• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1818-1823
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• 2007

In this paper, notched bar tensile tests of Inconel 617 were performed at room ($20^{\circ}C$) and elevated ($800^{\circ}C$) temperature. Finite element analyses are also performed. It is found that, at the room temperature, smooth bar tensile test results could be used to simulate notched bar tensile tests. However, at the elevated temperature, notched bar tensile test results can not be simulated from smooth bar tensile test results. Metallurgical examination reveals that strength weakening results from many cavities over the specimens for smooth bar test at the elevated temperature. "True" tensile properties at the elevated temperature is found using FE simulations. It also suggests that cautious should be taken to determine tensile properties of Inconel 617 at elevated temperatures using smooth bar tests.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.204-209
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• 2008

The interest in the mechanical behavior of materials at high strain rates has increased in recent years, and by now it is well known that mechanical properties can be strongly influenced by the speed of applied load. The split Hopkinson pressure bar (SHPB) has been widely used to determine mechanical properties of materials at high loading rates. However, to ensure test reliability, measurement error source must be accounted for and eliminated. During experiment, the specimens were located between the incident and the transmit bar. The presence of contact frictions between the test bars and specimen may cause errors. In this work, numerical experiments were carried out to investigate the effect of friction on test results. In SHPB test, the measured stress by the transmitted bar is assumed to be flow stress of the test specimen. Through the numerical experiments, however, it is shown that the measured stress by the transmit bar is axial stress components. When, the contact surface is frictionless, the flow stress and the axial stress of the specimen are about the same. When the contact surface is not frictionless, however, the flow stress and the axial stress are not the same anymore. Therefore, the measured stress by the transmitted bar is not flow stress. The effect of friction on the difference between flow stress and axial stress is investigated.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1997년도 봄 학술발표회 논문집
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• pp.669-675
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• 1997

This paper investigates the performances of GFRP bar and its possibility for using a substitute of steel bar. GFRO bar was made with introducing the glass fiber into GTR added UPE. We carried out the tensile test of GFRP and steel bar and out the three point bend test bond-test and fracture energy measurement on the GFRP bar and steel bar reinforced concrete. The GFRP bar was excellent as comparison with steel bar in the contribution to the energy absorption and the ductility of concrete. But its tensile, bond and bend strengthes were comparatively small. In order to improve these defects, we judged that glass fibers in GFRP bar must be completely adhesive one another by the impregnating glass fibers into UPE.

• Smart Structures and Systems
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• 제17권4호
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• pp.593-610
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• 2016

In this study, an innovative and smart glass fiber-reinforced polymer (GFRP) hybrid bar was developed for stronger durability of concrete structures. As comparing with the conventional GFRP bar, the smart GFRP Hybrid bar can promise to enhance the modulus of elasticity so that it makes the cracking reduced than the case when the conventional GFRP bar is used. Besides, the GFRP Hybrid bar can effectively resist the corrosion of conventional steel bar by the GFRP outer surface on the steel bar. In order to verify the bond performance of the GFRP hybrid bar for structural reinforcement, uniaxial pull-out test was conducted. The variables were the bar diameter and the number of strands and pitch of the fiber ribs. Tensile tests showed a excellent increase in the modulus of elasticity, 152.1 GPa, as compared to that of the pure GFRP bar (50 GPa). The stress-strain curve was bi-linear, so that the ductile performance could be obtained. For the bond test, the entire GFRP hybrid bar test specimens failed in concrete splitting due to higher shear strength resulting in concrete crushing as a function of bar deformation. Investigation revealed that an increase in the number of strands of fiber ribs enhanced the bond strength, and the pitch guaranteed the bond strength of 19.1 mm diameter hybrid bar with 15.9 mm diameter of core section of deformed steel the ACI 440 1R-15 equation is regarded as more suitable for predicting the bond strength of GFRP hybrid bars, whereas the CSA S806-12 prediction is considered too conservative and is largely influenced by the bar diameter. For further study, various geometrical and material properties such as concrete cover, cross-sectional ratio, and surface treatment should be considered.

• 한국공작기계학회논문집
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• 제17권3호
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• pp.47-52
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• 2008

The force transducer in the acceleration plant due to dynamic fracture is calibrated by dynamically using the stress pulses from a longitudinal bar. The bar is supported by two strings attached to the ceiling. The bar velocities before and after impact are measured and a full bridge at bar and transducer is formed by the four strain gauges. A transient recorder is used to store the stress pulse signals of force transducer and bar. For the first test series, three point bend test specimens can be chosen by means of test rig design and the inspection as sample experiment in this presented paper is sufficient for proving with the numerical simulation of the specimen model.

• 한국건설순환자원학회논문집
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• 제5권2호
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• pp.130-136
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• 2017

본 연구에서는 UV 폭로 및 동결융해 환경이 FRP Hybrid Bar의 인장거동 및 표면 열화에 미치는 영향을 평가하기 위해 FRP Hybrid Bar를 대상으로 UV 폭로 및 동결융해 시험을 실시하였다. FRP Hybrid Bar의 경우 UV 폭로 및 동결융해 180cycle 시험 전/후 외관적인 열화가 거의 발생하지 않았다. 또한 FRP Hybrid Bar의 주요 장점 중 하나인 인장경화특성은 동결융해 시험을 거친 이후에도 유지되었는데, 이는 UV 폭로시험을 거친 FRP Hybrid Bar에도 유효하게 평가되었다. UV 폭로시험을 거친 FRP Hybrid Bar는 일반 FRP Hybrid Bar와 거의 비슷한 인장거동을 나타내었으며, 동결융해 180cycle의 진행에도 불구하고 일반철근, FRP Hybrid Bar, UV 폭로를 거친 FRP Hybrid Bar의 인장거동은 큰 변화를 나타내지 않았다. 본 연구에서는 UV 폭로 및 동결융해 환경이 FRP Hybrid Bar의 외관 및 인장 특성에 큰 영향을 미치지 못하는 것으로 판단되지만, 충격에 따른 규사코팅의 박락은 콘크리트와의 부착력에 영향을 미치므로 이에 대한 고려가 필요하다.

• 한국건설순환자원학회논문집
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• 제5권1호
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• pp.53-58
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• 2017

FRP Hybrid Bar는 내부에 강재를 유리섬유와 에폭시 수지가 코팅된 형태로 사용되는데, 인장경화 성능이 있으며, 경량이므로 효과적인 보강재료로 사용될 수 있다. 자외선 및 동결융해에 노출된 에폭시는 표면 열화가 발생하기 쉬우며, 이는 매립된 철근 및 표면의 콘크리트와의 부착력 저하를 야기할 수 있다. 본 연구에서는 일반철근, FRP Hybrid Bar 및 자외선(UV) 폭로시험을 거친 FRP Hybrid Bar의 외관특성분석을 실시하였다. 또한 각 보강재를 사용하여 콘크리트 인발 공시체를 제조하였으며, 동결융해시험을 실시해 Cycle에 따른 부착성능을 분석하였다. FRP Hybrid Bar는 UV 폭로시험 후에도 표면 산화(Chalking)와 같은 에폭시계 재료의 열화가 나타나지 않았다. 동결융해시험은 120Cycle 및 180Cycle까지 진행하였는데, UV 폭로시험 후 FRP Hybrid Bar를 사용한 공시체는 $241{\pm}kN$ 부착력을 가지고 있었다. 이는 일반철근 대비 약 106.3%수준으로 개선된 부착강도인데, FRP Hybrid Bar 표면의 규사코팅에 따라 부착면적이 증가했기 때문이다. 3가지 조건(일반철근, FRP Hybrid Bar, UV 폭로시험 후의 FRP Hybrid Bar)에 대하여, 동결융해 Cycle이 증가함에 따라 부착력이 크게 감소하지는 않았으나, 코팅된 규사의 박락으로 인해 UV 시험 이후의 동결융해를 거친 조건에서는 실험 편차가 상대적으로 증가하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회논문집(II)
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• pp.621-626
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• 1998

An experimental investigation on the reinforcing bar corrosion and relationshid of reinforcing bar and concrete bond strength has been conducted to establish the allowable limit of rust in the construction field. The reinforcing bars used in this study were rusted before embedding in concrete. The first component of this experiment is to make rust of reinforcing bar rust artificially based on Faraday's theory at certain rates such as 2, 4, 6, 8 and 10% of reinforcing bar weight. For estimation of the amount of rust by weight, Clarke's solution and Shot blasting were adopted and compared. Parameters include 240 and 450kg/㎠ of compressive strengths and diameter of reinforcing bar (16, 19 and 25mm) corresponding development length for pull-ort test. And, pull-out tests were carried. out according to KSF 2441 and ASTMC 234 to investigate the effect of the corrosion rate on reinforcing bar-concrete bond behavior. It is found from the test results that the test techniques for corrosion of bar used in this study is relatively effective and correct test method. Results shows that up to 2% of rust increases the bond strength regardless of concrete strength and diameter of reinforcing bar like the existing data. It might be because of the roughness from rust. As expected, the bond strength increases as compressive strength of concrete increases and the diameter of bar decreases.

• 한국도로학회논문집
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• 제14권5호
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• pp.93-99
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• 2012

PURPOSES: The purpose of this study is to compare the alkali-silica reactivity for mortar bar and concrete prism specimens using crushed aggregates of 5 types in Korea. And the alkali-silica reactivity for those aggregates are measured by chemical test method. METHODS: The alkali-silica reactivity for those aggregates was measured by chemical test method of KS F 2545, mortar-bar test of KS F 2546, accelerated mortar-bar test method of ASTM C 1260 and concrete prism test method of ASTM C 1293, relatively. RESULTS: The alkali-silica reactivity for those aggregates was verified by chemical test of KS F 2546 and accelerated mortar-bar test of ASTM C 1260. However, it was not by mortar-bar test of KS F 2546 and concrete prism test of ASTM C 1293. CONCLUSIONS: The above results showed that relationship among the four test methods were very low. The results from 3 types of test methods using cement-aggregate combinations appeared to be different. Because the environmental conditions of test methods for measuring the alkali-silica reactivity such as equivalent alkali content(external source), humidity, temperature, and times were different though the aggregates were same. Moreover, alkali-silica reactivity showed the biggest impact when alkalis were supplied form outside and exposed to environmental conditions. The accelerated mortar-bar test method seems to be most appropriate test method for concrete structures exposed to alkali environment.

• Architectural research
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• 제22권1호
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• pp.33-39
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• 2020

In this study, side-face blowout failure strength of high strength headed reinforcing bar, which is vertically anchoring between RC or SFRC members, is evaluated throughout pullout test. The major test parameters are content ratio of high strength steel fibers, strength of rebar, length of anchorage, presence of shear reinforcement, and the side concrete cover thickness planned to be 1.3 times of the rebar. In pullout test, tensile force was applied to the headed reinforcing bar with the hinged supports positioned 1.5 and 0.7 times the anchorage length on both sides of the headed reinforcing bar. As a result, the cone-shaped crack occurred where the headed reinforcing bar embedded and finally side-face blowout failure caused by bearing pressure of the headed reinforcing bar. The tensile strength of specimens increased by 13.0 ~26.2% with shear reinforcement. The pullout strength of the specimens increased by 3.6 ~15.4% according to steel fiber reinforcement. Increasing the anchoring length and shear reinforcement were evaluated to reduce the stress bearing ration of the total stress.