• 한국지반공학회논문집
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• 제26권7호
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• pp.117-133
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• 2010

본 논문에서는 쏘일네일링 공법과 앵커 공법의 장점을 결합한 하이브리드 공법에 대한 연구를 수행하였다. 쏘일네일링과 앵커가 결합된 하이브리드 공법은 철근과 PC강연선을 보강재로 사용함으로써 일반적인 쏘일네일링에 비해 인발저항력이 증가하며, 프리스트레스를 가하기 때문에 지반의 변위를 억제하고 사면의 얕은파괴를 방지할 수 있다. 하지만 철근의 신장량이 PC강연선의 신장량보다 작기 때문에 철근에 하중이 집중되어 철근이 먼저 항복하게 된다. 따라서 PC강연선과 철근의 항복하중을 단순히 더하게 된다면 쏘일네일링과 앵커가 결합된 하이브리드 공법의 항복하중을 과대평가하는 것이다. 이에 본 연구에서는 두 보강재의 항복시점을 일체화하기 위해 앵커바에 프리스트레스를 가하였다. 즉, 하이브리드 공법에서 프리스트레스를 가하는 것은 지반의 변위를 억제하는 것과 동시에 선단에서부터 전이되는 압축력이 철근에 작용하는 인장하중을 감소시켜 전체 설계하중을 최대한 증가시키기 위한 것이다. 하이브리드 공법 내에서 하중전이 메커니즘을 체계적으로 분석하기 위하여 두 가지 비교대상을 정하여 현장인발시험을 실시하였다. 하이브리드 공법의 인발저항력 증가를 규명하기 위해 우선 쏘일네일링에 대한 인발시험을 실시하였으며, 또한 하이브리드 공법의 프리스트레스 변화에 따른 메커니즘을 규명하기 위해 프리스트레스를 0kN에서 196kN까지 변화시켜 인발시험을 실시하였다. 프리스트레스를 가하여 발생한 압축력은 철근에 전해지게 되어 철근의 하중-변위곡선 기울기가 감소하게 된다. 즉, 철근은 신장량이 증가하여 PC강연선과 비슷한 항복하중을 가지게 되며, 본 논문에서는 하중전이 이론을 통해 이를 규명하였다. 프리스트레스를 가하여 삽입된 두 보강재가 일체거동을 보이게 되면 하이브리드 공법의 인발저항력은 쏘일네일링의 인발저항력보다 2배정도 더 증가하게 된다.

• Structural Monitoring and Maintenance
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• 제5권4호
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• pp.463-488
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• 2018

In the last decades, research efforts have been spent to investigate the effect of prestressing on the dynamic behaviour of prestressed concrete (PSC) beams. Whereas no agreement has been reached among the achievements obtained by different Researchers and among the theoretical and the experimental results for simply supported beams, very few researches have addressed this problem in continuous PSC beams. This topic is, indeed, worthy of consideration bearing in mind that many relevant bridges and viaducts in the road and railway networks have been designed and constructed with this structural scheme. In this paper the attention is, thus, focused on the dynamic features of continuous PSC bridges taking into account the effect of prestressing. This latter, in fact, contributes to the modification of the distribution of the bending stress along the beam, also by means of the secondary moments, and influences the flexural stiffness of the beam itself. The dynamic properties of a continuous, two spans bridge connected by a nonlinear spring have been extracted by solving an eigenvalue problem in different linearized configurations corresponding to different values of the prestress force. The stiffness of the nonlinear spring has been calculated considering the mechanical behaviour of the PSC beam in the uncracked and in the cracked stage. The application of the proposed methodology to several case studies indicates that the shift from the uncracked to the cracked stage due to an excessive prestress loss is clearly detectable looking at the variation of the dynamic properties of the beam. In service conditions, this shift happens for low values of the prestress losses (up to 20%) for structure with a high value of the ratio between the permanent load and the total load, as happens for instance in long span, continuous box bridges. In such conditions, the detection of the dynamic properties can provide meaningful information regarding the structural state of the PSC beam.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2005년도 추계학술대회 논문집
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• pp.223-228
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• 2005

Precast concrete deck has many advantages comparing with the in-situ concrete deck, and has been successfully applied to replacement of the deteriorated decks and to the newly constructed highway bridges in domestic region. In order to apply the precast decks into the railway bridges, however, differences of the load characteristics between the highway and the railway should be properly taken into account including the train load, longitudinal force of the continuous welded rail. acceleration or braking force, temperature change and shrinkage. Proper level of the longitudinal prestress of the tendons that can ensure integrity of the transverse joints in the deck system is of a primary importance. To this aim, the longitudinal tensile stresses induced by the design loads are derived using three-dimensional finite element analyses, design codes and theoretical equations for the frequently adopted PSC composite girder railway bridge. The estimated proper prestress level to counteract those tensile stresses is over 2.4 MPa, which is similar to the case of the highway bridges.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.255-258
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• 2005

Experimental study has been performed in order to investigate the behavior of RC beams strengthened with externally bonded prestressed CFRP (Carbon Fiber Reinforced Polymer) strips. A total of 7 specimens have been manufactured of which specimens strengthened with bonded CFRP strips considering the level of prestress as experimental variable, and a specimen with simply bonded CFRP strips. The following phenomena have been observed through the experimental results. The specimen with simply bonded CFRP strips failed below 50$\%$ of its tensile strength due to premature debonding. On the other hand, all the specimens strengthened with prestressed CFRP strips showed sufficient strengthening performance up to the ultimate rupture load of the CFRP strips. Also, it was observed that the cracking loads and yield loads of the strengthened beams were increased proportionally to the prestress level, but the maximum loads were nearly equal regardless of the prestress level.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2006년도 추계학술대회 논문집
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• pp.1326-1331
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• 2006

The precast concrete deck is one of suitable solutions for replacement and new construction in urban area. However, the precast concrete deck could be a weak point of the steel plate girder bridges structurally due to the connections between precast panels in the longitudinal direction. Thereafter, it is necessary for improvement of durability and load carrying capacity to introduce the prestress force in the longitudinal direction Some cracks of connections at the precast concrete deck may be occurred due to live loads, the difference of temperature and long-term effects. The shrinkage and creep of concrete may significantly affect long-term behaviors which occur tensile stresses at the precast concrete deck of steel plate girder bridges. In this study, the time-dependant analysis program has been developed to determine the initial prestress force in the longitudinal direction considering loss of stress at the precast concrete deck. Also it has been estimated the initial prestress force by construction stages and shapes of girder.

• Computers and Concrete
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• 제20권5호
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• pp.617-625
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• 2017

Prestress force identification (PFI) is crucial to maintain the safety of prestressed concrete bridges. A synergic identification method has been proposed recently by the authors that can determine the prestress force (PF) and the excitation force simultaneously in prestressed concrete beams with good accuracy. In this paper, the ability of this method in the application with prestressed concrete box-girder bridges is demonstrated. A reasonable assumption is made to capture the similarity of the dynamic behavior of the prestressed concrete box-girder bridge and a beam under a certain loading scenario, and the feasibility of this method for application in a prestressed box-girder bridge is affirmed. A comprehensive laboratory test program is conducted, and the effects of PF, excitation, measuring time and uncertainties are studied. Results show that the proposed method can predict the PF and the excitation force in a prestressed concrete box-girder accurately and has a great robustness against uncertainties.

• 한국군사과학기술학회지
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• 제26권1호
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• pp.1-9
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• 2023

The skin structure of sensor pod mounted on the exterior of aircraft can be exposed to the acoustic dynamic load and static load such as aerodynamic pressure and inertial load during flight. Fatigue life prediction of structural model under acoustic load should be performed and also differential stiffness of model modified by static load should be considered. The acoustic noise test spectrum of MIL-STD-810G was applied to the structural model and the stress response power spectral density (PSD) was calculated. The frequency response analysis was performed with or without prestress induced by inplane static load, and the response spectrum was compared. Time series data was generated using the calculated PSD, and the time and frequency domain fatigue life were predicted and compared. The variation of stress response spectrum due to static load and predicted fatigue life according to the different structural model considering mean stress were examined and decreasing fatigue life was observed in the model with prestress of compressive static load.

• 한국구조물진단유지관리공학회 논문집
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• 제7권2호
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• pp.247-261
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• 2003

The technique of posttensioning has been used successfully to improve the performance of existing concrete structures. However, very few applications of this technique can be found in steel structures. Posttensioning by means of high strength cable or bar can be used to effectively increase the working load capacity of Truss Bridges. The benefits of posttensioning trusses can be achieved in strengthening of existing structures as well as in the design of new structures. In this paper, the elastic behavior of posttensioned trusses with straight and draped tendon profiles is examined. For the analysis of posttensioned trusses in the elastic range of behavior, two methods are presented, namely, the flexibility method and the mixed-method, i.e., a combination of the stiffness and flexibility methods. Using the presented methods, the effects of design variables such as the tendon profile, truss type, prestress force, and tendon eccentricity on the working load and deflection of trusses are studied. The results show that the allowable load of truss increases proportionally with increase in prestress force and eccentricity. Posttesioning enlarges the elastic range, increases redundancy, and reduces deflection and member stresses. Thus, the remaining life of a truss bridge can be increased relatively inexpensively.

• Structural Engineering and Mechanics
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• 제71권2호
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• pp.109-118
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• 2019

This paper presents the numerical simulation of membrane structure under impact load. Firstly, the numerical simulation model is validated by comparing with the test in Hao's research. Then, the effects of the shape of the projectile, the membrane prestress and the initial impact speed, are investigated for studying the dynamic response and failure mechanism, based on the membrane displacement, projectile acceleration and kinetic energy. Finally, the results show that the initial speed and the punch shape are related with the loss of kinetic energy of projectiles. Meanwhile, the membrane prestress is an important factor that affects the energy dissipation capacity and the impact resistance of membrane structures.

• 한국안전학회지
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• 제25권3호
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• pp.71-77
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• 2010

This paper presents the results of a study on flexural capacity of large size RC slabs strengthened with carbon fiber reinforced polymer(CFRP) plates. A total of 5 specimens of 6.0m length were tested in four point bending after strengthening them with externally bonded CFRP plates. The CFRP plates were bonded without prestress and with two prestress levels, 0.4% and 0.6% of CFRP plate strain. Test variables included the type of strengthening, prestressing level, and the effects according to each test variables are analysed. The experimental results show that proposed methods can increase significantly the flexural capacity such as strength, stiffness of the beam and the increase ranged between 36.2% and 63.2% of the load-carrying capacity of the control beams. The non-prestressed specimen failed by separation of the plate from the beam due to premature debonding while most of the prestressed specimens failed by CFRP plate fracture. And the cracking loads and maximum loads were increased proportionally to the prestress level.