• Smart Structures and Systems
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• 제17권6호
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• pp.917-933
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• 2016

In a prestressed concrete bridge, the magnitude of the prestress force (PF) decreases with time. This unexpected loss can cause failure of a bridge which makes prestress force identification (PFI) critical to evaluate bridge safety. However, it has been difficult to identify the PF non-destructively. Although some research has shown the feasibility of vibration based methods in PFI, the requirement of having a determinate exciting force in these methods hinders applications onto in-service bridges. Ideally, it will be efficient if the normal traffic could be treated as an excitation, but the load caused by vehicles is difficult to measure. Hence it prompts the need to investigate whether PF and moving load could be identified together. This paper presents a synergic identification method to determine PF and moving load applied on a simply supported prestressed concrete beam via the dynamic responses caused by this unknown moving load. This method consists of three parts: (i) the PF is transformed into an external pseudo-load localized in each beam element via virtual distortion method (VDM); (ii) then these pseudo-loads are identified simultaneously with the moving load via Duhamel Integral; (iii) the time consuming problem during the inversion of Duhamel Integral is overcome by the load-shape function (LSF). The method is examined against different cases of PFs, vehicle speeds and noise levels by means of simulations. Results show that this method attains a good degree of accuracy and efficiency, as well as robustness to noise.

• KCI Concrete Journal
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• 제11권3호
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• pp.99-107
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• 1999

In designing the Prestressed concrete box-girder bridge. dead load, prestressing force, creep and shrinkage of concrete are the main factors which influence the camber and deflection of segmental concrete structure under construction. Among these factors the creep and shrinkage are the functions of the time-dependent property which. therefore, must be considered with time. The prediction model for estimating creep and shrinkage of concrete has been suggested by ACI, CEB/FIP, JSCE and KSCE design code and EMM, AEMM, RCM, IDM and SSM has been suggested for analytical method in consideration of time-dependent characteristics. In this study the creep test was carried out for four different curing ages of concrete which were applied to the Prestressed concrete structure at the construction site, and the results of test were compared with the values of creep prediction proposed by the design code. Also the creep test was performed with step-wise incremental stresses and the results were compared to the analytical values.

• 한국안전학회지
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• 제15권3호
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• pp.102-107
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• 2000

The extensive use of pretensioned prestressed concrete in the modem construction industry, together with wider application of pretensioned components for structural purposes requires some important consideration on the adequate transfer of prestress force into the concrete, especially around the end zones of pretensioned member. The main objective of this paper is to study the effects of various important parameters on the bond characteristics of prestressing strand around the end zone of high strength pretensioned concrete members. To this end, a comprehensive experimental program has been set up. The principal test variables considered were strand diameter, concrete strength, concrete cover size. The present study provides valuable test data for the realistic and accurate determination of transfer length, which can be efficiently used for improving the design equation of transfer length in pretensioned prestressed concrete members.

• 콘크리트학회논문집
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• 제26권4호
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• pp.533-543
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• 2014

최근 들어, 지하주차장과 같은 모듈화 건물에 프리캐스트 콘크리트와 현장타설 콘크리트가 함께 사용되는 복합공법의 사용이 증가하고 있다. 일반적으로 프리캐스트 콘크리트는 공장에서 선 제작되기 때문에 재료의 효율성을 극대화하기 위해 프리텐션을 도입하여 사용한다. 현행 구조기준이 긴장력이 가해진 단일 단면의 전단 강도식은 제시하지만 긴장력이 가해진 프리캐스트와 현장타설 콘크리트 합성단면의 전단강도식은 제시하지 못하고 있는 실정이다. 따라서 긴장력이 가해진 합성 부재의 전단강도 실험을 통해 긴장력이 전단강도에 미치는 영향과 합성부재의 전단강도 산정시 고려해야할 사항에 대해 알아보았다. 변수로는 콘크리트의 면적비, 긴장재의 긴장력, 전단 경간비, 그리고 전단철근비를 고려하였다. 실험 결과를 분석해보면, 전단강도는 긴장력 크기와 긴장력이 가해진 단면의 면적비가 커질수록 증가하였고 전단경간비가 증가할수록 감소하였다.

• Computers and Concrete
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• 제14권2호
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• pp.109-125
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• 2014

The force transfer mechanism in positive moment continuity details for prestressed concrete girder bridges is investigated in this paper using a three-dimensional detailed finite element model. Positive moment reinforcement in the form of hairpin bars as recommended by the National Cooperative Highway Research Program Report No 519 is incorporated in the model. The cold construction joint that develops at the interface between girder ends and continuity diaphragms is also simulated via contact elements. The model is then subjected to the positive moment and corresponding shear forces that would develop over the service life of the bridge. The stress distribution in the continuity diaphragm and the axial force distribution in the hairpin bars are presented. It was found that due to the asymmetric configuration of the hairpin bars, asymmetric stress distribution develops at the continuity diaphragm, which can be exacerbated by other asymmetric factors such as skewed bridge configurations. It was also observed that when the joint is subjected to a positive moment, the tensile force is transferred from the girder end to the continuity diaphragm only through the hairpin bars due to the lack of contact between the both members at the construction joint. As a result, the stress distribution at girder ends was found to be concentrated around the hairpin bars influence area, rather than be resisted by the entire girder composite section. Finally, the results are used to develop an approach for estimating the cracking moment capacity at girder ends based on a proposed effective moment of inertia.

• Structural Engineering and Mechanics
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• 제67권3호
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• pp.255-265
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• 2018

The prestress force effect on the fundamental frequency and deflection shape of Prestressed Concrete I (PCI) beams was studied in this paper. Currently, due to the conflicts among existing theories, the analytical solution for properly considering the structural behavior of these prestressed members is not clear. A series of experiments were conducted on a large-scale PCI beam of high strength concrete with an eccentric straight unbonded tendon. Specifically, the simply supported PCI beam was subjected to free vibration and three-point bending tests with different prestress forces. Subsequently, the experimental data were compared with analytical results based on the Euler-Bernoulli beam theory. It was proved that the fundamental frequency of PCI beams is unaffected by the increasing applied prestress force, if the variation of the initial elastic modulus of concrete with time is considered. Vice versa, the relationship between the deflection shape and prestress force is well described by the magnification factor formula of the compression-softening theory assuming the secant elastic modulus.

• 콘크리트학회지
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• 제6권1호
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• pp.89-100
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• 1994

프리스트레스 프리텐숀 보의 전달길이를 위하여 콘크리트의 변형율에 의하여 부착력을 계측하는 간접적인 방법을 일반적으로 사용하여 왔다. 이 트랜스퍼 실험은 실제 보에서 행하여지므로, 실제 상태의 정착부착력을 계측할 수 있다는 장점이 있으나, 최대 정착부착응력과 부착강비를 구하기 난해하며, 그 결과가 매우 분산되어 있으므로, 구조 설계자가 안전한 적정기준을 이해하고 선택하기 어렵다. 콘크리트의 변형을 측정하지 않아도 PS 강선의 정착부착 성능을 얻을 수 있는 대안을 소개하였다. 실제 보에서 PS강재의 긴장을 풀 때와 유사한 상황에서 정축부착 응력을 직접 구하였다. 하중재하부에서 풀려진 PS강선의 긴장력은 하중재하부쪽 강선의 단면증가를 가져오고, 콘크리트 블록에 정착부착력을 발생시키며, 다른 방향(고정부 쪽)으로 슬립을 유발시킨다. 두 개의 중공 로드셀로 양단하중을 최대 부착응력 또는 전면슬립이 일어날 때까지 계측하였다. 프리텐션 콘크리트보의 정착부착 길이를 구하기 위하여 이 방법을 기존의 트랜스퍼 실험방법과 병행하여 사용할 것을 제안한다.

• 한국전산구조공학회논문집
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• 제21권3호
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• pp.287-294
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• 2008

이 연구에서는 교량 상부구조물의 보수 보강에 많이 사용되는 7연 강연선의 공용중 긴장력 관리를 위한 새로운 방법은 제안하였다. 제안된 스마트 강연선은 기존 강연선의 중앙 킹와이어를 강제튜브로 대체하고, 강제튜브의 내부에 FBG 광섬유센서를 설치하여 강연선의 변형률을 측정할 수 있도록 하였다. 내장된 센서를 통하여 이 스마트 강연선의 변형률을 쉽게 측정할 수 있으므로, 공용중 강연선의 긴장력을 모니터링할 수 있다. 본 연구에서 제안된 장력 모니터링 방법의 효용성을 증명하기 위하여 FBG센서 2개가 내장된 길이 7.0m인 스마트 강연선을 제작하고, 이를 길이 6.4m, 높이 0.6m인 RC T형 모형거더에 외장형 텐던으로 적용하였다. 그리고 이 시험거더에 대한 재하-제하시험을 실시하고 로드셀에서 계측된 긴장력과 스마트 강연선을 이용하여 예측한 긴장력을 비교하였다. 비교 결과, 제안된 스마트 강연선은 긴장력이 작용된 강연선의 장력을 정확하게 모니터링 하는데 유용함을 확인할 수 있었다.

• 한국구조물진단유지관리공학회 논문집
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• 제13권5호통권57호
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• pp.109-120
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• 2009

본 논문은 외부 긴장된 긴장재의 손실 긴장력 추정에 대한 새로운 방법을 소개한다. 제안된 방법은 HGA과 FEM이 조합된 시스템 인식 기법으로 외부긴장된 긴장재의 손실된 긴장력이 추정된다. 제안된 기법의 인식변수로는 외부긴장 긴장재의 긴장력, 유효공칭직경, 단위길이당 질량과 레일리 감쇠 계수가 사용되었다. 첫째로 감쇠의 효과가 적용된 유한요소 모델 시스템을 모형화되고, 시스템 인식변수를 반복적으로 추정하는 역해석 기법을 이용하여 인식하게 된다. 마지막으로 3번의 수치실험을 통하여, 제안기법의 수치적 타당성 여부가 확인된다. 이때, 레일리 감쇠 계수를 제외한 인식변수들의 오차는 1%미만으로 인식된다.

• Structural Engineering and Mechanics
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• 제52권4호
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• pp.723-738
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• 2014

Prestressing is the most commonly employed technique in bridges and long span beams in commercial buildings as prestressing results in slender section with higher load carrying capacities. This work is an attempt to study the performance of a minimum weight prestressed concrete beam adopting a non-prismatic section so that there will be a reduction in the volume of concrete which in turn reduces the self-weight of the structure. The effect of adopting a non-prismatic section on parameters like prestressing force, area of prestressing steel, bending stresses, shear stresses and percentage loss of prestress are established theoretically. The analysis of non-prismatic prestressed beams is based on the assumption of pure bending theory. Equations are derived for dead load bending moment, eccentricity, and depth at any required section. Based on these equations an algorithm is developed which does the stress checks for the given section for every 500 mm interval of the span. Limit state method is used for the design of beam and finite difference method is used for finding out the deflection of a non-prismatic beam. All the parameters of nonprismatic prestressed concrete beams are compared with that of the rectangular prestressed concrete members and observed that minimum weight design and economical design are not same. Minimum weight design results in the increase in required area of prestressing steel.