• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.5
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• pp.8-14
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• 2021

Post-tensioned prestressed concrete members experience immediate prestress losses as well as time-dependent prestress losses such as creep, dry shrinkage and relaxation. In addition, the stress of the upper and lower parts of the member changes due to the change in dead load due to the replacement of the upper slab and/or pavement. Such changes in fiber stress may affect the safety of the member, and it is necessary to adjust the prestressing force. Therefore, in this study, a screw type of re-tensioning post-tension kit is proposed, and it is verified that the safety against load and the stability against strain are satisfied through the load transfer test specified in EAD160004 and KCI-PS101.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.3
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• pp.301-308
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• 1985

본 논문에서는 불규칙 하중을 받는 부재에 대한 연구의 고초로서 간단한 응력 모델을 설정하고 이들 변동응력이 가해지는 시기를 명확히 구분하여 크랙전파곡선의 거동을 고찰하였다. 특히 부하되는 응력 진폭의 크기에 따라서 크랙선단부의 미시적 인 변화의 크기가 다르고 이로인하여 크랙전파에 대한 피해의 정도가 달라진다고 하면 크랙전파의 지연 및 가속현상이 나타날 것이 예측이 되고 따라서 이때 나타나는 피해 정도의 크기를 미소 경도치로 환산하여 그것과 피로크랙 전파 특성과를 비교 검토 하 였다.

• Tribology and Lubricants
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• v.2 no.1
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• pp.46-52
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• 1986

얇은 유막위의 타이어 변형해석이나, 압착막댐퍼 설계등의 해석에 응용되는 변동 하중하의 탄성 경계상 유체 압착막의 해석을 Newton-Raphson 반복법을 사용하여 하였다. 유막두께의 계산은 등계수 요소를 사용하여 정확한 계산을 하였고 슬라이더의 궤적은 강쇄진동의 응답곡선과 유사함을 알 수 있었다. 특히 본 연구에서는 미끄럼 속도의 영향을 고려하였으며 유체가 베어링내에 생긴 포켓에 정체하고 있어서 미끄럼의 영향은 속도가 클때를 제외하고는 큰 영향을 미치지 못함을 알 수 있었다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.1
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• pp.64-70
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• 2023

In this study, reliability tests of torsion control expansion anchors according to drill bit diameters were performed. The standard deviation and coefficient of variation of the anchor were reviewed through the tests for each variable, and the results were compared and evaluated with the standard test results. As a result of the reliability test of the M12 and M16 anchors with 1.04 times the drill bit diameter, they were within 20% of the ultimate tensile load permissible standard coefficient of variation. It was found that the pulling-out performance of the anchor installed in the large hole was sufficiently secured. However, it was found to be about 253% and 210% of the design strength, indicating that the pulling performance of the anchor installed in 1.04 times the drill bit diameter was sufficiently secured. As a result of the reliability test of the M12 and M16 anchors with 1.02 times the drill bit diameter, the value of the coefficient of variation of the ultimate tensile load limit was within 20%, which satisfies the test standard. It was shown to be about 136% and 168% of the design strength, indicating that the pulling-out performance of the anchor installed in 1.02 times the drill bit diameter is sufficiently secured.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.1082-1087
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• 2021

The propeller shaft has different pattern of behaviors at each static, dynamic, and transient condition to a ship shaft system due to the effects of propeller weight and eccentric thrust, which increases the potential risk of bearing failure by causing local load variations. To prevent this, the various research of the shafting system has been conducted with the emphasis on optimizing the relative slope and oil film retention between propeller shaft and stern tube bearing at quasi-static condition, mainly with respect to the Rules for the Classification of Steel Ships. However, to guarantee a stability of the shafting system, it is necessary to consider the dynamic condition including the transient state due to the sudden change in the stern wakefield during rudder turn. In this context, this study cross-validated the ef ect of propeller shaft behavior on the stern tube bearing during port turn operation, which is a typical transient condition, by using the strain gauge method and displacement sensor for 50,000 DWT medium class tanker. And it was confirmed that the propeller eccentric thrust change showing relief the load of the stern tube bearing.

• Journal of the Society of Naval Architects of Korea
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• v.34 no.2
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• pp.64-74
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• 1997

The necessity and importance of fatigue failure to variable load has been appreciated as the structural design technique develops and use of high tensile steel is increasing. This is much more appreciated for a large ship such as VLCC. The rigorous fatigue analysis and safety assessment should be, hence, carried out at the design stage to avoid the possibility of fatigue failure and to achieve the design result having a sufficient structural safety to fatigue strength. This paper deals with an efficient spectral fatigue analysis of ship structures by introducing the concept of stress influence coefficient. In the process included are probabilistic loading analysis, evaluation of long-term distribution of stress range and estimation of fatigue life applying the spectral fatigue analysis. An integrated computer program has been developed in which reliability analysis to fatigue strength is also included and has been applied to D/H VLCC.

• Journal of KSNVE
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• v.9 no.5
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• pp.1042-1049
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• 1999

In the Part I has been reported a rotordynamic analysis of the driving motor-bull gear rotor-bearing system of a turbo-chiller. In this study, Part II, a rotordynamic analysis is performed with the turbo-chiller compressor pinion-impeller rotor system supported on two fluid film bearings. The pinion-impeller rotor system is driven to a rated speed of 14,600 rpm through a speed-increasing pinion-bull gear. It is modeled utilizing the finite element method for analysis. As loadings on the bearings due to the gear action are significant in the system considered, each resultant bearing load is calculated statically by considering the generalized forces of the gear action as well as the rotor itself. The two support bearings, the generalized forces of the gear action as well as the rotor itself. The two support bearings, partial and 3-axial groove bearings, are designed to take their varying loads along with their varying load angles, and they are also analyzed to give their rotordynamic coefficients. Then, a complex rotordynamic analysis of the compressor pinion-impeller rotor-bearing system is carried out to evaluate its stability, whirl natural frequencies and mode shapes, and unbalance responses under various loading conditions. Results show that the bearings and entire rotor system are well designed regardless of operating conditions, i.e., loads and operating speeds.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.8
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• pp.2062-2067
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• 2009

During a construction of a road, a temporary bridge is often connected to a existing bridge. In this case, a fatigue stability problem, which was not considered in the design of the bridge, can be occurred in the main girder of the existing bridge due to the vehicle load direction change. In this study, the fatigue stability of the main girder and cantilever slab of the bridge was tested with the allowable fatigue stress of the design specifications of the road bridge. The big stress change was occurred at 55m away from the support, and the middle of the span. Furthermore, the excess of the allowable fatigue stress of the design specifications of the road bridge was confirmed at the cross section. The bridge after the reinforcement was tested for the fatigue stability, and it was confirmed that the bridge is safe.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.6
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• pp.53-60
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• 2019

The purpose of this study is to evaluate the degree of improvement in strengths by mixing blast-furnace slag and fly ash in polymer cement mortar(PCM). The test specimens are prepared with EVA polymer dispersion, two types of Admixtures (blast-furnace slag and fly ash), five kinds of polymer-cement ratios (0, 5, 10, 15 and 20%), and six kinds of admixtures (0, 3, 5, 10, 15 and 20%). Plain cement mortar is also made for comparison. From the test results, the flowing of PCM is greatly improved with the mixing of the admixtures, and strengths of PCM compared to ordinary cement mortar are also improved due to a decrease in water cement ratio. In addition, the strength characteristics of PCM by admixtures are greatly improved in flexural strength with fly ash compared to other strengths. It is apparent that the optimum mix proportions with polymer-cement ratio of 10% or more, admixture contents 5 to 10% of flay ash for flexural strength improvement of EVA-cement mortar are recommended in this study.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.6
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• pp.45-52
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• 2019

Steel corrosion due to carbonation in RC (Reinforced Concrete) structures easily occurs in urban cities with high CO₂ concentration. RC structures are always subjected to external loading with various boundary conditions. The induced stress level causes changes in diffusion of harmful ion like CO₂. In this work, a quantification of carbonation progress with stress level is carried out and carbonation prediction is derived through the relations. Determining the design parameters like cover depth, CO₂ diffusion coefficient, carbonatable materials, and exterior CO₂ concentration as random variables, service lifes under carbonation with design parameter's variation are obtained through MCS(Monte Carlo Simulation). Additionally the service life with different stress level is derived and the results are compared with those from deterministic method. Cover depth and cement hydrates are evaluated to be very effective to resist carbonation, and the proposed method which can consider the effect of stress on service life can be applied to maintenance priority determination.