• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.5
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• pp.123-134
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• 2007

A method to determine the initial force of external tendon is proposed to improve the load carrying capacity in existing steel-concrete composite bridges. This method is applied to tensioning external tendons prior to and after concrete replacement for strengthening composite girders. A procedure to determine the number of tendon and initial tendon force is described with the proposed rating factor, which considers the increment of tendon force due to live loads. The method is applied to the improvement of rating factor in an existing composite bridge and its validity is confirmed.

• Structural Engineering and Mechanics
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• v.65 no.2
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• pp.129-139
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• 2018

Post-tensioning (PT) tendons are commonly used for the assembly of modularized concrete members, and tension is applied to the tendons during construction to facilitate the integrated behavior of the members. However, the tension in a PT tendon decreases over time due to steel corrosion and concrete creep, and consequently, the stress on the anchor head that secures the PT tendon also diminishes. This study proposes an automatic detection system to identify tension reduction in a PT tendon using pulsed-eddy-current (PEC) measurement. An eddy-current sensor is installed on the surface of the steel anchor head. The sensor creates a pulsed excitation to the driving coil and measures the resulting PEC response using the pick-up coil. The basic premise is that the tension reduction of a PT tendon results in stress reduction on the anchor head surface and a change in the PEC intensity measured by the pick-up coil. Thus, PEC measurement is used to detect the reduction of the anchor head stress and consequently the reduction of the PT tendon force below a certain threshold value. The advantages of the proposed PEC-based tension-reduction-detection (PTRD) system are (1) a low-cost (< $ 30), low-power (< 2 Watts) sensor, (2) a short inspection time (< 10 seconds), (3) high reliability and (4) the potential for embedded sensing. A 3.3 m long full-scale monostrand PT tendon was used to evaluate the performance of the proposed PTRD system. The PT tendon was tensioned to 180 kN using a custom universal tensile machine, and the tension was decreased to 0 kN at 20 kN intervals. At each tension, the PEC responses were measured, and tension reduction was successfully detected.

• Journal of Ocean Engineering and Technology
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• v.20 no.2 s.69
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• pp.16-21
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• 2006

This paper discusses the behavior of post-tensioned and shaped hypar space truss, with consideration of the influence of removing some web members. Hypar space truss is post-tensioned at the bottom chords of one diagonal on the ground; the essential behavior characteristic of shape formation is discussed by using a small-scale test model. Results of experiments and nonlinear finite-element analysis indicate that a planar, rectangular- arranged structure can be deformed to a predicted hyper shape, by the proposed shape formation method. Also the feasibility of the proposed method for furnishing of a hypar shaped face truss has been presented, under the condition of both non-removed and partially removed web members. It follows that a nonlinear finite element analysis method can be used in predicting the behavior of the space shape and the post-tensioning force in sharing of hypar space truss. Further, in comparison to the other cases, the results of test and analysis show that the active diagonal shaping in the non-removed web members and passive diagonal shaping of partially removed web members are in relatively good agreement.

• Earthquakes and Structures
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• v.16 no.2
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• pp.209-219
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• 2019

Unbonded Post-Tensioned (UPT) precast concrete systems have been shown to provide excellent seismic resistance. In order to improve understanding of the dynamic response of UPT systems, a series of snap back tests on four UPT systems was undertaken consisting of one Single Rocking Wall (SRW) and three Precast Wall with End Columns (PreWEC) systems. The snap back tests provided both a static pushover and a nonlinear free vibration response of a system. As expected the SRW exhibited an approximate bi-linear inertia force-drift response during the free vibration decay and the PreWEC walls showed an inertia force-drift response with increased strength and energy dissipation due to the addition of steel O-connectors. All walls exhibited negligible residual drifts regardless of the number of O-connectors or the post-tensioning force. When PreWEC systems of the same strength were compared the inclusion of further energy dissipating O-connectors was found to decrease the measured peak wall acceleration. Both the local and global wall parameters measured at pseudo-static and dynamic loading rates showed similar behaviour, which demonstrates that the dynamic behaviour of UPT walls is well represented by pseudo-static tests. The SRW was found to have Equivalent Viscous Damping (EVD) between 0.9-3.8% and the three PreWEC walls were found to have maximum EVD of between 14.7-25.8%.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.40-43
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• 2004

A new design method for prestressed concrete girder is proposed in this study, which steps for manufacturing are; (1) the bottom part of concrete girder is placed and pretensioned by the first post-tensioning performed on the tendons located in the bottom part of concrete girder, and (2) the next step which consists of concrete placing and post-tensioning operation is followed by the previous step if required. This indicates that sufficient compressive stress can be effectively introduced at the bottom face in stepwise manner, when compared to conventional PSC girder. Two specimens are prepared and tested to investigate the short-term behavior of the PSC girders manufactured by the proposed method. Section Analysis results exhibit good agreements with the test results in terms of strain distribution across the girder section. In addition, flexural strength obtained from the tests is found to be similar to the expected based on Code(Korea). These demonstrate that the method proposed in this study is applicable to the design of PSC girders.

• Journal of Ocean Engineering and Technology
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• v.17 no.1
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• pp.41-46
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• 2003

본 논문은 공간구조의 기본 요소인 피라미드형 구조단위에 대한 해석과 포스트텐션 시험의 결과를 기술하였다. 시험과정 중에 관찰된 거동 특성을 분석하고 수치해석의 결과와 비교 검토하였으며 시험모델에 대한 미케니즘(Mechanism)을 기하학적 해법으로 확인하였다. 이 논문의 결과는 다 방향성을 가진 조인트 시스템(Mero Joint System)을 이용한 공간구조의 거동을 정확하게 예측할 수 있고 비교적 작은 포스트텐션력으로 공간구조의 형성과 시공이 가능함을 제안하고 있으며 공간구조가 미케니즘을 포함할 경우 큰 변형이 일어나므로 비선형 거동을 고려해야 함을 나타내고 있다.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.238-241
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• 2006

The needs for strengthening and rehabilitation of the concrete bridges are a growing concern in many countries and has been emphasized in various researches and papers. Traditional external post-tensioning method using either steel bars or tendons is commonly used as a strengthening method. However, the method has some disadvantages such as stress concentration at the anchorages. Multi-stepwise 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 on strengthening and rehabilitation of concrete girder are presented and an illustrative experiment is introduced.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.575-576
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• 2009

From the extensive review of literature on existing precast prestressed concrete pavement (PPCP) systems, an innovative PPCP system has been developed. After the analysis and design, the sample system has been built and experimented under service loads and the defects of the system has been noted. Further study has been done to improve the performance of the defects. The appeared cracks around post-tensioning pockets was a crucial problem which needed to be solved in order to satisfy the service life of the system without any doubt. In this paper, different shape and arrangement of the post-tensioning pockets in the joint panel has been designed and analysed in order to find best performance for the system.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.657-662
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• 2000

This paper presents the results from experimental study that investigated to explore the load transfer characteristics of post-tensioning anchorage zones. The experimental program investigated the primary variables which affect the ultimate load, lateral strains and crack width: concrete compressive strength, details of reinforcement and shape of anchorage. Through this research, it was found that the governing factor of the ultimate load was not compressive cylinder strength but tensile splitting strength. Ultimate load was increased and lateral strain was decreased as the ratio of spiral increased because the lateral expansion of th concrete inside the spiral was restrained by the spiral. Furthermore, the shape of anchorage which can diminish the wedge effect of anchorage and disperse the anchorage force in various depths was more effective.

• Proceedings of the Korea Concrete Institute Conference
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• 1997.10a
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• pp.797-802
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• 1997

The current study is a part of series o research about the development of new superstructure system to overcome the engineering problems in the design of bridges of 30m to 45m in span length using the existing bridge systems. The basic concept of new system is the continuation of adjacent tow simple spans composed of the precast prestressed concrete U-type sections. The partial post tensioning method is applied to create the continuity. In this study, the new technique was introduced and applied with an example design of tow span of 40m in span length to find the possibility for practical application as the feasibility study. The obtained results show that the new splicing method is expected to offer significant economical and serviceability advantages.