• 한국안전학회지
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• 제14권1호
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• pp.129-140
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• 1999

This study presents test results of RC beams strengthened by steel plates, carbon fiber sheets(CFS) and aramid fiber sheets(AFS) for increasing flexural and shear resistance. The test was performed with different parameters including the type of strengthening materials, flexural-strengthening methods and shear-strengthening methods. In case of flexural test, RC beams are initially loaded to 70% of the ultimate flexural capacity and in case of shear test loaded to 60 or 80 percent of the ultimate shear capacity and subsequently reinforced with steel plates, CFS and AFS. Experimental data on strength, steel strain, deflection, and mode of failure of the reinforced beams were obtained, and comparisons between the different shear reinforced schemes and the non-strengthened control beams were made. The test results showed that damaged RC beams strengthened by steel plates, CFS and AFS have more improved the flexural and shear capacity. For the beams with external reinforcement by steel plates, aramid fiber sheets and carbon fiber sheets increases in ultimate strength of 4 to 21, 17 to 43 and 26 to 36 percent were respectively achieved. Initial load had small effect on strength after reinforcement, but an important influence on deflection. One sheet reinforced was stronger than two sheets reinforced but less deflected than two sheets reinforced.

• Steel and Composite Structures
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• 제11권6호
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• pp.435-454
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• 2011

Bonding composite materials to structural members for strengthening purpose has received a considerable attention in recent years. The major problem when using bonded FRP or steel plates to strengthen existing structures is the high interfacial stresses that may be built up near the plate ends which lead to premature failure of the structure. As a result, many researchers have developed several analytical methods to predict the interface performance of bonded repairs. In this paper, a numerical solution using finite - difference method is used to calculate the interfacial stress distribution in beams strengthened with FRP plate having a tapered ends with different thinning profiles. These latter, can significantly reduce the stress concentration. In the present theoretical analysis, the adherend shear deformations are taken into account by assuming a parabolic shear stress through the thickness of both beam and bonded plate. Numerical results from the present analysis are presented to demonstrate the advantages of use the tapers in design of strengthened beams.

• Structural Engineering and Mechanics
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• 제61권1호
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• pp.1-13
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• 2017

The effectiveness of the repair scheme for the damaged captive-columns with CFRPs (Carbon Fiber Reinforced Polymer) was investigated in terms of response quantities such as strength, ductility, dissipated energy and stiffness degradation. Two 1/3 scale, one-story one-bay RC (Reinforced Concrete) frames were designed to represent the substandard RC buildings in Turkish building stock. The first one, which is the reference specimen, is the bare frame without infill wall. Partial infill wall with opening was constructed between the columns of the second frame and this caused captive column defect. Severe damage was observed with the concentration of shear cracks in the second specimen columns. Then, the damaged members were repaired by CFRP wrapping and retested. For the three test series, similar reversed cyclic lateral displacement under combined effect of axial load was applied to the top of the columns. Overall response of the bare frame was dominated by flexural cracks. Brittle type of shear failure in the column top ends was observed in the specimen with partial infill wall. It was observed that former capacity of damaged members of the second frame was recovered by the applied repair scheme. Moreover, ultimate displacement capacity of the damaged frame was improved considerably by CFRP wrapping.

• Radiation Oncology Journal
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• 제3권1호
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• pp.1-8
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• 1985

To determine the dose·survival and repair characteristics of the jejunal crypt cells, experimental study was carried out using total 70 mice. Single or split irradiations of 1,100 to 2,200 rad were delivered to whole bodies of $C_{57}$ BL mice, using a cesium 137 animal irradiator and those mice were sacrificed after 90 hours. The number of regenerating crypts per jejunal circumference was counted by a jejunal crypt cell assay technique and dose·response curve was measured. The results were as follows : 1. The average number of jejunal crypts per circumference in control group was 140. In a single irradiation group, the number of regenerated jejunal crypts was, 125, 56, 2 in each subgroup of 1,100 rad, 1,400 rad and 1,800 rad respectively. In split irraiation group, it was 105,44,2 in each subgroup of 1,400rad 1,800rad and 2,200rad respectively. 2. Mean lethal dose of mouse jejunal crypt cell was 167 and 169 rad respectively in a single and split irradiation. 3. Repair dose of sublethal damage was 280 rad. 4. Sublethal damage was completely repaired within 4 hours between the split dose of irradiation.

• Toxicological Research
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• 제30권4호
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• pp.277-282
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• 2014

To develop a composition for enhancing immunity, based on alcohol extracts of the bumblebee as an active ingredient, bumblebee ethanol extracts were evaluated for their protective effect in chronic models of inflammation, adjuvant induced rat arthritis. B. terrestris worker extract (SDIEX) and, B. hypocrita sapporoensis lava and pupa extract (SPDYBEX), significantly decreased paw edema in arthritic rats, at a dose 100 mg/kg, respectively. The cytokine levels related inflammation of COX-2, $sPLA_2$, VEGF, and TNF-${\alpha}$, were decreased, compared to positive control, indomethacin (5 mg/kg). Histopathological data demonstrated decreases inflammatory activity, hind paw edema, and repaired hyaline articular cartilage in DRG over a 2 wk administration. HPLC and GC-MS analysis of SDIEX and SPDYBEX revealed the presence of cantharidin.

• 국제강구조저널
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• 제18권4호
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• pp.1284-1296
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• 2018

Carbon fiber reinforced polymer (CFRP), plates bonding repair method is one of the simple repair methods for cracked steel structures. In this study, the influence of width of CFRP plates on bending fatigue life of out-of-plane gusset joint strengthened with CFRP plates was investigated from the experimental and numerical point of view. In the bending fatigue test of cracked out-of-plane gusset joint strengthened with CFRP plates, the effect of width of CFRP plates on crack growth life was clarified experimentally. Namely, it was revealed that the crack growth life becomes larger with increasing the width of CFRP plates. In the numerical approach, the stress intensity factor (SIF) at the surface point of a semi-elliptical surface crack was estimated based on the linear fracture mechanics. Furthermore, the extended fatigue life of cracked out-of-plane gusset joint strengthened with CFRP plates was evaluated by using the estimated SIF at the surface point and the empirical formula of the aspect ratio of semi-elliptical crack. As the results of numerical analysis, the estimated fatigue life of the specimen strengthened with CFRP plates showed the good agreement with the test results.

• 한국공간구조학회논문집
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• 제23권2호
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• pp.79-90
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• 2023

Existing reinforced concrete (RC) frame buildings have seismic vulnerabilities because of seismically deficient details. In particular, since cumulative damage caused by successive earthquakes causes serious damage, repair/retrofit rehabilitation studies for successive earthquakes are needed. This study investigates the repair effect of fiber-reinforced polymer jacketing system for the seismically-vulnerable building structures under successive earthquakes. The repair modeling method developed and validated from the previous study was implemented to the building models. Additionally, the main parameters of the FRP jacketing system were selected as the number of FRP layers associated with the confinement effects and the installation location. To define the repair effects of the FRP jacketing system with the main parameters, this study conducted nonlinear time-history analyses for the building structural models with the various repairing scenarios. Based on this investigation, the repair effects of the damaged building structures were significantly affected by the damage levels induced from the mainshocks regardless of the retrofit scenarios.

• 한국구조물진단유지관리공학회 논문집
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• 제14권6호
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• pp.153-161
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• 2010

1970년대에 콘크리트를 기반으로 지어진 많은 구조물과 빌딩은 안전성과 사용성을 고려하여 무수히 많은 연구를 현재까지 진행해 왔으나, 설계강도 보다 낮은 최대강도를 보이고 있다. 현재 노후화된 콘크리트 구조물들에 대한 다양한 보수 보강 공법이 개발되어 적용되고 있지만 기존 연구들은 구조물의 특성에 대해서는 고려하지 않고, 단지 기존 부재와 보수 재료의 부착에 관한 연구와 기존 부재를 효과적으로 보강하기 위한 새로운 방법을 개발하는 연구는 미흡한 실정이다. 따라서 본 연구는 보수 보강 재료를 이용한 효율적인 강도증진 방법에 대한 연구, 보강 재료와 기존 부재 사이의 거동에 대해 부족했던 연구를 보완하고자 한다. 또한 고강도 콘크리트는 높은 압축강도를 발현하기 때문에 부재의 단면을 축소시킬 뿐만 아니라 구조물의 자중 또한 감소시킬 수 있으므로 거대한 구조물 건설에 사용되고 있다. 고강도 콘크리트의 사용이 점차 증가하는 추세이지만 고강도 콘크리트를 이용한 구조물의 보수 보강에 대한 방법 연구 역시 미진한 실정이다. 따라서 본 연구에서는 효과적인 고강도 콘크리트 기둥에 대한 보수 보강 방법을 개발하고자 한다. 본 연구에서는 사각단명 형상을 가진 기둥을 팔각단면으로 형상 변형을 통해 CFS로 보수 보강하여 단면 형상이 변함에 따른 효과를 파악하고, CFS로 보강된 고강도 콘크리트(HSC) 기둥의 강도 증대 효과와 파괴 거동에 대해 파악하고자 한다.

• 한국지반환경공학회 논문집
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• 제8권6호
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• pp.45-52
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• 2007

국내 노후화된 필댐의 경우에는 수문학적 안정성과 더불어 구조적 안정성 확보가 국가재난 예방차원에서 요구되고 있는 실정이다. 설계 및 시공시의 문제나 지진 등 자연현상으로 인하여 댐체가 손상되었거나 노후화로 문제된 댐의 대부분이 필댐 타입이며, 이중 일부는 차수(코아) 존이 손상되어 과다한 누수현상이 발생되고 있어 홍수시 댐 붕괴로까지의 진행이 우려되는 바 차수보강대책에 대한 체계적인 연구가 시급하다고 여겨진다. 본 연구에서는 침투그라우팅으로 보강된 필댐에 있어서 보수.보강 전후의 차수 성능변화를 전기비저항탐사 등의 물리조사를 이용하여 분석 평가하고자 하였다. 연구결과 전기비저항탐사는 그라우팅으로 보강된 필댐의 보강효과를 판단하는 유효한 도구로 사용될 수 있음을 알 수 있었으며, 그라우팅으로 보강된 필댐의 누수량은 크게 저하되어 안정성이 향상 되었음을 알 수 있었다.

• Toxicological Research
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• 제29권3호
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• pp.195-201
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• 2013

The anti-inflammatory effects of glycosaminoglycan (GAG) derived from Isaria sinclairii (IS) and of IS extracts were investigated in a complete Freund's adjuvant (CFA)-treated chronic arthritis rat model. Groups of rats were treated orally with 30 mg/kg one of the following: [1] saline control, extracts of [2] water-IS, [3] methanol-IS, [4] butanol-IS, [5] ethyl acetate-IS, or [6] Indomethacin(R) as the positive control for a period of two weeks. The anti-paw edema effects of the individual extracts were in the following order: water-IS ex. > methanol ex. > butanol ex. > ethyl acetate ex. The water/methanol extract from I. sinclairii remarkably inhibited UV-mediated upregulation of NF-${\kappa}B$ activity in transfected HaCaT cells. GAG as a water-soluble alcohol precipitated fraction also produced a noticeable anti-edema effect. This GAG also inhibited the pro-inflammatory cytokine levels of prostaglandin $E_2$-stimulated lipopolysaccharide in LAW 264.7 cells, cytokine TNF-${\alpha}$ production in splenocytes, and atherogenesis cytokine levels of vascular endothelial growth factor (VEGF) production in HUVEC cells in a dose-dependent manner. In the histological analysis, the LV dorsal root ganglion, including the articular cartilage, and linked to the paw-treated IS GAG, was repaired against CFA-induced cartilage destruction. Combined treatment with Indomethacin(R) (5 mg/kg) and IS GAG (10 mg/kg) also more effectively inhibited CFA-induced paw edema at 3 hr, 24 hr, and 48 hr to levels comparable to the anti-inflammatory drug, indomethacin. Thus, the IS GAG described here holds great promise as an anti-inflammatory drug in the future.