• 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.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.1
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• pp.91-100
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• 2008

Multi-stepwise Thermal Prestressing Method(TPSM) is a newly proposed prestressing method, which is combined the external prestressing method and the external bonding method. Multi-stepwise thermal prestressing force is induced by cooling process of cover-plate in the multi-stepwise temperature distribution after the cover-plate being bolted to the girder. In this study, the heating capacity test of the developed heating system for applying the multi-stepwise TPSM effectively and multi-stepwise TPSM inducing test of H-beam is performed. Also, a field test of the rhamen type temporary bridge is carried out to evaluate the effect and application of the multi-stepwise TPSM. Truck load was loaded and compared with the structure analysis results.

• Journal of the Korea Concrete Institute
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• v.15 no.4
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• pp.585-593
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• 2003

This study deals with literature review, developing a predicting equation for the ultimate stress of prestressing steel, and experimental test with the parameters affecting the ultimate stress of prestressing steel in reinforced concrete beams strengthened by external prestressing. The ACI predicting equation for the ultimate stress of unbonded prestressing steel is analyzed to develop a new integrated predicting equation. The proposed predicting equation takes rationally the effect of internal reinforcing bars into consideration as a function of prestressing steel depth to neutral depth ratio. In the experimental study, steel reinforced concrete beams strengthened using external prestressing steel are tested with the test parameters having a large effect on the ultimate stress of prestressing steel. The test parameters includes reinforcing bar and external prestressing steel reinforcement ratios, 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 external prestressing steel.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.1
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• pp.181-192
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• 2007

The purpose of this study is to analyse and compare experimentally flexural behavior of RC beams strengthened with CFRP plates by different methods, and finally suggest the evaluation equations of flexural capacity of RC beams with the aim of application of prestressed CFRP strengthening. The experimental parameters are compressive strength, reinforcement ratio, prestressing level and strengthening methods. The non-prestressed specimens failed on account of separation of the plates from the beams due to premature de-bonding, while most of the prestressed specimens failed due to CFRP plate fracture. The evaluation equations of flexural capacity of RC beams is suggested and these equations have a good reliability in predicting flexural strength of RC beams.

• Journal of Korean Society of Steel Construction
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• v.20 no.2
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• pp.247-258
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• 2008

In this study, static loading tests were performed on H-beam specimens to assess the static behavior of H-beam prestressed with multi-stepwise thermal prestressing method (TPSM). The amount of induced thermal prestress and connection type were differentiated among the 400-mm-high and 6,000-mm-long H-beam specimens to evaluate their effect on the behavior of the beams. From the experimental results, it between the H-beam and the cover-plate increased in yielding load by 13~18%, whereas stiffness increased by 27~34%. In case of specimens with both bolting and welding connection, yie lding load increased by 18~29% and stiffness increased by 43~51%. Multi-stepwise initial stress distribution was also observed from the prestressed specimens, verifying the effectiveness of the multi-stepwise TPSM. By application of the multi-stepwise TPSM, a significant increase in yielding load and stiffness can be achieved, hence increasing sectional and prestressing efficiencies.

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.483-490
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• 2007

Traditional external post-tensioning method using either steel bars or tendons is commonly used as a retrofitting method for concrete bridges. However, the external post-tensioning method has some disadvantages such as stress concentration at anchorages and inefficient load carrying capability regarding live loads. Thermal prestressing method is a newly proposed method for strengthening and rehabilitation of concrete girder bridges. Founded on a simple concept of thermal expansion and contraction of steel, the method is a hybrid method of external post-tensioning and steel plate bonding, combining the merits of two methods. In this paper, basic concepts of the method are presented and an illustrative experiment is introduced. From actual experimental data, the thermal prestressing effect is substantiated and the FEM approach for its analysis is verified.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.641-644
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• 2010

프리스트레싱 시스템이 도입된 구조물의 사용수명이 오래됨에 따라, 이들 구조물의 잔존수명 평가와 보수 및 보강 등의 유지관리 차원에서 프리스트레싱 시스템의 현재 긴장력에 대한 평가는 매우 중요한 현안이 되어왔다. 따라서, 본 논문에서는 프리스트레싱 시스템의 현재 긴장력을 평가하기 위한 첫 단계로서 프리스트레싱 시스템의 긴장력이 구조계의 강성에 미치는 영향을 평가하였다. 이를 위하여 부착식 텐던 형식의 프리스트레싱 시스템이 도입된 시험체를 대상으로 SIMO sine sweep test를 수행하고 긴장력과 시험체의 유효 강성에 대한 상관성을 규명하였다. 그 결과, 프리스트레싱 시스템의 긴장력은 시험체의 유효강성을 증가시키며, 저차 고유진동수가 긴장력과 높은 상관성을 지니는 것으로 나타났다.

• Journal of the Korea Concrete Institute
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• v.19 no.6
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• pp.735-744
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• 2007

This study deals with literature review, developing a predicting equation for the ultimate stress of prestressing (PS) CFRP, and experimental test with the parameters affecting the ultimate stress of prestressing CFRF in prestressed concrete beams strengthened by external prestressing. The ACI (American Concrete Institute) predicting equation for the ultimate stress of unbonded prestressing CFRP is analyzed to develop a new integrated predicting equation. The proposed predicting equation takes rationally the effect of internal PS steel into consideration as a function of prestressing tendon depth to neutral depth ratio. In the experimental study, prestressed concrete beams strengthened using external prestressing CFRP are tested with the test parameters having a large effect on the ultimate stress of prestressing CFRP. The test parameters includes infernal prestressing steel and external prestressing CFRP tendon reinforcement ratios, 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 external prestressing CFRP.

• Journal of Korean Society of Steel Construction
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• v.22 no.6
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• pp.563-572
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• 2010

This study evaluates the load-carrying capacity of a thermal prestressed steel beam with an eccentric bracket. The steel beam that is proposed in this study has an eccentrically installed cover plate through application of the eccentric bracket. The eccentric bracket helps the steel beam achieve greater sectional stiffness and more efficiently induces prestress. A material non-linear characteristic applied finite element analysis was also conducted to check the validity of the experiments. The results of this study showed that the structural stiffness, yield load, and ultimate strength of the TPSM-applied steel beam with the eccentric bracket increased due to the eccentricity of the cover plate.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.4 s.56
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• pp.159-169
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• 2009

In this study, static loading tests and numerical analyses of the composite beam strengthened by multi-stepwise thermal prestressing method were carried out to evaluate the prestressing effect of the thermal prestressing prestress and the sectional effect of the installed cover-plate on the increase in the load-carrying capacity of composit beam. From this study, the strengthening method using multi-stepwise thermal prestressing method (TPSM) can be applied to reduce the deflection of the composite beam as well as to strengthening the composite beam by inducing the prestress in case of the occurrence in the large deflection by the insufficiency of the section properties of the composite beam. because of the expectation of the increase in the yield load and the sectional properties of the composite beam.