• Advances in concrete construction
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• 제9권6호
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• pp.597-610
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• 2020

Stress-strain models of fibre reinforced polymer (FRP) confined concrete have been widely investigated; however, the existing load which is always supported by structures during the retrofitting phase, namely 'preload', has been neglected. Thus, preload effects should be clarified, providing insightful information for FRP retrofitting of structures with preload conditions. Towards this aim, experiments were performed for 27 cylinder concrete specimens with the diameter 150 mm and the height 300 mm. Three specimens were used to test the compressive strength of concrete to compute the preloads 20%, 30% and 40% of the average strength of these specimens. Other 24 specimens were divided into 2 groups; each group included 4 subgroups. Four subgroups were subjected to the above preloads and no preload, and were then wrapped by 2 FRP layers. Similar designation is applied to group 2, but wrapped by 3 FRP layers. All specimens were tested under axial compression to failure. Explosive failure is found to be the characteristic of specimens wrapped by FRP. Experimental results indicated that the preload decreases 12-13% the elastic and second stiffness of concrete specimens wrapped by 2 FRP layers. The stiffness reduction can be mitigated by the increase of FRP layers. Preload negligibly reduces the ultimate force and unclearly affects the ultimate displacement probably due to complicated cracks developed in concrete. A mechanism of preload effects is presented in the paper. Finally, to take into account preload effects, a modification of the widely used model of un-preload FRP confined concrete is proposed and the modified model demonstrated with a reasonable accuracy.

• 항공우주시스템공학회지
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• 제10권1호
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• pp.35-42
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• 2016

Bearing friction and disturbance are the important parameters in control spacecraft using reaction wheel. In this paper, those parameters are estimated by preload and oil quantity. In order to determine the bearing preload's impact on performance, measure the disturbance and the bearing friction coefficient with increasing the preload to the allowed amount. And, find the relationship between oil quantity and bearing friction coefficient, measure it with increasing the oil amount in the bearing. With these results as a reference, find the appropriate amount of preload and oil quantity.

• 한국컴퓨터정보학회논문지
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• 제13권4호
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• pp.87-95
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• 2008

경계면 스캔 구조는 시험대상회로의 출력 값들을 캡쳐하여 스캔경로를 이용하여 TDO로 직렬출력하여 출력 값을 관찰할 수 있는 시험구조이며, Sample/preload명령어를 이용하여 시험대상회로의 특정한 한 순간의 출력만을 캡쳐하여 직렬출력하여 분석할 수 있다. 본 논문에서는 4비트 비동기 카운터회로를 시험대상회로로 선정하고, 정상동작중인 카운터의 특정 출력을 지정하여 특정한 순간의 정적인 출력이 아닌, 연속적인 동적인 출력 값들을 다른 출력결과의 영향 없이 지속적으로 TDO로 출력하여 관찰할 수 있는 선택 가능한 관측점을 가진 시험구조와 시험절차를 개발하였다. 본 논문에서 제안하는 선택 가능한 관측점을 가진 시험구조는 표준에서 정한 시험동작을 정상적으로 수행하며, 관측점의 설정을 위한 명령어가 추가되었다. 4비트 카운터회로에 제안된 선택 가능한 관측점 시험구조를 적용 설계하고, 관측점 설정 명령어를 사용한 시험절차를 Altera의 Max 10.0을 이용한 시뮬레이션을 통해 동작의 정확성을 확인하였다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2004년도 추계학술대회 논문집
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• pp.428-432
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• 2004

The important problem in the high speed spindles is to reduce and minimize the thermal effect by the motor and ball bearings. Thermal characteristics according to the bearing preload and hollow shaft cooling are studied for the test spindle with the oil mist lubrication and high frequency motor. Bearings and motor e main heat generation, and heat generation by ball bearings as a function of load, viscosity and gyroscopic moment effect are considered. Temperature distribution and thermal displacement according to the speed of spindle are measured by thermocouple and gap sensor. The results show that the fitting preload and hollow haft cooling are very effective to minimize the thermal effect by the motor and ball bearings.

• Tribology and Lubricants
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• 제30권1호
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• pp.1-8
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• 2014

In this study, a three-pad gas foil journal bearing with a diameter of 40 mm and an axial length of 35 mm was modeled to predict the static and dynamic performances with regard to an increasing mechanical preload. The Reynolds equation for an isothermal and isoviscous ideal gas was coupled with a simple elastic foundation foil model to calculate the hydrodynamic pressure solution iteratively. In the prediction results, the journal eccentricity, journal attitude angle, and minimum film thickness decreased, but the friction torque increased with the preload. A quick comparison implied a lower load capacity but higher stability for a three-pad gas foil bearing compared to a one-pad gas foil journal bearing. The direct stiffness coefficients increased with the preload, but the cross-coupled stiffness coefficients decreased. The direct damping coefficient increased in the horizontal direction but decreased in the vertical direction as the preload increased. These model predictions will be useful as a benchmark against experimental test data.

• Steel and Composite Structures
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• 제35권1호
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• pp.93-109
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• 2020

Developed from conventional concrete filled steel tubular (CFST) members, concrete-encased CFST has attracted growing attention in building and bridge practices. In actual construction, the inner CFST is erected prior to the casting of the outer reinforced concrete part to support the construction preload, after which the whole composite member is under sustained service load. The complex loading sequence leads to highly nonlinear material interaction and consequently complicated structural performance. This paper studies the full-range behaviour of concrete-encased CFST columns with initial preload on inner CFST followed by sustained service load over the whole composite section. Validated against the reported data obtained from specifically designed tests, a finite element analysis model is developed to investigate the detailed structural behaviour in terms of ultimate strength, load distribution, material interaction and strain development. Parametric analysis is then carried out to evaluate the impact of significant factors on the structural behaviour of the composite columns. Finally, a simplified design method for estimating the sectional capacity of concrete-encased CFST is proposed, with the combined influences of construction preload and sustained service load being taken into account. The feasibility of the developed method is validated against both the test data and the simulation results.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.865-868
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• 2006

An experimental investigation was carried out to evaluate the transient strain of concrete at high temperature. Two level of W/B ratio were selected as 46% and 32%. Four level of preload were adopted as 0, 15, 30, 45% of compressive strength. The entire temperature range was between room temperature and $700^{\circ}C$. Based on the test results, transient strain of concrete at high temperature was affected by the compressive strength as well as the preload level.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2006년도 춘계학술대회논문집
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• pp.1396-1403
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• 2006

This study shows that the system performance of a positioning system composed of a piezoelectric actuator-driven flexure guide depends largely on the preload applied on the flexure guide and the driving input amplitude. We used a flexure guided system that had an original resonant frequency of 54Hz. Our experiment showed that we could increase the driving bandwidth above the original resonant frequency, for a case involving a large preload and a small input amplitude. Results show that there is a specific 'separation frequency' where the response of the moving mass of the flexure system decouples from the response oi the piezoelectric actuator, and this specific separation frequency can be selected by a proper choice of the preload and the input amplitude. To find the separation frequency, sine sweep tests were performed. To confirm the increased system bandwidth frequency, open-loop sine tracking experiments were performed. Test results show that the system responds very well up to 130 Hz frequency higher than the original natural frequency (54Hz).

• 한국소음진동공학회논문집
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• 제16권4호
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• pp.346-354
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• 2006

This study shows that the system performance of a positioning system composed of a piezoelectric actuator-driven flexure guide depends largely on the preload applied on the flexure guide and the driving input amplitude. We used a flexure guided system that had an original resonant frequency of 54 Hz. Our experiment showed that we could increase the driving bandwidth above the original resonant frequency, for a case involving a large preload and a small input amplitude. Results show that there is a specific 'separation frequency' where the response of the moving mass of the flexure system decouples from the response of the piezoelectric actuator, and this specific separation frequency can be selected by a proper choice of the preload and the input amplitude. To find the separation frequency, sine sweep tests were performed. To confirm the increased system bandwidth frequency, open-loop sine tracking experiments were performed. Test results show that the system responds very well up to 130 Hz frequency higher than the original natural frequency (54 Hz).

• 대한치과보철학회지
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• 제45권3호
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• pp.345-353
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• 2007

Statement of problem. Implant abutment screw joints tend to loosen under clinical conditions. Abutment screw loosening results in loss of preload in function. Purpose. Anti-rotational inner post screw (ARIPS) systems were compared with conventional abutment screws to reduce screw loosening. Reverse torque values were evaluated. Material and methods. 32 implant assemblies (Warentec, Co, Ltd, Seoul, Korea) were organized as the 30-Ncm-torque conventional groups and 30-Ncm-torque ARIPS groups in external and internal system. The specimens were tested to 106 cycles at a load of 200N. Preload reverse torque, postload reverse torque, and the ratio of postload reverse torque to preload reverse torque were evaluated. The data were analyzed with unpaired t-test in external and internal systems. Results. In the ratio of postload reverse torque to preload reverse torque, the ARIPS groups showed significant differences than the conventional screw group in both external and internal system. Conclusion. Within the limitations of this study, abutment screw loosening was effectively reduced using ARIPS system.