• Title/Summary/Keyword: repeated loads

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HA Study on the Selection of Mobile Crane Model for Heavy Equipments Installation (중량물 설치 시 이동식 크레인 기종선정에 관한 연구)

  • Jeong, Jae-Bok;Yoo, Ho-Seon
    • Plant Journal
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    • v.8 no.2
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    • pp.59-69
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    • 2012
  • This study focuses on avoiding the failures from the wrong selections by experiences as simulation programs is not available, and suggests the methods which effectively select the alternatives when the selected model is not appropriate for the original plan. First, CC8800-1K of DEMAG has the longest boom whose length is 216 m at the maximum. The combination of the boom is feasible to second level except for MANITIWOC M 2250 (M-1200 RINGER) which is possible to third level. Second, the angle of boom is from 20 degrees to 82 degrees. Suitable angle to work is in the 55-78 degrees. The working load of crawler type and hydraulic one to be applied is 75-85% in the critical loads capacity. As increasing operating radius, crawler type is a favorable position over hydraulic one. Lastly, related problems were verified through examination by suggestions for the design of the selection methods for the case analysis. The major problems are stemming from the selection based on its experiences, unreasonable demand for the existing facility and repeated selections by the designer who accumulates his experiences via same or similar projects.

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Comparative Analysis of Muscle Activities for Upper Extremity During Resistance Exercises Using Variable and Elastic Loads (가변부하 및 탄성부하를 이용한 저항성 기구 운동 시 발현되는 상지근육의 근 활동치 비교분석)

  • Lim, Young-Tae
    • Korean Journal of Applied Biomechanics
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    • v.16 no.2
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    • pp.37-44
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    • 2006
  • The purposes of this study were to analyze and compare EMG activities of the pectoralis major, biceps brachii, triceps brachii, and brachioradialis muscles during biceps curls using a VRT device and an elastic tubing. Fifteen male college students were recruited as subjects and they performed 10-RM and 20-RM biceps curls. For each load and device condition, the mean and peak normalized EMG levels during different phases of a biceps curl were computed. For each load and phase, paired t-test (p.05) was used to find the significant difference between two devices. ANOVA with repeated measures was also used to find the significant difference among phases in terms of EMG values for each muscle. For each load and device condition, the peak and mean EMG levels during different phases of a biceps curl were computed The significant differences between devices were found in biceps brachii for EA, MD, LD phases, and triceps brachii muscles for all phases, respectively. However, no differences were found among phases for any muscle. This indicated that elastic band could have a similar characteristics of VRT. High antagonistic muscle activity as a function of injury prevention which found particularly in VRT device may suggest that elastic tubing can be a safer training device than VRT. This also imply that elastic tubing could be very effective as a home exercise tool for rehabilitation patients and elderly people.

Performance and modeling of high-performance steel fiber reinforced concrete under impact loads

  • Perumal, Ramadoss
    • Computers and Concrete
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    • v.13 no.2
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    • pp.255-270
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    • 2014
  • Impact performance of high-performance concrete (HPC) and SFRC at 28-day and 56-day under the action of repeated dynamic loading was studied. Silica fume replacement at 10% and 15% by mass and crimped steel fiber ($V_f$ = 0.5%- 1.5%) with aspect ratios of 80 and 53 were used in the concrete mixes. Results indicated that addition of fibers in HPC can effectively restrain the initiation and propagation of cracks under stress, and enhance the impact strengths and toughness of HPC. Variation of fiber aspect ratio has minor effect on improvement in impact strength. Based on the experimental data, failure resistance prediction models were developed with correlation coefficient (R) = 0.96 and the estimated absolute variation is 1.82% and on validation, the integral absolute error (IAE) determined is 10.49%. On analyzing the data collected, linear relationship for the prediction of failure resistance with R= 0.99 was obtained. IAE value of 10.26% for the model indicates better the reliability of model. Multiple linear regression model was developed to predict the ultimate failure resistance with multiple R= 0.96 and absolute variation obtained is 4.9%.

Evaluation of the Permanent Deformation Behavior on Geosynthetics-Reinforced Asphalt Pavement by using the Wheel Tracking Tests (휠트래킹 시험을 통한 토목섬유시트 보강 아스팔트포장의 소성변형 거동특성 평가)

  • Cho, Sam-Deok;Lee, Dae-Young;Kim, Jin-Hwan;Kim, Nam-Ho
    • Journal of the Korean Geosynthetics Society
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    • v.2 no.3
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    • pp.39-46
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    • 2003
  • The major pavement distress types found in the domestic roadways include rutting, fatigue cracking, and reflection cracking which are results of the environment and repeated traffic loads. These distresses usually occur before pavements approach their design life, and therefore, a significant amount of national budget is spent for maintenance of roadway pavements. The purpose of this study is to establish a geosynthetics-asphalt pavement system. For the study, wheel tracking tests are conducted to analyze the controlling effect of geosynthetics on rutting of asphalt pavement. On the basis of these works, the reinforcement effect of geosynthetics on the rutting of the asphalt pavement is clarified and deformation characteristics of geosynthetics-asphalt mixture is examined.

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Effect of Repetitive Impacts on the Mechanical Behavior of Glass Fiber-reinforced Polyurethane Foam (반복 충격이 유리섬유 강화 폴리우레탄 폼의 기계적 성능에 미치는 영향)

  • Kim, Myung-Sung;Kim, Jeong-Hyeon;Kim, Seul-Kee;Lee, Jae-Myung
    • Journal of Ocean Engineering and Technology
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    • v.33 no.1
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    • pp.85-91
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    • 2019
  • In a cryogenic storage structure, the insulation system is in an environment in which fluid impact loads occur throughout the lifetime of the structure. In this study, we investigated the effect of repetitive impact loading on the mechanical performance of glass fiber-reinforced polyurethane foam. The repeated impact loading test was conducted in accordance with the required impact energy and the required number of repetitive impacts. The impact behavior of glass fiber-reinforced polyurethane foam was analyzed in terms of stress and displacement. After the impact test, the specimen was subjected to a compression test to evaluate its mechanical performance. We analyzed the critical impact energy that affected mechanical performance. For the impact conditions that were tested, the compressive strength and elastic modulus of the polyurethane foam can be degraded significantly.

The Estimation of Fatigue Life for Al/CFRP Hybrid Laminated Composites using the Strain-Life Method (변형률-수명 평가기법을 이용한 Al/CFRP 하이브리드 적층 복합재의 피로수명 측정)

  • Yang, Seong Jin;Kwon, Oh Heon;Jeon, Sang Koo
    • Journal of the Korean Society of Safety
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    • v.36 no.3
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    • pp.7-14
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    • 2021
  • Hybrid laminated Al/carbon-fiber-reinforced plastic (CFRP) composites are attracting considerable attention from industries such as aerospace and automobiles owing to their excellent specific strength and specific rigidity. However, when this material is used to fabricate high-pressure fuel storage containers subjected to repeated fatigue loads, fatigue life evaluation for the working load is regulated as an important criterion for operational safety and ease of maintenance. Among the existing evaluation methods for these vessels, the burst test and the hydraulic repeat test require expensive facilities. Thus, the present study aims to develop an improved fatigue life test for Al/CFRP laminated hybrid composites. The test specimen was manufactured using a curved mold considering the shape of a type III high-pressure storage container. The strain-life method was used for fatigue life evaluation, and the life was predicted based on the transition life. The results indicate that the more complex the CFRP stacking sequence, the longer is the transition life. This test method is expected to be useful for ensuring the fatigue safety and economy of hybrid laminate composites.

Application of Nanoindentation Technique for Characterizing Surface Properties of Carburized Materials (침탄 처리 소재의 표면 분석을 위한 나노압입시험법의 응용)

  • Choi, In-Chul;Oh, Myung-Hoon
    • Journal of the Korean Society for Heat Treatment
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    • v.35 no.3
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    • pp.139-149
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    • 2022
  • In the automobile and shipbuilding industries, various materials and components require superior surface strength, excellent wear resistance and good resistance to repeated loads. To improve the surface properties of the materials, various surface heat treatment methods are used, which include carburizing, nitriding, and so on. Among them, carburizing treatment is widely used for structural steels containing carbon. The effective carburizing thickness required for materials depends on the service environment and the size of the components. In general, however, there is a limit in evaluation of the surface properties with a standardized mechanical test method because the thickness or cross-sectional area of the carburized layer is limited. In this regard, the nanoindentation technique has lots of advantages, which can measure the mechanical properties of the material surface at the nano and micro scale. It is possible to understand the relationship between the microstructural change in the hardened layer by carburizing treatment and the mechanical properties. To be spread to practical applications at the industrial level, in this paper, the principle of the nanoindentation method is described with a representative application for analyzing the mechanical properties of the carburized material.

Combined resonant column and cyclic triaxial tests to estimate the dynamic behavior of undisturbed saturated clayey soils of Adapazarı, Turkey

  • Ersin Guler;Kamil Bekir Afacan
    • Geomechanics and Engineering
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    • v.33 no.3
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    • pp.243-259
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    • 2023
  • Turkey is one of the most important earthquake regions in Europe. This region has been exposed to many earthquakes of different magnitudes from past to present. It is of great importance to determine the dynamic properties of the soils for structures to be built in earthquake zones. In order to minimize the damages that may occur, the behavior of the soils under repeated loads should be known and taken into consideration in the design. In this study, 4 different point borings were taken near active fault lines in the North Anatolian fault zone (NAFZ). In order to determine the dynamic parameters of soils, both dynamic triaxial (TRX) and resonant column (RC) tests were carried out on undisturbed samples at every 5 m. As a result of the experiments, Vs and Gmax values were obtained from the field and differences were determined. The dynamic behavior of the soil was examined at varying depths with the comparison of reference models in the literature and compatible results were obtained. Finally, the behavior at the transition region is highlighted. As a result, three shear modulus and dumping ratio models have been proposed for clay soils to be used in different soil conditions.

Estimation of the soil liquefaction potential through the Krill Herd algorithm

  • Yetis Bulent Sonmezer;Ersin Korkmaz
    • Geomechanics and Engineering
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    • v.33 no.5
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    • pp.487-506
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    • 2023
  • Looking from the past to the present, the earthquakes can be said to be type of disaster with most casualties among natural disasters. Soil liquefaction, which occurs under repeated loads such as earthquakes, plays a major role in these casualties. In this study, analytical equation models were developed to predict the probability of occurrence of soil liquefaction. In this context, the parameters effective in liquefaction were determined out of 170 data sets taken from the real field conditions of past earthquakes, using WEKA decision tree. Linear, Exponential, Power and Quadratic models have been developed based on the identified earthquake and ground parameters using Krill Herd algorithm. The Exponential model, among the models including the magnitude of the earthquake, fine grain ratio, effective stress, standard penetration test impact number and maximum ground acceleration parameters, gave the most successful results in predicting the fields with and without the occurrence of liquefaction. This proposed model enables the researchers to predict the liquefaction potential of the soil in advance according to different earthquake scenarios. In this context, measures can be realized in regions with the high potential of liquefaction and these measures can significantly reduce the casualties in the event of a new earthquake.

Evaluation of Static Behaviour of Orthotropic Steel Deck Considering the Loading Patterns (하중재하 패턴을 고려한 강바닥판의 정적거동 평가)

  • Kim, Seok Tae;Huh, Young
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.15 no.2
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    • pp.98-106
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    • 2011
  • The deck of steel box girder bridges is composed of deck plate, longitudinal rib, and transverse ribs. The orthotropic steel decks have high possibility to fatigue damage due to numbers of welded connection part, the heavy contact loadings, and the increase of repeated loadings. Generally, the local stress by the repeated loadings of heavy vehicles causes the orthotropic steel deck bridge to fatigue cracks. The increase of traffic volume and heavy vehicle loadings are promoted the possibility of fatigue cracks. Thus, it is important to exactly evaluate the structural behavior of bridge considering the contact loading area of heavy vehicles and real load patterns of heavy trucks which have effects on the bridge. This study estimated the effect of contact area of design loads and real traffic vehicles through the finite element analysis considering the real loading conditions. The finite element analysis carried out 4 cases of loading patterns in the orthotropic steel deck bridge. Also, analysis estimated the influence of contact area of real truck loadings by the existence of diaphragm plate. The result of finite element analysis indicated that single tire loadings of real trucks occurred higher local stress than one of design loadings, and especially the deck plate got the most influence by the single tire loading. It was found that the diaphragm attachment at joint part of longitudinal ribs and transverse ribs had no effects on the improvement of structural performance against fatigue resistance in elastic analysis.