• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.30-31
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• 2014

Since consists of regression equation by penetration depth prediction calculated by existing NDRC formula mainly considers properties of projectile, impact velocity, compressive strength as parameter, it is difficult to apply it to fire reinforced concrete. In this study, scabbing limit thickness was predict considering fiber reinforcement effect by local fracture of concrete was evaluated through high-velocity impact test. As a result of applying fracture reduction coefficient to NDRC, it was possible to predict scabbing limit thickness of fiber reinforced concrete similarly with actual measurement.

• Journal of the Korea Concrete Institute
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• v.27 no.2
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• pp.157-167
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• 2015

Cement composites subjected to high-velocity projectile shows local failure and it can be suppressed by improvement of flexural toughness with reinforcement of fiber. Therefore, researches on impact resistance performance of cement composites are in progress and a number of types of fiber reinforcement are being developed. Since bonding properties of fiber with matrix, specific surface area and numbers of fiber are different by fiber reinforcement type, mechanical properties of fiber reinforced cement composites and improvement of impact resistance performance need to be considered. In this study, improvement of flexural toughness and failure reduction effect by impact of high-velocity projectile have been evaluated according to fiber type by mixing steel fiber, polyamide, nylon and polyethylene which are have different shape and mechanical properties. As results, flexural toughness was improved by redistribution of stress and crack prevention with bridge effect of reinforced fibers, and scabbing by high-velocity impact was suppressed. Since it is possible to decrease scabbing limit thickness from impact energy, thickness can be thinner when it is applied to protection. Scabbing of steel fiber reinforced cement composites was occurred and it was observed that desquamation of partial fragment was suppressed by adhesion between fiber and matrix. Scabbing by high-velocity impact of synthetic fiber reinforced cement composites was decreased by microcrack, impact wave neutralization and energy dispersion with a large number of fibers.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.11a
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• pp.30-31
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• 2015

High velocity impact of projectile generate local failure such as penetration, scabbing, perforation on concrete. It has been reported that local failure is affected by such as nose shape, mass of projectile. In this study, comparing and weighing the impact failure properties of concrete by high velocity impact test that using spherical nose and flat nose type projectile. As a result, It was considered that scabbing of Flat nose projectile reduced more than spherical nose projectile by dispersion of impact force.

• Magazine of the Korea Concrete Institute
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• v.4 no.2
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• pp.127-137
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• 1992

원자력발전소의 콘크리트 격납용기구조물등과 같이 안전성이 높게 요구되는 구조물들은 예기치 않은 혹은 부주의한 사고로 인하여 발생하는 비산물체에 의한 충격에 충분히 저항할 수 있도록 설계되어야 한다. 이러한 물체에 의한 충격은 벽면의 국부적인 피해와 벽 전체의 전반휨응답으로 나타나며, 이에 저항하기 위해서는 벽체의 관통이나 스캐빙(scabbing)이 일어나지 않도록 벽두께를 결정하여야 하고 또한, 파괴가 일어나지 않도록 벽체를 설계하여야 한다. 본 논문에서는 지금까지 연구된 충격현상에 대한 이론 및 실험결과를 토대로 하여 벽면의 국부효가 발생시 이와 동시에 진행되는 탄성효과 및 전반거동효과를 고려하여 관입깊이를 계산할 수 있는 이론을 유도하였으며, 기존의 실험결과를 이용하여 이론적인 결점을 보완한 반이론식을 제안하였다. 또한, 본 논문에서는 실험결과와 기존식성충격과 소성충격을 구분짓는 스폴링속도에 대한 개념을 제시하였다. 본 논문은 충격을 받는 철근콘크리트 구조물의 벽체설계에 유용한 토대를 제공할 것으로 사료된다.

• Biomolecules & Therapeutics
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• v.5 no.2
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• pp.133-149
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• 1997

4-week repeated dose toxicity of DA-5018, a new capsaicin analogue analgesic agent, was examined in 5D rats at dosage levels of 0,0.4,2, 10 and 50 mg/kg/day. DA-5018 was administered orally to 17 males and 17 females per group at doses of 0, 10 and 50 mg/kg and to 12 males and 12 females per group at doses of 0.4 and 2 mg/kg. After the administration period, 5 males and 5 females at the 0, 10 and 50 mg/kg were placed on withdrawal for 2 weeks. Treatment-related clinical signs were observed at 10 and 50 mg/kg. Clinical signs observed immediately after the administration of DA-5018 were grooming, sedation or depression, lacrimation, atacia, reddening of extremities and ears, ventral or lateral recumvincy, respiratory distress, cyanosis and convulsion. Delayed-type clinical signs including focal scabbing and depilation around nose were also observed 1 or 2 weeks after the start of administration of DA-5018. Only at the 50 mg/kg group, corneal opacities, reduced body weight gain (male) and death (male 6/17, female 3/17) were noted. In blood biochemical analysis, serum levels of glucose and triglyceride decreased at 10 and 50 mg/kg. In hematological examination, there were increases in the number of red blood cell, hemoglobin content and percent of hematocrit at 10 and 50 mg/kg. Pulmonary enlargement and hemorrhagic spot, focal scabbing and depilation around nose and corneal opacities were seen at the necropsy of the animals died during the dosing of DA-5018 50 mg/kg. Focal scabbing and depilation around nose were observed in the animals terminally necropsied at doses of 10 and 50 mg/kg. Histopathological examination revealed pulmonary hemorrhage, focal necrosis in the scabbed area, corneal necrosis, fibrosis and neovasculization in the stroma. At 0.4 and 2 mg/kg, there were no significant toxic changes attributable to the administration of DA-5018. In conclusion, target organs following to 4-week repeated dose of DA-5018 in the rat were determined to be lung, skin and eyes. Definite toxic dose and no-observed-adverse-effect-level (NOAEL) were estimated to be 50 and 2 mg/kg/day, respectively.

• Journal of the Korea Concrete Institute
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• v.28 no.4
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• pp.455-462
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• 2016

This experimental study aims to evaluate the impact performance of UHPC exterior panels through high velocity impact tests. The impact performance of UHPC was compared with that of granite in terms of panel thickness, and strain histories were recoded on the rear face of panel specimens. The UHPC turned out to be a good exterior facade material, because the appearance of UHPC is natural enough and impact performance was superior to granite. After colliding, compression pulse reached to the rear face but that pulse was reflected in tension pulse with respect to the free point outside the rear face of the panel. This tension pulse caused the scabbing from the rear side, as the strain histories on the rear face showed three different regions as compression region, steady region and tension region. The shear plug deformation by shear force also was one of the primary reasons for the scabbing based on the observation. Therefore, the scabbing seemed to be affected by both tension and shear forces.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.6A
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• pp.543-560
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• 2010

Safety-related concrete structures in a nuclear power plant must be protected against the impact of flying objects, referred to in the profession as missiles. In practice, the structural verification is usually carried out by means of empirical formulas, which relate the velocity of the impinging missile to the wall thickness needed to prevent scabbing or perforation. The purpose of this study is to reevaluate the predictability of the local effect prediction formulas for the penetration and scabbing depths and perforation thickness. Therefore, available formulas for predicting the penetration depth, scabbing thickness, and perforation thickness of concrete structures impacted by solid missiles are summarized, reviewed, and compared. A series of impact analyses is performed to predict the local effects of the projectile at impact velocities varing from 95 to 215 m/s. The results obtained from the numerical simulations have been compared with tests that were carried out at Kojima to validate numerical modelling. The simulation results show reasonable agreement with the Kojima test results for the overall impact response of the RC slabs. From these results, it seems that the Degen equation give a very good estimate of perforation thickness against a tornado projectile for test data. Finally, the results obtained from the impact analysis have been compared with Degen formula to determine the perforation thickness of the RC slab.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4A
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• pp.311-321
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• 2011

To analysis the effect of reinforcement ratio and impact velocity on local damage, a series of impact analyses are performed to predict local effects. According to these results, the reinforcement ratio has no effect on the penetration depth and perforation thickness, but notable change to the scabbing area were observed. The higher the missile velocity becomes, the greater the degree of local damage to the reinforced concrete slabs is. Analysis results will be useful in the impact-resistance design of containment buildings and structures.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.254-255
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• 2017

The aim of this study is to investigate the impact resistant performance of steel short fiber-reinforced cement based composites (SFRCCs) containing 1.0, 1.5, 2.0 and 3.0% volume fraction of steel short fibers subjected to high velocity impact of steel projectile (the diameter of 19.05mm and the mass of 28.13g). The gunpowder impact facility was used for impact tests, and the impact velocity was from about 350 to 700m/s. The specimens were damaged in various failure modes, which are penetration, scabbing, and perforation. Comparing with Plain specimen, SFRCCs have superior capacity on the scabbing limit, and slightly bulged in the back side under the impact velocity of 700m/s. In addition, the impact resistant performance of SFRCCs improved with increase of steel short fiber volume ratio. The fibers play an important role in controlling the local damage of SFRCCs.

• Journal of the Korea Institute of Military Science and Technology
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• v.22 no.2
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• pp.151-161
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• 2019

In this study, to evaluate the High Altitude Electromagnetic Pulse(HEMP) protection performance of UHPC/CNT composites by the content of Carbon nanotubes(CNTs), Electromagnetic Shielding Effectiveness(SE) test was performed based on MIL-STD-188-125-1. And the results were verified by applying the Antenna theory. In the case of UHPC with a thickness of 200 mm mixed with 1 % CNT of cement weight, the SE was 28.98 dB at 10 kHz and 45.94 dB at 1 GHz. Then the Scabbing limit thickness for bullet proof was computed based on the result of compressive strength test which was 170 MPa, and it was examined whether it satisfied the HEMP protection criteria. As a result, the required HEMP shielding criteria were satisfied in all frequency ranges as well as the scabbing limit thickness was reduced by up to 43 % compared with that of ordinary concrete.