• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.1A
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• pp.15-24
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• 2008

This paper presents the analytical method for the long-term behavior of simply supported composite beams with precast decks prestressed in the longitudinal direction. The objectives of time-dependent analysis are to estimate losses of prestress on the concrete slab and long-term deflection due to creep and shrinkage of concrete, relaxation of prestressing steel. Also, the time-dependent analysis was carried out using the presented analytical method to evaluate the effects of several parameters on the long-term behavior of composite bridge with precast deck, including geometrical shapes of composite beams, compressive strength of concrete and magnitude of initial prestress. The results of the analysis indicated that, in the effects of geometrical shapes of composite beams, the main parameters affecting the losses of prestress and the long-term deflection were the cross sectional area and the moment of inertia of steel beam, respectively. Finally, the determination method for the required initial prestress was proposed by evaluation of the loss characteristics due to shrinkage and creep of concrete.

• Journal of Korean Society of Steel Construction
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• v.24 no.5
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• pp.571-582
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• 2012

Prestressed composite girders provide efficient composite action by applying prestress to the sub-encasing concrete. In this study, an enhanced prestressed composite girder with forms suspended from the steel girder is utilized. Long-term behavior of the prestressed composite girder is estimated using age-adjusted effective modulus method, which is verified experimentally using measurements obtained from an in-service bridge. Then, parametric study is carried out to investigate the influences caused by ambient temperature, humidity, prestressing and concrete casting date.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.75-82
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• 2021

The objective of this study is to examine the loss of prestressing stress in the developed prestressing reinforcing units using steel bar and pipe (SP). The main parameters were the reinforcing bar type, the magnitude of prestressed force, and prestressing method. The test results showed that the loss of prestressing stress for SP was highest in the initial prestressing step, which was higher for the compression introduction typed specimens than tension introduction typed specimens. The loss of prestressing stress of SP made with P800 was 1.6% for the compression introduction typed specimen with 0.8f_y, which was lowest than the other specimens. Meanwhile, the relaxation of SP with the respect to the time ranged between 0.4 and 1.9%, irrespective of SP material type, the magnitude of prestressed force, and prestressing method. These values were less than 2.5%, which is the maximum value for the relaxation of prestressed reinforcing steel bars in design codes. Consequently, considering the loss of stress developed in the initial prestressing step, the developed SP material type, prestressing introduction method, and magnitude are recommended to be P800, compression introduction type, and 0.8f_y.

• Journal of the Korea Concrete Institute
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• v.18 no.4 s.94
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• pp.507-515
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• 2006

The purpose of the paper is to propose a method to give a more accurate prediction of prestress changes in prestressed concrete(PSC) bridges. The statistical approach of the method is using the measurement data of the structural system to develop a nonlinear regression analysis. Long-term prediction of prestress is achieved using nonlinear regression analysis. The proposed method is applied to the prediction of prestress of an actual prestressed concrete box girder bridge. The present study represents that confidence interval of long-term prediction becomes progressively narrower with the increase of in-situ measurement data. Therefore, the numerical results prove that a more realistic long-term prediction of prestress changes in PSC structures can be achieved by employing the proposed method. The prediction results can be efficiently used to evaluate prestress during the service life of structure so that the remaining prestress exceeds the control criteria.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.178-181
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• 2011

본 연구에서는 광섬유센서를 내장한 스마트강연선을 이용하여 초고성능콘트리트로 제작된 하이브리드 사장교 세그먼트의 횡방향 도입 긴장력을 계측하고 세그먼트 내부의 프리스트레스를 계측하여 즉시손실에 해당하는 정착장치 활동에 의한 손실과 마찰손실을 도로교설계기준(2005)의 설계 마찰손실과 비교하였다. 제작된 2개의 UHPC 사장교 세그먼트는 횡방향 길이 16.7m, 종방향 길이 1.75m, 높이 1.5m이며 각 시험체의 1/4, 1/2, 3/4지점에 긴장력을 계측하기 위해 3개의 FBG센서를 배치하였다. 긴장력은 유압잭을 이용하여 5개의 강연선에 동시에 순차적으로 도입되었으며, 단부에서 최대 도입 긴장력은 세그먼트 1은 734kN, 세그먼트 2는 639kN이었다. 도로교설계기준에 제시된 마찰계수의 중간값(파상마찰계수=0.00405, 곡률마찰계수=0.20)을 사용하여 FBG센서 위치에서 계산된 긴장력은 계측치와 5% 이내의 차이를 보였으며, 정착장치 활동에 의한 순간손실은 긴장단에서 최대 12.8%로 계측되었다. 이로부터 이 연구에서 제시하는 긴장력계측방법의 적용성을 입증할 수 있었으며, 향후 이 방법은 프리스트레스트 콘크리트 교량의 설계기준 마찰계수 개정을 위한 연구에 좋은 도구로 활용될 수 있을 것으로 기대된다.

• Journal of the Korean Institute of Gas
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• v.18 no.1
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• pp.31-40
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• 2014

LNG storage outer tank is a vertically and horizontally prestressed concrete wall structure. Therefore, when the storage tanks become larger, prestressing tendons become longer and eventually the prestressing loss becomes larger. Also, recently, bomb terrors and accidental crashes have occurred frequently on important infrastructures. Therefore, LNG storage tanks are also exposed to these dangerous scenarios, where they need to be evaluated and protected from these threats. Therefore, in this study, the behavior of 270,000 kL LNG storage outer tank impacted by a flying object is evaluated using implicit FEM code, LS-DYNA. In the analysis, the prestress loss due to the increased length of prestressing tendons from enlargement of outer tank is considered. A comparison study between the LNG tanks with and without prestress loss is performed to investigate the impact behavior and the effect of prestressing force change on the safety and serviceability prestressed concrete containment.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.205-208
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• 2008

Steel-embedded composite piers can enhance the resistance of core concrete by confinement of the steel elements and also can strengthen the stability of the embedded steel elements by concrete parts, so that the resistance of the composite members and seismic requirements can be provided without increasing section dimensions and self-weight. While modular composite piers with single segment do not need prestressing, precast segment composite piers with multiple segments need to have prestressing to prevent excessive cracking at the joints. Initial stresses and deformation by the introduced prestress are changed by long-term properties of concrete and need to be considered in the design. This paper deals with the prestress losses by the measurement of load cells, strains of reinforcements, concrete and embedded steel tubes.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.4
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• pp.237-244
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• 2020

This study investigates the effect of the outrigger wall reinforced with post-tension on reducing differential column shortening. Since the outrigger wall is a concrete structure, the effect of its long-term behavior should be considered. The long-term behavior of the outrigger wall increases differential column shortening and decreases the shear force acting on the outrigger. When the stiffness of the outrigger becomes small, the effect of its long-term behavior increases. Furthermore, a method of reinforcing with post-tension to reduce differential column shortening is proposed. Following the analysis, it was confirmed that the post-tension method shows a significant reduction in the differential column shortening. This study shows that the effect of the outrigger wall reinforced with post-tension on reducing differential column shortening increases with the prestressing force of tendon.

• Proceedings of the Korean Nuclear Society Conference
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• 1995.05b
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• pp.981-986
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• 1995

이 논문의 목적은 축대칭 프리스트레스트 콘크리트 탱크의 시간의존성 유한요소해석법을 제안하는 것이다. 오늘날 PC구조물은 교량, 포장판, 해상구조물, 원자로 격납구조물, 대규모 액체저장용 탱크 등 여러 형태의 구조물에서 그 사용 예를 쉽게 찾아볼 수 있다. 특히 본 논문에서 고려하고자 하는 압력창기나 액체 저장용 탱크의 경우 유체압력 등의 내부압력에 의해 발생하는 균열은 프리 스트레스를 도입함으로써 매우 효과적으로 제어할 수 있기 때문에 상당히 유리한 구조형식이 된다. 그러니 이러한 구조물의 해석과 설계에 있어서 균열의 예측과 더불어 콘크리트의 크리이프, 건조수축 및 PC강재의 리락세이션 등과 같은 시간 의존성 변형으로 인한 프리스트래스의 손실, 여러 단계의 긴장력을 도입함으로써 발생하는 순간변형인 탄성단축 및 이로 인한 긴장력 감소 등을 정확히 계산하는 일은 매우 복잡하고 어려운 일이다. 본 논문에서는 크리이프, 건조수축 및 리락세이션 등과 같은 시간의존성 변형과 순차적으로 다단계의 프리스트레스 도입으로 인한 순간변형 및 탄성단축의 영향을 고려한 축대칭 PC 탱크 구조물의 시간에 따른 거동 및 긴장력의 변화를 유한요소법을 적용하여 해석할 수 있는 해법체계를 정리하고 이를 전산 프로그램화하여, 축대칭 PC탱크 구조물의 시간 의존성 거동에 대한 보다 정밀한 해석을 수행하였다.

• 한국방재학회:학술대회논문집
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• 2010.02a
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• pp.39.2-39.2
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• 2010

본 논문에서는 프리스트레스트 콘크리트 거더 구조물의 긴장력 손실을 검색하기 위한 유한요소모델 개선기법을 제시하였다. 먼저, 유한요소모델개선 기법의 이론적 배경을 제시하였다. 두 번째로, 다수의 긴장력 조건하의 모형 PSC 거더에 대한 모드파라메터들을 측정하기위해 진동실험을 수행하였다. 세 번째로, 유한요소모델의 구조파라메터 개선을 통해 실험결과와 유사한 고유진동수를 얻기 위한 진동기반 구조식별을 수행하였다. 마지막으로, 다수의 긴장력 조건하에서 실험을 통해 측정된 고유진동수와 수치적으로 식별된 고유 진동수를 이용하여 모델개선 기법의 적합성을 검증하였다.