• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.4
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• pp.77-83
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• 2014

Prestressed concrete 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. In certain situations, the prestressing tendon is supposed to be bent by the construction error and the radius of curvature at the continuous joint of PSC girders, and this leads to the loss of prestressing force. However, this kind of prestress loss is not considered in the design and construction processes. This study proves that the prestress loss occurs at the continuous joint due to the local bending of tendon by the construction error or the radius of curvature. Also, a method that can reduce this type of prestress loss is proposed, and proved by the experiment. The result shows that maximum 10% of prestress loss occurs at the continuous joint and the proposed block-out method can reduce the prestress loss ratio by maximum 5%, approximately. This means that the block-out method can enhance the prestressing efficiency of continuous PSC girder bridges.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.2A
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• pp.363-370
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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. The strain of those materials was controlled instead of the stress during the experiment. It is found that the relation of carbon fibers can be modelled by a parabolic(or hyperbolic) function in the early stage of deformation. However because the relation is not consistent when it is unloaded and reload, carbon fibers are not suitable for this purpose. Metallic heat wires show a consistent linear relation during loading and unloading in the elastic deformation and are suitable for this purpose. To estimate the electromechanics relation of metallic wires, we developed a simple formula based on the rigid plasticity. We propose a new kind of prestressing tendons whose stress can be monitored. As a side result of this study, we found that the electromechanical relation of carbon fibers without epoxy matrix becomes almost linear after a certain strain.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.6
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• pp.525-532
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• 2014

The purpose of this study is to analyze the deflection for serviceability assessment of the prestressed concrete one-way slab using finite element program. Proposed finite element analysis method was verified comparing with existing experimental results, and it showed a good agreement. Also, a parametric study has been conducted to analyze the influence of concrete compressive strength, eccentricity, live load, and tendon profile. The finite element analysis results were compared with hand calculation results. Deflections were decreased as the concrete compressive strength increases, eccentricity increases, and the live load decreases. The deflection of straight tendon was smallest. And regression analysis has been conducted to analyze the correlation between parameters and camber.

• Computational Structural Engineering
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• v.10 no.4
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• pp.315-325
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• 1997

This paper describes the application of discretized continuum-type optimality criteria (DCOC) and the development of optimum design program for the multispan partially prestressed concrete beams. The cost of construction as objective function which includes the costs of concrete, prestressing steel, non-prestressing steel and formwork is minimized. The design constraints include limits on the maximum deflection, flexural and shear strengths, in addition to ductility requirements, and upper and lower bounds on design variables as stipulated by the design Code. Based on Kuhn-Tucker necessary conditions, the optimality criteria are explicitly derived in terms of the design variables-effective depth, eccentricity of prestressing steel and non-prestressing steel ratio. The prestressing profile is prescribed by parabolic functions. The self-weight of the structure is included in the equilibrium equation of the real system, as is the secondary effect resulting from the prestressing force. An iterative procedure and computer program for updating the design variables are developed. Two numerical examples of multispan PPC beams with rectangular cross-section are solved to show the applicability and efficiency of the DCOC-based technique.

• Magazine of the Korea Concrete Institute
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• v.6 no.1
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• pp.89-100
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• 1994

The current test procedure for transfer length, which determine transfer length by measuring concrete strain, has an actual bond stress state in the prestressed pretensioned member : however, it is difficult to determine the bond properties of maximum bond stress and bond stiffness with this method. It is also difficult for design engineer to understand and select a correct safety criterion from the widely distributed results of such a ransfer test alone. An alternative testing procedure is provided here to determine the bond properties without measuring the concrete strain. In this test the bond stress is measured directly by creating a similar boundary condition within the transfer length in a real beam during the transfer of prestressing force. The prestressing force was released step by step by step from the unloading side. The release of force induces a swelling of the strand at the unloading side of concrete block, bonding force in the block, and a bond slip of the strand toward the other side of the block. Two center-hole load cells are used to record the end loads until the point of general bond slip(maximum bond stress). It is suggested that this test procedure be performed with the ordinary transfer test when determining the transfer length in a prestressed, pretensioned concrete beam.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.28 no.6
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• pp.715-722
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• 2015

The prestressing force has not been managed after construction nevertheless it is one of the importrant factors that maintain the structural safety of PSC girder bridges. The prestressing force is just measured during construction using jacking device and after that, it can not be managed practically. For this reason, this study investigated the measurements of prestress using embedded sensors that can be available now with an ultimate goal to propose smart prestressed girders that can measure the prestress from the birth to the end of service life. 4 types of sensors were installed on the small prestressed girders, and the applicability and the accuracy of those sensors were tested while the prestress was applied to the girders. The results show that a center-hole type loadcell has a tendency to measure a prestressing force higher than a reference value, especially when it is loaded with an eccentricity. a EM sensor shows several advantages that has a good practical accuracy, that can be installed anyplace along the tendons.

• 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.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.3 s.55
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• pp.225-231
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• 2009

This study introduces the CFTA girder(Concrete-Filled and Tied Steel Tubular Arch Girder) which is a combined structural system of traditional CFT, arch, and prestress structures. Static load tests and structural behavior analyses were carried out for a 25m long CFTA girder. In the analysis, each load of 58kN, 88kN, 148kN, 207kN,and 298kN was applied incrementally at the positions of 1.0 m distances in both directions from the center of the girder. On each test, strain and displacement were measured. Linear static FEM analyses using Strand7 code were also performed to check the structural stability and to investigate the effects of prestressing(${\pm}$20%) and material property(Young's modulus) on the displacement and strain. The results of this study are summarized as follows: the initial strain & displacement under selfweight and prestressing were influenced with the variation of prestressing, but they were mainly effected only by Young's modulus when additional loads were applied.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.993-999
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• 2008

A girder height limitation is the critical parameter for rapid construction of bridge deck and construction space limitation especially in urban area such as high population area and high density habitats. A standard post-tensioned I-shaped concrete girder usually demands relatively higher girder height in order to retain sufficient moment arm between compression force and tensile force. To elaborate this issue, a small U-shaped section with wide flanges can be used as a possible replacement of I-shaped standard girder. This prestressed concrete box girder allows more flexible girder height adjustment rather than standard I-shaped post-tensioned girder plus additional torsion resistance benefits of closed section. A 30m-long, 1.7m-high and 3.63m-wide actual small prestressed concrete box girder is designed and a laboratory test for its static behaviors by applying 6,200kN amount of load in the form of 4-point bending test was performed. The load-deflection curve and crack patterns at different loading stage are recorded. In addition, to extracting the dynamic characteristics such as natural frequency and damping ratio of this girder, several excitation tests with artificial mechanical exciter with un-symmetric mass are carried out using operational frequency sweep-up. Nonlinear finite element analysis of this 4 point bending test under monotonic static load is investigated and discussed with aids of concrete damaged plasticity formulation using ABAQUS program.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.85-94
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• 2005

Post-tensioned Precast concrete System(PPS) consists of U-shaped precast wide beams and concrete column. The continuity of beam-column joint is provided with floor concrete cast on the PC shell beam and post-tensioning. The purpose of this paper is to evaluate the response of PPS interior beam-column joint subjected to cyclic lateral loading. To this end, an experimental investigation was performed with three half-scale specimens of interior connection. The design parameters are the amount of beam reinforcement placed inside the joint core. The test results showed that cracks were distributed well without my significant degradation of strength and ductility. Also, it was found that the prestressing may affect to alter the torsional crack angle. And the specimens sufficiently resist up to limiting drift ratio of 0.035 in accordance with the provisional by ACl of acceptance criteria for concrete special moment frames.