• Journal of the Korean Society of Safety
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• v.11 no.4
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• pp.42-48
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• 1996

Since the fatigue phenomenon is characterized as a probability feature and test data cannot be easily collected number its small sample data are uncertain. Therefore, statistical evaluation methods should necessarily be introduced into data evaluation. With such a basic concept in mind, this study attempted to apply conventional statistical processing methods to the fatigue data and thereby present a new evaluation method in consideration of the fact that the fatigue test is usually performed within a limited number. That is a package evaluation method was adopted which co-realtes parameters between different levels of capacity in E-N or S-N level. So far fatigue limits have been found by means of stiarcase method. But it was also disclosed that this new method has its own disadvantage because limited frequencies are not duely considered.

• Journal of the Korea Concrete Institute
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• v.24 no.3
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• pp.249-258
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• 2012

Integral and rigid frame bridges have advantages in bridge maintenance and structural efficiency by eliminating expansion joints and bridge supports. However, the detail of typical girder-abutment connection is rather complex and increases construction cost depending on construction detail. For the purpose of compensating disadvantages such as complexity and additional cost, a new type of bridge is proposed in this study, which improves the efficiency of construction by simplifying the construction detail of girder-abutment connection. The proposed bridge has the connection detail of steel girder and abutment integrated by prestressed PS bar installed in the connection. In this study, finite element analysis and fatigue load test are conducted to evaluate the fatigue capacity of the proposed girder-abutment connection. The results of the finite element analysis revealed that the possibility of the fatigue damage in the girder-abutment connection is very low. The results of the fatigue load test verified that the integrity of the girder and abutment connection is maintained after 2,000,000 cycles of fatigue loading.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.965-972
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• 2011

Unlike metallic materials, the importance of fatigue performance of concrete has been ignored. However, it is reported that environmental effects, if it cause deterioration, may increase the risk of fatigue failure under repeated loadings. In case of railroad bridges, the risk may increase due to highly periodic, repetitive, heavier nature of train load, which runs through the fixed passage called the track. Especially, when new material or structure is implemented for a main bridge member, experimental validation should be performed to avoid damage or failure due to unexpected behavior. In this paper, the fatigue performance of an IT girder is examined via a repeated loading test. The IT girder is a new type of a prestressed concrete (PSC) girder with two prestressed H-beams in the top of the girder, which provide additional sectional capacity, and it can be applied to the span longer than 30m which is a typical limit for a usual PSC girder. To obtain the fatigue performance, a 10m IT girder specimen is designed, and a repeated load test is performed by applying the cyclic load two million times. The fatigue performance of the girder is examined according to the Japanese and the CEB-FIB design codes. The fatigue test result shows that the IT girder satisfies both design codes.

• Proceedings of the KSR Conference
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• 2011.05a
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• pp.1533-1538
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• 2011

The dynamic characteristics such as resonant frequencies and dampings have been utilized as important parameters in dynamic behavior and inverse analyses. In general, the dynamic parameters have been determined based on design and experimental data, but experimental studies on the time-dependent changes of the dynamic parameters during service have rarely been conducted. Especially, unlike highway bridges, it is much easier for railroad bridges to estimate accumulated amount of fatigue because of the controlled train operation, and the study of dynamic characteristic change due to fatigue is useful, since it can enhance the accuracy of dynamic analysis. In this paper, the dynamic characteristic change due to fatigue is measured via the modal test on the PSC girder during a fatigue test. The test specimen utilized in the test is the IT girder which enhances the sectional capacity of the conventional PSC girders. The test specimen is designed 10m long and the modal tests are conducted during the application of fatigue load two million times. The test result shows that considerable changes in the measured dynamic parameters are observed as the fatigue accumulates, and these changes during the service life should be considered in designing railroad bridges.

• Textile Coloration and Finishing
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• v.26 no.3
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• pp.181-186
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• 2014

This paper surveys improvement characteristics in muscle fatigue with bio-activity material imbedded fabric. For this purpose, the subjects wear the garment which is covered by bio-activity materials all over every day during 2 weeks of experimental period. After 2 weeks period, VAS(Visual Analogue Scale) index evaluation regarding muscle fatigue and pain has been conducted in comparison between before wearing and after so that we can evaluate the effect on muscle fatigue improvement. The effectiveness survey for testing products consists of improvement on krunkle, muscle fatigue and exercise capacity. As a result, 100% of test subject group completes a questionnaire with positive answer as above normal in every question. In addition the preference of testing products is researched in wearing comfort, activity and convenience. And it is marked above normal by 100% of test subject group as well. Moreover any kind of unusual skin reaction has not been detected in safety evaluation. Therefore this testing products is being judged as a beneficent product for improvement on muscle fatigue without any skin irritation.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.5 no.4
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• pp.65-71
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• 2006

The lightness of components required on marine and shipbuilding industry is requiring high strength of components. In particular, fatigue failure phenomena, which happen in metal, bring on danger in human life and property. Therefore, antifatigue failure technology takes an important part on current industries. In this study, it is investigated about endurance and fatigue crack propagation rate of according to welding methods such as SMAW, FCAW and SAW commonly used for welding structures in present. Endurance limits carried out highly in the order of SMAW, FCAW, SAW and fatigue crack propagation rate out lowly in the order of SMAW, FCAW, SAW. By these results, it is needed to use SMAW welding method for welding structures with small welding capacity and FCAW, SAW methods for large welding structures after consideration about economic gains and operation efficiency of welding. Fatigue crack propagation rate is more affected by strength of welding materials than endurance limit of welding materials according to welding methods.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.333-336
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• 2008

CFRP tendons have been attempted in concrete structures as a substitute for steel tendons considering their many advantages such as the corrosion-resistance, light weight etc. However, the elastic behavior up to failure is likely to result in ductility problems. To overcome such problems, prestress concrete beams with partially bonded tendons have been developed and suggested. In this new system, the un-bonded part near the mid-span contributes to the improvement of ductility. And the bonded parts at both ends play a role as a safe anchorage. According to the previous research on the static behavior, the suggested method has demonstrated enough ductility and strength. However it is essential to verify the long-term safety for repetitive fatigue loads under service states. For this purpose, flexural fatigue loading tests were carried out in this research. This paper includes an experimental investigation on the static load-carrying capacities of the beams with or without fatigue tests. The results showed that the beams prestressed with partially bonded CFRP tendons possessed good fatigue capacity under the constant cyclic loads.

• Computers and Concrete
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• v.29 no.1
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• pp.47-57
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• 2022

The increase in waste tires has brought serious environmental problems. Using waste tires rubber particles as aggregate in concrete can reduce pollution and decrease the usage of natural aggregate. The paper describes an investigation on flexural bearing capacity of self-compacting concrete (SCC) pavement slabs containing crumb rubber. Cyclic loading tests with different stress ratios and loading frequencies are carried out on SCC pavement slabs containing crumb rubber. Based on Paris Law and test data, the fatigue life of SCC pavement slab containing crumb rubber is discussed, and a revised mathematical model is established to predict the fatigue life of SCC pavement slab containing crumb rubber. The model applies to different stress ratios and loading frequencies. The fatigue life of SCC pavement slab containing crumb rubber is affected by the stress ratio and loading frequency. The fatigue life increases with the increase of stress ratio and loading frequency. Real-time acoustic emission (AE) signals in the SCC pavement slab containing crumb rubber under cyclic loading are measured, and the characteristics of crack propagation in the SCC pavement slab containing crumb rubber under different stress ratios and loading frequencies are compared. The AE signals provide abundant information of fracture process zone and crack propagation. The variation of AE ringing count, energy and b-value show that the fracture process of SCC pavement slab containing crumb rubber is divided into three stages.

• Nutrition Research and Practice
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• v.16 no.3
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• pp.298-313
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• 2022

BACKGROUND/OBJECTIVES: The effectiveness of natural compounds in improving athletic ability has attracted attention in both sports and research. Gynostemma pentaphyllum (Thunb.) leaves are used to make traditional herbal medicines in Asia. The active components of G. pentaphyllum, dammarane saponins, or gypenosides, possess a range of biological activities. On the other hand, the anti-fatigue effects from G. pentaphyllum extract (GPE) and its effective compound, gypenoside L (GL), remain to be determined. MATERIALS/METHODS: This study examined the effects of GPE on fatigue and exercise performance in ICR mice. GPE was administered orally to mice for 6 weeks, with or without treadmill training. The biochemical analysis in serum, glycogen content, mRNA, and protein expressions of the liver and muscle were analyzed. RESULTS: The ExGPE (exercise with 300 mg/kg body weight/day of GPE) mice decreased the fat mass percentage significantly compared to the ExC mice, while the ExGPE showed the greatest lean mass percentage compared to the ExC group. The administration of GPE improved the exercise endurance and capacity in treadmill-trained mice, increased glucose and triglycerides, and decreased the serum creatine kinase and lactate levels after intensive exercise. The muscle glycogen levels were higher in the ExGPE group than the ExC group. GPE increased the level of mitochondrial biogenesis by enhancing the phosphorylation of peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) protein and the mRNA expression of nuclear respiratory factor 1, mitochondrial DNA, peroxisome proliferator-activated receptor-δ, superoxide dismutase 2, and by decreasing the lactate dehydrogenase B level in the soleus muscle (SOL). GPE also improved PGC-1α activation in the SOL significantly through AMPK/p38 phosphorylation. CONCLUSIONS: These results showed that GPE supplementation enhances exercise performance and has anti-fatigue activity. In addition, the underlying molecular mechanism was elucidated. Therefore, GPE is a promising candidate for developing functional foods and enhancing the exercise capacity and anti-fatigue activity.

• Proceedings of the KWS Conference
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• v.43
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• pp.153-155
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• 2004

Vibration occurs due to the wind and vehicles, etc., in the field welded joints of steel bridges. However, the effect of vibration on the fatigue strength of field welded joints in steel bridge are not yet clearly understood. In this paper, the effect of vibration on the fatigue strength of welded joints was elucidated in order to improve reliability in the field welded joints of steel bridge. The base material used in this investigation was SM 490A steel of weldable grade. Flux Cored Arc Welding(FCAW) process was used to fabricate the doubte 'V' butt joints. Welding was performed on the steel under the mechanical vibration of given frequency. The applied frequency was resonant frequency. Also, weldments formed under no vibration were fabricated. Fatigue tests were conducted using a servo hydraulic controlled 50ton1 capacity UTM with a frequency of 5Hz under constant amplitude loading.