• 대한기계학회논문집
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• 제3권1호
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• pp.35-41
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• 1979

In order to improve the load capacity of externally pressurized air-lubeicatedjournal bearings, a new type(doubly-stepped type) bearing was revised and experimented. Through the results of experiment, the load capacity of doubly-stepped bearings was discussed and compared with equivalent conventional circular journal bearings. Results were obtained for speed up to 18000rpm and for supply pressure ratio(Ps/Pa) 4.8,6,7. Compared with equivalent conventional bearings, doubly-stepped bearings resultd a high gain in load capacity. It is also shown that the increasing rate of load capacith increases with decreasing the eccentricity ratio. Furthermore, the increasing rate is higher in the case of great clearanceratio than small dleatance ratio of doubly-stepped bearings. Such an increase in load capacity is confirmed by pressure distributions in the bearings.

• 한국지반신소재학회논문집
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• 제22권1호
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• pp.39-51
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• 2023

매입말뚝의 지지력은 많은 연구자들에 의해 연구되었다. 하지만 하중분담률과 침하량에 대하여 설계 자료와 말뚝재하시험 지료를 비교한 연구는 미미하였다. 그래서 매입 개단 강관말뚝에 대하여 설계식 자료와 정재하시험 결과를 비교하였다. 압축재하시험에서는 선단지지하중과 주면마찰하중의 분담률이 각각 13%~40%, 60%~87%로 나타났고, 이때의 침하량은 2.2mm~4.7mm로 측정되었다. 현행 지지력 산정식에서는 선단지지력과 주면마찰력이 각각 54%~75%, 25%~46%를 분담하는 것으로 나타났고, 침하량은 19.8mm~23.6mm로 계산되었다. 현행지지력 산정식에서의 침하량은 시험에서의 침하량보다 321%~776% 만큼 크게 나타났으며, 평균적으로 445%만큼 크게 나타났다. 말뚝재하시험에서의 하중분담률을 이용하여 침하량을 산정하면, 시험 침하량보다 137%~525% 만큼 크게 나타났으며, 평균적으로 204% 만큼 크게 나타났다. 하중분담률의 적절한 평가는 말뚝 기초의 침하량 산정에 중요한 영향을 미치는 것으로 확인되었다.

• 한국지반공학회논문집
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• 제32권11호
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• pp.61-72
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• 2016

구조물의 고층화가 진행됨과 동시에 효율적인 기초 설계를 위해 대구경 PHC 말뚝의 사용이 증가하고 있으며, 특히 600mm PHC 말뚝의 사용량이 급증하고 있다. 본 연구에서는 현재 사용되고 있는 설계법의 적정성을 평가하기 위하여, 직경 600mm PHC 매입말뚝에 대하여 수행된 46본의 동재하시험 결과를 분석하였다. 선단지지력은 초기항타시험의 결과를 이용하였으며 주면마찰력은 재항타시험 결과를 이용하여 각각의 허용지지력을 산정하였다. 동재하시험으로부터 산정된 허용지지력을 현재 사용되는 설계법으로 평가된 허용지지력과 비교하였다. 분석결과, 동재하시험으로 산정된 허용선단지지력은 대부분의 말뚝에서 설계기준보다 컸지만, 허용주면마찰력은 많은 말뚝에서 설계기준보다 작게 산정되었다. 이와 같은 큰 선단지지력과 작은 주면마찰력은 천공장비의 성능 향상 및 굴착 깊이의 증가 때문이며 이로 인해 전체지지력에서 선단지지력이 차지하는 비율이 높아졌기 때문이다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 봄 학술발표회 논문집
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• pp.291-298
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• 2001

It is very difficult to accomplish load tests of piles with large diameter constructed on the offshore area, because of requirement for large scaled loading equipment and bad testing conditions. Therefore, so far in many cases pile driving dynamic formulas have applied to quality control, and recently dynamic load test method is widely used for confirming bearing capacities of such piles. However, in cases of piles with very large diameter about 2,500mm, it is nearly impossible for regular type load test methods of piles such as static and dynamic to apply owing to very large design load. This is case studies of load tests such as modified static and dynamic load tests of piles and point load tests of rock samples for estimating rational allowable bearing capacity of very large diameter piles constructed on the marine area.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2002년도 춘계학술대회논문집
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• pp.197-203
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• 2002

The estimation of pile bearing capacity is important since the design details are determined from the result. There are numerous ways of determining the pile design load, but only few of them are chosen in the actual design. According to the recent investigation in Korea, the formulas proposed by Meyerhof based on the SPT N values are most frequently chosen in the design stage. In the study, various static and dynamic formulas have been used in predicting the allowable bearing capacity of a pile. Further, the reliability of these formulas has been verified by comparing the perdicted values with the static and dynamic load test measurements. Also in cases, these methods of pile bearing capacity determination do not take the time effect consideration, the actual allowable load as determined from pile load test indicates severe deviation from the design value. The principle results of this study are summarized as follows : A a result of estimate the reliability in criterion of the Davisson method, in was showed that Terzaghi & Peck > Chin > Meyerhof > Modified Meyerhof method was the most reliable method for the prediction of bearing capacity. Comparisons of the various pile-driving formulas showed that Modified Engineering News was the most reliable method. However, a significant error happened between dynamic bearing capacity equation was judged that uncertainty of hammer efficiency, characteristics of variable , time effect etc... was not considered. As a result of considering time effect increased skin friction capacity higher than end bearing capacity. It was found out that it would be possible to increase the skin friction capacity 1.99 times higher than a driving. As a result of considering 7 day's time effect, it was obtained that Engineering News. Modified Engineering News. Hiley, Danish, Gates, CAPWAP(CAse Pile Wave Analysis Program ) analysis for relation, respectively, $Q_{u(Restrike)}$ $Q_{u(EOID)}$ = 0.971 $t_{0.1}$, 0.968 $t_{0.1}$, 1.192 $t_{0.1}$, 0.88 $t_{0.1}$, 0.889 $t_{0.1}$, 0.966 $t_{0.1}$, 0.889 $t_{0.1}$, 0.966 $t_{0.1}$

• 한국지반공학회논문집
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• 제34권6호
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• pp.37-47
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• 2018

본 연구에서는 모래다짐말뚝(sand compaction pile, SCP)과 자갈다짐말뚝(gravel compaction pile, GCP)으로 보강된 지반의 극한지지력을 예측할 수 있는 식을 제안하고자 34개의 국내외 실내재하시험 데이터를 수집하고 이를 분석하였다. 수집된 자료를 기존의 이론식에 의한 극한지지력 산정 값과 비교하여 기존 이론식의 예측 정도를 파악하였다. 또한 극한 지지력 예측식을 제안하고자 다중회귀분석을 수행하였으며, 단일잔류 교차검증에 따른 예측오차평가를 통하여 가장 효율적인 입력변수의 수 및 조합을 선정하였다. 최종적으로 SCP와 GCP의 실내재하시험에 대한 극한 지지력을 예측하기 위한 다중회귀식을 제안하였으며 그 성능을 평가하였다.

• Tribology and Lubricants
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• 제29권1호
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• pp.13-18
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• 2013

Slider bearing is a widely used load-carrying element in the industry. While a large number of studies have investigated the effect of overall surface curvature, very few have considered sinusoidal surface. Recently, consideration of surface roughness/waviness or intentional wave design has been identified as an important issue in the manufacture of hard disk driver, mechanical seal, hydraulic machine, and etc. This study investigated the load-carrying capacity of a finite-width slider bearing with a wavy surface. Film thickness ratios, length-width ratio, ambient pressure, amplitude, and partial distribution were selected as the simulation parameters. The calculation results showed that the load-carrying capacity rapidly varied at small film thickness ratio, but the waviness near the area of minimum film thickness made much more influence with an increase in film thickness ratio. As the length-width ratio of bearing was increased, ambient pressure became more influential at small film thickness ratios. Furthermore a particular partial distribution of the wavy area led to higher load-carrying capacity than did the whole distribution. Consequently, the results of this study are expected to be of use in surface micro-machining of finite-width slider bearings.

• 한국지반공학회논문집
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• 제19권5호
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• pp.343-354
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• 2003

재하판과 실제기초의 크기가 상이하므로 평판재하시험으로부터 실제 기초지반의 지지력 및 침하량을 산정할 때, Scale Effect가 고려되어야 한다. 본 논문에서는 5종류의 모형기초지반을 형성하고, 크기가 각각 l0cm, 15cm, 20cm, 25cm인 4가지 크기의 정사각형 평판으로 재하시험을 실시하여 재하판의 크기에 따른 지지력 및 침하 특성을 분석하였다. 또한 분석된 결과를 토대로 하여, 평판재하시험으로부터 실제기초의 지지력 및 침하량을 산정할 때, 모래와 점토의 혼합비율에 따라 Scale Effect를 합리적으로 고려할 수 있도록 식을 제안하였으며, 식에서 지지력 산정계수(a,b)와 침하량 산정계수(c,d)는 모래와 점토의 혼합비율에 따라 구할 수 있도록 그림으로 제시하였다. 지금까지는 현장기초지반에 대한 지지력 및 침하량을 합리적으로 평가할 수 없어 비경제적인 시공이 되어왔으나, 본 연구에서 제안한 지지력 및 침하량 산정방법에서는 모래와 점토의 혼합비율을 고려하여 기초지반의 지지력 및 침하량을 보다 합리적으로 추정할 수 있으므로 기초지반의 안정성 여부에 대한 확신과, 또한 경제적인 시공이 가능할 것으로 판단된다.

• Tribology and Lubricants
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• 제25권2호
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• pp.108-113
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• 2009

This paper presents a experimental results for the performance evaluation of a double-bumped air foil bearing. The test results of a double-bumped AFB is compared with a single-bumped AFB at a heavily-loaded condition. The diameter of the test bearing is 50 mm, and the axial length is 50 mm. Nominal clearance of the single-bumped AFB is evaluated as $105{\mu}m$, and that of the double-bumped AFB is as $95{\mu}m$. The test of the AFBs are demonstrated at 3 test mode; the load variation mode, the speed variation mode, and start-stop mode. The single-bumped AFB demonstrated a upward load-carrying capacity of 95 N and a downward load-carrying capacity of 130 N at 20,000 rpm. The double-bumped AFB demonstrated a upward load-carrying capacity of 170 N and a downward load-carrying capacity of 170 N at 20,000 rpm. The single-bumped AFB demonstrated a downward lift-off speed of 16,300 rpm at 105 N. The double-bumped AFB demonstrated a downward lift-off speed of 15,400 rpm at 105 N. The start-stop test of the AFBs assure 5,000 cycle endurance life. The test results are compared with the theoretical calculation results. The test and theorectical results show thata double-bump air foil bearing provides a higher load-carrying capacity, stiffness and damping than a single-bump air foil bearing in a heavily-loaded condition.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2011년도 춘계학술대회 논문집
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• pp.1253-1254
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• 2011