• Title/Summary/Keyword: Strengthening effect

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Strengthening Effect of R/C Beams with different Strengthening Level

  • Park, Sang-Yeol;Park, Jeong-Won;Min, Chang-Shik
    • KCI Concrete Journal
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    • v.12 no.1
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    • pp.113-120
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    • 2000
  • This paper presents the behavior and strengthening effect of reinforced concrete rectangular beams strengthened using CFRP sheets with different strengthening level. In general, normally strengthened beams are failed by interfacial shear failure (delamination) within concrete, instead of by tensile failure of the CFRP sheets. The delamination occurred suddenly and the concrete cover cracked vertically by flexure was spalled off due to the release energy. The strengthened beams were stiffer than the control beam before and after reinforcement yielding. The ultimate load considerably increased with an increase of strengthening level, while the ultimate deflection significantly decreased. The tensile force of CFRP sheets and average shear stress of concrete at delamination failure were curvilinearly proportional to the strengthening level. Therefore, the increment of ultimate load obtained by strengthening was curvilinearly proportional to the strengthening level. The averaged horizontal shear stress of concrete at the interface ranges between (equation omitted) and (equation omitted) (in kg/$\textrm{cm}^2$) depending on strengthening level.

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Strengthening Depth Effect in Externally Post-tensioning Shear Strengthening of Pre-cracked Reinforced Concrete Beam (사전균열이 발생한 철근콘크리트 보의 외적 포스트텐셔닝 전단보강에서 보강깊이의 효과)

  • Lee, Swoo-Heon;Shin, Kyung-Jae;Lee, Hee-Du
    • Journal of the Architectural Institute of Korea Structure & Construction
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    • v.34 no.11
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    • pp.19-26
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    • 2018
  • This paper presents the shear strengthening effect of externally post-tensioning (EPT) method using high-strength steel rod in pre-cracked reinforced concrete (RC) beams. Three- and four-point bending tests were performed on a total of 8 specimens by adjusting the strengthening depths in the deviator position of EPT. The effective strengthening depths were 435, 535, and 610 mm. The pre-loading up to about 2/3 of ultimate load capacity measured in unstrengthened RC beam were applied in the beam to be post-tensioned. The EPT method was then applied to the pre-damaged RC beams and re-loading was added until the end of the test. EPT restored deflections of 3 mm or more, which account for about 40% of deflection when the pre-loading was applied. The shear strengthening increases more than 3 times and 36~107% in terms of the stiffness and load-carrying capacity compared to unstrengthening RC beams. The increased load-carrying capacities of the post-tensioned beam with strengthening depths of 435 and 535 mm are almost the same as 36~61%, and those of 610 mm are 84~107%, which shows the greatest shear strengthening effect.

Strengthening Effect Evaluation Technique of R/C Beams using the Vibration Test (진동시험을 통한 R/C Beam의 보강효과 검증기법)

  • 심종성;유태석
    • Proceedings of the Korea Concrete Institute Conference
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    • 1994.10a
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    • pp.255-260
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    • 1994
  • This study suggests a strengthening effect evaluation technique of reinforced concrete beams using the vibration test. To evaluate the strengthening effect of R/C beams, Strengthening Factor(Sf) was suggested. Using the value of Sf, 20 beams were evaluated. According to these results the effects of R/C beams strengthened by steel plate is superior than those of R/C beams strengthened by carbon fiber sheet.

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Numerical Analysis on External Strengthening Effects in Aged Structures (사용중인 구조물의 보강효과에 대한 해석적 연구)

  • 신승교;임윤묵;김문겸;박동철
    • Proceedings of the Korea Concrete Institute Conference
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    • 2002.05a
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    • pp.455-460
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    • 2002
  • In this study, a numerical analysis that can effectively predict the effect of strengthening of cracked flexural members is developed using axial deformation link elements. Concrete and interface between concrete and repair material are considered as quasi-brittle material. Reinforcing bars and reinforcing steel plates are assumed to perform as elasto-plastic materials. Unloading behavior of axial deformation link element is implemented. In the developed numerical model, a flexural member is intentionally cracked by pre-loading, then, the cracked member is repaired using extra elements, and reloaded. The results from analysis of repaired flexural members agrees well with available experiment results. Also, it was shown that the effect of strengthening and the change of failure mode with respect to the time for strengthening and thickness of repair materials. Based on the results, it was determined that the developed numerical model has a good agreement for determining failure modes and effect of strengthening in cracked flexural members. By utilizing the developed numerical analysis, the time and dimension of external strengthening in an existing cracked flexural member with predition of failure mechanism can be determined.

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Strengthening Effect of CFRP on the R/C Rahmen Bridge (R/C 라멘교에 적용된 CFRP의 보강효과)

  • 심종성;정영수;윤선원;김규선
    • Proceedings of the Korea Concrete Institute Conference
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    • 1996.04a
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    • pp.328-333
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    • 1996
  • Concrete can be defective for several reasons, including an inadequate design, material selection of workmanship, failure to appreciate the hazards associated with prevailing enviromental conditions. Concrete can also deteriorate or be damaged in use. Thus, it is necessary to evaluate the safety of existing concrete strucutres. On the basis of these reasons, they must be performed for repair or rehabilitation. Presently, strengthening methods of R/C structure used in Korea, are an enlargement of concrete member, strengthening with steel plate or CFRP on the R/C structure. It has been widely estabilished that strengthening effect of CFRP is superior to steel plate in terms of it's lighter unit weight and higher tensile strength. But there are no construction results of CFRP on the civil R/C structure in Korea. The strengthening design technique with CFRP, it's const겨ction, and it's strengthening effect for deteriorated R/C rahmen bridge is introduced in this paper.

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An Experimental Study on the Strengthening Effect of RC Beam subjected to Repeated Loading during CFS Strengthening Process (탄소섬유 보강 중에 반복하중을 받은 RC보의 보강효과에 관한 실험적 연구)

  • Jang, Hee-Suk;Kim, Hee-Sung
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.10 no.1
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    • pp.183-189
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    • 2006
  • When RC structures are repaired or strengthened using FRP, it is required to cure for some Period under certain air temperature and then it is hopeful to avoid detrimental action caused by external vibration sources during that period. Therefore, an effect of repeated loading during Carbon Fiber Sheet(CFS) strengthening Process on the strengthening efficiency is studied through an experiment for a number of RC beams. Experimental results showed that the curing time of 24 hours without any repeated loading after CFS attachment were recommended for 1 ply strengthening, and 12 hours for 2 plies strengthening.

Effect of Continuous Antagonistic Muscle Strengthening and Evjenth-Hamberg Stretching on Pulmonary Function of Forward Head Posture Subjects

  • Park, Joo Hyun
    • Journal of International Academy of Physical Therapy Research
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    • v.6 no.2
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    • pp.871-877
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    • 2015
  • This research was conducted to investigate the effect of continuous antagonistic muscle strengthening exercise and Evjenth-Hamberg stretching on the pulmonary function of university students with abnormal transformation of forward head posture(FHP). The results of study subject to the continuous antagonistic muscle strengthening(CAS) group(n=10) and Evjenth- Hamberg stretching(EHS) group(n=10) that was conducted 3 times a week for 6 weeks are as follow. FVC, IVC, and MVV all were shown to be significant in the pre post comparison between the CAS group and EHS group(p<.05), and significant difference was shown for MW between the two groups(p<.05) in which the CAS group showed better effect. Based on the results above, it is considered that combining continuous antagonistic muscle strengthening exercise has better effect on pulmonary function compared to application of only Evjenth-Hamberg stretching.

An Experimental Study on Flexural Repair of Reinforced Concrete Beams with the CFRP Sheet (탄소섬유시트를 사용한 철근콘크리트 구조물의 휨 보강에 관한 실험적 연구)

  • 박정원;박상렬;민창식
    • Proceedings of the Korea Concrete Institute Conference
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    • 2000.04a
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    • pp.781-786
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    • 2000
  • This paper presents the behavior and strenghening effect of reinforced concrete rectangular beams strengthened sing CFRP sheets with different strengthening level. In general, normally strengthened beams are failed by interfacial shear failure (delamination) within concrete, instead of by tensile failure of the CFRP sheets. The delamination occurred suddenly and the concrete cover cracked vertically by flexure was spalled off due to the release energy. The ultimate load considerably increased with an increase of strengthening level, while the ultimate deflection significantly decreased. The tensile force of CFRP sheets and average shear stress of concrete at delamination failure were curvilinearly proportional to the strengthening level. Therefore, the increment of ultimate load obtained by strengthening was curvilinearly proportional to th strengthening level.

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Strengthening Effect Analysis of Circular Concrete Column Strengthened with Laminated CFS (적층성을 띤 CFS로 보강된 원형 콘크리트 기둥의 보강효과 해석)

  • 이상호;허원석
    • Journal of the Korea Concrete Institute
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    • v.11 no.3
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    • pp.89-100
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    • 1999
  • The purpose of this study is to develop an analytic model of the concrete column strengthened with laminated CFS, and to provide a basic guideline for the strengthening design by CFS considering orthotropic properties of laminate. In this study, an analytical stress-strain model of laminated CFS is presented based on Tsai-Hill failure criterion. This model has been implemented in an algorithm which can evaluate the confinement effect of CFS. Through this algorithm, the stress-strain relationship of confined concrete is obtained and compared with experimental results of other studies. Using the constitutive relationships, section analyses of concrete column strengthened with CFS are done, and load-moment and load-curvature interaction curves are obtained. In addition, the strengthening effects of CFS according to various laminated angles are analyzed. Analytical results show that the strengthening effects of the strengthened concrete columns are significantly different in compression, flexure, and ductility according to the laminated ways. In compressive direction of principal stress shows the superiority, where an in flexural strengthening effects, [0/90]s does. In the aspect of ductility, [90]s shows the best effect.

Numerical Study for the Estimation of Strengthening Effect of Concrete Column Strengthened with CFS (CFS 보강 콘크리트 기둥의 보강효과 산정을 위한 해석적 연구)

  • 이상호;허원석;박재우
    • Proceedings of the Korea Concrete Institute Conference
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    • 1999.04a
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    • pp.709-714
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    • 1999
  • The objectives of this study are to estimate the strengthening effect of concrete column strengthened with CFS and to provide basic guideline for the strengthening design with laminated composite materials. Analysis stress-strain model of laminated CFS is presented based on laminate theory. This model has been implemented in the algorithm of evaluating confinement effect of CFS. From results of the algorithm, stress-strain relationship of confined concrete is obtained. Using this stress-strain relationship, section analyses of circular and rectangular concrete columns strengthened with CFS are carried our, and load-moment interaction and load-ductility curves of the columns are obtained. To evaluate the strengthening effects of CFS, parametric study is also conducted for the angle of ply, thickness of CFS, shape of section, and reinforcement ratio. Based on this investigation, design recommendations and basic guidelines for the strengthening design with CFS are proposed.

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