• Journal of the Korea institute for structural maintenance and inspection
• /
• v.20 no.6
• /
• pp.30-39
• /
• 2016

An experimental study was performed to investigate flexural performance and bond characteristics of RC beams strengthened using ductile polyethylene terephthalate(PET) with low elastic modulus. Bond tests were planned and completed following CSA S806. Test variables were fiber type and fiber amount. Also, total of 8 RC beams was tested. Major test variables of the beam tests included section ductility(${\mu}=3.4$, 7.0), fiber type(CF, GF, PET) and amount of fiber strengthening. Moment-curvature analyses of the beam sections were also performed. In bond tests, the bond stress distribution as well as the maximum bond stress increased with increasing amount of PET. In case of 10 layers of PET, the effective bond length was 60 mm with the maximum and the average bond stress of 2.33 and 2.10 MPa, respectively. RC beam test results revealed that the moment capacity of the RC beams strengthened using PET 10 and 20 layers increased over the control beam with little reduction in ductility by fiber strengthening. All beams strengthened using PET resulted in ductile flexural failure without any sign of fiber debonding or fiber rupture. It was important to include the mechanical properties of adhesive in the moment-curvature analysis of PET-strengthened beam sections.

• Journal of the Korea Concrete Institute
• /
• v.24 no.4
• /
• pp.473-480
• /
• 2012

In order to develop an effecive seismic strengthening metghod for existing concrete structure, structural tests of aramid FRP reinforced RC columns are performed. The test variables were strengthening methods of aramid sheet and strip. The test results were evaluated by comparing strength and energy dissipation capacities of non-reinforced and reinforced specimens. The test result comparison showed that aramid sheet reinforcement on RC column was evaluated as the most efficient way to increase strength and energy dissipation capacity.

• International Journal of Concrete Structures and Materials
• /
• v.7 no.1
• /
• pp.3-16
• /
• 2013

Strengthening concrete structures using FRP composites is a commonly considered technology in many practical situations. The success of the strengthening intervention largely depends on adequate bond between FRP sheets and the concrete substrate. In recent years, techniques to anchor FRP sheets in applications where sheets must develop strength in a short length have been proposed. One of these techniques includes use of FRP anchors embedded into the concrete substrate and forming part of the composite strengthening system. This paper presents the results of studies conducted recently at the University of Massachusetts Amherst to advance the understanding on the behavior of FRP anchored systems.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2002.05a
• /
• pp.399-404
• /
• 2002

This paper presents the results cf research on improved flexural performance cf reinforced concrete beams strengthened with bonded carbon fiber reinforced polymer plate. Recently, strengthening technique with CFRP plate were almost carried out by external bonding. But current external bonding technique cf CFRP plates may result in debonding CFRP plate. Therefore, this study proposes a strengthening method that prevents or delays debonding between CFRP plates and concrete and at the same time improves the strength. For this test, there were only 14 test beams manufactured and failure load, deflection, strains and modes cf failure have been examined Test variables included the type cf strengthening, steel ratio and strengthening length, and the effects according to each test variables were analyzed. The experimental results show that the strength and stiffness cf the beam significantly increased between 34.55 and 116.51% and the increase cf the more lead-carrying capacity than the control beams.

• Structural Engineering and Mechanics
• /
• v.60 no.1
• /
• pp.163-173
• /
• 2016

Nowadays using Carbon Fiber Reinforced Polymer (CFRP) has been expanded in strengthening steel structures. Given that few studies have taken about strengthening of steel hollow pipe sections using CFRP, in present study, the effects of CFRP sheets using two layers as well as in combination with additional reinforcing strips has been assessment. Strengthening of five specimens was carried out in laboratory tests. As well as numerical simulation was performed for all specimens by Finite Element Method (FEM) using ABAQUS software and high correlation between the results of numerical models with experimental data indicate the power of FEM in this field. The results of both laboratory and simulated specimens showed that load-bearing capacity of circular cross-sections can be significantly increased using CFRP retrofitting technique. Also, application of additional CFRP reinforcing strips and layers caused more strength for the strengthened specimens.

• Structural Engineering and Mechanics
• /
• v.72 no.6
• /
• pp.723-736
• /
• 2019

The efficacy of a technique for the rehabilitation and strengthening of RC beam-column connections damaged due to cyclic loading was investigated. The repair mainly uses epoxy resin infused under pressure into the damaged region to retrieved back the lost capacity and then strengthening using fiber reinforced polymer (FRP) sheets for capacity enhancement. Three common types of reduced scale RC exterior beam-column connections namely (a) beam-column connection with beam weak in flexure (BWF) (b) beam-column connections with beam weak in shear (BWS) and (c) beam-column connections with column weak in shear (CWS) subjected to reversed cyclic loading were considered for the experimental investigation. The rehabilitated and strengthened specimens were also subjected to similar cyclic displacement. Important parameters related to seismic capacity such as strength, stiffness degradation, energy dissipation, and ductility were evaluated. The rehabilitated connections exhibited equal or better performance and hence the adopted rehabilitation strategies could be considered as satisfactory. Confinement of damaged region using FRP sheet significantly enhanced the seismic capacity of the connections.

• Journal of the Korea Concrete Institute
• /
• v.23 no.4
• /
• pp.405-411
• /
• 2011

Using combinations of carbon and glass fiber composites normally used for strengthening of concrete structures, the hybrid effect from strengthening concrete structures using the composite is studied. To produce the hybrid effects, the specimens were made with optimum proportions of carbon fibers with glass fibers. Then, direct tensile tests were conducted on the hybrid FRP (fiber reinforced polymer) specimens. Unlike the woven fiber sheet currently used in construction sites, the FRP specimens have to be directly combined with the fibers, which make the work very complicated. Therefore, direct tensile test specimens manufacturing method based on the combination of high-tension carbon fibers and E-type glass fibers was proposed and the effects of hybridization is studied through the direct tensile test. By comparing the ductility index, the modulus of elasticity, and the stress-strain curves of the specimens, the most optimum glass to carbon fiber combination ratio for the hybrid FRP was found to be 9 to 1 with ductile K-type epoxy. The study results are discussed in detail in the paper.

• Journal of the Korea Concrete Institute
• /
• v.16 no.5 s.83
• /
• pp.667-675
• /
• 2004

This paper presents the failure mode and strengthening design of reinforced concrete slab strengthened with Carbon Fiber Reinforced Polymer(CFRP) grid. Parameters involved in this experimental study are FRP grid reinforcement quantity, repair mortar thickness, the presence of anchor, and strengthening in compression. In this study, there are different failure types with increasing the CFRP grid strengthening reinforcement. On the low strengthening level, CFRP grid in repair mortar cover ruptures. On the moderate strengthening level, there is a debonding shear failure in the interface of carbon FRP grid because of the excessive shear deformation. On the high strengthening level, diagonal shear failure occurs. With the increasing of FRP grid reinforcement, the strengthening effect increased, but the ductility decreased. By limiting the strengthening level, it can be achieved to prevent shear failure which result in sudden loss in the resisting load capacity. CFRP rupture failure is desirable, because CFRP ruptured concrete slab keeps the same load capacity and ductility haying before strengthening even after failure. Finally, design guideline and procedure are given for strengthening of concrete slab with CFRP grid.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 1994.10a
• /
• pp.160-166
• /
• 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.

• Structural Engineering and Mechanics
• /
• v.56 no.1
• /
• pp.123-136
• /
• 2015

The proposed techniques to repair concrete members such as steel plates, fiber-reinforced polymers or concrete have important deficiencies in adherence and durability. The use of ultra high performance fiber concrete (UHPFC) can overtake effectively these problems. In this paper, the possibility of using UHPFC to strengthen reinforced concrete beams under torsion is investigated. Seven specimens of concrete beams reinforced with longitudinal and transverse reinforcements. One of these beams consider as control specimen while the others was strengthened by UHPFC on four, three, and two sides. This study includes experimental results of all beams with different types of configurations and thickness of UHPFC. As well as, finite element analysis was conducted in tandem with experimental test. Results reveal the effectiveness of the proposed technique at cracking and ultimate torque for different beam strengthening configurations, torque - twist graphs and crack patterns. The UHPFC can generally be used as an effective external torsional reinforcement for RC beams. It was noted that the behavior of the beams strengthen with UHPFC are better than the control beams. This increase was proportional to the retrofitted beam sides. The use of UHPFC had effect in delaying the growth of crack formation. The finite element analysis is reasonably agreement with the experimental data.