• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.579-584
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• 1998

The purpose of this study is to evaluate the flexural strengthening effects of RC beams reinforced with carbon fiber sheets (CFS) in variable of strengthening amount and anchorage length of CFS. This study can be summarized as follows. The CFS shares the tensile stress such as rebar during loading test. Also, as the strengthening amount of CFS is increased, the maximum flexural strength of RC beams reinforced with CFS is increased. Therefore, it is confirmed that the CFS's strengthening method is very effective to improve the flexural strength of RC beams. The maximum flexural strength of RC beams with CFS is determined by bond failure between CFS and concrete surface. So, the evaluation of CFS's strengthening effect can be calculated using the tensile stress of CFS which is peeling. When the anchorage length of CFS. But, in case of same anchorage length of CFS, when the strengthening amount of CFA is increased, the ductility is decreased. Therefore, it is considered that the anchorage of CFS in the end zone is necessary.

• Journal of the Korea institute for structural maintenance and inspection
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• v.2 no.2
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• pp.195-201
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• 1998

The purpose of this study is to evaluate the flexural strengthening effects of RC beams reinforced with carbon fiber sheets (CFS) in variable of strengthening amount and anchorage length of CFS. This study can be summarized as follows ; The CFS shares the tensile stress such as rebar during loading test. Also, as the strengthening amount of CFS is increased, the maximum flexural strength of RC beams reinforced with CFS is increased. Therefore, it is confirmed that the CFS's strengthening method is very effective to improve the flexural strength of RC beams. The maximum flexural strength of RC beams with CFS is determined by bond failure between CFS and concrete surface. So, the evaluation of CFS's strengthening effect can be calculated using the tensile stress of CFS which is peeling. When the anchorage length of CFS is increased, the ductility of RC beams is increased because of delaying the peeling of CFS. But, in case of same anchorage length of CFS, when the strengthening amount of CFS is increased, the ductility is decreased. Therefore, it is considered that the anchorage of CFS in the end zone is necessary.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.3A
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• pp.329-336
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• 2010

An experimental study to evaluate bursting behavior in anchorage zone of the standard PSC I girders (span length : 30 m) has been carried out. The arrangement of bursting reinforcement in anchorage zone of the standard PSC I girders is considered to be designed without accurately reflecting the stress flows in the end zone of the PSC I girders caused by presstressing forces of the tendons. Also, due to excessive arrangement of the bursting bars, the workability of the girder is decreased greatly. In this study, three specimens with the same dimensions as the end zone of the standard PSC I girder are prepared and the experiment is carried out by applying PS forces. The bursting reinforcement of each specimen consists of 100 mm, 200 mm, and 300mm spacings, respectively. The experimental results show that the range of the PS forces to cause crack in the anchorage zone of the specimen are more than 1.6 times of the design PS forces. The bursting cracks occur in the vertical direction on the inside of all specimens. After applying 2.7 times of the design PS force, some of the transverse bursting reinforcements only in the specimen reinforced by 300 mm spacing yielded. The experimental results show that the anchorage zone of the standard PSC I girders arranged by 300 mm spacing of the bursting reinforcements which is the maximum spacing allowed in the road bridge design specifications, can be considered safe enough.

• International Journal of Concrete Structures and Materials
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• v.10 no.2
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• pp.149-161
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• 2016

This paper presents an experimental work to study the flexural strength of reinforced concrete (RC) beams strengthened by partially de-bonded near surface-mounted (NSM) fiber reinforced polymer (FRP) strip with various de-bonded length. Especially, considering high anchorage capacity at end of a FRP strip, the effect of de-bonded region at a central part was investigated. In order to check the improvement of strength or deformation capacity when the bonded surface area only increased without changing the FRP area, single and triple lines of FRP were planned. In addition, the flexural strength of the RC member strengthened by a partially de-bonded NSM FRP strip was evaluated by using the existing researchers' strength equation to predict the flexural strength after retrofit. From the study, it was found that where de-bonded region exists in the central part of a flexural member, the deformation capacity of the member is expected to be improved, because FRP strain is not to be concentrated on the center but to be extended uniformly in the de-bonded region. Where NSM FRP strips are distributed in triple lines, a relatively high strength can be exerted due to the increase of bond strength in the anchorage.

• Earthquakes and Structures
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• v.5 no.5
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• pp.527-552
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• 2013

Development of flexural yielding and large rotation ductilities in the plastic hinge zones of frame members is synonymous with the spread of bar reinforcement yielding into the supporting anchorage. Yield penetration where it occurs, destroys interfacial bond between bar and concrete and reduces the strain development capacity of the reinforcement. This affects the plastic rotation capacity of the member by increasing the contribution of bar pullout. A side effect is increased strains in the compression zone within the plastic hinge region, which may be critical in displacement-based detailing procedures that are linked to concrete strains (e.g. in structural walls). To quantify the effects of yield penetration from first principles, closed form solutions of the field equations of bond over the anchorage are derived, considering bond plastification, cover debonding after bar yielding and spread of inelasticity in the anchorage. Strain development capacity is shown to be a totally different entity from stress development capacity and, in the framework of performance based design, bar slip and the length of debonding are calculated as functions of the bar strain at the loaded-end, to be used in calculations of pullout rotation at monolithic member connections. Analytical results are explored parametrically to lead to design charts for practical use of the paper's findings but also to identify the implications of the phenomena studied on the detailing requirements in the plastic hinge regions of flexural members including post-earthquake retrofits.

• Steel and Composite Structures
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• v.27 no.4
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• pp.509-523
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• 2018

This paper presents experimental results on the residual bond-slip behavior of high strength concrete-filled square steel tube (HSCFST) after elevated temperatures. Three parameters were considered in this test: (a) temperature (i.e., $20^{\circ}C$, $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$, $800^{\circ}C$); (b) concrete strength (i.e., C60, C70, C80); (c) anchorage length (i.e., 250 mm, 400 mm). A total of 17 HSCFST specimens were designed for push-out test after elevated temperatures. The load-slip curves at the loading end and free end were obtained, in addition, the distribution of steel tube strain and the bond stress along the anchorage length were analyzed. Test results show that the shape of load-slip curves at loading ends and free ends are similar. With the temperature constantly increasing, the bond strength of HSCFST increases first and then decreases; furthermore, the bond strength of HSCFCT proportionally increases with the anchoring length growing. Additionally, the higher the temperature is, the smaller and lower the bond damage develops. The energy dissipation capacity enhances with the concrete strength rasing, while, decreases with the temperature growing. What is more, the strain and stress of steel tubes are exponentially distributed, and decrease from the free end to loading end. According to experimental findings, constitutive formula of the bond slip of HSCFST experienced elevated temperatures is proposed, which fills well with test data.

• Steel and Composite Structures
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• v.4 no.5
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• pp.333-353
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• 2004

Strength of reinforced concrete beams can easily be increased by the use of externally bonded CFRP composites. However, the mode of failure of CFRP strengthened beam is usually brittle due to tension-shear failure in the concrete substrate or bond failure near the CFRP-Concrete interface. In order to improve the ductility of CFRP strengthened concrete beams, critical variables need to be investigated. This experimental and analytical research focused on a series of reinforced concrete beams strengthened with CFRP composites to enhance the flexural capacity and ductility. The main variables were the amount of CFRP composites, the amount of longitudinal and shear reinforcement, and the effect of CFRP end diagonal anchorage system. Sixteen full-scale beams were investigated. A new design guideline was proposed according to the effects of the above-mentioned variables. The experimental and analytical results were found to be in good agreement.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.374-379
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• 1994

This paper deals with the problem of plate separation and anchorage at the ends of steel plates strengthened by EBSP. Test results show that the reinforced concrete beams strengthened by EBSP occurs the premature failure without the beams achieving their full flexural strength at the end of plates. The premature failure is the cause of stress concentrations in the adhesive layer of plate, reinforced concrete incase of lack of plate length. Then a simple, approximate procedure for predicting the shear and normal stress concentrations is investigated by Robert's the ory based on partial interaction theory. The theoretical results are compared, and show close agreement with test results. A method is derived for determining the plate length that prevents the premature anchorage zone failure

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.451-452
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• 2010

Prestressed concrete I girder bridge has been one of the most widely used bridges in the world because of its excellent construction feasibility, economic efficiency, serviceability, and safety. But in Korea, the PSC bridge has not been utilized for long span because of high girder height in its standard design. Thus, the results confirm that it is possible to applicate the continuous PSC girder with end cross beam anchorage system using multi-stage prestressing technique.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.512-517
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• 2003

The repeated loading responses of four shear-critical reinforced concrete beams, with two different shear span-to-depth ratios, were studied. One series of beams was reinforced using pairs of bundled stirrups with $90^{\circ}C$ standard hooks, having free end extensions of $6d_b$. The companion beams contained shear reinforcement made with larger diameter headed bars anchored with 50mm diameter circular heads. A single headed bar had the same area as a pair of bundled stirrups and hence the two series were comparable. The test results indicate that beams containing headed bar stirrups have a superior performance to companion beams containing bundled standard stirrups, with improved ductility, larger energy adsorption and enhanced post-peak load carrying capability. Due to splitting of the concrete cover and local crushing, the hooks of the standard stirrups opened, resulting in loss of anchorage. In contrast, the headed bar stirrups did not lose their anchorage and hence were able to develop strain hardening and also served to delay buckling of the flexural compression steel. Excellent load-deflection predictions were obtained by reducing the tension stiffening to account for repeated load effects.