Kenaf 섬유함량이 증가함에 따라 천연고무의 가황에 요구되는 토크는 높아진 반면 가황시간은 감소되었다. Kenaf/천연고무 복합재료의 경도, 인장탄성률과 인열강도는 섬유함량이 증가할수록 점차적으로 증가한 반면, 인장강도와 파단신장률 은 감소하는 경향을 보여주었다. 또한 kenaf 섬유함량이 증가함에 따라 천연고무의 정적 특성보다는 동적 특성의 변화가 더욱 크게 나타났다. 고무에 가해지는 에너지의 감쇄 또는 흡수와 밀접한 관계가 있는 손실인자도 섬유함량에 비례하여 증가하였다.

• Journal of Acupuncture Research
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• 제24권2호
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• pp.155-167
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• 2007

Objectives : This study was performed to evaluate the general distribution and the efficacy of oriental medical treatment for low back pain. Methods: We have selected of the moxa bucket moxibustion. We make a comparative study of the thermodynamic characteristics of moxa bucket moxibustion. We examined combustion times, temperatures, temperature gradients in each period during a combustion of moxa bucket moxibustion made by oak wood. Results : The 80 cases of low back pain patients was analyzed according to the distribution of sex, age, the period of disease, contributing factor, the patient-condition on admission, the symptom on admission, the duration of admission, the reading of the X-ray and the treatment efficacy was evaluated respectively. 1. Female was more than male in the ratio of 1:1.2, and thirties and seventies 25% the most, the acutest phase 46.3% the most, reason unknown 33.8% the most, Grade III 50% the most, L.B.P. only 51.3% the most, the day of 6-10 30% the most, compression Fx 30% the most. 2. In the total treatment result, the good was 51.3%, the excellent 22.5%, the fair 17.5%, the poor 8.8% in order. About 'the effective rate'(the percentage of positive effective treatment cases) of each distribution, the fifties 100% the most, the acutest phase 97.3% the most, the slip down, weight lifting, overuse 100% the most respectively, Grade III 97.5% the most, L.B.P. only 95.1% the most, the day of 11-15 100% the most, HN.P. 93.3% the most. Conclusions : We have known the efficacy of oriental medical treatment for L.B.P. was good and early treatment was better than late treatment and main cause of L.B.P. was degenerative change.

• 천문학회보
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• 제41권1호
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• pp.73.1-73.1
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• 2016

We present preliminary results of the submillimeter continuum observations of 14 Planck Galactic Cold Clumps (PGCCs), located in the ${\lambda}$ Orionis Complex. This region is the nearest large HII region, which is an ideal site for a study of the stellar feedback to its surroundings. We observed 14 PGCCs with JCMT/SCUBA-2 and used J=1-0 transitions of CO isotopologues from the PMO mapping observation. Several sub-clumps toward three PGCCs were detected at $850{\mu}m$. In order to examine whether these clumps can be candidates for pre-stellar cores, we compared each clump mass calculated from the $850{\mu}m$ continuum map to its Virial mass and Jeans mass calculated from the $^{12}CO$ and $C^{18}O$ (1-0) spectra, respectively. All clumps have masses smaller than their Virial and Jeans masses, indicating that none of them are gravitational bound and thus in the pre-stellar core stage. Also, the CO depletion factor, which has been derived from the dust continuum and the $C^{18}O$(1-0) line and can be an indicator of core evolution, toward the clumps is in the range of 1 to 5, suggesting that they are not very evolved dense pre-stellar cores. In addition, within individual PGCCs, we found clear gradients of velocity (${\sim}1km\;s^{-1}\;pc^{-1}$) and temperature (${\sim}10K\;pc^{-1}$) in the $^{13}CO$ (1-0) first moment map and the $^{12}CO$(1-0) excitation temperature map, respectively. This can be attributed to the compression and external heating by the HII region, which may prevent clumps from forming gravitationally bound structures and eventually disperse clumps. These results could be a hint about the negative effect of stellar feedback on core formation.

• Steel and Composite Structures
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• 제22권3호
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• pp.497-520
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• 2016

The confined concrete stress-strain curves utilised in computational models of concrete-filled steel tubular (CFST) columns can have a significant influence on the accuracy of the predicted behaviour. A generic model is proposed for predicting the stress-strain behaviour of confined concrete in short circular, elliptical and octagonal CFST columns subjected to axial compression. The finite element (FE) analysis is carried out to simulate the concrete confining pressure in short circular, elliptical and octagonal CFST columns. The concrete confining pressure relies on the geometric and material parameters of CFST columns. The post-peak behaviour of the concrete stress-strain curve is determined using independent existing experimental results. The strength reduction factor is derived for predicting the descending part of the confined concrete behaviour. The fibre element model is developed for the analysis of circular, elliptical and octagonal CFST short columns under axial loading. The FE model and fibre element model accounting for the proposed concrete confined model is verified by comparing the computed results with experimental results. The ultimate axial strengths and complete axial load-strain curves obtained from the FE model and fibre element model agree reasonably well with experimental results. Parametric studies have been carried out to examine the effects of important parameters on the compressive behaviour of short circular, elliptical and octagonal CFST columns. The design model proposed by Liang and Fragomeni (2009) for short circular, elliptical and octagonal CFST columns is validated by comparing the predicted results with experimental results.

• Journal of Advanced Marine Engineering and Technology
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• 제32권4호
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• pp.534-541
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• 2008

This paper deals with the heat transfer characteristics of R-290 (Propane), R-600a (Iso-butane) and R-1270 (Propylene) as an environment friendly refrigerant and R-22 as a HCFC's refrigerant for evaporating. The experimental apparatus has been set-up as conventional vapor compression type refrigeration and air-conditioning system. The test section is a horizontal double pipe heat exchanger. Evaporating heat transfer measurements were performed for smooth tube with the outer diameters of 12.70, 9.52 and 6.35 mm and micro-fin tube 12.70 mm, respectively. For the smooth and micro-fin tubes measured in this study, the evaporating heat transfer coefficient was enhanced according to the increase of the mass flux and decrease of the tube diameter. The local evaporating heat transfer coefficients of hydrocarbon refrigerants were superior to those of R-22 and the maximum increasing rate of heat transfer coefficient was found in R-1270. The average evaporating heat transfer coefficients in hydrocarbon refrigerants showed 20 to 28% higher values than those of R-22. Also, the evaporating heat transfer coefficients of R-22 in the tube diameter of the 12.70 mm smooth and micro-fin tube were compared. Generally, the local heat transfer coefficients for both types of tubes increased with an increase of the mass flux. The heat transfer enhancement factor (EF) between smooth and micro-fin tube varied from 1.9 to 2.7 in all experimental conditions.