• Journal of the Korean Society for Railway
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• v.13 no.5
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• pp.521-527
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• 2010

The Paved Track is applied to reduce maintenance cost of conventional line. The Paved Track could be used in all types of lines including earthwork, bridge, tunnel and turnout sections. In case of earthwork section, the construction joint is the most critical factor to track durability. The construction joint does not affect to the track structure directly, but the gap due to discontinuity of slabs may affect to the long-term serviceability. To evaluate this problem, the accelerated track test has been performed on the construction joint and the middle part to of the real scale Paved Track. The purpose of this test is that evaluate the vulnerability of construction joint section comparing the trends of settlement and earth pressure under repeated loads of construction joint with those of the middle slab part.

• Korean Journal of Applied Biomechanics
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• v.30 no.3
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• pp.275-283
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• 2020

Objective: The purpose of this study was to investigate the effect pf flexibility of hip flexor muscles on a conventional deadlift movement. Method: Eighteen healthy male were participated in this study and were divided into normal group (NG: age: 24.0±1.8 yrs, height: 174.5±2.37 cm, body mass: 74.4±5.5 kg, 1RM: 138.0±23.8 kg) and restricted group (RG: age: 24.6±1.7 yrs, height: 171.5±5.3 cm, body mass: 74.0±5.7 kg, 1RM: 137.5±18.3 kg) by Thomas test, which measure flexibility of hip flexor muscles. A 3-dimensional motion analysis with 8 infrared cameras and 3 channels of EMG was performed in this study. A two-way ANOVA (group x load) with repeated measure was used for statistical verification. The significant level was set at α=.05. Results: RG revealed significantly increased muscle activation in erector spinae on 70% and 90% of 1RM and decreased muscle activation in gluteus maximus on 90% of 1RM compared to NG (p<.05). For the muscle activation ratio for agonist to synergist, erector spinae showed the difference in 90% of 1RM while hamstring was observed differences in all loads (p<.05). Conclusion: Our results indicated that hip flexibility affects conventional deadlift movement. Therefore, it is necessary to assess the flexibility of the hip flexor muscles before performing the movement and, as needed, to train to address the lack of flexibility.

• Structural Engineering and Mechanics
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• v.64 no.5
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• pp.671-681
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• 2017

This study investigates the structural performance of 3D steel pipe rack suspended scaffolding systems. For the purpose, a standard full scale 3D steel pipe rack suspended scaffolding system considering two frames, two plane trusses, purlins and wooden floor is constructed in the laboratory. A developed load transmission system was placed in these experimental systems to distribute single loads to the center of a specific area in a step-by-step manner using a load jack. After each load increment, the displacements are measured by means of linear variable differential transducers placed in several critical points of the system. The tests are repeated for five different system conditions to determine the structural performance. The means of system conditions is the numbers of the tie bars which are used to connect plane trusses under level. Finite elements models of the 3D steel pipe rack suspended scaffolding systems considering different systems conditions are constituted using SAP2000 software to support the experimental tests and to use the models in future studies. Each of models including load transmission platform is analyzed under a single loading and the displacements are obtained. In addition, to calibrate the numerical models some uncertain parameters such as elasticity modulus of wooden floor and connection rigidity of purlins to plane trusses are assessed experimentally. The results of this work demonstrate that when increasing numbers of tie bars the displacement values are decreased. Also the results obtained from developed numerical models have harmony with those of experimental. In addition, the scaffolding system with two tie bars at the beginning and at the end of the plane truss has the optimum structural performance compared the results obtained for other scaffolding system conditions.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.40 no.8
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• pp.721-724
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• 2016

Because of the inherent uncertainties caused by the manufacturing process variations, future loading conditions, and incomplete damage models, the lifetimes of mechanical structures under field conditions are significantly different from the results obtained in the laboratories. In this study, a dual sensor was developed to prognosticate the fatigue failure of structures under these uncertain conditions, and its effectiveness was demonstrated on a rectangular columnar structure under repeated uni-axial loading. The dual sensor is a slightly weaker structure embedded in the target structure, so that failure occurs in the sensor earlier than in the target structure. From the signal differences in the strain gauges in the embedded dual sensor, it is possible to differentiate between the normal status and warning status, even under variable loads.

• The Journal of the Korea Contents Association
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• v.8 no.5
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• pp.1-8
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• 2008

The centralized conference architecture, one of the conference architectures in SIP(Session Initiation Protocol) environment, is widely used as it has the advantage of conference management and control. However it has been limited in scalability. Therefore we have proposed an efficient distributed conference architecture to improve scalability of centralized conference model. In our architecture, if the number of conference participants exceeds the predefined maximum number, a new conference server is added to the conference dynamically. In this case, the focus of existing server acts as primary focus and the focus of added server acts as secondary focus, and dynamic reallocation of participants between servers is done to equally divide the loads. This process is repeated as the number of conference participants increases. For this behavior, we have proposed procedure of adding the conference server, SIP call signal exchange, signaling procedure for RTP(Real Time Transport Protocol) sessions between conference servers, and procedure of conference event package between conference servers. The performance of our proposed model is evaluated by experiments.

• Korean Journal of Applied Biomechanics
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• v.19 no.2
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• pp.369-377
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• 2009

The purpose of this study was to determine the relationship between different soccer cleat designs and knee joint moments. Twelve physically active males (mean(SD): age: 26.4(6.2)yrs; height: 176.4(4.1)cm; mass: 74.0 (7.4)kg) were recruited Kinematic and force plate data were collected for all subjects during normal running and a $45^{\circ}$ cutting maneuver, called a v-cut. Both motions were performed at $4.0{\pm}0.2\;m/s$ on infilled artificial turf with three pairs of soccer cleats of different sole plate designs, and one pair of neutral running shoes. Inverse dynamics were used to calculate three dimensional knee joint moments, with repeated measures ANOVA and post hoc paired Student's t-test used to determine significance between shoe conditions. Significant differences were found in the extension moments of the knee for running trials, and for external rotation and adduction moments in the v-cutting trials. Knee moments were greater in v-cut than running, and the traditional soccer cleats (Copa Mondial and World Cup) tended to result in greater knee moments than the Nova runner or TRX soccer cleat. Cleat design was found to influence 3-dimensional knee moments in a v-cut maneuver. In the translational traction test, there were significant differences between all conditions. In the rotational traction test, friction with soccer shoes were greater than friction with running shoes. However, no differences were found between soccer shoes. Higher moments may lead to increased loads and stresses on knee joint structures, and thus, greater injury rates.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.2 s.146
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• pp.213-219
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• 2006

Low cycle fatigue cracks are mainly detected at discontinuous welded locations with high stresses under repeated cyclic static loads due to cargo leading and unloading. Theoretical and analytical methods have been used for evaluation of local stress and strain which have an effect on a prediction of fatigue life, but those have difficulties of considering stress concentration at notched location and complicated material behavior of welded joint or heat affected zone. Electronic speckle pattern interferometry(ESPI) system is nondestructive and non-contact measurement system which can get the relatively accurate full field strain at critical positions such as welded zone and structural discontinuous location. In this study, local strain was measured on welded cruciform joint by ESPI system and then low cycle fatigue test was performed. Effect of local strain on low cycle fatigue life was examined by measured values using ESPI system. Moreover, experimental fatigue life was compared with established S-N curves using theoretical local strain and stress calculated by Neuber's rule.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.556-565
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• 2002

The concrete bridge decks on the main girder will usually develop initial cracks in the longitudinal or the transverse direction due to dry shrinkage and temperature change, and as the bridge decks age the crack will gradually develop in different directions due to repeated cyclic loads. The strengthening direction of the concrete bridge deck is a very important factor in improving proper structural behavior. Therefore, in this study, theoretical analyses of strengthened bridge decks were performed using the nonlinear finite element method. To improve the accuracy of the analytical result, boundary conditions and material property of strengthening material was simulated by laboratory condition and test results, respectively. The effect of the strengthening direction and the amount of strengthening material were estimated and compared to the experimental results. The efficiency of the strengthened bridge decks by strengthening variables such as the amount, width and thickness of CFS was observed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.7
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• pp.1524-1531
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• 2004

This study analyzes a load balancing technique using Round Robin Algorithm. The study uses two software packages (Packet Capture and Round Robin Test Package) to check packet volume from Virtual Network structure (data generator, virtual server, Server1,2,3), and finds out traffic distribution toward Server1,2 and 3. The functions of implemented Round Robin Load Balancing Monitoring System include round robin testing, system monitoring, and graphical indication of data transmission and packet volume. As the result of the study shows, Round Robin Algorithm allows servers to ensure definite traffic distribution, unless incoming data loads differ much. Although error levels are high in some cases, they were eventually alleviated by repeated tests for a long period of time.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.3
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• pp.21-28
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• 2008

To evaluate the seismic performance of multi-degree of freedom(MDF) systems, repeated nonlinear response history analyses are often conducted, which require extensive computational efforts. To reduce the amount of computation required, equivalent single degree of freedom(SDF) systems representing complex multi-degree of freedom(MDF) systems have been developed. For the equivalent SDF systems, bilinear models and trilinear models have been most commonly used. In these models, the P-$\Delta$ effect due to gravity loads during earthquakes can be accounted for by assigning negative stiffness after elastic range. This study evaluates the adequacy of equivalent SDF systems having these hysteretic models to predict the actual response of steel moment resisting frames(SMRF). For this purpose, this study conducts cyclic pushover analysis, nonlinear time history analysis and incremental dynamic analysis(IDA) for SAC-Los Angeles 9-story buildings using nonlinear MDF models(exact) and equivalent SDF models(approximate). In addition, this study considers the strength limited model.