• Steel and Composite Structures
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• 제41권5호
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• pp.637-648
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• 2021

Nowadays, one of the practical, fast and easy ways to strengthen steel elements is the use of Carbon Fiber Reinforced Polymer (CFRP). Most previous research in the CFRP strengthening of steel members has carried out on straight steel members. The main difference between horizontal curved beams and straight beams under vertical load is the presence of torsional moment in the horizontal curved beams. In the other words, the horizontal curved beams are analyzed and designed for simultaneous internal forces included bending moment, torsional moment, and shear force. The horizontal curved steel beams are usually used in buildings, bridges, trusses, and others. This study explored the effect of the CFRP strengthening on the behavior of the horizontal curved square hollow section (SHS) steel beams. Four specimens were analyzed, one non-strengthened curved steel beam as a control column and three horizontal curved steel beams strengthened using CFRP sheets (under concentrated load and uniform distributed load). To analyze the horizontal curved steel beams, three dimensional (3D) modeling and nonlinear static analysis methods using ANSYS software were applied. The results indicated that application of CFRP sheets in some specific locations of the horizontal curved steel beams could increase the ultimate capacity of these beams, significantly. Also, the results indicated when the horizontal curved steel beams were under distributed load, the increase rate in the ultimate capacity was more than in the case when these beams were under concentrated load.

• Structural Engineering and Mechanics
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• 제88권5호
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• pp.419-437
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• 2023

The use of reinforced concrete (RC) shear walls (SW) as an efficient lateral load-carrying system has gained recent attention. However, creating openings in RC shear walls is unavoidable due to architectural requirements. This reduces the walls' strength and stiffness, resulting in the development of wall piers. In this study, the cyclic behavior of RC shear walls with openings, reinforced with carbon fiber reinforced polymer (CFRP) sheets in various patterns, was numerically investigated. Finite element analysis (FEA) using ABAQUS software was employed. Additionally, the retrofitting of sub-standard buildings (5, 10, and 15-story structures) designed based on the old and new versions of the Iranian Code of Practice for Seismic-Resistant Structures was evaluated. Nonlinear static analyses, specifically pushover analyses, were conducted on the structures. The best pattern of CFRP wrapping was determined and utilized for retrofitting the sub-standard structures. Various structural parameters, such as load-carrying capacity, ductility, stress contours, and tension damage contours, were compared to assess the efficiency of the retrofit solution. The results indicated that the load-carrying capacity of the sub-standard structures was lower than that of standard ones by 57%, 69%, and 67% for 5, 10, and 15-story buildings, respectively. However, the retrofit solution utilizing CFRP showed promising results, enhancing the capacity by 10-25%. The retrofitted structures demonstrated increased yield strength, ultimate strength, and ductility through CFRP wrapping and effectively prevented wall slipping.

• 멤브레인
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• 제28권4호
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• pp.271-278
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• 2018

본 연구에서는 활성탄소섬유를 이용하여 축전식 탈염공정에 적용할 탄소전극을 제조하였다. polyvinylidene fluoride (PVDF)를 바인더로 사용했으며 적절한 용매에 활성탄소섬유를 배합한 후 상용의 그라파이트 시트에 캐스팅하여 탄소전극을 제조하였다. 이 때 활성탄소섬유의 입자 크기를 달리하였고, 용매, 고분자 바인더 그리고 활성탄소섬유를 80 : 2 : 18, 80 : 5 : 15의 배합비율로 전극을 제조하였다. 그런 다음 염 제거 효율을 흡착전압과 시간, 탈착전압과 시간, NaCl 공급액의 농도와 유속 등에 운전조건에 대하여 염 제거 효율을 측정하였다. 대표적으로 활성탄소섬유의 입자크기가 $32{\mu}m$ 이하이며 80 : 2 : 18의 배합비율에서 1.2 V, 3분의 흡착조건, -0.1 V, 1분의 탈착조건, NaCl 100 mg/L, 15 mL/min의 공급액 조건에서 53.6%의 염 제거 효율을 보였다.

• Steel and Composite Structures
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• 제38권5호
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• pp.477-496
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• 2021

The main objective of this paper is to study vibration of sandwich open cylindrical panel with damaged core and FG face sheets based on three-dimensional theory of elasticity. The structures are made of a damaged isotropic core and two external face sheets. These skins are strengthened at the nanoscale level by randomly oriented Carbon nanotubes (CNTs) and are reinforced at the microscale stage by oriented straight fibers. These reinforcing phases are included in a polymer matrix and a three-phase approach based on the Eshelby-Mori-Tanaka scheme and on the Halpin-Tsai approach, which is developed to compute the overall mechanical properties of the composite material. Three complicated equations of motion for the panel under consideration are semi-analytically solved by using 2-D differential quadrature method. Several parametric analyses are carried out to investigate the mechanical behavior of these multi-layered structures depending on the damage features, through-the-thickness distribution and boundary conditions. It is seen that for the large amount of power-law index "P", increasing this parameter does not have significant effect on the non-dimensional natural frequency parameters of the FG sandwich curved panel. Results indicate that by increasing the value of isotropic damage parameter "D" up to the unity (fully damaged core) the frequency would tend to become zero. One can dictate the fiber variation profile through the radial direction of the sandwich panel via the amount of "P", "b" and "c" parameters. It should be noticed that with increase of volume fraction of fibers, the frequency parameter of the panels does not increase necessarily, so by considering suitable amounts of power-law index "P" and the parameters "b" and "c", one can get dynamic characteristics similar or better than the isotropic limit case for laminated FG curved panels.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1994년도 가을 학술발표회 논문집
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• pp.160-166
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• 1994

In general, the problems of strengthening and repairing of deteriorated or damaged reinforced concrete members are usually worked out in situ by externally bounding steel plates using epoxy resins, which has been recognized to be one of effective and convenient methods. But the disadvantages of strengthening/repairing concrete members with externally bonded steel plates include ; (a) deterioration of the bond at the steel-concrete interface caused by the corrosion of steel ; (b) difficulty in manipulating the plate at the construction site ; (c) improper formation of joints, due to the limited delivery lengths of the steel plates ; and etc. Therefore these difficulties eventually have led to the concept of replacing the steel plates by fiber-reinforced composite sheets which are characterized by their light weight, extremely high stiffness, excellent fatigue properties, and outstanding corrosion resistance. In the paper, for the reliability assessment of reinforced concrete beams externally strengthened by carbon fiber plastic(CFRP) laminates, an attempt is made to suggest a limit state model based on the strain compatibility method and the concept of fracture mechanics. And the reliability of the proposed models is evaluated by using the AFOSM method. The load carrying capacity of the deteriorated and/or damaged RC beams is considerably increased. Thus, it may be stated that the post-strengthening of concrete beams with externally bonded CFRP materials may be one of very effective way of increasing the load carrying capacity and stiffeness characteristics of existing structures.

• 한국지진공학회논문집
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• 제23권1호
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• pp.43-54
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• 2019

Existing reinforced concrete frame buildings designed for only gravity loads have been seismically vulnerable due to their inadequate column detailing. The seismic vulnerabilities can be mitigated by the application of a column retrofit technique, which combines high-strength near surface mounted bars with a fiber reinforced polymer wrapping system. This study presents the full-scale shaker testing of a non-ductile frame structure retrofitted using the combined retrofit system. The full-scale dynamic testing was performed to measure realistic dynamic responses and to investigate the effectiveness of the retrofit system through the comparison of the measured responses between as-built and retrofitted test frames. Experimental results demonstrated that the retrofit system reduced the dynamic responses without any significant damage on the columns because it improved flexural, shear and lap-splice resisting capacities. In addition, the retrofit system contributed to changing a damage mechanism from a soft-story mechanism (column-sidesway mechanism) to a mixed-damage mechanism, which was commonly found in reinforced concrete buildings with strong-column weak-beam system.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.463-468
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• 2002

For the Externally bonded FRP systems, flexural design method is studied focusing on the reinforcement layer of the carbon fiber sheets. As the FRP layer is added, strengthening rate increases, but not proportionally as the FRP layer increases. This is reflected in the design formula appropriately by the bond cofficients from the added layers. As the number of FRP layer increases, the stress reinforcement and FRP sheet decreases, and it generally corresponds to the decrease rate of member flexural strength. This phenomenon is appearing indentically in a design formula and experimental result. The rate of $M_{test}$ and $M_n$ is 1.19 and it is estimated as safety factor which is the reduction factor, ${\psi}_f = 0.85$.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.471-474
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• 1999

An interface always appears when a repair is applied to an aged infrastructure system for repair. These repaired structures have the high chance to fail along the interface because of the stress concentration/discontinuity along the interface. So, mechanical properties of the interface have much influence on the behavior of repaired structure systems. In this paper, numerical tool that can predict effectively the interfacial fracture behavior is developed using axial deformation link elements, and this numerical technique is applied to the interfacial failure behavior. The results coincide with the ultimate strength and failure profile on the interfacial behavior of carbon fiber sheets for strengthening with epoxy adhesion. Thus, the mechanical behavior of the interface up to failure can be predicted using numerical technique with the proposed axial deformation link elements.

• 한국산학기술학회논문지
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• 제11권10호
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• pp.4024-4030
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• 2010

본 연구에서는 FRP 보강된 각형 CFT기둥의 중심축하중 실험과 이력거동실험을 수행하였다. 실험변수는 중심축하중 실험에서는 폭-두께비, FRP보강겹수이며, 이력실험에서는 콘크리트 강도와 FRP 보강겹수이다. 실험체의 내력과 연성능력을 정리하였고, FRP로 보강된 각형 CFT기둥의 압축내력 설계식을 제안한다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2001년도 가을 학술발표회 논문집
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• pp.751-756
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• 2001

This paper deals with the experimental evaluation of the performance of R.C beams strengthened with aramid, glass and carbon fiber sheets. To evaluate the effects of FRPs on the flexural strengthening of the beams, strengthening ratio is adopted as a main variable. Seven beams were fabricated and strengthened under same tensile strength based on ultimate strength of FRPs and strengthening length. Deflection, flexural stiffness, strain of FRP, ultimate load and failure load are compared to evaluate the effects of FRPs on structural behavior of retrofitted beams. The results shows that little effects of FRPs on behavior of strengthened beams can be estimated and the fail modes are more influenced on structural behavior than that.