• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.2
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• pp.181-190
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• 2005

The objective of this work is to study the flexural strengthening effectiveness of Carbon Fiber Mesh (CFM) in reinforced concrete beams. Flexural strengthening for a simply supported reinforced concrete (RC) beam using CFM is developed by bonding CFM to the soffit of the beam. In this experimental program, five medium-sized reinforced concrete beams strengthened with CFM are tested in bending to evaluate reinforcing effects of the CFM. The beams are designed to have high shear capacity so that expected dominant failure mode of specimens is bending. The reinforcing effect of CFM is small at crack initiation, but is considerable in flexural rigidity of the beam after crack initiation. In comparing the behaviors of strengthened and virgin beams each other, it is shown that the strength of RC beams can be enhanced by attaching CFM. A fairly good agreement between the measured values and the calculated ones is obtained at both the cracking strength and yield strength of the strengthened beams.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.1
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• pp.56-63
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• 2018

The present study examined the reversal cyclic flexural behavior of walls with jacket section approach for seismic strengthening through forming the boundary elements at both ends of the wall. The prestressed wire ropes were used for the lateral reinforcement to confine the boundary element of the wall. The main parameter investigated was the height of the jacket section for strengthening. The limit height of the strengthening jacket section was determined by comparing the moment distributions between the existing and strengthened walls. Test results showed that the examined jacket section approach was significantly effective in enhancing the flexural resistance of walls, indicating 46% higher stiffness at peak strength and 210% greater work damage indicator, compared with the flexural performance of the unstrengthened wall. The ductility of the strengthened walls was insignificantly affected by the height of the jacket section when the height is greater than twice the wall length. The flexural capacity of the strengthened walls was 22% higher than the predictions obtained using the equivalent stress block specified in ACI 318-14.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.4
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• pp.100-107
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• 2018

The objective of this study is to assess the strengthening effects of fiber reinforced polymer(FRP) sheets such as Carbon fiber, Glass fiber, and PET(polyethylene terephthalate) on reinforced concrete flexural members. Variables of theoretical analysis are types of strengthening materials, material properties and amount of strengthening materials. A virtual flexural member without FRP sheets was created as a control specimen to understand the structural behavior of the non-strengthened specimen in terms of elastic and ultimate cross section. In total, 11 specimens including one non-strengthened and ten strengthened specimens were investigated. Various variables such as types of strengthening, strengthening properties, and amount of strengthening were studied to compare the behavior of the control specimen with those of strengthened specimens with regard to moment-curvature relationship. Results of theoretical analysis showed that the moment capacity of strengthened specimens was superior to that of the control specimen. However, the control specimen indicated the best ductility among all the specimens. As the amount of strengthening increased, flexural performance was improved. Furthermore, the results indicated that the ductile effect of members was affected by the ultimate strain of FRP sheets. The strengthening effect on the damaged member was similar to that on the non-damaged one since there was less than 10% difference in terms of flexural strength and ductility. Therefore, even if a damaged member is treated as non-damaged for analysis there is probably no noticeable difference.

• Journal of the Korean Society of Safety
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• v.25 no.3
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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.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.835-842
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• 2005

This paper presents an experimental investigation of bond-strengthening hooks as a new method to increase bond strength along flexural reinforcing bars in reinforced concrete (RC) beams and columns. The RC members, which consisted of 1,300 MPa-class spirals as shear reinforcement, often suffered from bond splitting failure. The proposed method attempts to increase confining stiffness around the flexural bars by placing U-shaped hooks and to prevent premature bond splitting failure. Twelve specimens with varied amounts and sizes of the hooks were prepared to verify the strengthening effectiveness under monotonic and cyclic loading conditions. The test result indicated that the hooks increased the bond strength along the flexural bars although the strengthening effectiveness was limited by effective reinforcement ratio $P_{be}$. This limit is determined by size of stress-transmitting zones of concrete around anchors of the hooks. Anchors of the hooks are recommended to be longer than twelve times the hook diameter and inserted deeper than a quarter of the member depth (D/4). Proposed design equations provide modest estimates of the shear strengths.

• Journal of the Korean Society for Advanced Composite Structures
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• v.3 no.2
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• pp.11-18
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• 2012

This study proposes flexural failure design criteria of continuous slabs enhanced by a hybrid system of fiber reinforced polymer (FRP) and ultra high performance concrete (UHPC). The proposed hybrid retrofit system is designed to be placed at the top surface of the slabs for flexural strengthening of the sections in both positive and negative moment zones. The enhancing mechanisms of the proposed system for both positive and negative moment regions are presented. The neutral axis of the enhanced sections in positive moment zone at flexural failure is enforced to be in UHPC overlay for preventing the compression in FRP. From this condition, a relationship between design parameters of FRP and UHPC is established. Although the capacity of the proposed retrofit system to enhance flexural strength and ductility is confirmed through experiments of one-way RC slabs having two continuous spans, the retrofitted slabs failed in shear. To prevent this shear failure, a design criteria of flexural failure is proposed.

• Journal of the Korea Concrete Institute
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• v.12 no.3
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• pp.103-114
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• 2000

Recently, the need for strengthening reinforced concrete and prestressed concrete structure is increasing, particularly when there is an increase in load requirements, a change in use, a degradation problem, or some design/construction defects. Therefore, use of composite materials for structural repair presents several advantages and has been investigated all over the world. In this paper, the reinforced concrete slabs with epoxy - bonded AFRP sheed were experimentally investigated. Experimental data on strength. stiffness, material strain, deflection and mode of failure of strengthened slabs were obtained, and comparisons between the different flexural reinforcing schemes and reinforced concrete slabs without AFRP sheets were made It can be concluded that flexural strength of RC slabs strengthened with AFRP has increased, and that ductility of strengthened slabs has decreased.

• KCI Concrete Journal
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• v.12 no.1
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• pp.69-77
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• 2000

The reinforced concrete(RC) flexural members strengthened with steel plate/CFS at soffit have initial stresses and strains in reinforcements and concrete caused by the service loads at the time of retrofitting works. These initial residual stresses and strains of strengthened beams may affect the flexural performance of the rehabilitated beams. The objective of this study is to evaluate and verify the effectiveness of rehabilitation by external bonded steel plates and CFS to the tension face of the beams under three conditions of pre-loading. Thirteen beam specimens are tested and analyzed. Main test parameters are pre-loading conditions, strengthening materials and reinforcement ratio of specimens. The effect of test parameters on the strengthened beams is analyzed from the maximum load capacity, load-deflection relationship, state of stress of the materials. crack propagation phase, and failure modes. Both test results and design formulas of ACI Code provisions are compared and evaluated.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.125-128
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• 2006

Many research have been carried out concerned with the flexural performance of FRP composite in a various ways. Most of them, however, have used a small-scale specimen, so haven't been fully verified by full-scale model test. In this study, a full-scale RC beam model test for flexural strengthening with CFRP composites has been performed in order to verify test results obtained through a series of small-scale model test with respect to FRP stiffness affecting strengthening performance in the previous studies. A total of 4 specimens have been manufactured including control beam. The specimens strengthened with CFRP composites consist of 3 different CFRP stiffness with 2 types of CFRP composite. Consequently, the purpose of this study is to estimate influence of the size effect of specimens and FRP stiffness on the flexural performance. As a result, the effective strain of FRP composite is inversely proportional to FRP stiffness and ensures the same performance with small-scale model test.

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