• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.595-602
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• 2007

Recently, concrete structures with carbon fiber reinforced polymer (CFRP) reinforcements have been commonly used for the bridge and building construction. In this paper, pier caps were strengthened by prestressed near surface mounted CFRP. To verify the effectiveness of the strengthening method, 7 pier cap specimens were fabricated. One specimen was designed for control, two for external prestressing steel strands, two for CFRP plates, and two for CFRP bars. Experimental variables consist of type of reinforcement materials and prestressing levels. The results of laboratory have shown that the ultimate load capacities of prestressed near surface mounted CFRP specimens were about $20{\sim}33%$ greater than that of a control specimen. Also, ultimate load capacities of prestressed near surface mounted CFRP specimens were similar to those of external prestressing specimens with steel strands.

• Journal of the Korea Concrete Institute
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• v.21 no.4
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• pp.419-429
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• 2009

This study focuses on the effect of the cutting order of prestressing strands on the strain change in the strands and on the state of stress of concrete, experimentally and numerically. In the experiment, strain of strands and of transversal reinforcement were measured for three different cutting orders during detensioning process by using flame-cutting procedure. The experimental results were compared with those obtained from the FE analysis. As a results of the experiment, it is confirmed that the cutting order of prestressing strands affected on the strain of strands as well as of transversal reinforcement. The FE analysis gave similar results to those obtained from the experiment. Therefore, the cutting order should be chosen appropriately to when the strands get detensioned.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.95-96
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• 2009

In this paper, the transfer lengths in pretensioned prestressed Ultra High Performance Concrete members are verified to collect the basis data of UHPC increased in practical uses recently. The cover sizes and pretension forces were the main parameters of UHPC.

• Structural Monitoring and Maintenance
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• v.9 no.2
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• pp.129-155
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• 2022

In this study, parametric analyses on a hoop-type PZT (lead-zirconate-titanate) interface are performed to estimate the effects of the PZT interface's materials and geometries on sensitivities of impedance responses under strand breakage. The paper provides a guideline for installing the PZT interface suitable in tendon anchorages for damage-sensitive impedance signatures. Firstly, the concept of the PZT interface-based impedance monitoring technique in prestressed tendon anchorage is briefly described. A FE (finite element) analysis is conducted on a multi-strands anchorage equipped with a hoop-type PZT interface for analyzing materials and geometric effects. Various material properties, geometric sizes of the interface, and PZT sensor are simulated under two states of prestressing force for acquiring impedance responses. Changes in impedance signals are statistically quantified to analyze the effect of these factors on damage-sensitive impedance monitoring in the tendon anchorage. Finally, experimental analyses are performed to demonstrate the effects of materials and geometrical properties of the PZT interface on damage-sensitive impedance monitoring.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.1
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• pp.147-153
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• 2019

The prestressing steel wire, which is applied a tension to reinforce the structure, is applied flexure simultaneously by the duct and the deviator. In order to evaluate the deflected tensile performance of the prestressing steel wire subjected to both tensile and flexural stresses, the numerical analysis for 600 cases with variables of wire diameters, mandrel diameters, and friction coefficient between mandrel and steel wire was performed. As the result of analysis, the larger the diameter of the steel wire was, the lower the deflected tensile performance was, and the effect decreased with the increase of the wire elongation. The effect of mandrel diameter and friction coefficient between mandrel and wire on the deflected tensile performance of the wire was very small. But the deflected tensile performance and the friction coefficient between mandrel and strand showed a relatively high correlation. Therefore, it is necessary to make enough large elongation to secure the deflected tensile performance. If there is a restriction on the elongation, it is necessary to reduce the diameter of the steel wire to an appropriate value, and to increase the friction between steel wires by adjusting the surface condition of the steel wire.

• Journal of Korean Society of Steel Construction
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• v.29 no.4
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• pp.311-321
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• 2017

This paper deals with the flexural performance of a composite girder system designed to readily form a composite section without a formwork and to easily realize multistage preflexing and prestressing. After a 3-Dimensional finite element modeling for construction stage analysis, the parametric numerical analysis was performed to analyse the stress distribution on the composite girder sections and the prestressing effects along with concrete pouring method and strand tensioning method. Based on the stress distribution analysis, a favorable construction stage model has been rationally chosen and then the ultimate flexural strengths were evaluated to conduct a comparative study, which exceed the nominal flexural strength suggested by the current design specification(ASD). It can be concluded that the proposed composite girder and fabrication procedure should have a sufficient structural performance.

• Smart Structures and Systems
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• v.7 no.4
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• pp.303-317
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• 2011

A specially designed tendon, which is proposed by embedding an FBG sensor into the center king cable of a 7-wire strand tendon, was applied to monitor the prestress force and load transfer of ground anchor. A series of tensile tests and a model pullout test were performed to verify the feasibility of the proposed smart tendon as a measuring sensor of tension force and load transfer along the tendon. The smart tendon has proven to be very effective for monitoring prestress force and load transfer by measuring the strain change of the tendon at the free part and the fixed part of ground anchor, respectively. Two 11.5 m long proto-type ground anchors were made simply by replacing a tendon with the proposed smart tendon and prestress forces of each anchor were monitored during the loading-unloading step using both FBG sensor embedded in the smart tendon and the conventional load cell. By comparing the prestress forces measured by the smart tendon and load cell, it was found that the prestress force monitored from the FBG sensor located at the free part is comparable to that measured from the conventional load cell. Furthermore, the load transfer of prestressing force at the tendon-grout interface was clearly measured from the FBGs distributed along the fixed part. From these pullout tests, the proposed smart tendon is not only expected to be an alternative monitoring tool for measuring prestress force from the introducing stage to the long-term period for health monitoring of the ground anchor but also can be used to improve design practice through determining the economic fixed length by practically measuring the load transfer depth.

• Smart Structures and Systems
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• v.17 no.4
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• pp.577-591
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• 2016

In this study, the transfer length of 2400 MPa, seven-wire high-strength steel strands with a 15.2 mm diameter in pretensioned prestressed concrete (PSC) beams utilizing high strength concrete over 58 MPa at prestress release was evaluated experimentally. 32 specimens, which have the variables of concrete compressive strength, concrete cover depth, and the number of PS strands, were fabricated and corresponding transfer lengths were measured. The strands were released gradually by slowly reducing the pressure in the hydraulic stressing rams. The measured results of transfer length showed that the transfer length decreased as the concrete compressive strength and concrete cover depth increased. The number of strands had a very small effect, and the effect varied with both the concrete cover depth and concrete strength. The results were compared to current design codes and transfer lengths predicted by other researchers. The comparison results showed that the current transfer length prediction models in design codes may be conservatively used for 2400 MPa high-strength strands in high-strength concrete beams exceeding 58 MPa at prestress release.

• Journal of the Korea institute for structural maintenance and inspection
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• v.5 no.2
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• pp.111-120
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• 2001

This paper aims at estimating instantaneous prestress losses by measuring the actual prestress forces in prestressed concrete (PSC) box girder bridges. Measurement were taken to study initial prestress losses such as friction losses and slip losses. A new strain gauge system was developed to measure strains in internal tendons. The system was installed on a total of 20 tendons in a PSC box girder bridges. The variation of prestress forces were monitored during prestressing tendon and after prestress transfer. The prestress losses are also calculated including friction losses and slip losses. The measured data were compared with the theoretical values. The result shows that the measured prestress forces agree well with the theoretical values. It is shown that prestress force of each strand in the same tendon is a bit different. This study also shows that prestress losses of continuity tendons during prestress transfer are significantly different each other, which results from the variety of buttress location and tendon profile. The present study provides realistic information on the estimation of actual prestress forces and losses in PSC box girder bridges.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.93-96
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• 2008

This paper deals with the shaking table test(STT), the Quasi-Static Test(QST), and the Pseudo-Dynamic Test(PDT) to evaluate the seismic performance of RC bridge piers under near fault ground motion. Five scaled specimens were constructed the weight of the superstructure was applied through the prestressing strand at the centroid of the column section during the QST and PDT. However, the STT was simulated. The lateral inertia force of the superstructure by the mass frame which was linked with the pier because of the limited payload of shaking table. Particularly for the STT, friction underneath the mass frame was minimized by special details and it was verified by a series of pre-load test. Scale factor of the RC piers was 4.25.