• Structural Engineering and Mechanics
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• v.66 no.2
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• pp.229-235
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• 2018

This study investigated the behaviour of the simply supported hollow steel tube (HST) beams, either concrete filled or unfilled when strengthened with carbon fibre reinforced polymer (CFRP) sheets. Eight specimens with varied tubes thickness (sections classification 1 and 3) were all tested experimentally under static flexural loading, four out of eight were filled with normal concrete (CFST beams). Particularly, the partial CFRP strengthening scheme was used, which wrapped the bottom-half of the beams cross-section (U-shaped wrapping), in order to use the efficiency of high tensile strength of CFRP sheets at the tension stress only of simply supported beams. In general, the results showed that the CFRP sheets significantly improved the ultimate strength and energy absorption capacities of the CFST beams with very limited improvement on the related HST beams. For example, the load and energy absorption capacities for the CFST beams (tube section class 1) were increased about 20% and 32.6%, respectively, when partially strengthened with two CFRP layers, and these improvements had increased more (62% and 38%) for the same CFST beams using tube class 3. However, these capacities recorded no much improvement on the related unfilled HST beams when the same CFRP strengthening scheme was adopted.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.5
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• pp.68-77
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• 2012

The joint of existing steel grid composite deck is composed of lap splice of reinforcing bar with end hooks and field-placed concrete. In this study, bending tests of deck joint composed of concrete shear key and high tension bolts are carried out for the design variable, concrete shear key strengthened with steel plate or not, and test results are compared with flexural performance of the existing deck joint. Test results showed that the mechanical deck joint has about 30% ~ 60% more ultimate bending strength than the existing joint. According to analysis results of moment-curvature relationship, the initial bending stiffness of the existing deck joint is some higher than that of mechanical joint. But, after crack failure the structural performance of the existing deck joint is rapidly reduced. Furthermore, the deck joint with the strengthened shear key with steel plate has more bending moment capacity than the deck joint without strengthening. And strengthening of shear key has positive influence on the increase of bending stiffness.

• Structural Engineering and Mechanics
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• v.87 no.6
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• pp.585-599
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• 2023

Geopolymer concrete (GC) can be competently utilized as a practical replacement for cement to prevent a high carbon footprint and to give a direction toward sustainable concrete construction. Moreover, previous studies mostly focused on the axial response of glass fiber reinforced polymer (glass-FRP) concrete compressive elements without determining the effectiveness of repairing them after their partial damage. The goal of this study is to assess the structural effectiveness of partially damaged GC columns that have been restored using carbon fiber reinforced polymer (carbon-FRP). Bars made of glass-FRP and helix made of glass-FRP are used to reinforce these columns. For comparative study, six of the twelve circular specimens-each measuring 300 mm×1200 mm-are reinforced with steel bars, while the other four are axially strengthened using glass-FRP bars (referred to as GSG columns). The broken columns are repaired and strengthened using carbon-FRP sheets after the specimens have been subjected to concentric and eccentric compression until a 30% loss in axial strength is attained in the post-peak phase. The study investigates the effects of various variables on important response metrics like axial strength, axial deflection, load-deflection response, stiffness index, strength index, ductility index, and damage response. These variables include concentric and eccentric compression, helix pitch, steel bars, carbon-FRP wrapping, and glass-FRP bars. Both before and after the quick repair process, these metrics are evaluated. The results of the investigation show that the axial strengths of the reconstructed SSG and GSG columns are, respectively, 15.3% and 20.9% higher than those of their original counterparts. In addition, compared to their SSG counterparts, the repaired GSG samples exhibit an improvement in average ductility indices of 2.92% and a drop in average stiffness indices of 3.2%.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.99-100
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• 2009

In this paper, wish to achieve an experimental study to investigate enhanced performance of the masonry walls strengthened in shear and ductility using Aramid fiber strip.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.1
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• pp.125-132
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• 2010

In the recent construction industry, an external strengthening method using fiber reinforced polymers has been widely used. Since reinforced concrete structures strengthened with fiber reinforced polymers are always under sustained loads, influence of creep and shrinkage on the structures is inevitable. Due to the creep and shrinkage, behaviors of the structures, such as deflection, deformation, recovery capability, strength and so on are also under the influence of creep and shrinkage. Thus, in order to estimate efficacy, creep recovery and residual strength of FRP strengthened RC beams, long-term flexural experiments and static flexural experiments were carried out. As the result of the experiments, FRP strengthened RC beams were very effective in terms of deflection control. Furthermore, the strengthened beams had higher immediate deformation recovery than immediate deformation. Through the static flexural experiments, it was shown that the CFRP strengthened beam had high residual strength. It seems that the sustained loads did not affect bond and residual strength of the beams.

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

• Journal of the Korea Concrete Institute
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• v.18 no.4 s.94
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• pp.527-534
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• 2006

This paper outlines a new strengthening technique for concrete beams using externally unbended high-strength bars. The advantages of proposed method lie in speed and simplicity of construction compared to the alternative strengthening method. Externally unbended reinforcement retains many of the advantages over external unbended prestressed tendons. It eliminates time consuming stressing operations. Clearance requirements around anchorages are reduced as access is not required for prestressing jacks. Test results of eight specimens on reinforced concrete beams using different reinforcement materials such as carbon fiber sheet, steel plate and high-tension bar are reported. The beam strengthened by carbon fiber sheet showed a brittle failure mode due to the separation of fiber. As a result of draped profile of external bar, the maximum strength of the beam were increased by up to 212 percent and the deflections were reduced by up to 65 percent. Test results show that the beams reinforced with high-tension bar are superior to reference specimens, especially for the strength and deformation capacity.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.31-38
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• 2011

In this study, in order to observe the behaviors of fiber reinforced polymer (FRP) strengthened and steel fiber reinforced concrete specimens for impact and static loads, flexural and punching tests were performed. For the one-way flexural and two-way punching tests, concrete specimens with the dimensions of $50{\times}100{\times}350$ mm and $50{\times}350{\times}350$ mm were fabricated, respectively. The steel fiber reinforced concrete specimens showed much enhanced resistance on two-way punching of static and impact loads. In addition the FRP strengthening system provided the outstanding performance under a punching load. Because of a large tensile strength and toughness of ultra high performance concrete (UHPC), the UHPC specimens retrofitted with FRP showed marginally enhanced strength and energy dissipating capacity.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.1
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• pp.46-53
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• 2023

In this paper, we evaluated the flexural performance of three types of reinforced concrete beams (SHCC-RB, SHCC-SB, SHCC-FRP) strengthened with ordinary steel rebar, very high strength (super strength) rebar, and FRP bars together with strain-hardening cement composite (SHCC). For this purpose, a series of beam specimens were manufactured and four-point load bending experiments were performed. As a result of the experiment, all specimens strengthened with SHCC exhibited tightly controlled flexural microcrakcs with the crack width of less than 100 ㎛. This is mostly due to the material properties of SHCC showing tensile strain hardening properties with multiple microcracks under uniaxial tension. The specimen SHCC-FRP showed lower initial cracking moment and yield flexural strength than SHCC-RB, whereas the maximum flexural strength of SHCC-FRP was superior to that of SHCC-RC. This is because the tensile strength of FRP bars is higher than that of ordinary steel reabr. The initial cracking moment of the beam specimen SHCC-SB was similar to that of SHCC-RB, but the yield flexural strength and maximum flexural strength of SHCC-SB were evaluated to be the highest.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.4
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• pp.35-42
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• 2018

This study evaluated the fire resisting capacity and post-fire serviceability of the concrete beams retrofitted by near surface mounted method(NSM) using GFRP plates. Main parameters in the test are grout materials and fire exposure. For the test, two types of grout materials between concrete substrate and GFRP plate were used; flame resisting epoxy and filling mortar. Four RC beam specimens were made and two of them were exposed to fire according to real scale fire curve proposed KS F 2257. After the fire exposure test, flexural test were performed to investigate the flexural performance of concrete beams including strength and deformation. From the test results, it was found that the beam retrofitted by NSM-GFRP presented higher flexural strength than that of the beam without retrofit, which indicates NSM-GFRP retrofit technologies is effective to maintain flexural strength even after fire exposure. In addition, the specimens grouted by epoxy showed good performance in strength but bad performance in ductility.