• Proceedings of the KWS Conference
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• 2002.10a
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• pp.493-498
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• 2002

Friction stir welding (FSW) is a relatively new solid-state joining process which can homogenize the heterogeneous microstructure by intensely plastic deformation arising from the rotation of the welding tool. The present study applied the FSW to an A356 aluminum (AI) alloy with the as-cast heterogeneous microstructure in the T6 temper condition, and examined an effect of microstructure on mechanical properties in the weld. The base material consisted of Al matrix with a high density of strengthening precipitates, large eutectic silicon and a lot of porosities. The FSW led to fragment of the eutectic silicon, extinction of the porosities and dissolution of the strengthening precipitates in the Al alloy. The dissolution of strengthening precipitates reduced the hardness of the weld around the weld center and the transverse ultimate tensile strength of the weld. Longitudinal tensile specimen containing only the stir zone showed the roughly same strength as the base material and a much larger elongation. Moreover, Charpy impact tests indicated that the stir zone had remarkably the higher absorbed energy than the base material. The higher mechanical properties of the stir zone were attributed to a homogenization of the as-cast heterogeneous microstructure by FSW.

• Structural Engineering and Mechanics
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• v.44 no.6
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• pp.735-751
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• 2012

Although being one of the most popular strengthening techniques in reinforced concrete beams, the use of steel plates bonded to the soffit raises problems of ductility. This study aims at investigating the influence of the use of perforated steel plates instead of solid steel plates on the ductility of reinforced concrete beams. A total of nine reinforced concrete beams were tested. In addition to an unplated beam, eight beams with perforated steel plates of two different thicknesses (3 mm and 6 mm) were subjected to monotonic loading. Effect of bonding the plates to the beams with anchor bolts and with additional side plates bonded to the sides of the beam with and without anchors is also investigated. The use of bolts in addition to epoxy was found to greatly contribute to the ductility and energy absorption capacity of the beams, particularly in specimens with thick plates (6 mm) and the use side plates in addition to the bottom plate was found to be ineffective in increasing the ductility of a concrete beam unless the side plates are attached to the beam with anchors bolts. The thickness of the plate was found to have little effect on the bending rigidity of the beam.

• Structural Engineering and Mechanics
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• v.42 no.6
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• pp.799-813
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• 2012

Five two-span reinforced concrete (RC) slabs and seven two-span RC beams were tested under the ISO 834 standard fire with different durations. CFRP strengthening was then applied to some of the specimens after the damaged concrete was removed from the specimens and replaced with polymer mortar. All the specimens were loaded to failure to investigate the influence of fire-damage and the effectiveness of strengthening methods. Test results indicated that the flexural capacities of specimens decrease with the fire duration increases. Moreover, fire exposure had more significant effect on the flexural rigidity than on the bearing capacity of the specimens. After rehabilitation, the bearing capacities of specimens reached or even exceeded that of the reference RC specimen, and the strengthening methods seemed to have limited effect on flexural rigidity recovery. From the analysis of moment redistribution of tested beams, elevated temperature is found having different impacts on sagging moment region and hogging moment region. The damage of RC continuous member is definitely a comprehensive response of different regions.

• Advances in concrete construction
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• v.8 no.2
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• pp.145-154
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• 2019

The present experimental study addresses the structural response of reinforced concrete (RC) beams strengthened in shear. Thirteen RC beams were divided into four different sets to investigate the effect of transverse and longitudinal steel reinforcement ratios, concrete compressive strength change and orientation for installing carbon fiber-reinforced polymer (CFRP) laminates. Then, we employed a shear strengthening solution through externally bonded reinforcement in grooves (EBRIG) and externally bonded reinforcement (EBR) techniques. In this regard, rectangular beams of $200{\times}300{\times}2000mm$ dimensions were subjected to the 4-point static loading condition and their load-displacement curves, load-carrying capacity and ductility changes were compared. The results revealed that using EBRIG method, the gain percentage augmented with the increase in the longitudinal reinforcement ratio. Also, in the RC beams with stirrups, the gain in shear strength decreased as transverse reinforcement ratio increased. The results also revealed that the shear resistance obtained by the experimental tests were in acceptable agreement with the design equations. Besides, the results of this research indicated that using the EBRIG system through vertical grooves in RC beams with and without stirrups caused the energy absorption to increase about 85% and 97%, respectively, relative to the control.

• Journal of The Korean Society of Integrative Medicine
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• v.2 no.2
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• pp.31-40
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• 2014

Purpose : To evaluate the effect of cervical strengthening exercise on balance ability in healthy adults. Method : The subjects consisted of forty healthy people. The subjects were divided into two group. The control group(n=14) received no exercise and/or stimulation. The cervical strengthening exercise group(n=14) performed therapeutic intervention using cervical exercise for strengthening of cervical spine muscle. The exercise group were accomplished during 6 weeks(2~3set, 5times/week). All tests were completed before and after experiment. The static balance ability was measured by normal standing when subjects open and close their eyes on GOOD BALANCE SYSTEM, respectively. For each case, the experimental data were obtained in 3 items: mean X speed, mean Y speed and velocity moment. Result : The results of this study were as follows; 1. In the exercise group, the statistically significant difference were shown on X speed and Y speed in the case of normal standing when subjects open and close their eyes and X speed, Y speed and velocity moment in the case of normal standing when subjects close their eyes(p<0.05). 2. In control group, the statistically significant difference were not shown on all posture(p>0.05). 3. There were a statistically significant difference in the X speed and Y speed in the case of normal standing when subjects open their eyes between control group and the exercise group(p<0.05). There were a statistically significant difference in the X speed, Y speed and velocity moment in the case of normal standing when subjects close their eyes between control group and exercise group(p<0.05). Conclusion : The above results revealed that therapeutic intervention for muscle strengthening of cervical there were positive changes to balance ability.

• Journal of the Korean Society for Railway
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• v.12 no.5
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• pp.641-648
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• 2009

Concrete structures become more common in railway systems with an advancement of high speed train technologies. As the service life of concrete structures increases, structural strengthening for concrete structures may be necessary. There are several typical strengthening techniques using steel plate and fiber reinforced polymer (FRP) materials, which have their own inherent shortcomings. In order to enhance greater durability and resistance to fire and other environmental attacks, basalt fiber material attracts engineer's attention due to its characteristics. This study investigates bonding performance of basalt fiber sheet as a structural strengthening material. Experimental variables include bond width, length and number of layer. From the bonding tests, there were three different types of bonding failure modes: debonding, rupture and rip-off. Among the variables, bond width indicated more significant effect on bonding characteristics. In addition the bond length did not contribute to bond strength in proportion to the bond length. Hence this study evaluated effective bond length and effective bond strength. The effective bond strength was compared to those suggested by other researches which used different types of FRP strengthening materials such as carbon FRP.

• The Journal of Korean Academy of Orthopedic Manual Physical Therapy
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• v.15 no.1
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• pp.49-57
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• 2009

Purpose : To evaluate the effects hip abductor strengthening exercise using elastic band on static balance. Methods : The subjects consisted of twenty healthy people. The subjects were divided into two group. The control group(n=10) received no exercise and/or stimulation. The elastic band strengthening exercise(E/E) group(n=10) performed hip abductor for strengthening exercise using elastic band. E/E group were accomplished during 6weeks(3day/week, 30-40min/day). All tests were completed before and after experiment. The static balance ability was measured by normal standing when eye open and close on GOOD BALANCE System, respectively. For each case, the experimental data were obtained in 3 items: mean X speed, mean Y speed and velocity moment. Results : The results of this study were as follows; 1. In E/E group, the statistically significants were shown on Y speed and velocity moment in the case of normal standing when eye open and X speed and velocity moment in the case of normal standing when eye close(p<0.05). 2. In control group, the statistically significants were not shown on all posture(p>0.05). 3. There was a statistically significant difference on the X speed and velocity moment in the case of normal standing when eye close between control group and E/E group(p<0.05). Conclusion : The above results revealed that hip abductor strengthening exercise using elastic band were partly effective for improving the static balance ability.

• PNF and Movement
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• v.19 no.1
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• pp.57-65
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• 2021

Purpose: This study investigated the effects of proprioceptive neuromuscular facilitation (PNF) respiratory muscle strengthening exercise on the pulmonary function, back pain, and disability level of patients with chronic low back pain (CLBP). Methods: There were 24 CLBP patients randomly divided into the experimental group (n = 12) who took part in PNF respiratory muscle strengthening exercise and the control group (n = 12) who performed a mock treatment. Both groups performed their respective interventions for 15 min five times per week for four weeks. The pulmonary function was measured using a portable spirometer. The back pain of the participants was assessed using a visual analogue scale. The Oswestry disability index was conducted to measure disability level. A paired t-test was performed to compare within-group changes before and after the PNF respiratory muscle strengthening exercise. Differences between the experimental and the control groups were analyzed using an independent t-test. For all tests, the level of statistical significance was α = 0.05. Results: The within-group change in pulmonary function was significantly different in the experimental group (p < 0.05), and the levels of back pain and disability were significantly different between the groups (p < 0.05). There was also a significant between-group difference in pulmonary function, back pain, and disability level after intervention (p < 0.05). Conclusion: These results suggest that PNF respiratory muscle strengthening exercise enhances pulmonary function and reduces levels of back pain and disability in patients with CLBP.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.3
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• pp.135-146
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• 2008

In this study, the effect of epoxy mortar panel as the shear strengthening material of reinforced concrete beam is investigated by loading test. The main variables are the kind of strengthening material, the amount of reinforcement and the spacing of CFS(Carbon Fiber Sheet) stirrups. The design method to use epoxy mortar panel as shear strengthening of reinforced concrete beam took the shear capacity as the form of the sum of $V_c$, $V_s$, $V_{sheet}$ and $V_p$. By making a comparison between the values calculated by the proposed shear strength prediction formula and those from the loading test results, the mean value was 1.10 and the standard deviation was 8.16%.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.04a
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• pp.25-29
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• 1994

A series of 6 reinforced concrete beams was tested to verify the effects of EBSP strengthened on cracked beams and to identify the various parameters affecting structure strengthening design(SSD). The parameters were the cross-sectional area of steel plates, the thickness of steel plates, and bond length of steel plates. In addition to these parameters, the effect of existing cracks on the strengthening was investigated. Test results show that EBSP is very effective and predictable for strengthening damaged structures. The results also show that the bond length of steel plates is the most important factor to develop ultimate load carrying capacities of strengthened beams. However, considerations in SSD should be given to assure the ductile failure at ultimate load such as the low ratio of thickness to the width of plates.