• Title/Summary/Keyword: 외부 부착 프리스트레스

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Post-tensioning System with Externally Bonded CFRP Strips for Strengthening RC Members (RC 부재의 휨 보강을 위한 외부 부착형 탄소섬유판 포스트텐션 시스템)

  • You, Young-Chan;Choi, Ki-Sun;Kim, Keung-Hwan
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.12 no.6
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    • pp.155-163
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    • 2008
  • Experimental study has been performed in order to investigate the behavior of RC beams strengthened with externally bonded post-tensioned CFRP (Carbon Fiber Reinforced Polymer) strips. Specimens consist of 9 small-scaled specimens with the different post-tensioning level as a main test parameter. A control specimen and specimens with simply bonded CFRP strips have been manufactured to compare the structural performances of prestressed system. From the test results, it was observed that the specimens strengthened with simply bonded CFRP strips showed debonding failure below 50% of CFRP tensile strength due to premature debonding. On the other hand, all the specimens strengthened with post- tensioned CFRP strips reached the rupture strength of the CFRP strip. The cracking and yielding loads were also increased proportionally to the post-tensioning level, but the ultimate loads were nearly equal regardless of the post-tensioning level.

Post-tensioning System with Externally Unbonded CFRP Strips for Strengthening RC Members (RC 부재의 휨 보강을 위한 외부 비부착형 탄소섬유판 포스트텐션 시스템)

  • You, Young-Chan;Choi, Ki-Sun;Kim, Keung-Hwan
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.12 no.6
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    • pp.147-154
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    • 2008
  • Experimental study has been performed in order to investigate the behavior of RC beams strengthened with externally unbonded post-tensioned CFRP (Carbon Fiber Reinforced Polymer) strips using embedded or stud-type plate anchorages. Total 10 small-scaled specimens were manufactured with the different post-tensioning level and types of mechanical anchorage as a main test parameter. A control specimen and specimens with simply bonded CFRP strips were included to compare the structural performances of each system. From the test results, it was observed that the specimens strengthened with simply bonded CFRP strips showed debonding failure below 50% of CFRP tensile strength due to premature debonding. On the other hand, all the specimens strengthened with post- tensioned unbonded CFRP strips reached the rupture strength of the CFRP strip. Also, it was observed that the specimens with stud-type anchorage have equivalent strengthening performance compared with embedded-type anchorage.

Debonding Failure Model for RC Beams Strengthened with Externally Bonded Prestressed CFRP Plates (탄소섬유판 긴장재로 외부 긴장 보강된 철근콘크리트 보의 부착파괴 모델)

  • Park, Jong Sup;Jung, Woo Tai;Park, Young Hwan
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.28 no.4A
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    • pp.447-456
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    • 2008
  • This paper suggests a modified debonding failure model for the externally bonded prestressed CFRP plate strengthening system. In order to reduce the error that may occur in the experimental results, statistical analysis of the experimental results produced by previous researchers was conducted to propose a debonding failure model. The experimental results of beams strengthened with bonded CFRP plates have made it possible to verify the debonding failure occurring before the final failure in the prestressing system. The corresponding strain increased with the effective prestress. Accordingly, the debonding failure model was modified by considering the effective prestress so as to fit with the CFRP prestressing system.

Ultimate Stress of Prestressing Steel in Prestressed Concrete Beams Strengthened by External Prestressing (외부 프리스트레싱으로 보강된 프리스트레스트 콘크리트 보에서 프리스트레싱 강재의 극한응력)

  • Park Sang-Yeol
    • Journal of the Korea Concrete Institute
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    • v.16 no.5 s.83
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    • pp.677-686
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    • 2004
  • This study deals with literature review, developing a predicting equation for the ultimate stress of internal and external prestressing steel, and an experimental test with the parameters affecting the ultimate stress of prestressing steel in prestressed concrete beams strengthened by external prestressing tendons. The proposed predicting equation takes rationally the effect of internal and external prestressing steels into consideration as a function of prestressing steel depth to neutral depth ratio. In the experimental study, prestressed concrete beams strengthened using external steel tendons are tested with the test parameters having a large effect on the ultimate stress of internal and external prestressing steel. The test parameters include internal and external prestressing steel reinforcement ratio and span to depth ratio. The test results are analyzed to confirm the rationality and applicability of the proposed equation for predicting the ultimate stress of internal and external prestressing steel. This research shows that the results obtained by the proposed equation for predicting the ultimate stress agreed very well with the test results.

A study on Development of Methods to Rehabilitate the Damaged Prestressed Concrete beam Using Glass Fiber (유리섬유를 이용한 손상된 프리스트레스트 콘크리트 보의 보강공법 개발연구)

  • Kang, Won-Ho;Han, Man-Yop;Lee, Taek-Sung;Rhu, Young-Min
    • Magazine of the Korea Concrete Institute
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    • v.11 no.2
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    • pp.167-175
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    • 1999
  • Many composite girder bridges have been constructed for about thirty five years. Nowadays they are aged or deteriorated because of the increase in traffic and vehicle loads. In this study, the effect of strengthening with glass fiber sheet is investigated to estimate the possibility for applying to damaged prestressed concrete bridges. One normal and eight cracked specimens which had been preloaded were tested. The cracked specimens were strengthened with either external prestressing or bonding glass fiber sheet, or using both methods. The results showed that the maximum loads are almost same for both methods. So it seems that the strengthening with glass fiber sheet can be used for strengthening damaged prestressed concrete girders. It is important that proper devices should be selected to prevent glass fiber sheet from premature bonding failure below its maximum load, which is similar to end anchorage problem in external prestressing method. It is proved that the devices proposed in this paper have sufficient anchoring capability to increase load carrying capacity.

A Study on the Prediction of Ultimate Stress of Tendon in Unbonded Prestressed Concrete Beams without Slip (비부착 PSC 보에서 슬립이 없는 강선의 극한 응력 예측에 관한 연구)

  • Hong, Sung-Su;Yoo, Sung-Won;Park, Seung-Bum
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.28 no.4A
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    • pp.537-548
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    • 2008
  • Recently, the prestressed unbonded concrete structures are increasingly being built. The mechanical behavior of prestressed concrete beams with unbonded tendon is different from that of normal bonded PSC beams in that the increment of tendon stress was derived by whole member behavior. The purpose of the present paper is therefore to evaluate the flexural behavior and to propose the equation of ultimate tendon stress by performing static flexural test according to span/depth, concrete compression strength, reinforcement ratio and the effect of existing bonded tendon. From experimental results, for cracking, yielding and ultimate load, the effect of reinforcement ratio was more effective than concrete compression strength, and the beams having high strength concrete had a good performance than having low concrete, but there was no difference between high strength and low strength. And as L/dp was larger, test beams had a long region of ductility. This means that unbonded tendon has a large contribution after reinforcement yielding. Especially, the equation of ACI-318 was not match with test results and had no correlations. After analysis of test results, the equation of ultimate unbonded tendon stress without slip was proposed, and the proposed equation was well matched with test results. So the proposed equation in this paper will be a effective basis for the evaluation of unbonded tendons without slip, analysis and design.

Experiment of Flexural Behavior of Prestressed Concrete Beams with External Tendons according to Tendon Area and Tendon Force (강선량 및 긴장력에 따른 외부 강선을 가진 PSC 보의 휨거동 실험)

  • Yoo, Sung-Won;Yang, In-Hwan;Suh, Jeong-In
    • Journal of the Korea Concrete Institute
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    • v.21 no.4
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    • pp.513-521
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    • 2009
  • Recently, the externally prestressed unbonded concrete structures are increasingly being built. The mechanical behavior of prestressed concrete beams with external unbonded tendon is different from that of normal bonded PSC beams in that the slip of tendons at deviators and the change of tendon eccentricity occurs as external loads are applied in external unbonded PSC beams. The purpose of the present paper is therefore to evaluate the flexural behavior by performing static flexural test according to tendon area and tendon force. From experimental results, before flexural cracking, there was no difference between external members and bonded members. However, after cracking, yielding load of reinforcement, ultimate load, and the tendon stress of external members was lower than that of bonded members. For the relationship of load-tendon stress, the increasing of tendon strain was inversely proportional to the initial tendon force. However, even if the initial tendon force was large, the tendon strain with small effective stress was smaller than that with large effective stress. The concrete compressive strain was proportional to the effective stress of external tendon. From the comparison between test results and codes, the ACI-318 could not consider the effect of tendon force or effective stress, and especially the results of ACI-318 were very small, so it was very conservative. And the AASHTO 1994 could be influenced on the tendon area, initial force and effective stress, but as it was made on the basis of internal unbonded tendon, its results were much larger than the test results. For this reason, the new correct predict equation of external tendon stress will be needed.

Development of Analysis Program for PSC Beams with Unbonded External Tendons (외부 비부착 강선을 갖는 PSC보의 해석프로그램 개발)

  • Kwak, Hyo-Gyoung;Son, Je-Kuk;Kim, Sun-Yong;Park, Young-Hwan
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.2A
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    • pp.247-260
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    • 2006
  • In this paper, an analytical method which can describe the structural behavior of prestressed concrete (PSC) bridges reinforced with the unbonded external tendon is developed. Since the unbonded external tendon is directly installed to the deviators while maintaining a straight configuration, it has a different deformation field from that of concrete and accompanies the secondary effect caused by the change of the primary eccentricity between concrete and external tendon. In advance, the friction slip at the deviators is also taken into consideration on the basis of the force equilibrium between the friction force and the driving force. Through correlation studies between experimental data and analytical results, it is verified that the proposed numerical model can effectively predict the structural behavior of PSC beam bridges with comparative precision.

An Experimental Study on Flexural Behavior of RC Beams Strengthened with Hi-Strength Bars(3) (고장력 인장봉으로 보강된 RC 보의 휨 거동에 관한 실험적 연구(3))

  • Shin, Kyung-Jae;Kim, Yoon-Jung;Moon, Jeong-Ho
    • Journal of the Korea Concrete Institute
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    • v.19 no.3
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    • pp.351-358
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    • 2007
  • Unlike external bonded steel plate or carbon fiber, the external unbonded strengthening using hi-strength bar has some advantages in speed and simplicity of installation. It is not required surface preparations and not affected by environmental conditions. A set of nine laboratory tests on RC beams strengthened using the hi-tension bars are reported. Anchoring pin developed in former research is installed at the end of beam to connect the hish-tension bar to RC beam. The test results strengthened by hi-tension bars are compared with those of non-strengthened specimens. The main test parameters are the cross-sectional area of the high-tension bar, distance of stirrups and condition of supports. Test results show that the beams reinforced are superior to reference specimens, especially for the strength and deformation capacity. Also, shear resisting effect of hi-strength bar can be confirmed in the specimens which have lack of stirrups.

An Experimental Study on the Flexural Behavior of RC Beams Strengthened with High-Strength Bars(1) (고장력 인장봉으로 보강된 RC보의 휨거동에 관한 실험적 연구(1))

  • Shin, Kyung-Jae;Kwak, Myong-Keun;Heo, Byung-Wook;Na, Jung-Min;Oh, Young-Suk
    • Journal of the Korea Concrete Institute
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    • v.18 no.4 s.94
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    • pp.527-534
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    • 2006
  • This paper outlines a new strengthening technique for concrete beams using externally unbended high-strength bars. The advantages of proposed method lie in speed and simplicity of construction compared to the alternative strengthening method. Externally unbended reinforcement retains many of the advantages over external unbended prestressed tendons. It eliminates time consuming stressing operations. Clearance requirements around anchorages are reduced as access is not required for prestressing jacks. Test results of eight specimens on reinforced concrete beams using different reinforcement materials such as carbon fiber sheet, steel plate and high-tension bar are reported. The beam strengthened by carbon fiber sheet showed a brittle failure mode due to the separation of fiber. As a result of draped profile of external bar, the maximum strength of the beam were increased by up to 212 percent and the deflections were reduced by up to 65 percent. Test results show that the beams reinforced with high-tension bar are superior to reference specimens, especially for the strength and deformation capacity.