• 대한통합의학회지
• /
• 제9권3호
• /
• pp.145-153
• /
• 2021

Purpose : The purpose of this study was to compare and analyze whether there are changes in muscle elasticity when resistance using an elastic band is present or absent during a bridge exercise on an unstable surface with a gymball. Methods : Eighteen healthy adult college students attending E University in Gyeonggi-do, who voluntarily agreed to participate were included in this study. The subjects were instructed to perform the bridge exercise using a gymball both without resistance and with resistance using an elastic band. Myoton was used during the exercise to measure the elasticity of the rectus abdominis and biceps femoris muscles. Results : There was a significant difference in the stiffness of the rectus abdominis muscle on both sides before and after using the elastic band (p<.05). however, no significant difference was observed in the biceps femoris on either side (p>.05). Based on the evaluation of the frequency before and after using the elastic band, no significant difference was observed between the rectus abdominis and biceps femoris muscles on both sides (p>.05). The logarithmic decrement was significantly different in the right rectus abdominis muscle (p<.05), and there was no significant difference in the left rectus abdominis and both biceps femoris (p>.05). Conclusion : Resistance exercise using an elastic band is more effective in improving elasticity of the rectus abdominis muscle than without a elastic band during bridge exercise with a gymball.

• Physical Therapy Rehabilitation Science
• /
• 제9권4호
• /
• pp.287-294
• /
• 2020

Objective: This study aimed to investigate the effects of an ultrasound-based bar graph proportional to the quadriceps muscle thickness as a real-time visual feedback training tool in the elderly. Design: Cross-sectional study. Methods: Twenty-four elderly persons participated in this study and were randomly divided into three groups: oral training group (n=8, group 1), ultrasound imaging group (n=8, group 2), and graph group (n=8, group 3). In the pre condition, all participants performed maximal voluntary isometric contraction (MVIC) of the quadriceps with knee extension three times with oral training. In the post condition, group 1 performed MVIC of the quadriceps with oral training, group 2 performed MVIC of the quadriceps with real-time visual feedback using ultrasound imaging, and group 3 performed MVIC of the quadriceps with real-time visual feedback using a bar graph proportional to the quadriceps muscle thickness, three times for all groups. Muscle thickness, activity (mean, peak), tone, stiffness, logarithmic decrement, relaxation, and creep were measured in both conditions in all participants. Results: Visual feedback with a bar graph showed significant effects on muscle thickness, mean muscle activity, and peak muscle activity compared with oral training and visual feedback with ultrasound imaging (p<0.05). Conclusions: Isometric training of the quadriceps with real-time visual feedback using a bar graph proportional to the quadriceps muscle thickness may be more effective than other methods in improving muscle thickness and muscle activity. This study presented a tool that can help increase muscle thickness in the elderly.

• Earthquakes and Structures
• /
• 제22권2호
• /
• pp.121-135
• /
• 2022

Many public buildings such as schools, hospitals, etc., where partial infill walls are present in reinforced concrete (RC) structures, have undergone undesirable damage/failure attributed to captive column effect during a moderate to severe earthquake shaking. Often, the situation gets worsened when these RC frames are non-ductile in nature, thus reducing the deformable capability of the frame. Also, in many parts of the Indian subcontinent, it is mandatory to use fly-ash bricks for construction so as to reduce the burden on the disposal of fly-ash produced at thermal power plants. In some scenario, when the non-ductile RC frame, partially infilled by fly-ash bricks, suffers major structural damage, the challenge remains on how to retrofit and restore it. Thus, in this study, two full-scale one-bay, one-story non-ductile RC frame models, namely, bare frame and RC partially infilled frame with fly-ash bricks in 50% of its opening area are considered. In the previous experiments, these models were subjected to slow-cyclic displacement-controlled loading to replicate damage due to a moderate earthquake. Now, in this study these damaged frames were retrofitted and an experimental investigation was performed on the retrofitted specimens to examine the effectiveness of the proposed retrofitting scheme. A hybrid retrofitting technique combining epoxy injection grouting with an innovative and easy-to-implement steel jacketing technique was proposed. This proposed retrofitting method has ensured proper confinement of damaged concrete. The retrofitted models were subjected to the same slow cyclic displacement-controlled loading which was used to damage the frames. The experimental study concluded that the hybrid retrofitting technique was quite effective in enhancing and regaining various seismic performance parameters such as, lateral strength and lateral stiffness of partially fly-ash brick infilled RC frame. Thus, the steel jacketing retrofitting scheme along with the epoxy injection grouting can be relied on for possible repair of the structural members which are damaged due to the captive column effect during the seismic shaking.

• 대한통합의학회지
• /
• 제10권2호
• /
• pp.73-83
• /
• 2022

Purpose : Low back pain (LBP) is reported as a risk of experiencing musculoskeletal disorders due to muscle stiffness and hypokinetics. The lumbar spine in an unstable state causes imbalance and lumbar instability. Therefore, This study examined the effects of lumbar stabilization exercise and self-complex exercise program on pain, function, psychosocial level, static balance ability, and transverse abdominal muscle (TrA) thickness and contraction ratio in patients with lumbar instability. Methods : The design of this is a randomized controlled trial (RCT). Twenty-six LBP patients participated in this study. Screening tests were performed and assigned to the experimental group (n=13) and control group (n=13) using a random allocation program. Both groups underwent a lumbar stabilization exercise program. In addition, the experimental group implemented the self-complex exercise program. All interventions were applied three times per week for four weeks. The quadruple visual analog (QVAS), the Korean version of the Oswestry disability index (K-ODI), Korean version of fear-avoidance belief questionnaire (FABQ), static balance ability, TrA thickness, and contraction ratio were compared to evaluate the effect on intervention. Statistical significance was set at 𝛼=.05. Results : Both groups showed significant differences before and after the intervention in QVAS, K-ODI, FABQ, static balance ability, and TrA thickness in contraction (p<.05). In addition, significant differences in K-ODI and FABQ were observed between the experimental group and control group (p<.05). Conclusion : A lumbar stabilization exercise and self-complex exercise program resulted in reduced dysfunctions, psychosocial stability in patients with lumbar instability. Therefore, Lumbar stabilization exercise and self-complex exercise program for patients with lumbar instability are effective method with clinical significance in improving the function and psychosocial stability.

• 한국추진공학회지
• /
• 제26권3호
• /
• pp.10-21
• /
• 2022

우주 발사체 구조인 추진제 탱크는 지상운송, 발사대기, 이륙 및 비행 과정 동안 다양한 정적 및 동적 하중이 작용하여 이에 대해 구조건전성을 보유해야 하며 더불어 추진제를 많이 싣기 위해서 크고 가벼워야 한다. 이런 특성으로 본 연구의 구조 대상인 추진제 탱크 실린더는 얇은 두께를 가지게 되어 실린더 설계에서 압축하중에 의한 좌굴이 중요하게 고려된다. 하지만 기존의 수립된 NASA 및 유럽 등의 좌굴 설계 기준은 상당히 보수적인 값으로 최신 설계 및 제작 기술을 반영하지 못하고 있다. 본 연구에서는 초기 결함이 반영된 다양한 해석 모델을 이용하여 비선형 좌굴 해석을 수행하고 실린더 구조의 새로운 좌굴 설계 기준 수립 방안을 제시한다. 결론적으로 공통격벽 추진제 탱크 실린더 구조의 효과적인 경량 설계가 구현될 수 있음을 확인하였다.

• Composites Research
• /
• 제35권2호
• /
• pp.106-114
• /
• 2022

탄소섬유 강화 플라스틱(CFRP)은 우수한 비강도 및 비강성으로 인하여 항공산업에서 널리 사용되고 있다. CFRP는 대부분 탄소섬유나 프리프레그를 적층한 구조로 사용되고 있으며, 이러한 구조는 박리가 발생할 수 있다는 치명적인 단점이 있다. 이는 보통 두께방향 섬유의 부재에서 기인한다. 본 연구에서는 탄소섬유가 세 방향으로 직조된 3차원 탄소섬유 프리폼 및 이를 적용한 항공기 날개 단위구조체를 제조하였다. 단위구조체는 항공기 날개의 핵심 요소인 스킨, 스트링거, 리브로 구성되며 수지 이송 성형공정을 이용하여 제조하였다. 압축시험을 통하여 기존의 적층형 구조물과 비교한 결과, 3차원 프리폼은 구조물의 박리예방 뿐만 아니라 강도향상에도 효과적임을 보여 주었으며, 이는 3D 프리폼 구조물이 박리 예방을 필요로 하는 다양한 분야, 특히 항공 분야에서 널리 사용될 수 있음을 의미한다.

• Steel and Composite Structures
• /
• 제44권3호
• /
• pp.309-324
• /
• 2022

The post-fire elastic stiffness and performance of concrete-filled steel tube (CFST) columns containing recycled aggregate concrete (RAC) has rarely been addressed, particularly in terms of material properties. This study was conducted with the aim of assessing the modulus of elasticity of recycled aggregate concrete-filled steel tube (RACFST) stub columns following thermal loading. The test data were employed to model and assess the elastic modulus of circular RACFST stub columns subjected to axial loading after exposure to elevated temperatures. The length/diameter ratio of the specimens was less than three to prevent the sensitivity of overall buckling for the stub columns. The gene expression programming (GEP) method was employed for the model development. The GEP model was derived based on a comprehensive experimental database of heated and non-heated RACFST stub columns that have been properly gathered from the open literature. In this study, by using specifications of 149 specimens, the variables were the steel section ratio, applied temperature, yielding strength of steel, compressive strength of plain concrete, and elastic modulus of steel tube and concrete core (RAC). Moreover, parametric and sensitivity analyses were also performed to determine the contribution of different effective parameters to the post-fire elastic modulus. Additionally, comparisons and verification of the effectiveness of the proposed model were made between the values obtained from the GEP model and the formulas proposed by different researchers. Through the analyses and comparisons of the developed model against formulas available in the literature, the acceptable accuracy of the model for predicting the post-fire modulus of elasticity of circular RACFST stub columns was seen.

• Steel and Composite Structures
• /
• 제43권1호
• /
• pp.91-106
• /
• 2022

This paper has focused on presenting a three dimensional theory of elasticity for free vibration of 3D-graphene foam reinforced polymer matrix composites (GrF-PMC) cylindrical panels resting on two-parameter elastic foundations. The elastic foundation is considered as a Pasternak model with adding a Shear layer to the Winkler model. The porous graphene foams possessing 3D scaffold structures have been introduced into polymers for enhancing the overall stiffness of the composite structure. Also, 3D graphene foams can distribute uniformly or non-uniformly in the shell thickness direction. The effective Young's modulus, mass density and Poisson's ratio are predicted by the rule of mixture. Three complicated equations of motion for the panel under consideration are semi-analytically solved by using 2-D differential quadrature method. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. Because of using two-dimensional generalized differential quadrature method, the present approach makes possible vibration analysis of cylindrical panels with two opposite axial edges simply supported and arbitrary boundary at the curved edges. It is explicated that 3D-GrF skeleton type and weight fraction can significantly affect the vibrational characteristics of GrF-PMC panel resting on two-parameter elastic foundations.

• 한국지반공학회논문집
• /
• 제38권9호
• /
• pp.45-52
• /
• 2022

암반내 불연속면이나 지반-구조물의 접촉면은 열-수리-역학적으로 연계된 거동 특성을 보이므로, 온전한 지배방정식에 근거한 경계면 요소의 개발이 필요하다. 본 논문은 경계면 요소에 대한 힘평형 방정식, 유체의 연속방정식 그리고 에너지 평형 방정식을 유도하였다. 그리고 경계면 요소에 대한 탄소성 역학 모델의 강성행렬을 제시하였다. 개발된 유한요소는 2차원 조건에서 변위는 6절점, 수압과 온도는 4절점을 사용한다. 단층내 유체 주입에 대한 완전연계된 THM 해석은 단층내의 유효응력 감소와 주위 암반의 온도 수축에 의한 주입압의 복합적인 변화을 모델링 할수 있었다. 하지만, 열적 현상을 무시한 HM해석은 수리-역학적 변수를 과다하게 산정하였다.

• 대한조선학회논문집
• /
• 제58권6호
• /
• pp.400-406
• /
• 2021

The primary effect of the far-field underwater explosion (UNDEX) is the whipping of the ship hull girder. This paper aims to verify why inelastic effects should be considered in the whipping response estimations from the UNDEX simulations. A navy ship was modeled using Timoshenko beam elements over the ship length uniformly keeping the constant midship section modulus. The transient UNDEX pressure was produced using two types of the Geers-Hunter doubly-asymptotic models: compressible and incompressible fluids. Because the UNDEX model based on incompressible fluid assumption provided more increased fluid volume acceleration in the bubble phase, the incompressible fluid-based UNDEX model was adopted for the inelastic whipping response analyses. The non-linear hull girder bending moment-curvature curve was used to embed inelastic effects in the UNDEX analyses where the Smith method was applied to derive the non-linear stiffness. We assumed two stand-off distances to see more apparent inelastic effects: 40.5 m and 35.5 m. In the case of the 35.5 m stand-off distance, there was a statistically significant inelastic effect in terms of the average of peak moments and the average exceeding proportional limit moments. For the conservative design of a naval ship under UNDEX, it is recommended to use incompressible fluid. In the viewpoint of cost-effective naval ship design, the inelastic effects should be taken into account.