• Smart Structures and Systems
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• 제4권3호
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• pp.367-389
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• 2008

Shape Memory Alloys (SMAs) are unique materials with a paramount potential for various applications in bridges. The novelty of this material lies in its ability to undergo large deformations and return to its undeformed shape through stress removal (superelasticity) or heating (shape memory effect). In particular, Ni-Ti alloys have distinct thermomechanical properties including superelasticity, shape memory effect, and hysteretic damping. SMA along with sensing devices can be effectively used to construct smart Reinforced Concrete (RC) bridges that can detect and repair damage, and adapt to changes in the loading conditions. SMA can also be used to retrofit existing deficient bridges. This includes the use of external post-tensioning, dampers, isolators and/or restrainers. This paper critically examines the fundamental characteristics of SMA and available sensing devices emphasizing the factors that control their properties. Existing SMA models are discussed and the application of one of the models to analyze a bridge pier is presented. SMA applications in the construction of smart bridge structures are discussed. Future trends and methods to achieve smart bridges are also proposed.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2009년도 춘계 학술대회 제21권1호
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• pp.53-54
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• 2009

강재매입형 합성교각은 단면 자체의 설계 변수의 다양성을 통해 요구하는 성능을 만족하도록 할 수 있는 유연성을 갖고 있다. 급속시공을 위한 합성교각의 설계를 위해서 작은 규모에서는 볼트 연결을 통한 조립식 구조물이 가능하고 큰 규모에서는 세그먼트를 분리하여 시공하고 포스트 텐션을 도입하는 방식을 사용할 수 있다. 이 논문에서는 합성교각의 실험적 결과를 비교 분석하여 강재 매입형 조립식 합성교각의 설계 변수가 거동에 미치는 영향을 분석하였다. 이를 통해서 교각의 설계 여건에 따른 적합한 설계 단면 설정 및 일체화 방안을 제안하였다. 조립식 시공을 위해서는 적절한 중량 규모에 따른 단면 분할이 필요하고 제작 및 시공 오차 보정을 위한 별도의 상세가 요구된다. 또한, 코핑부를 포함한 경우에는 교각 세그먼트와 코핑부와의 연결 상세를 함께 고려해야 하기 때문에 이를 위한 연결상세를 제시하였다.

• 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.

• Computers and Concrete
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• 제5권2호
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• pp.117-134
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• 2008

An experimental and numerical research was conducted to gain a deeper insight on the structural behaviour of deep-beams with indirect supports and to assess the size effects in the ultimate state behaviour. The experimental campaign focused on the influence of the reinforcement tie distribution height on the compression check of the support region and on the benefits of using unbonded prestressing steel. Three reduced scale specimens were tested and used to validate the results obtained with a nonlinear finite element model. As a good agreement could be found between the numerical and the experimental results, the numerical model was then further used to perform simulations in large scale deep-beams, with dimensions similar to the ones to be adopted in a practical case. Two sources of size effects were identified from the simulation results. Both sources are related to the concrete quasi-brittle behaviour and are responsible for increasing failure brittleness with increasing structural size. While in the laboratory models failure occurred both in the experimental tests as well as in the numerical simulations after reinforcement yielding, the numerically analysed large scale models exhibited shear failures with reinforcement still operating in the elastic range.

• Earthquakes and Structures
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• 제9권2호
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• pp.339-352
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• 2015

Ancient masonry towers constitute a relevant part of the cultural heritage of humanity. Their earthquake protection is a topic of great concern among researchers due to the strong damage suffered by these brittle and massive structures through the history. The identification of the seismic behavior and failure of towers under seismic loading is complex. This strongly depends on many factors such as soil characteristics, geometry, mechanical properties of masonry and heavy mass, as well as the earthquake frequency content. A deep understanding of these aspects is the key for the correct seismic vulnerability evaluation of towers and to design the most suitable retrofitting measure. Recent tendencies on the seismic retrofitting of historical structures by means of prestressing are related to the use of smart materials. The most famous cases of application of prestressing in towers were discussed. Compared to horizontal prestressing, vertical post-tensioning is aimed at improving the seismic behavior of towers by reducing damage with the application of an overall distribution of compressive stresses at key locations.

• 대한토목학회논문집
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• 제26권5A호
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• pp.817-822
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• 2006

프리캐스트 바닥판들의 이음부에 발생하는 교축방향 인장응력을 제어하고, 이음부의 누수 등을 방지하기 위하여 교축 방향으로 프리스트레스를 도입한다. 효과적인 압축력 도입을 위하여 합성 전에 프리캐스트 바닥판에 압축력을 도입한다. 이때 프리캐스트 바닥판에 존재하는 전단포켓으로 인하여 바닥판에 균일한 압축력 도입이 어렵고, 전단포켓의 주변 콘크리트에 국부적인 응력집중이 발생한다. 따라서 본 연구에서는 상용 구조해석 프로그램을 이용하여 서로 다른 4가지 형상의 전단포켓을 갖는 프리캐스트 바닥판에 대하여 유한요소해석을 수행하였다. 그 결과 전단포켓의 모서리 부분이 원형인 전단포켓이 응력집중이 가장 작은 것으로 나타났다.

• 한국전산구조공학회논문집
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• 제28권6호
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• pp.699-706
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• 2015

이 연구에서는 FBG센서가 내장된 강연선을 포스트텐션 UHPC 교량(길이 11.0m, 폭 5.0m, 높이 0.6m)에 적용하고 약 1년간의 긴장력 장기모니터링 결과를 정리하였다. 그리고 초기 도입 긴장력과 차량재하시험을 통하여 콘크리트 내부 강연선의 긴장력 변화를 계측하고 계측결과에 대한 분석을 수행하였다. 연구결과, 이 연구에서 제안하는 콘크리트 내부 긴장력 측정방법이 공영 중인 교량에서 외력으로 인한 콘크리트 내부의 작은 프리스트레스 변화를 효과적으로 측정할 수 있음을 알 수 있었다. 아울러 장기 계측결과를 이용하여 응력변화에 의한 유효변형률을 정확하게 얻기 위해서는 온도보정에 사용되는 열팽창계수의 선택이 매우 중요함을 알 수 있었다.

• Earthquakes and Structures
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• 제3권6호
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• pp.821-838
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• 2012

This paper proposes a new three-layer pillar-type hysteretic damper system for residential houses. The proposed vibration control system has braces, upper and lower frames and a damper unit including hysteretic dampers. The proposed vibration control system supplements the weaknesses of the previously proposed post-tensioning vibration control system in the damping efficiency and cumbersomeness of introducing a post-tension. The structural variables employed in the damper design are the stiffness ratio ${\kappa}$, the ductility ratio ${\mu}_a$, and the ratio ${\beta}$ of the damper's shear force to the maximum resistance. The hysteretic dampers are designed so that they exhibit the targeted damping capacity at a specified response amplitude. Element tests of hysteretic dampers are carried out to examine the mechanical property and to compare its restoring-force characteristic with that of the analytical model. Analytical studies using an equivalent linearization method and time-history response analysis are performed to investigate the damping performance of the proposed vibration control system. Free vibration tests using a full-scale model are conducted in order to verify the damping capacity and reliability of the proposed vibration control system. In this paper, the damping capacity of the proposed system is estimated by the logarithmic decrement method for the response amplitudes. The accuracy of the analytical models is evaluated through the comparison of the test results with those of analytical studies.

• Smart Structures and Systems
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• 제17권1호
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• pp.107-122
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• 2016

We propose an effective methodology using electromechanical impedance characteristics for estimating the remaining tensile force of tendons and simultaneously detecting damages of the anchorage blocks. Once one piezoelectric patch is attached on the anchor head and the other is bonded on the bearing plate, impedance responses are measured through these two patches under varying tensile force conditions. Then statistical indices are calculated from the impedances, and two types of relationship curves between the tensile force and the statistical index (TE Curve) and between statistical indices of two patches (SR Curve) are established. Those are considered as database for monitoring both the tendon and the anchorage system. If damage exists on the bearing plate, the statistical index of patch on the bearing plate would be out of bounds of the SR curve and damage can be detected. A change in the statistical index by damage is calibrated with the SR curve, and the tensile force can be estimated with the corrected index and the TE Curve. For validation of the developed methodology, experimental studies are performed on the scaled model of an anchorage system that is simplified only with 3 solid wedges, a 3-hole anchor head, and a bearing plate. Then, the methodology is applied to a real scale anchorage system that has 19 strands, wedges, an anchor head, a bearing plate, and a steel duct. It is observed that the proposed scheme gives quite accurate estimation of the remaining tensile forces. Therefore, this methodology has great potential for practical use to evaluate the remaining tensile forces and damage status in the post-tensioned structural members.

• 한국안전학회지
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• 제31권3호
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• pp.75-81
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• 2016

Tendon corrosion reliability in KICT-ultra high performance concrete (K-UHPC) bridges is assessed and predicted considering uncertainties in flexural bending capacity and corrosion occurrence. In post-tensioning bridge systems, corrosion is a one of most critical failure mechanisms due to strength reduction by it. During the entire service life, those bridges may experience lifetime corrosion deterioration initiated and propagated in tendons which are embedded not only in normal concrete but also in K-UHPC. For this reason, the time-variant corrosion performance has to be assessed. In the absence of in-depth researches associated with K-UHPC tendon corrosion, a reliability-based prediction model is developed to evaluate lifetime corrosion performance of tendon in K-UHPC bridges. In 2015, KICT built a K-UHPC pilot bridge at 168/5~168/6 milestone on Yangon-Mandalay Expressway in Myanmar, by using locally produced tendons which post-tensioned in longitudinal and lateral ways of K-UHPC girders. For an illustrative purpose, this K-UHPC bridge is used to identify the time-variant corrosion performance.