• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.181-184
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• 2008

콘크리트는 비교적 내화성이 있는 재료이다. 그러나 화재 등의 고온에 장기 노출될 경우는 콘크리트 강도 등이 급격하게 저하하는 현상이 발생한다. 이와 같은 경우, 저강도 콘크리트를 일반 비파괴검사 강도추정식을 이용하여 추정하는 것은 적절하지 않다. 이 문제를 해결하기 위해 각종 배합조건의 콘크리트시편을 200, 400, 600, $800^{\circ}C$의 온도변화 조건에서 가열한 후, 초음파속도와 콘크리트강도간의 상관관계를 분석하였다. 아울러 이들 결과를 통해 고온에서 손상된 콘크리트 비파괴검사 강도추정식을 제안하였다.

• 대한토목학회논문집
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• 제7권4호
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• pp.61-71
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• 1987

콘크리트의 품질판정기준(品質判定基準)은 재령(材令) 28일(日)의 압축강도(壓縮强度)이지만, 실질적인 품질관리(品質管理)를 위해서는 조기(早期)에 강도(强度)를 파악해야 한다. 콘크리트 강도(强度)를 조기판정(早期判定)하는 방법은 크게 "강도촉진법(强度促進法)"과 굳지 않은 콘크리트의 "분석법(分析法)"이 있으나, 본(本) 연구(硏究)에서는 $70^{\circ}C$의 열수양생법(熱水養生法)으로 다양한 양생방법을 시도하여 기존의 외국기준(外國規準)보다 개선된 방법을 제시하였다. 실험자료의 분석(分析)에 있어서는 각 강도의 변동을 검토함은 물론, 합리적인 추정식(推定式)을 제안하기 위하여 각 강도의 분포(分布)를 고려하고 확률적(確率的) 관계(關係) 및 품질기준(品質基準)의 적합성(適合性)을 검토하였다. 실험결과 촉진강도(促進强度)의 변동은 비교적 작게 나타났으며, 본 연구에서 제안한 대부분의 방법이 좋은 상관성(相關性)을 가지고 있어 유용한 조기판정방법(早期判定方法)으로 판명되었다.

• Computers and Concrete
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• 제7권3호
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• pp.271-283
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• 2010

Testing of ultrasonic pulse velocity (UPV) is one of the most popular and actual non-destructive techniques used in the estimation of the concrete properties in structures. In this paper, artificial neural network (ANN) approach has been proposed for the evaluation of relationship between concrete compressive strength, UPV, and density values by using the experimental data obtained from many cores taken from different reinforced concrete structures with different ages and unknown ratios of concrete mixtures. The presented approach enables to find practically concrete strengths in the reinforced concrete structures, whose records of concrete mixture ratios are not yet available. Thus, researchers can easily evaluate the compressive strength of concrete specimens by using UPV values. The method can be used in conditions including too many numbers of the structures and examinations to be done in restricted time duration. This method also contributes to a remarkable reduction of the computational time without any significant loss of accuracy. Statistic measures are used to evaluate the performance of the models. The comparison of the results clearly shows that the ANN approach can be used effectively to predict the compressive strength of concrete by using UPV and density data. In addition, the model architecture can be used as a non-destructive procedure for health monitoring of structural elements.

• 대한기계학회논문집A
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• 제20권12호
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• pp.3847-3855
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• 1996

In order to study the relationship between static and cynamic behaviors of silion caride, both quasi-static indentaiton and impact experiments of spherical particle have been conducted. The difference inmaterial behavior when using the two mehtods suggests a loading rate difference in the damate pattrern and fracture strength of silicon carbide. This investigation showed some difference in damage pattern according to particla property, especially inthe case of particle impact. There was no differences in deformation behaviors according to the loading rate when the crater profiles were compared with each other at the same contact radius. From the result of residual strength evaluation, it was found that the strength degradation began at the initiation of ring crack and its behavior was colsely related to morphologies of the damage developed which was also dependent upon the extent of deformation atthe loaidng point. In the case of static indentation, there didnot exist the particle property effects onthe strength degradation behavior.

• 천문학회보
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• 제37권2호
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• pp.114.1-114.1
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• 2012

To measure the magnetic field strength in the solar corona, we examined 10 fast (>1000 km/s) limb coronal mass ejections (CMEs) that show clear shock structures in Solar and Heliospheric Observatory/Large Angle and Spectrometric Coronagraph images. By applying the piston-shock relationship to the observed CME's standoff distance and electron density compression ratio, we estimated the Mach number, Alfven speed, and magnetic field strength in the height range 3-15 solar radii (Rs). The main results from this study are as follows: (1) the standoff distance observed in the solar corona is consistent with those from a magnetohydrodynamic model and near-Earth observations; (2) the Mach number as a shock strength is in the range 1.49-3.43 from the standoff distance ratio, but when we use the density compression ratio, the Mach number is in the range 1.47-1.90, implying that the measured density compression ratio is likely to be underestimated owing to observational limits; (3) the Alfven speed ranges from 259 to 982 km/s and the magnetic field strength is in the range 6-105 mG when the standoff distance is used; (4) if we multiply the density compression ratio by a factor of two, the Alfven speeds and the magnetic field strengths are consistent in both methods; and (5) the magnetic field strengths derived from the shock parameters are similar to those of empirical models and previous estimates.

• 한국산학기술학회논문지
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• 제16권2호
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• pp.1541-1548
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• 2015

본 연구에서는 공동주택 바닥미장 모르타르의 균열을 저감하기 위하여 균열 방지제, 고성능 감수제, 수지 등의 재료혼입에 따른 균열촉진실험을 실시하였다. 그 결과 고성능 감수제와 수지를 혼입한 시편이 균열방지제를 사용한 시편보다 균열수와 압축강도에서 더 우수한 결과를 나타내었다. 그리고 가장 높은 압축강도를 나타낸 시편이 상대적으로 매우 적은 균열을 나타냈으며, 가장 낮은 압축강도를 나타낸 시편에서 많은 균열을 관찰할 수 있었다. 그러므로 압축강도가 우수한 시편이 균열 저항성도 우수한 것으로 나타나 압축강도와 균열저항성은 비례하는 것으로 측정되었다. 모의부재 실험을 바탕으로 실제 아파트 현장에 적용된 배합 3의 장기 모니터링 결과, 장기 재령에서 균열발생이 전혀 관찰되지 않았다.

• 한국운동역학회지
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• 제23권2호
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• pp.149-157
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• 2013

In the present study, we aimed to elucidate how muscle strength and activity are affected by movement pattern(bilateral [BLM] & unilateral movement [ULM]) and movement velocity($0^{\circ}$/s, $60^{\circ}$/s, $120^{\circ}$/s) at maximum effort, and to elucidate the relationship between a left/right asymmetry and bilateral deficit. A total of 18 healthy males participated in the study. Each participant performed maximum knee extension bilaterally and unilaterally while the EMG and moment were recorded, and then the relationships between the asymmetry and bilateral deficit were analyzed. The peak moments for the isokinetic motion at $60^{\circ}$/s and $120^{\circ}$/s and overall muscle activities of lower extremity were significantly reduced for the BLM in comparison to the ULM. And though the asymmetry in ULM were maintained during BLM at all velocities, the bilateral deficits at the velocity of $0^{\circ}\acute{y}$/s and $120^{\circ}\acute{y}$/s were significantly correlated with increased asymmetries of muscle strength in ULM. In conclusion, the reduction in the muscle strength exhibited in bilateral knee extension was shown to arise partially from a reduction in muscle activity, and left/right asymmetry was found to be associated with mechanical reduction in bilateral movement. These findings suggest that training aimed at increasing muscle strength must involve methods and strategies intended to reduce left/right asymmetry.

• 동력기계공학회지
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• 제17권4호
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• pp.72-78
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• 2013

Compacted graphite iron 340 was carried out the heat treatment from 873 to 1,273 K. Compacted graphite iron 340 was evaluated relationship between the sound velocity, the attenuation coefficient and the tensile strength. The obtained results are as following. The signal strength of C scan images were weak according to increasing of heat treatment temperature and time. The amplitude of A scan and B scan was also low. This can be cause that the graphite was grown into the type of vermicular, and the many of grain boundary with ultrasound scattering were increase. The sound velocity was depend upon the heat treatment temperature and time, the attenuation coefficient had nothing to do with the temperature and time. The higher the heat treatment temperature, the tensile strength and the sound velocity were decreased. However, the tensile strength was proportional to the sound velocity. The higher tensile strength, the faster the sound velocity.

• 한국운동역학회지
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• 제31권4호
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• pp.227-233
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• 2021

Objective: The purpose of this study was to in this study. The maximum grip force of the elderly hand was measured using a custom-designed grasping apparatus mounted with five three-component force transducers. The Jebsen-Tayler hand function test and Purdue Pegboard test were performed to evaluate the dexterity of the hand. Method: Twenty-six elderly women participated in the left hand between the maximum grip force and the Jebsen-Taylor hand function test results (r=-.513, p=.007). A significant correlation was also shown in the hand maximum grip force and the hand Purdue Pegboard results (r=.514, p=.007). However, no significant correlation was found in the right hand. Results: We found a significant correlation investigate the relationship between hand grip strength and hand dexterity in the elderly. Conclusion: Our findings in the current study support the theory of 'Strength-dexterity complementariness' which states that improvement in dexterity is associated with the grip force strength.

• Geomechanics and Engineering
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• 제18권5호
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• pp.471-480
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• 2019

The constructions of engineering structures such as airports, highways and railway on clayey soils may create many problems. The economic losses and damages caused by these soils have led researchers to do many studies using different chemical additives for the stabilization of them. Lime is a popular additive used to stabilize the clayey soils. When the base course is stabilized by mixing with an additive, inevitable delays may occur during compaction due to reasons like insufficient workers, breakdown of compaction equipment, etc. The main purpose of this study is to research the effect of compaction delay time (7 days) on the strength, compaction, and dynamic properties of a clay soil stabilized with lime content of 0, 3, 6, 9, 12 and 15% by dry weight of soil. Compaction characteristics of these mixes were determined immediately after mixing, and after 7 days from the end of mixing process. Within this context, unconfined compressive strength (UCS) under the various curing periods (uncured, 7 and 28 days) and dynamic triaxial tests were performed on the compacted specimens. The results of UCS and dynamic triaxial tests showed that delayed compaction on the strength of the lime-stabilized clay soil were significantly effective. Especially with the lime content of 9%, the increase in the shear modulus (G) and UCS of 28 days curing were more prominent after 7 days mellowing period. Because of the complex forms of hysteresis loops caused by the lime additive, the damping ratio (D) values differed from the trends presented in the literature and showed a scattered relationship.