• KCI Concrete Journal
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• v.12 no.1
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• pp.131-138
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• 2000

The research purpose of this paper is to investigate the influential Parameters on the unbonded tendon stress. The parameters were the reinforcing ratio, the prestressing ratio, and the loading type. To this end. first, the influence of parameters were examined with twenty eight test results obtained from references. Then, an experimental study was carried out with nine specimens. Test variables were the reinforcing ratio and the prestressing ratio. Specimens were divided equally into three groups and each group had a different level of the reinforcing ratio. Each specimen within a group has a different level of the prestressing ratio. The investigation with previous and current tests revealed the followings; (1) the length of crack distribution zone does not have a close relation with the length of plastic hinge. (2) the prestressing ratio does not affect both the length of crack distribution and the length of plastic hinge, (3) the tendon stress variation is in reverse relation with the ratios of mild steels and tendons, (4) the loading type nay not affect significantly the length of crack distribution zone, (5) AASHTO LRFD Code equation and Moon/Lim's design equation predicted the test results well with some safety margins.

• Journal of the Korea Concrete Institute
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• v.17 no.4 s.88
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• pp.521-526
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• 2005

Prestressing tendons in a nuclear containment building dome are non-axisymmetrically arranged in most cases. However, simple axisymmetric modeling of the containment has been often employed in practice to estimate structural behavior for the axisymmetric loadings such as an internal pressure. In this case, the axisymmetric approximation is required for the actual tendon arrangements in the dome. Some procedures are proposed that can implement the actual 3-dimensional tendon stiffness and prestressing effect into the axisymmetric model. Prestressing tendons, which are arranged in 3 or 2-ways depending on a containment type, are converted into an equivalent layer to consider the stiffness contribution in meridional and hoop directions. In order to reflect the prestressing effect, equivalent load method and initial stress method are devised and the corresponding loads or stresses are derived in terms of the axisymmetric model. In a companion paper, the proposed schemes are applied into CANDU and KSNP(Korean Standard Nuclear Power Plant) type containments and are verified through some numerical examples comparing the analysis results with those of the actual 3-dimensional model.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.475-480
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• 2002

This study is to develop a strengthening method for slab bridges with external prestressing. There are so many different strengthening methods for damaged slab bridges, external prestressing method is the most effective, economical and durable strengthening method among them. But, its problem lies in anchoring devices, so recently, an effective anchoring method was developed and showed its improvements. In this study, a more improved method is suggested. Longitudinal tendons placed on both side of slab strengthens the whole bridge, and lateral tendons placed under the slab strengthens the middle of slab, and conveys the load at middle slab to both sides. Structural analysis for the tensile force for strengthening were analysed. Generally, 200-280tons for longitudinal tendon and 130-190 tons for lateral tendons are good enough to strengthen the damaged slab. This method has no upward roof work, so it is very convenient for installing. And no spaces under the slab are need, so it is good for shallow slabs which has less space under the slab.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.501-506
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• 2002

The unbonded prestressed concrete(PSC) members exhibit very different structural behavior from that of bonded PSC members because of having different tendon stress increment. Recently, AASHTO changed the provision of ultimate tendon stress with unbonded tendons, because some researches tried to improve the provision of ultimate tendon stress with unbonded tendons. The purpose of the present study is to compare various Codes with the ultimate failure stresses of prestressing(PS) steels for the unbonded PSC members. To this end, Some national Codes have been collected and analyzed. A series of major influencing variables have been included in the analysis. It was found that the span-depth ratio, neutral axis depth-effective depth ratio, concrete compressive strength, effective prestress, and prestressing steel ratio have great influence on the ultimate failure stress of PS steel in unbonded PSC members. The Comparison indicates that existing formulas including ACI and domestic Code's equations shows some unwarranties. The present study allows more realistic analysis and design of prestressed concrete structures with internal unbonded tendons.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.570-573
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• 2006

It is proposed that the electromechanical relation of the conductive materials with high electrical resistance may be used to estimate the current stress of prestressing tendons. To choose the best conductive material to this end, we studied the electromechanical relations of carbon fibers and metalic heat wires experimentally. It is found that the relation of carbon fibers can be modelled by a parabolic(or hyperbolic) function in the early stage of deformation. Metallic heat wires show a consistent linear relation during loading and unloading in the elastic deformation and are suitable for this purpose. We propose a new kind of prestressing tendons whose stress can be monitored.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.758-761
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• 2004

Prestressing tendons of the nuclear containment building dome are arranged in a non-axisymmetric manner. However, simple axisymmetric modeling of the containment building is often employed to estimate the structural behavior for, e.g. the ultimate pressure, which requires the axisymmetric approximation of the actual tendon arrangements of the dome. A procedure is proposed that can devise the actual 3-dimensional tendon stiffness and prestressing effect into the axisymmetric model. A numerical example of the CANDU type is presented to verify the procedure and to estimate the amount of approximation.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.639-644
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• 2000

Prestressing steels are susceptible to corrosion, which is considered the major reason in the deterioration of prestressed concrete structures. To solve this problem, many research have been made to utilize new type of tendons. FRP tendons have many advantages compared to steel tendons. However, FRP tendons have some disadvantages, such as no plastic behavior. This study focused on the flexural behavior of prestresssed concrete beams which is fabricated by post-tensioning method with CFRP (Carbon Fiber Reinforced Plastic) tendons. Th results drawn from the study, prestressed concrete beams with CFRP tendons have higher flexural cracking load, flexural yielding load, and flexural fracture load. While displacement at the fracture stage is lower compared to prestressed concrete beams with steel tendon. Excessive steel reinforcement lead lower ductility index. So, appropriate reinforcement guideline is needed. Further more, prestressed concrete beams with CFRP tendons can have sufficient ductility index when ruptured by crushing of concrete or used unbonded tendon. Therefore, the best design method for prestressed concrete beams with CFRP tendons is over-reinforcement, and use of unbonded tendon.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.643-648
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• 1998

Despite many advantages of FRP materials, such as corrosion resistance, their linear elastic behavior up to rupture is likely to result in a lack of ductility. This paper discusses ductility improvement methods for prestressed concrete beams using FRP tendons. The methods were evaluated thorough extensive analytical and experimental investigations. The methods include optimization of sectional ductility through proper reinforcement, concrete confinement, concrete reinforcement with fibers, and prestressing with unbonded tendons.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.1
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• pp.227-238
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• 2003

Due to deterioration of bridge, usually be using the external prestressing method among repair reinforcement method. But, there is much to be desired about a detailed account, almost it has analysed by cambers of girders, deflections of middle span and upper, bottom stresses of girders. Also, it is not examined closely that effect of internal prestress by external prestressing. The purpose of this study is confirmed the effect of internal tendons by external prestressing, estimation of additional external prestressing force and look for exact external prestressing force.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.685-688
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• 1999

The analysis and design of composite girders prestressed by external tendons involve difficulties related to the position of anchorages and the construction sequences. In this paper, the efficiency of the external tendon profiles and the position of anchorages in examined for the internal and external prestressing of statically indeterminate structures. It is shown that strengthening of a prestressed girder can be accomplished using a variety of methods; bonded external prestressing, tendon replacement and unbonded external prestressing.