• Journal of the Korea Concrete Institute
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• v.17 no.3 s.87
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• pp.313-322
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• 2005

Recently, as the remodeling market gradually substitute for new construction market and safety diagnosis for reconstruction apartment become a matter of principal Interest, it is demanded that scientific diagnosis and evaluation for existing concrete structure state. And it is increasing that the significance for reliability of data which is used for estimating the concrete compressive strength by nondestructive test. As a result, it is found that different proposal to material age and hitting angle is good to improving the reliability of presumption of concrete compressive strength in the linear hitting rebound test hammer. And for the reason that mutual relation between the compressive strength and rebound degree is highest in linear hitting rebound test hammer 25mm in all portion according to early md middle material age and hitting angle except the early material age $-45^{\circ}$, analysis showed that linear hitting rebound test hammer is more reliable than existing schmidt hammer in presumption of concrete compressive strength.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05d
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• pp.535-542
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• 1996

원전입지에 대한 주민반발문제는 경제성장과 더불어 가일층 증가일로에 있는 전력수요에 안정적으로 대처해야만 한다는 측면에서 시급히 극복해야만 할 사회문제이다. 본 연구에서는 바로 이러한 사회문제를 극복하기 위해 원전입지반발과 주민참여와 관계를 이론적으로 고찰하였고, 또한 삼척 원전 반발사례를 분석하였다. 분석결과, 원전반발과 주민참여는 매우 밀접한 관계에 있는 것으로 나타났다. 즉, 미흡한 주민참여는 원전반발에 직접적인 영향을 미치는 것으로 나타났다. 따라서 원전을 성공적으로 입지시키기 위해서는 정부가 일방적으로 원전정책을 결정하고 집행해서는 곤란하며, 원전정책에 반드시 지역주민들의 의사를 적극적으로 반영할 필요가 있다.

• Physical Therapy Korea
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• v.5 no.4
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• pp.20-29
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• 1998

연구의 배경 앉은 자세에서 일어서기는 일상생활동작중 흔한 동작중의 하나이다. 노인들을 포함한 많은 환자들은 앉은 자세에서 일어서기에 어려움이 있고 속도가 감소한다. 이 연구의 목적은 다른 두 속도로 앉은 자세에서 일어서는 동작을 실행할 때 최대 지면반발력의 세개의 요소를 비교하는 것이다. 대상자 22명의 건강한 성인 (20-36세)을 대상으로 하였다. 실험방법 앉은 자세에서 일어서기동작 수행중 최대 지면반발력을 측정하기 위하여 힘판을 사용하였다. 대상자들은 메트로놈을 이용하여 각각 느린 속도 (3초: 총 앉은 자세에서 일어서기동작 수행시간)와 빠른 속도(1.5초)에서 앉은 자세에서 일어서기를 수행하였다. 느린 속도와 빠른 속도중 최대 지면반발력을 비교하기 위해 짝비교 t-검정을 사용하였다. 결과 빠른 속도시 최대 지면반발력의 수직(p<0.05), 전-후(p<0.05), 내-외(p<0.05) 요소에서 느린 속도시와 차이가 있었다. 최대 지면반발력의 모든 요소가 움직임의 속도의 증가에 비례하여 증가하였다. 토의 및 결론 빠른 속도의 앉은 자세에서 일어서기를 수행하기 위해서는 최대 지면반발력의 수직, 전-후요소의 추진력이 요구된다. 최대 지면반발력의 내-외요소는 상전방으로 작용하는 모멘트의 증가에 대한 제동력으로 생각된다. 또한, 빠른 속도로 앉은 자세에서 일어서기 동작을 수행하기 위하여 추진력은 일어서는 순간의 모멘트에 대한 지면반발력의 내-외요소에 영향을 미친다. 이라한 결과들은 앉은 자세에서 일어서기 동작에 어려움을 갖는 노인이나 환자들의 노력을 덜기위해 느린 속도의 움직임이 필요함을 제안한다.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.782-788
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• 2002

Several non-destructive test methods have been developed to estimate compressive strength of concrete in other countries. However, their applications are limited in domestic concrete due to their inaccuracies. The purpose of this study is to propose an aging coefficient of compressive strength of structural concrete in rebound number method and ultrasonic pulse velocity method for domestic concrete. The test variables include type of aggregate, curing condition, and compressive strength. Two approaches are used to estimate aging coefficient. One is evaluated by uniform linear regression equation for all ages and shows uniform strength reduction coefficient regardless of material properties and the other is evaluated by individual regression equation for each ages and shows nonuniform strength reduction and rebound increasing coefficients which decrease with increasing of rebound number and compressive strength. The latter result which can include the effect of rebound number and compressive strength is more resonable than the former.

• The Journal of the Convergence on Culture Technology
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• v.6 no.4
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• pp.655-661
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• 2020

In this study, the correlation between concrete core compressive strength and rebound hardness of urban railway underground structures was analyzed. The equations for the range of rebound hardness were derived and compared with the measured concrete core strengths for each range of rebound hardness to confirm the adequacy of the estimated compressive strength. As the result, the linear regression analysis results of the average compressive strength by the Gaussian probability density function (representative compressive strength estimation formula) and the estimation formula by the rebound hardness range were founded to match well within 3% of the experimental concrete core compressive strength test results. Therefore, the stochastic statistical analysis using the rebound hardness measurement results suggested in this study could be help to secure the confidence level of the correlation between the rebound hardness and the concrete compressive strength which are relatively large deviation according to the estimation equations.

• Journal of the Korean GEO-environmental Society
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• v.18 no.2
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• pp.39-45
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• 2017

This paper is to grasp the applicability of a cumulative rebound angle measured from the rebound action generated after impacting an object for the assessment of compressive strength of construction materials nondestructively and to propose the test results. For this study, an impact device was devised and used for impacting an object by an initial rotating free falling impact and following repetitive impacts from the rebound action which eventually disappears. Five types of construction materials, which are soil cement, cement paste, wood (pine tree), and two types of rock (shale and granite), were tested and both peak rebound angle and cumulative rebound angle were measured for each material by using a high-speed camera. The measured angles were compared with the directly measured compressive strength for each material. The comparison showed that for materials such as cement and rock the cumulative rebound angle, which reflects energy dissipation, rather than the peak rebound angle is more appropriate indicator for assessing the compressive strength of a material, but for a construction material such as wood which has a high toughness the magnitude of rebound is not an indicator to assess the compressive strength of a material.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.6
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• pp.599-607
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• 2011

In this paper, a reaction-force compensation system for an XY linear motion stage, without an additional external isolation structure or extra motors, is developed. This system consists of a movable magnet track, a spring, a dummy weight, and a dedicated sensor module that measures the relative positions of the movable magnet track with respect to the motor coil. The reaction force compensation system is modeled, and simulations are carried out to optimize design parameters such as the moving distance of the magnet track, the transmission force, the dummy weight, and the allowed size of the mechanism. An XY linear motion stage is built, incorporating the reaction force compensation system, and the performance of the system is verified experimentally. For acceleration and deceleration values of 10 m/$s^2$, 85% of the reaction force is absorbed by the reaction force compensation system.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.6
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• pp.371-383
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• 2021

Steel-concrete single-leaf blast-resistant doors, having steel box and slab inside, are installed on the wall using supporting members such as hinges and latches. Several studies have been conducted on their deflection behavior in the same direction as that of the blast pressure, but studies on their deflection behavior in the opposite direction, that is, studies on negative deflection behavior are relatively insufficient. In this study, we conducted a parameter analysis using finite element analysis on blast-resistant doors, on their rebound behavior in the negative deflection phase. Results revealed that the plastic deformation of the door, and the change in momentum and kinetic energy during rebound, were major factors influencing the rebound behavior. Greater rebound force was developed on the supporting members in the impulsive region, than in the quasi-static region; due to the characteristics in the impulsive region, where the kinetic energy developed relatively greater than the strain energy. In the design process, it is necessary to consider excessive deformation that could occur in the supporting members as the rebound behavior progresses. Additionally, it was found that in the case of steel-concrete blast doors, the rebound force increased relatively more, when the effects of both rebound and negative blast pressure contributed to the negative deflection of the door. Since conditions for the occurrence of this superposition effect could vary depending on structural characteristics and explosion conditions, further investigation may be required on this topic.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.3
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• pp.199-207
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• 2008

As infrastructures are being deteriorated, nondestructive evaluation of existing structures and construction quality control are increasingly demanded. The importance of predicting compressive strength of concrete structure is also gradually increasing in construction industry. The estimation of concrete compressive strength is a critical factor of the construction management and quality control. This study has been conducted using Schmidt hammer test and Impact echo method, which are nondestructive test methods for the comparison of the concrete compressive strength. It is focusing to examine the relationship between compressive strength of concrete and rebound number by Schmidt hammer test result by Impact echo method. It was found that concrete compressive strength and rebound number have a close correlation.

• Journal of the Korean Magnetics Society
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• v.9 no.1
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• pp.48-54
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• 1999

For the high speed linear motor and the transportation device at clean room, a magnetic levitation rail without contact using the repulsive force of permanent magnets was newly developed. The characteristics of repulsive and lateral forces of the magnetic levitating system using permanent magnet was studied and the devised magnetic levitating system was evaluated by analytical and experimental approaches. This system is composed of two fixed guide rails with the rare earth permanent magnet array and a moving unit which is attached two magnet pairs at each sides. Because this system was forcedly levitated by the face to face repulsive forces, levitating air gap length can be repulsive force of an auxiliary magnetic repulsion system on the center of moving unit.