• KCI Concrete Journal
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• 제12권1호
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• pp.131-138
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• 2000

The research purpose of this paper is to investigate the influential Parameters on the unbonded tendon stress. The parameters were the reinforcing ratio, the prestressing ratio, and the loading type. To this end. first, the influence of parameters were examined with twenty eight test results obtained from references. Then, an experimental study was carried out with nine specimens. Test variables were the reinforcing ratio and the prestressing ratio. Specimens were divided equally into three groups and each group had a different level of the reinforcing ratio. Each specimen within a group has a different level of the prestressing ratio. The investigation with previous and current tests revealed the followings; (1) the length of crack distribution zone does not have a close relation with the length of plastic hinge. (2) the prestressing ratio does not affect both the length of crack distribution and the length of plastic hinge, (3) the tendon stress variation is in reverse relation with the ratios of mild steels and tendons, (4) the loading type nay not affect significantly the length of crack distribution zone, (5) AASHTO LRFD Code equation and Moon/Lim's design equation predicted the test results well with some safety margins.

• 한국강구조학회 논문집
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• 제18권6호
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• pp.717-726
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• 2006

교량의 보강공법으로 주로 사용되는 외부강봉을 이용한 후인장공법은 적용범위가 넓고 교량의 극한 및 항복에 대한 강성을 증가시켜 휨 보강 효과가 뛰어나지만, 모재접합부의 응력집중, 비효율적인 하중분배, 고정앵커부설치, 유지관리의 어려움 등의 단점이 있다. 본 연구는 기존의 외부강봉을 이용한 후인장공법이 가지는 단점을 보완하고 강판접합공법의 장점을 접목한 새로운 개념의 보강공법으로 커버플레이트의 열변형 특성을 이용한 다단계 프리스트레싱 보강공법을 제안하고자 한다. 커버플레이트의 열변형 특성을 이용한 다단계 프리스트레싱 보강공법은 커버플레이트를 다단계로 가열하여 가열단계별로 거더의 하부플랜지에 고장력볼트로 접합한 뒤, 열원을 제거하여 발생하는 다단계 수축력을 보강에 필요한 프리스트레싱력으로 이용하는 보강공법이다. 커버플레이트의 다단계 프리스트레싱에 의한 보강효과는 커버플레이트의 온도분포와 가열구간에 따라 결정되므로 본 연구에서는 커버플레이트의 열전달 모형실험 및 강거더 모형 실험을 통하여 커버플레이트의 열전달해석과 프리스트레스 도입효과를 분석하였으며, 단경간 강거더 교량을 대상으로 제안된 보강공법의 효율성 및 적용성을 검토하였다.

• Nuclear Engineering and Technology
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• 제55권5호
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• pp.1567-1576
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• 2023

The reactor containment building (RCB) in nuclear power plants (NPPs) plays an important role in protecting the reactor systems from external loads as well as preventing radioactive leaking. As we witnessed the nuclear disaster at Fukushima Daiichi (Japan) in 2011, the earthquake is one of the major threats to NPPs. The purpose of this study is to evaluate effects of concrete material models and presstressing forces on the seismic performance evaluation of RCB in NPPs. A typical RCB designed in Korea is employed for a case study. Detailed three-dimensional nonlinear finite element models of RCB are developed in ANSYS. A series of pushover analyses are then performed to obtain the pushover curves of RCB. Different capacity curves are compared to recognize the influence of different material models on the nonlinear behavior of RCB. Additionally, the effects of prestressing forces on the seismic performances of the structure are also investigated. Moreover, a set of damage states corresponding to damage evolutions of the structures is proposed in this study.

• Steel and Composite Structures
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• 제34권6호
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• pp.853-862
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• 2020

In recent years, due to the many advantages cable-stayed bridges have often constructed in medium and long span. These advantages can be listed as an aesthetically pleasing appearance, economic and easy construction, etc. The main structural elements of cable-stayed bridges are listed as deck, pylon, cables and foundation. Perhaps one of the most vital and expensive of these structural elements is stay-cables. Stay-cables ensure the allowable displacement and distribution of bending moments along the bridge deck with prestressing force. Therefore the optimum design of the stay-cables and prestressing force are very important in achieving the performance expected from the cable-stayed bridges. This paper aims to obtain the stay-cables size and prestressing force optimization of the cable-stayed bridge. For this purpose, single pylon and fan type cable configuration Manavgat Cable-Stayed Bridge was selected as an example. The three dimensional (3D) finite element model (FEM) of the bridge was created with SAP2000. Analysis of the 3D FEM of the bridge was conducted under the different combined effects of the self-weight of the structural element, prestressing force of stay-cable and live load. Stay-cable stress and deck displacement were taken into account as constraints for the optimization problem. To optimize this existing bridge a metaheuristic algorithm named Jaya was used in the optimization process. 3D FEM of the selected bridge was repeatedly analyzed by using Open Applicable Programming Interface (OAPI) properties of SAP2000. To carry out the optimization process the developed program which integrates the Jaya algorithm and the required codes for calling SAP2000 is coded in MATLAB. At the end of the study, the total weight of the stay-cables was reduced more than 40% according to existing stay cables under loads taken into account.

• 대한토목학회논문집
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• 제30권1A호
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• pp.15-26
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• 2010

부착 긴장재를 이용한 프리스트레스를 도입하는 조립식 교각의 구조 성능을 평가하기 위한 준정적 실험을 수행하였다. 프리캐스트 교각의 이음부를 가로질러 축방향으로 연속배치되는 강재로 강봉과 일반철근, 매입강관과 강연선의 조합을 선택하였다. 주요 설계 변수는 강재량, 프리스트레스의 수준, 단면 상세로 하였다. 이음부 벌어짐 이후에 연속 강재가 하중을 모두 부담하여 응력의 증감을 일으키는데 강재비가 높을수록 휨강도가 높게 나타나고 에너지 소산능력도 현저하게 증가하였다. 매입강재를 갖는 프리캐스트 교각은 최대하중 이후의 거동이 안정적으로 나타나 높은 변위연성도를 나타내었고 프리스트레스 증가에 따른 에너지 소산능력의 증가도 나타내었다. 프리스트레스의 수준이 높을수록 초기 변형 회복능력이 양호하게 나타났고 횡철근의 응력증가도 크게 나타났다. 조립식 교각의 최대하중 도달 이후의 강도 저하가 급격하게 발생하지 않도록 긴장재와 일반강재의 조합을 결정하여야 한다.

• Structural Engineering and Mechanics
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• 제4권2호
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• pp.177-190
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• 1996

A method to numerically evaluate the behaviour of single span beams, prestressed with external tendons and symmetrically loaded is presented. This algorithm, based on the Finite Difference Method, includes second order effects and large displacements in an attempt to more fully understand the behaviour of the beam up to collapse. The numerical technique discussed is particularly appropriate for the analysis of R.C. and P.C. beams rehabilitated or strengthened by means of external prestressing but it is reliable for the analysis of new beams as well.

• Steel and Composite Structures
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• 제19권1호
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• pp.43-58
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• 2015

There are many studies on the optimization of steel trusses in literature; and, a large number of them include a shape optimization. However, only a few of these studies are focused on the prestressed steel trusses. Therefore, this paper aims to determine the amounts of the material and cost savings in steel plane trusses in the case of prestressing. A parallel-chord simply supported steel truss is handled as an example to evaluate the used approach. It is considered that prestressing tendon is settled under the bottom bar, between two end supports, using deviators. Cross-sections of the truss members and height of the truss are taken as the design variables. The prestress losses are calculated in two steps as instantaneous losses and time-dependent losses. Tension increment in prestressing tendon due to the external loads is also considered. A computer program based on genetic algorithm is developed to solve the optimization problem. The handled truss is optimized for different span lengths and different tendon eccentricities using the coded program. The effects of span length and eccentricity of tendon on prestressed truss optimization are investigated. The results of different solutions are compared with each other and those of the non-prestressed solution. It is concluded that the amounts of the material and the cost of a steel plane truss can be reduced up to 19.9% and 14.6%, respectively, by applying prestressing.

• Structural Engineering and Mechanics
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• 제48권5호
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• pp.615-642
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• 2013

In this paper a study on prestressed concrete slab bridges is presented. A design philosophy based on the concept of load balancing through prestressing is proposed in order to minimize the effects of delayed deformations due to creep. Aspects related to the stress redistribution inside these bridges for time-dependent phenomena are analyzed and discussed, by applying the principles of aging linear visco-elasticity. Prestressing is seen as an equivalent external load which counterbalances the permanent loads applied to the bridge, nullifying the elastic deflections due to sustained loads, and thus avoiding the related delayed deformations. An optimization of the structural behavior through the use of one-way prestressing is achieved. The determination of a convenient variable depth of slab bridges and the correspondent layout of tendons is considered as a useful means for applying the load balancing concept in actual cases of structures like long cantilevers or bridge decks. A case-study related to the slab bridges built 30 years ago at Jeddah in Saudi Arabia is presented and discussed, in order to show the effectiveness of the proposed approach to the conceptual design of prestressed concrete bridges.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2005년도 춘계 학술발표회 논문집
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• pp.408-415
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• 2005

Existing results of some related experiments report that variation in the magnitude of prestressing force may leads to a change of dynamic properties of a PSC girder system. Since a usual dynamic equilibrium equation doesn't explain these phenomena, a modified dynamic equilibrium equation is derived in this paper by considering prestressing force as an internal energy of the system. The derived equation is applied to a modified beam element model is proposed. The proposed model validated by comparing the natural frequencies computed by the model with those from an existing experiment result.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2004년도 춘계 학술발표회 제16권1호
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• pp.96-99
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• 2004

PSC bridges are deteriorated by many reasons and are difficult to measure residual prestressing forces. It is considered that one of the methods for measuring the prestressing forces is vibration test. This study reports on the change of natural frequency for damaged PSC beams using vibration test which have been carried out to evaluate the effects of cross-section and prestressing forces on natural frequency of PSC beams. According to the results of vibration test results, natural frequency is more sensitive to the changes of cross-section than those of prestress.