• Title/Summary/Keyword: lift-off test

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Improvement of Lift-off Tests via Field Evaluation of Residual Load in Ground Anchor (현장 잔존긴장력 평가를 통한 리프트오프 시험 방법 개선)

  • Song, minkwon;Park, Seong-yeol;Lee, Sangrae;Cho, Wanjei
    • Journal of the Korean Geotechnical Society
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    • v.35 no.5
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    • pp.43-51
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    • 2019
  • At present, the ground anchor method is commonly applied to securing the slope stability in Korea. The ground anchor is reported to decrease in tensile load due to aging and environmental influences with time such as corrosion, relaxation, creep and so on. In Korea, the lift-off test is performed for the periodic inspection or cases when the symptoms of deterioration on anchors and the residual tensile load of the anchors is checked. However, the current lift-off test standard (MOLIT, 2010) is not fully specified in details. In this study, the factors affecting the lift-off test were investigated based on the previous research and foreign standards and lift-off tests were performed with consideration for the loading and unloading cycle, load increment method, and tensioning tendon method. Based on the results, this paper proposes improved testing and evaluation procedures of the lift-off test considering the workability and time limits in the field.

A Study on the Durability Characteristics of an Air-lubricated Bump Foil Journal Bearing (공기윤활 범프포일 저널 베어링의 내구성 특성에 관한 연구)

  • 이용복;김태호;김창호;이남수;장건희
    • Tribology and Lubricants
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    • v.18 no.2
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    • pp.153-159
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    • 2002
  • This paper describes a durability characteristics of an air-lubricated bump foil journal bearing for high speed turbomachinerys at room temperature. At first, lift-off test and load capacity test were performed to understand the general characteristics of an air-lubricated bump foil Journal bearing. A 52 N weighted bump foil bearing sleeve was lilted off from a rotating Journal at about 3,000 rpm, and produced a load capacity of 500 N at an operating speed of 15,000 rpm. The next was 500 cycles lift-off test with an air-lubricated bump foil journal bearing that had a molybdenum disulfide(MoS$_2$) solid lubricant coated top foil. Data from measuring bearing torque and temperature and the observation of rubbing surfAce were included in results. Therefore the results of this work will aid in proving durability of air-lubricated bump foil journal bearings.

A Study on the Durability Characteristics of an Air-lubricated Bump Foil Journal Bearing (공기윤활 범프포일 저널 베어링의 내구성 특성에 관한 연구)

  • 김태호;이용복;김창호;이남수;장건희
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • pp.212-219
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    • 2001
  • This paper describes a durability characteristics of an air-lubricated bump foil journal bearing for high speed turbomachinerys at room temperature. At first, lift-off test and load capacity test were performed to understand the general characteristics of an air-lubricated bump foil journal bearing. A 52N weighted bump foil bearing sleeve was lifted off from a rotating journal at about 3,000rpm, and produced a load capacity of 500N at an operating speed of 15,000rpm. The next was 500 cycles lift-off test with an air-lubricated bump foil journal bearing that had a molybdenum disulfide(MoS$_2$) solid lubricant coated top foil. Data from measuring bearing torque and temperature and the observation of rubbing surface were included in results. Therefore the results of this work will aid in proving durability of air-lubricated bump foil journal bearings.

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Experimental Study on the Load Carrying Performance and Driving Torque of Gas Foil Thrust Bearings (가스 포일 스러스트 베어링의 하중지지 성능 및 구동 토크에 관한 실험적 연구)

  • Kim, Tae Ho;Lee, Tae Won;Park, Moon Sung;Park, Jungmin;Kim, Jinsung;Jeong, Jinhee
    • Tribology and Lubricants
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    • v.31 no.4
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    • pp.141-147
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    • 2015
  • Gas foil thrust bearings (GFTBs) have attractive advantages over rolling element bearings and oil film thrust bearings, such as oil-free operation, high speed stability, and high-temperature operation. However, GFTBs have lower load carrying capacity than the other two types of bearings owing to the inherent low gas viscosity. The load carrying capacity of GFTBs depends mainly on the compliance of the foil structure and the formed hydrodynamic wedge, where the gas pressure field is generated between the top foil and the thrust runner. The load carrying capacity of the GFTBs is very important for the suitable design of oil-free turbomachinery with high performance. The aim of the present study is to identify the characteristics of the load carrying performance of GFTBs. A new test rig for the experimental measurements is designed to provide static loads up to 800 N using a pneumatic cylinder. The maximum operating speed of the driving motor is 30,000 rpm. A series of experimental tests—lift-off test, static load performance test, and maximum load capacity test—estimate the performance of a six-pad GFTB, in terms of the static load, driving torque, and temperature. The maximum load capacity is determined by increasing the static load until the driving torque rises suddenly with a sharp peak. The test results show that the torque and temperature increase linearly with the static load. The estimated maximum load capacity per unit area is approximately 80.5 kPa at a rotor speed of 25,000 rpm. The test results can be used as a design guideline for GFTBs for realizing oil-free turbomachinery.

Stability Evaluation of Anchors Using Lift-off Field Test (리프트오프 현장시험을 이용한 앵커의 안정성 평가)

  • Choi, Tae Sic;Yun, Jung Mann;Kim, Yong Seong;You, Seung Kyong;Lee, Kang Il
    • Journal of the Society of Disaster Information
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    • v.17 no.1
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    • pp.128-142
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    • 2021
  • Purpose: This study examines the safety management of anchors that have already been constructed and evaluates the results of lift-off tests conducted at the site. The purpose of the project is to study countermeasures if necessary. Method: Compare the residual load gained after the lift-off test at 36 points behind the site with the preemptive load, allowable load, and design load. We also analyze stability through this and evaluate the stability of anchors. Results and Conclusion: The residual tension at 26 points remained stable. However, the residual load at 10 points was analyzed to be greater than the designed load and less than the allowable load, and it was evaluated as an instability that could cause fracture problems. Therefore, anchors with unstable conditions at 10 points should be monitored and monitored through periodic measurements and quality tests, and the anchor should be observed at the surrounding points as well as the relevant points to maintain stability.

Comparative Study of Cable Tension Measurement Methods by In-situ Measurements on a Cable-stayed Bridge under Construction (시공 중 사장교 실측을 통한 케이블 장력 추정 기법 비교 연구)

  • Cho, Soo-Jin;Yim, Jin-Suk;Shin, Sung-Woo;Jung, Hyung-Jo;Yun, Chung-Bang;Wang, Ming.L.
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.48-51
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    • 2011
  • 사장교에서 케이블은 하중을 지지하는 주요 부재로, 케이블 장력은 사장교의 건전성과 안전도 평가에 있어서 매우 중요한 변수이다. 케이블 장력을 추정하기 위한 대표적인 방법으로는 로드셀을 이용한 직접법과 진동 계측 자료를 이용한 간접법 등이 있으며, 최근에는 자기장-응력 관계를 이용한 EM(Elasto-Magnetic) 센서 측정법이 개발되어 케이블 장력 추정에 적용되었다. 본 논문에서는 세 가지 장력 추정 기법을 실제 시공중인 사장교에 적용하여, 그 성능을 상호 비교하였다. 본 연구는 한국의 KAIST와 미국 Northeastern 대학교의 공동연구로 수행되었다. 대상 교량은 부산 화명동과 김해 초정리를 연결하기 위해 현재 건설중인 화명대교이다. 화명대교의 교량 형식은 2주탑 콘크리트 사장교 (주탑 경간장 270m, 총 사장교 구간장 500m)이며, 사장재로는 MS (Multi-Strand) 형 케이블이 사용되었다. 실험 당시 화명대교는 중앙경간의 폐합 후 선형관리를 위한 장력조정작업을 수행하였으며, 케이블 재긴장시의 정확한 장력관리를 위하여 로드셀을 이용한 Lift-off test방법으로 케이블의 장력을 측정하였다. 이와 동시에 두 개의 케이블을 대상으로 진동 가속도 센서와 EM 센서를 설치하고 장력 계측을 수행하였으며, 재긴장 단계별 장력 변화치를 지속적으로 계측하였다. 계측된 결과를 바탕으로 케이블 장력 추정 기법의 정확성 및 실교량에서의 활용성을 비교하였다.

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Evaluation of Cable Tension Forces Using Vibration Method for a Cable-stayed Bridge under Construction (진동법을 이용한 사장교의 시공 중 장력 평가)

  • Cho, Soojin;Yun, Chung-Bang;Sim, Sung-Han
    • Journal of the Korean Society of Safety
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    • v.29 no.2
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    • pp.38-44
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    • 2014
  • When a cable-stayed bridge is under construction, the cable tension that changes according to the construction phase is the index indicating the proper construction management. In this study, the vibration method using the least-square estimation has been implemented to monitor changing tensions of two multi-strand cables of a cable-stayed bridge under construction. The test bridge is Hwamyung Bridge in Korea with a prestressed concrete box girder. The field tests are executed during the second tensioning stage just after the installation of the key segment. The tensions of two cables are measured before and after the tensioning and 5 days later (i.e., after finishing the tensioning of all cables). The accuracy of the estimated tensions by the vibration method has been improved by employing proper effective lengths of the cables. The measured tensions are compared with the result of the lift-off tests and design tensions. The vibration method shows very good performance in monitoring the changing tensions according to the construction phase with minimal error.

A Study on the Reliability of an Air Foil Journal Bearing for High Speed Turbomachinery (고속 터보기계용 공기 포일 저널 베어링의 신뢰성에 관한 연구)

  • Lee, Yong-Bok;Kim, Tae-Ho;Kim, Chang-Ho;Lee, Nam-Soo
    • 유체기계공업학회:학술대회논문집
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    • pp.199-206
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    • 2002
  • This paper describes a reliability characteristics of an air foil journal bearing for high speed turbomachinery at room temperature. To verify the reliability of air foil journal bearing, lift-off characteristics, load carrying capacity, and 10,000 cycle start-stop test were performed with motor driven test rig. Lift-off test shows the relationship between the rotating speed of the shaft and the frictional torque with bearing surface. About load carrying capacity, the tested air foil journal bearing produced a load capacity of 500N at an operating speed of 15,000rpm, which is compared with results of numerical analysis and empirical coefficients. Finally, The trends in change of start torque, stop torque, and bearing temperature were shown during 10,000 cycle start-stop test of an air foil journal bearing. from the results of this work, an air foil bearing will be done well, as a supported bearing for high speed turbo-compressor.

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A Study on the Reliability of an Air Foil Journal Bearing for High Speed Turbomachinery (고속 터보기계용 공기 포일 저널 베어링의 신뢰성에 관한 연구)

  • Kim, Tae-Ho;Lee, Yong-Bok;Kim, Chang-Ho;Lee, Nam-Soo
    • The KSFM Journal of Fluid Machinery
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    • v.6 no.2
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    • pp.7-14
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    • 2003
  • This paper describes reliability characteristics of an air foil journal bearing for high-speed turbomachinery at a room temperature. To verify the reliability of air foil journal bearing, lift-off characteristics, load carrying capacity, and 10,000 cycle start-stop test were performed with a motor-driven test rig. A lift-off test shows the relationship between the rotating speed of the shaft and the frictional torque with bearing surface. About a load-carrying capacity, the tested air foil journal bearing produced a load capacity of 500N at an operating speed of 15,000rpm, which is compared with results of numerical analysis and empirical coefficients. Finally, the trends in change of start torque, stop torque, and bearing temperature were shown during a 10,000-cycle start-stop test of an air foil journal bearing. We found that an air foil bearing performs well, as a supported bearing for the high-speed turbocompressor.

System identification of a cable-stayed bridge using vibration responses measured by a wireless sensor network

  • Kim, Jeong-Tae;Ho, Duc-Duy;Nguyen, Khac-Duy;Hong, Dong-Soo;Shin, Sung Woo;Yun, Chung-Bang;Shinozuka, Masanobu
    • Smart Structures and Systems
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    • v.11 no.5
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    • pp.533-553
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    • 2013
  • In this paper, system identification of a cable-stayed bridge in Korea, the Hwamyung Bridge, is performed using vibration responses measured by a wireless sensor system. First, an acceleration based-wireless sensor system is employed for the structural health monitoring of the bridge, and wireless sensor nodes are deployed on a deck, a pylon and several selected cables. Second, modal parameters of the bridge are obtained both from measured vibration responses and finite element (FE) analysis. Frequency domain decomposition and stochastic subspace identification methods are used to obtain the modal parameters from the measured vibration responses. The FE model of the bridge is established using commercial FE software package. Third, structural properties of the bridge are updated using a modal sensitivity-based method. The updating work improves the accuracy of the FE model so that structural behaviors of the bridge can be represented better using the updated FE model. Finally, cable forces of the selected cables are also identified and compared with both design and lift-off test values.