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Simulation of Repair Grout Flow in External Tendon System
임석빈,Stefan Hurlebaus 대한토목학회 2012 KSCE JOURNAL OF CIVIL ENGINEERING Vol.16 No.7
The corrosion of voided tendons has been a long-standing issue in Post-Tensioned (PT) systems because it can lead to the failure of tendons and deteriorate bridge performance. Repair grouting in voided tendons can be one of many rehabilitation options if there are no galvanic couples between the new grouts and original grouts. To identify an appropriate repair grouting method for voided tendons, numerical analysis using a commercial Computational Fluid Dynamics (CFD) program, FLUENT, is utilized in this research. The geometry of voided tendons is a complicating factor when creating reliable models for numerical analysis; thus, a research for the simulation of repair grout flow proposed a simplified model and verified the model with experimental results. Thus,this research performs numerical analyses using the simplified model and assesses various parameters of repair methods and materials. The numerical results indicate that the Pressure-Vacuum Grouting (PVG) method with repair grouts having low viscosity exhibits the best performance for filling voids. If it is determined that filling voids with repair grout is appropriate and prevents future corrosion, it is recommended that voids in the field be filled using the PVG method with grouts exhibiting low viscosities.
Enhanced damage index method using torsion modes of structures
임석빈,Stefan Hurlebaus,Harding C. Cloudt,Jeffrey A. Fogle 국제구조공학회 2013 Smart Structures and Systems, An International Jou Vol.12 No.4
A growing need has developed in the United States to obtain more specific knowledge on the structural integrity of infrastructure due to aging service lives, heavier and more frequent loading conditions, and durability issues. This need has spurred extensive research in the area of structural health monitoring over the past few decades. Several structural health monitoring techniques have been developed that are capable of locating damage in structures using modal strain energy of mode shapes. Typically in the past, bending strain energy has been used in these methods since it is a dominant vibrational mode in many structures and is easily measured. Additionally, there may be cases, such as pipes, shafts, or certain bridges, where structures exhibit significant torsional behavior as well. In this research, torsional strain energy is used to locate damage. The damage index method is used on two numerical models; a cantilevered steel pipe and a simply-supported steel plate girder bridge. Torsion damage indices are compared to bending damage indices to assess their effectiveness at locating damage. The torsion strain energy method is capable of accurately locating damage and providing additional valuable information to both of the structures’ behaviors.
Non-Destructive Testing Methods to Identify Voids in External Post-Tensioned Tendons
임석빈,Stefan Hurlebaus 대한토목학회 2012 KSCE JOURNAL OF CIVIL ENGINEERING Vol.16 No.3
A considerable number of Post-Tensioned (PT) bridges have been constructed because PT systems enable them to carry significant traffic loads and have an aesthetical structure. However, strand corrosion has been a long-standing issue because it may lead to the failure of tendons and the deterioration of structural performance. The corrosion typically occurs in voided locations with exposed strands; thus, the inspection of voids in external PT tendons is important and necessary in order to protect strands before corrosion occurs. Based on literature review, several Non-Destructive Testing (NDT) methods are compared for effectiveness of identifying voids in external PT tendons, and the Impact Echo (IE), ultrasonic, and sounding inspection methods are then selected and assessed using small-scale and mock-up specimens. From the experimental results, the wave-based inspection methods, IE and ultrasonic methods, are difficult to apply in the field because the imperfect bonds between ducts and grouts obstruct the transmission of waves. However, the sounding inspection method is not affected by the discontinuities and successfully identifies voids in test specimens. Thus, the sounding inspection can be an effective tool for identifying voids because of its easy application in the field.
임석빈(Im Seok Been),한택희(Han Taek Hee),한상윤(Han Sang Yun),강영종(Kang Young Jong) 대한토목학회 2006 대한토목학회논문집 A Vol.26 No.4A
다축 응력 상태의 구속된 콘크리트는 구속되지 않은 콘크리트에 비해 강도가 크게 증가한다고 알려져 왔고, 많은 연구자 들은 아직도 여러 분야에서 구속된 콘크리트에 대한 연구를 진행 중에 있다. 최근 FRP를 이용한 구속된 콘크리트에 대한 많은 연구가 진행 중에 있지만, FRP는 높은 강도에 비해 취성 재료여서 실제 구조물 적용에 많은 어려움이 있다. 본 연구 에서는 높은 강도 및 연성을 갖는 강재로 구속된 콘크리트에 대하여 강재의 구속 강성이 콘크리트의 강도 증진 및 연성 거동에 미치는 영향을 알아보기 위해 51개의 시험체를 통해 비교 분석해 보았다. 이 실험을 통해 구속된 콘크리트의 강도 증진 효과 및 연성 거동이 뛰어나게 증가함을 확인하였다. 또한 실험 결과를 회귀분석하여 구속 강성이 콘크리트 응력-변형률 곡선에 미치는 영향을 고려한 CSS(원형 강재 구속 시험체)와 R4S(사각형 이방향 강재 구속 시험체)에 대한 응력-변형률 모델을 제안하였다. Confined concrete has enhanced strength and ductility compared with unconfined strength. Cause of these merits of confined concrete, many researches have been performed for confining effects of concrete and been studied in many fields. Although many researches about concrete confined by FRP sheets have been studied recently, it is difficult to apply concrete confined by FRP in real structures because FRP is a brittle material. In this study, the enhanced strength and ductility of concrete which is confined by steel tubes or steel plates were investigated. Fifty one specimens were tested and each specimen has different confining condition. Test results showed enhanced ductility and strength of confined concrete and concrete models were suggested under various confining conditions by regression of experimental data.