• Korean Journal of Applied Biomechanics
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• v.16 no.2
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• pp.97-108
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• 2006

C. H. OH, S. N. CHOI, T. G. NAM, The Kinematic Analysis of the Tennis Flat Serve Motion, Korean Jiurnal of Sports Biomechanics, Vol. 16, No. 2, pp. 97-108, 2006. By the comparison and the analysis of the different factors during the tennis flat serve motion such as the required time per section, the movement displacement of the racket, the velocity of the upper limbs joints, the physical center of gravity, and the angle and the angular velocity of the upper limbs joints between an ace player and a mediocre player, these following results were drawn. First, the experiment result of the total time required per section in a tennis flat serve motion showed that an ace player was faster than a mediocre player by 0.4 seconds. This result suggested that it was required to increase the speed of the racket head by a swift swing to perform an effective flat serve motion. Second, the experiment result of the movement displacement of the racket in the tennis flat serve motion showed that an ace player greatly moved toward the left side on an x-axis. But both an ace and a mediocre player were shown to be at the similar points on a y-axis at the moment of the impact of the racket. An ace player was also shown to be located at a higher position on a z-axis by 0.23m. Third, the velocity of the center of gravity of an ace player was faster in every phase than that of a mediocre player in a tennis flat serve motion. Fourth, the velocity of the upper limb joints of an ace player was faster in every phase than that of a mediocre player in a tennis flat serve motion. Fifth, the experiment result of the speed of the racket head in tennis flat serve motion showed that a mediocre player was faster than an ace player in the first phase, but the latter was faster than the former in the second, third, and the fourth phases. Sixth, at the moment of impact of a tennis flat serve, an ace player had greater flexion of the angle of the wrist joints by an 11.8 degree than a mediocre player. An ace player also had greater extension of the angle of the elbow joint and the shoulder joint respectively by a 5.2 degree and a 1.4 degree with a mediocre player. Seventh, an ace player had greater angular velocity of the upper limb joints and the hip joints than a mediocre player at the moment of the impact of tennis flat serve. Eighth, an ace player was shown to have a greater change of the forward and the backward inclination (or the anterior and posterior inclination) of the upper body

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.9
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• pp.3952-3958
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• 2011

This study was to investigate the difference in gait pattern between the visual handicap children and non handicap children in by analyze the biomechanical variation and pattern of lower limb. Therefore, we have made a choice of four visually handicapped children and two subjects, who had no medical disorder for the last six months. In order to collect the gait pattern data of each group, we have used six infrared cameras and one forceplate Also, we have used QTM program to collect the raw data and Visual3D program to calculate kinetic variable. The results were as follows, An/Posterior GRF of breaking phase and propulsion phase in stance phase was lower in visual handicapped children than that of non handicapped children and breaking phase was longer than propulsion phase. extension moment at the ankle was quite lower than general gait pattern and there was little variation at the knee joint which makes the results differ from the general gait pattern. However, hip joint moment was relatively higher than that of other joints. Mechanical variation of lower limb, in case of foot and shank, showed similar results. but generated very low mechanical energy. In thigh, the form of mechanical energy generation was slightly different in each group but generated more mechanical energy than other segments.

• Journal of Korean Society of Steel Construction
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• v.16 no.6 s.73
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• pp.833-846
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• 2004

This study presents a non-prismatic beam element for modeling the elastic behavior of steel beams, which have the post-Northridge connections in steel moment frames. The elastic stiffness matrix, including the shear effects for non-prismatic members with reduced beam section (RBS) connection, is in closed form. A simplified approach is also suggested, which uses a prismatic beam element to model beams with the RBS connection. This method can estimate quiteexactly the maximum story drift ratios of frames with the RBS connection. The effects of reduced beam section connection on the elastic stiffness of steel moment frames were investigated. The selection of a proper model to account for deformations at the joint might have a more important role in estimating the maximum story drift ratios of frames with better accuracy than the RBS cutouts.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.10
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• pp.1893-1895
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• 2008

In this paper, we investigated the maximum ankle joint plantarflexion moment(MPM) of young and elderly subjects during various modes of isokinetic contractions with special interest in the elderly females who were reported to have higher fall rate than the elderly males. Subjects include the young subjects(14 males: $22.7{\pm}2.5yrs$, 13 females: $20.5{\pm}1.3yrs$) and the elderly subjects(17 males: $65.8{\pm}10.5yrs$, 26 females: $71.4{\pm}5.2yrs$). The MPM was normalized by each subject's body weight. The MPM of elderly females was the weakest among the groups, particularly, at the eccentric contractions. The male-to-female ratio of MPM was greater in the elderly than in the young and the young-to-elderly ratio of MPM was greater in female than in male, both during the eccentric contractions. The result suggests that the decreased muscle force per body weight, especially at the eccentric contraction, may be one reason for the more frequent fall of the elderly female than the elderly male.

• Korean Journal of Applied Biomechanics
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• v.17 no.4
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• pp.209-219
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• 2007

The purpose of this study was to analyze biomechanical mechanism (posture, moment of back joint, EMG) when athletes (Judo, Ssirum) and lay people lifted a load according to two different lift methods; backlift and leglift. The number of subjects was 12; 8 athletes (4 for Judo, 4 for Ssirum) and 4 lay people. We recorded a lift motion in backlift and leglift using 7 real time infrared cameras (vicon) and analyzed EMG pattern of major muscles for a lift (lattisimus dorsi, erector spinae, biceps femoris). In a backlift Judo players showed a biggest range of back flexion and extension motion and lay people flexed more than other groups at phase 2 in which an interaction between groups and events was statistically significant (p=.024). In a leglift Ssirum players more flexed their back in a barbell lift and there was a statistical significance (p=.021) between groups and events. For moment of back joints, 1) in a backlift a larger loading on back joints in all three groups at phase 2 when lifting down a barbell, 2) in a leglift a larger loading on back joints when lifting down a barbell in two athlete groups but a larger loading when lifting up a barbell in lay people group, and all groups did not show any statistical significance. For EMG, right lattisimus dorsi muscle in a backlift was statistical significant (p=.006) in an interaction between groups and phase but left lattisimus dorsi muscle was insignicant, and there was not any significance in a leglift. Generally atheletes (Judo and Ssirum) used more their muscles of lower extremity in lifting up and down and lay people did more their ones of upper extremity.

• Steel and Composite Structures
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• v.35 no.4
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• pp.579-598
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• 2020

Consideration of the panel zone (PZ) deformations in the analysis of steel moment frames (SMFs) has a substantial effect on structural response. One way to include the PZ effect on the structural response is Krawinkler's PZ model, which is one of the best and conventional models. However, modeling of Krawinkler's PZ model has its complexity, and finding an alternative procedure for PZ modeling is of interest. In this study, an efficient model is proposed to simplify Krawinkler's PZ model into an Adjusted Rigid-End Zone (AREZ). In this way, the rigid-end-zone dimensions of the beam and column elements are defined through an appropriate rigid-end-zone factor. The dimensions of this region depend on the PZ stiffness, beam(s) and columns' specifications, and connection joint configuration. Thus, to obtain a relationship for the AREZ model, which yields the dimensions of the rigid-end zone, the story drift of an SMF with Krawinkler's PZ model is equalized with the story drift of the same structure with the AREZ model. Then, the degree of accuracy of the resulting relationship is examined in several connections of generic SMFs. Also, in order to demonstrate the applicability of the proposed model in SMFs, several SMFs ranging from 3- to 30-story representing low- to high-rise buildings are examined through linear static and dynamic time history analysis. Furthermore, non-linear dynamic analyses of three SMFs conducted to validate the degree of accuracy of the proposed model in the non-linear analysis of SMFs. Analytical results show that there is considerable conformity between inter-story drift ratio (IDR) results of the SMFs with Krawinkler's PZ model and those of the centerline SMFs with AREZ.

• Korean Journal of Applied Biomechanics
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• v.15 no.4
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• pp.55-66
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• 2005

The present study used a video analysis system to quantify the kinematical data of step shoot motion by male university handball players. From the results of analyzing dynamic variables of step shoot motion according to shooting direction were drawn conclusions as follows. 1. The height of release was proportional to the height of players, and the height of release appeared low in left-side attacks. This is probably because the left-right-throwing angle is larger in left-side attacks than that in center attacks and right-side attacks and, as a result, the throwing arm is lowered down in throwing. 2. The leftward inclination angle of the body was larger in order of right-side attacks > center attacks > left side attacks. 3. Players' throwing form was close to three quarter style in left-side attacks. In center and right-side attacks, the arm was somewhat more upright but still it was more three quarter style than overhand style. 4. The front-rear throwing angle at the moment of release was much higher in right-side attacks than in left-side ones. This is probably because the point of time for releasing the ball is usually late in right-side attacks and, as a result, the front-rear throwing angle becomes quite large. 5. The contribution of body parts on the ball speed was higher in order of the forearm > upper arm, hand > shoulder joint. 6. In players whose distance between the two legs at the moment of release, their body usually did not incline to the side much. Thus it is considered necessary to correct the right leg in their shooting motion. 7. According to the result of analyzing throwing form, the speed of the ball at the moment of leaving the hand was faster in right-side attacks than in left-side and center attacks.

• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.5
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• pp.203-211
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• 2023

For fast-built and safe precast concrete (PC) construction, the dry mechanical splicing method is a critical technique that enables a self-sustaining system (SSS) during construction with no temporary support and minimizes onsite jobs. However, due to limited experimental evidence, traditional wet splicing methods are still dominantly adopted in the domestic precast industry. For PC beam-column connections, the current design code requires achieving emulative connection performances and corresponding structural integrity to be comparable with typical reinforced concrete (RC) systems with monolithic connections. To this end, this study conducted the standard material tests on mechanical splices to check their satisfactory performance as the Type 2 mechanical splice specified in the ACI 318 code. Two PC beam-column connection specimens with dry mechanical splices and an RC control specimen as the special moment frame were subsequently fabricated and tested under lateral reversed cyclic loadings. Test results showed that the seismic performances of all the PC specimens were fully comparable to the RC specimen in terms of strength, stiffness, energy dissipation, drift capacity, and failure mode, and their hysteresis responses showed a mitigated pinching effect compared to the control RC specimen. The seismic performances of the PC and RC specimens were evaluated quantitatively based on the ACI 374 report, and it appeared that all the test specimens fully satisfied the seismic performance criteria as a code-compliant special moment frame system.

• Journal of the Earthquake Engineering Society of Korea
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• v.27 no.3
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• pp.129-137
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• 2023

This study presents a dry precast concrete (PC) beam-column connection, and its target seismic performance level is set to be emulative to the reinforced concrete (RC) intermediate moment resisting frame system specified in ACI 318 and ASCE 7. The key features include self-sustaining ability during construction with the dry mechanical splicing method, enabling emulative connection performances and better constructability. Test specimens with code-compliant seismic details were fabricated and tested under reversed cyclic loading, which included a PC beam-column connection specimen with dry connections and an RC control specimen. The test results showed that all the specimens failed in a similar failure mode due to plastic deformations in beam members, while the hysteretic response curve of the PC specimen showed comparable and emulative performances compared to the RC specimen. Seismic performance evaluation was quantitatively addressed, and on this basis, it confirmed that the presented system can fully satisfy all the required performance for the intermediate RC moment resisting frame.

• Korean Journal of Applied Biomechanics
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• v.25 no.2
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• pp.183-190
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• 2015

Objective : Walking with a Material handling is an activity frequently undertaken by agricultural workers in Korea, due to the nature of their work. This study aimed to investigate differences in biomechanical variables according to the mechanical alignment of the lower limbs when walking with a heavy load, and to use this as basic data in the design of various working environments to reduce the skeletomuscular burden on the knee joint. Method : The study subjects comprised of 22 right-foot dominant adult men and women aged between 20 and 23 years. The subjects were divided into a varus or valgus group according to the mechanical alignment of the lower limb by using radiographic findings. The subjects walked without any load and with a load of 10%, 20%, or 30% of their body weight held in front of them. The Kwon3d XP program was used to calculate biomechanical variables. Results : The flexion/extension moment of the knee joint showed a decreasing trend with increased load, irrespective of the mechanical alignment of the lower limb, while the varus group did not show normal compensatory action when supported by one leg at the point of maximum vertical ground reaction force. In addition, in terms of the time taken, subjects showed no difficulties in one-foot support time up to 20%/BW, but at 30%/BW, despite individual differences, there was an increase in single limb. The increased load resulted in a decrease in the ratio of standing phase to ensure physical stability. The valgus group showed a trend of increasing the stability of their center of mass with increasing load, through higher braking power in the early standing phase. Conclusion : In conclusion, although there was no statistical difference in biomechanical variables according to the mechanical alignment of the lower limbs, the varus group showed a more irregular walking pattern with a Material handling than the valgus group, partially proving the association between lower limb alignment and walking with a Material handling.