• Geomechanics and Engineering
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• 제34권2호
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• pp.197-208
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• 2023

Rate-dependent mechanical response of sand, subjected to loading of medium to high strain rate range, is of interest for several civilian and military applications. Such rate-dependent response can vary significantly based on the initial density state of the sand, applied confining pressure, considered strain rate range, drainage condition and sand morphology. A numerical study has been carried out employing a recently proposed visco-plastic constitutive model to explore the rate-dependent mechanical behaviour of Toyoura sand under drained triaxial loading condition. The model parameters have been calibrated using the experimental data on Toyoura sand available in published literature. Under strain rates higher than a reference strain rate, the simulation results are found to be in good agreement with the experimentally observed characteristic shearing behaviour of sand, which includes increased shear strength, pronounced post-peak softening and suppressed compression. The rate-dependent response, subjected to intermediate strain rate range, has further been assessed in terms of enhancement of peak shear strength and peak friction angle over varying initial density and confining pressure. The simulation results indicate that the rate-induced strength increase is highest for the dense state and such strength enhancements remain nearly independent of the applied confinement level.

• Advances in concrete construction
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• 제14권2호
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• pp.79-92
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• 2022

The amount and configuration of transverse reinforcement are known as critical parameters that significantly affect the lateral confinement of concrete, the ductility capacity, and the plastic hinge length of RC columns. Based on test results, this study investigated the effect of the three variables on structural indexes such as neutral axis depth, lateral expansion of concrete, and ductility capacity. Five reinforced concrete column specimens were tested under cyclic flexure and shear while simultaneously subjected to a constant axial load. The columns were reinforced by two types of reinforcing steel: rectangular hoops and spiral type reinforcing bars. The variables in the test program were the shape, diameter, and yield strength of transverse reinforcement. The interactive influence of the amount of transverse reinforcement on the structural indexes was evaluated. Test results showed that when amounts of transverse reinforcement were similar, and yield strength of transverse reinforcement was 600 MPa or less, the neutral axis depth of a column with spiral type reinforcing bars was reduced by 28% compared with that of a column reinforced by existing rectangular hoops at peak strength. While the diagonal elements of spiral-type reinforcing bars significantly contributed to the lateral confinement of concrete, the strain of diagonal elements decreased with increases of their yield strength. It was confirmed that shapes of transverse reinforcement significantly affected the lateral confinement of concrete adjacent to plastic hinges. Transverse reinforcement with a yield strength exceeding 600 MPa, however, increased the neutral axis depth of normal-strength concrete columns at peak strength, resulting in reductions in ductility and energy dissipation capacity.

• Geomechanics and Engineering
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• 제31권5호
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• pp.461-476
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• 2022

Research studies on the scale effect on triaxial strength of intact rocks are scarce, being more common those in uniaxial strength. In this paper, the authors present and briefly interpret the peak and residual strength trends on a series of triaxial tests on different size specimens (30 mm to 84 mm diameter) of an intact granitic rock at confinements ranging from 0 to 15 MPa. Peak strength tends to grow from smaller to standard-size samples (54 mm) and then diminishes for larger values at low confinement. However, a slight change in strength is observed at higher confinements. Residual strength is observed to be much less size-dependent. Additionally, this study introduces preliminary modelling approaches of these laboratory observations with the help of three-dimensional particle flow code (PFC3D) simulations based on bonded particle models (BPM). Based on previous studies, two modelling approaches have been followed. In the first one, the maximum and minimum particle diameter (D_max and D_min) are kept constant irrespective of the sample size, whereas in the second one, the resolution (number of particles within the sample or ϕ_v) was kept constant. Neither of these approaches properly represent the observations in actual laboratory tests, even if both of them show some interesting capabilities reported in this document. Eventually, some suggestions are provided to proceed towards improving modelling approaches to represent observed scale effects.

• 펄프종이기술
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• 제31권1호
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• pp.79-88
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• 1999

The stability and performance (peel strength) of the acrylic copolymer and various modified rosin systems were investigated. The peel strength was measured over a wide range of scaling rates, and the influence of the viscoelasticity of the PSA(pressure sensitive adhesive) was considered. In the case of miscible systems, the peak of peel strength (PSA performance) over wide peel rates was changed and modified systematically with increasing glass transition temperature of the blends. The peak of the peel strength for blended systems shifts toward the lower rate side as glass transition temperature ($T_g$) of the blend increased. The influence of esterification of the rosin on performance and stability against deterioration was greatly modified by blending with rosin of glycerol ester and rosin pentaerythritol ester. The failure mode of the blend varies with the combination with acrylic copolymer and modified rosin, and cohesive failure was found at a lower peel rate while interfacial failure was found at a high peel rate. A few systems where a single Tg could be measured, despite the fact that two phases were observed microscopically, were detected.

• 터널과지하공간
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• 제4권3호
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• pp.261-273
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• 1994

Direct shear tests were carried out on the rock joints and artificial discontinuities to investigate the influence of joint roughness on the shear strength and deformation behaviour. Single direct shear testing apparatus used in experiment was designed and manufactured. Its capacity is 200 tons of shear load, 20 tons of normal load and 50$\textrm{cm}^2$ of maximum shear area. Test samples were cement mortar with artificial discontinuity and sandstone with natural joint. Peak shear strength was increased as joint roughness or normal stress was increased, especially, linearly increased with roughness angle in cement mortar. If joint roughness angle was constant at low normal stress, shear strength was not affected by width and height of joint roughness in cement mortar. Peak shear strengths obtained from tests were larger than the values calculated by Barton's equation, and shear stiffness was increased with joint roughness coefficient.

• 한국산학기술학회논문지
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• 제18권10호
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• pp.442-447
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• 2017

이 연구의 목적은 등속성 장비를 이용하여 고등학교 야구선수들을 대상으로 주관절 근육의 평가 기준치를 설정하는데 있다. 상지에 의학적으로 문제가 없는 고등학교 야구선수 201명을 대상으로 하였다. 주관절 검사는 HUMAC NORM(CSMI, USA) system을 이용하여 굴곡, 신전운동을 부하속도 $60^{\circ}/sec$에서 4회를 실시하였으며, 절대근력(peak torque)와 상대근력(peak torque % body weight)을 측정하였다. Cajori의 5단계(6.06%, 24.17%, 38.30%, 24.17%, and 6.06%)로 구분한 구간추정(interval estimation)방식에 의해 평가 기준치를 나타내었다. 이 연구의 결과에서 각속도 $60^{\circ}/sec$에서 주관절의 절대근력(peak torque) 굴근의 평균은 $37.88{\pm}8.14Nm$ 신근은 $44.59{\pm}11.79Nm$으로 나타났으며, 상대근력(peak torque % body weight) 굴근의 평균은 $50.06{\pm}8.66Nm$ 신근은 $58.28{\pm}12.84Nm$로 나타났다. 각속도 $60^{\circ}/sec$에서 주관절 굴근(flexer)과 신근(extensor)의 절대근력(peak torque)과 상대근력(peak torque % body weight)의 평가기준치는 설정하였다. 이 연구에서 분석 된 결과를 토대로 다음과 같이 결론을 이끌어 냈다. 주관절은 야구선수들에게 가장 많이 발생되는 손상임에도 불구하고 국내외 주관절 근력에 관한 연구가 미비한 실정이다. 주관절 손상을 예방하고 경기력 향상을 위해 상대적 근력 수준과 훈련효과를 보다 객관적으로 평가할 수 있는 근력 척도가 필요하다. 주관절의 절대근력과 상대근력의 평가기준치를 제시함으로서 고교선수, 야구지도자, 선수트레이너, 재활전문가 등에게 손상회복 및 재활 복귀 시 유용하게 자료가 될 것으로 생각되며, 객관적인 임상 평가 데이터로 활용하는 데 매우 유용한 정보라고 사료된다.

• Geomechanics and Engineering
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• 제14권4호
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• pp.387-398
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• 2018

The present study evaluates the interface shear strength between sand and different construction materials, namely steel and concrete, using direct shear test apparatus. The influence of surface roughness, mean size of sand particles, relative density of sand and size of the direct shear box on the interface shear behavior of sand with steel and concrete has been investigated. Test results show that the surface roughness of the construction materials significantly influences the interface shear strength. The peak and residual interface friction angles increase rapidly up to a particular value of surface roughness (critical surface roughness), beyond which the effect becomes negligible. At critical surface roughness, the peak and residual friction angles of the interfaces are 85-92% of the peak and residual internal friction angles of the sand. The particle size of sand (for morphologically identical sands) significantly influences the value of critical surface roughness. For the different roughness considered in the present study, both the peak and residual interaction coefficients lie in the range of 0.3-1. Moreover, the peak and residual interaction coefficients for all the interfaces considered are nearly identical, irrespective of the size of the direct shear box. The constitutive modeling of different interfaces followed the experimental investigation and it successfully predicted the pre-peak, peak and post peak interface shear response with reasonable accuracy. Moreover, the predicted stress-displacement relationship of different interfaces is in good agreement with the experimental results. The findings of the present study may also be applicable to other non-yielding interfaces having a similar range of roughness and sand properties.

• PNF and Movement
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• 제17권2호
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• pp.303-310
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• 2019

Purpose: This study aimed to investigate the correlation between abdominal muscle strength and measures of respiratory function in stroke patients. Methods: The study participants comprised 17 (male: 12, female: 5) stroke patients hospitalized at W rehabilitation hospital in Busan, South Korea. Abdominal muscle strength was assessed using a digital manual dynamometer for 5 seconds contacting the sternal notch of the participants to bend the trunk. Respiratory function (forced vital capacity, forced expiratory volume in one second, forced expiratory volume in one second/forced vital capacity, and peak expiratory flow) was assessed using a spirometer. The collected data were analyzed using Pearson's correlation analysis, and the significance level was set 0.05. Results: A statistically significant correlation was found between abdominal muscle strength and forced vital capacity, forced expiratory volume in one second, and peak expiratory flow. However, abdominal muscle strength and forced expiratory volume in one second/forced vital capacity were not significantly correlated. Conclusion: This study demonstrated that there is a relationship between abdominal muscle strength and respiratory function. Exercise programs to strengthen the abdominal muscles are therefore necessary to improve respiratory function in stroke patients.

• Steel and Composite Structures
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• 제37권6호
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• pp.649-662
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• 2020

Although several types of rigid shear connectors have been developed particularly to increase load-carrying capacity, application is limited due to the complicated details of such connection. In this study, push-out tests were performed for specimens with hybrid shear connectors using headed studs and shear plates to identify the effects of each parameter on the structural performance of such shear connection. The test parameters included steel ratios of headed stud to shear plate, connection length, and embedded depth of shear plates. The peak strength and residual strength were estimated using various shear transfer mechanisms such as stud shear, concrete bearing, and shear friction. The hybrid shear connectors using shear plates and headed studs showed large load-carrying capacity and deformation capacity. The peak strength was predicted by the concrete bearing strength of the shear plates. The residual strength was sufficiently predicted by the stud shear strength of headed studs or by shear friction strength of dowel reinforcing bars. Further, the finite element analysis was performed to verify the shear transfer mechanism of the connection with hybrid shear connector.

• The Journal of Korean Physical Therapy
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• 제23권6호
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• pp.37-42
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• 2011

Purpose: The aim of this study is to suggest the basic materials for proposing effective and efficient methods when stretching by measuring isokinetic muscular strength according to static, dynamic and PNF stretching. Methods: This study was conducted on 45 healthy persons (male and female) in their twenties who are attending universities. The subjects are randomly divided into three (3) groups, and static stretching is applied in group 1, dynamic stretching is applied in group 2 and PNF stretching is applied in group 3. After carrying out static, dynamic and PNF stretching, peak torque was measured using isokinetic muscular strength measurement. Results: According to the results, at $60^{\circ}$/sec and $180^{\circ}$/sec isokinetic peak torque of the knee joint according to types of stretching, the largest changes were shown in Group 2 extension and flexion, and the least changes were shown in Group 1. There were significant differences among the three groups (p<0.05), and the result of after-analysis by LSD showed that there were significant differences between Groups 1 and 2, and Groups 1 and 3 (p<0.05). Conclusion: The intention of this study was to determine the peak torque using Cybex after applying three stretching methods to hamstring muscles, and the case of dynamic and PNF stretching was found to be more significant in both the $60^{\circ}$/sec and $180^{\circ}$/sec angular speeds than that of static stretching. Using the results of such studies, if dynamic and PNF stretching are applied together with warming-up before performing sports, the risk of suffering wounds would reduce and the exactness of sports would increase.