• Steel and Composite Structures
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• v.23 no.1
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• pp.87-94
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• 2017

Steel structures often require strengthening due to the increasing life loads, or repair caused by corrosion or fatigue cracking. Carbon Fiber Reinforced Polymers (CFRP) is one of the materials used to strengthen steel structures. Most studies on strengthening steel structures have been carried out on steel beams and steel columns under centric compression load. No independent article, to the author's knowledge, has studied the effect of CFRP strengthening on steel columns under eccentric compression load, and it seems that there is a lack of understanding on behavior of CFRP strengthening on steel columns under eccentric compression load. However, this study explored the use of adhesively bonded CFRP flexible sheets on retrofitting square hollow section (SHS) steel columns under the eccentric compression load, using numerical investigations. Finite Element Method (FEM) was employed for modeling. To determine ultimate load of SHS steel columns, eight specimens with two types of section (Type A and B), strengthened using CFRP sheets, were analyzed under different coverage lengths, the number of layers, and the location of CFRP composites. Two specimens were analyzed without strengthening (control) to determine the increasing rate of the ultimate load in strengthened steel columns. ANSYS was used to analyze the SHS steel columns. The results showed that the CFRP composite had no similar effect on the slender and stocky SHS steel columns. The results also showed that the coverage length, the number of layers, and the location of CFRP composites were effective in increasing the ultimate load of the SHS steel columns.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.10a
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• pp.501-507
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• 1996

The final objectives of this study are to present the theoretical formula for reasonable structural analysis and practical codes on the repair/strengthening of damaged reinforced concrete structrues. For that purpose, in last year, preliminary experiments for flexure and shear of beam structure using carbon sheet and steel plate were performed, and in sequence, in this year, using aramid fiber sheet and steel plate more extensive experiment were performed. Repair for the performance of flexure and shear was focused on, and main variables were selected considering aplicablilty for practical field, such as, spacing of anchor bolt, lapping, jacking up, preloading level, and fiber difection as well as length of repairing plate and thickness. so new results from various angles are to be presented.

• Journal of Sensor Science and Technology
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• v.8 no.3
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• pp.232-238
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• 1999

Single mode fiber optic interferometers using the Fabry-Perot configuration were embedded in a reinforced concrete structure. These interferometers investigated the character of phase shift and strain for internal loads. The 10 mm length of FFPI in the continuous length of single mode fiber (SMF) were produced with two pieces of SMF coated were $TiO_2$ dielectric film utilizing the fusion splicing technique. The fabricated fiber optic Fabry-Perot interferometer(FFPI) and the 6 mm length of steel bar were buried with specimen ($100{\times}100{\times}50\;mm^3$) which was made of concrete structure. The resin protects FFPI and fiber leads from squeezed concrete. Sensors at different point in the structure were multiplexed by TDM (Time Division Multiplexing) method and the deformation to the external loads at each point could be monitored simultaneously. The output signals were proportional to the external loads applied to the structure and the sensitivity of the sensors were $1.03^{\circ}/kg$ and $0.76^{\circ}/kg$ respectively.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.223-234
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• 2016

In this study, direct tension test for hybrid steel fiber reinforced ultra-high performance concrete (UHPC) containing two different steel fibers with a length of 16 and 19 mm was performed to investigate the fracture behavior of UHPC. Test results showed that crack strength and tensile strength, and fracture energy increased with increasing the fiber volume ratio. Based on the test results, the peak cohesive stress at the crack tip, tensile strength, and fracture energy depending on the fiber volume ratio were proposed. The proposed tensile strength of UHPC was suggested as a function of the fiber volume ratio and compressive strength. The peak cohesive stress at the crack tip and fracture energy were also proposed as a function of the tensile strength. The predicted values were relatively agree well with the test results. Thus, the proposed equations is expected to be applicable to UHPC with a compressive strength of 140~170 MPa and a fiber volume ratio of less than 2%.

• Journal of the Korea Concrete Institute
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• v.23 no.3
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• pp.257-264
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• 2011

This paper contains the experimental performance evaluation results of bond-type anchorage systems with the CFRP(carbon fiber reinforced polymer) tendon. The preliminary tests were performed to find the appropriate filling materials in the steel molds. A total of five materials including epoxy or cement mortar have been used as fillers in the steel molds. Results of the preliminary tests showed that specimen filled with non-shrinkage mortar showed maximum tensile strength. Based on the finding, the non-shrinkage mortar was selected as filler for anchoring CFRP tendons. Additional tests were performed as a parametric study to select proper size of steel molds such as external diameter, thickness, and length. The proper size of steel molds with non-shrinkage mortar was selected based on the test results, which gave stable tensile performance.

• Advances in concrete construction
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• v.10 no.1
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• pp.81-92
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• 2020

Flexural and splitting strength behavior of conventional concrete can significantly be improved by incorporating the fibers in it. A significant number of research studies have been conducted on various types of fibers and their influence on the tensile capacity of concrete. However, as an important property, tensile capacity of fiber reinforced concrete (FRC) is not modelled properly. Therefore, this paper intends to formulate a model based on experiments that show the relationship between the fiber properties such as the aspect ratio (length/diameter), fiber content, compressive strength, flexural strength and splitting strength of FRC. For the purpose of modeling, various FRC mixes only with steel fiber are adopted from the existing research papers. Automated neural network search (ANS) is then developed and used to investigate the effect of input parameters such as fiber content, aspect ratio and compressive strength to the output parameters of flexural and splitting strength of FRC. It is found that the ANS model can be used to predict the flexural and splitting strength of FRC in a sensible precision.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.762-765
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• 2004

The main objective of this study is to provide a parametric evaluation of the pull-out response of steel fibers embedded in cementitious matrices. The various parameters controlling the behavior of the bond stress versus end slip relationship are analyzed; their effects on the entire pull-out load versus end slip response and the corresponding pull-out energy up to total pull-out are investigated. Also discussed are the effects of the fiber length, the water/binder ratio of the mixtures and embedded length.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.12
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• pp.697-704
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• 2017

High-Performance Fiber-Reinforced Cement Composites (HPFRCC) has outstanding durability, and has attracted interest because of its ductility and development of strength, which allows a reduction of the self-weight of a structural member by substantially decreasing the cross section. Therefore, the present study aimed to improve the economic efficiency of HPFRCC by examining experimentally the flexural performance considering various characteristics of the steel fiber. To find an efficient fiber reinforcement method, the flexural performance was evaluated for different shapes, aspect ratios, and volume ratios of the steel fiber. Straight, hooked, and twisted fiber configurations were considered by adopting a fiber length longer than the usual 13 mm. The test results showed that HPFRCC reinforced by 19.5 nun-long straight fibers with a volume fraction of 1.5% shows better flexural performance than that reinforced by 13 mm-long straight fibers with a volume fraction of 2.0%. Consequently, HPFRCC with enhanced economic efficiency can be produced by adopting a reduced amount of steel fiber.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.325-333
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• 2008

This study evaluated the mechanical performance, shrinkage crack and fire resistance of hybrid fiber (blended steel and polypropylene fiber with different diameter and length) reinforced concrete at elevated temperature. The compressive, splitting tensile, flexural, plastic shrinkage test were conducted to the evaluate the mechanical properties and the resistance of shrinkage crack. Also, the surface investigation, reduction rate of mass and residual compressive test were performed to evaluate the physical and mechanical properties after 400$^{\circ}C$, 600$^{\circ}C$, 800$^{\circ}C$ and 1,200$^{\circ}C$ exposure. Test results showed that the hybrid fiber reinforced concrete improved the mechanical performance, shrinkage crack and fire resistance. The reduction of performance with a temperature change were high at the temperature of $600\sim800^{\circ}C$.

• Steel and Composite Structures
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• v.9 no.5
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• pp.419-444
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• 2009

Flange and web local buckling in beam plastic hinge regions of steel moment frames can prevent beam-column connections from achieving adequate plastic rotations under earthquake-induced forces. Reducing the flange-web slenderness ratios (FSR/WSR) of beams is the most effective way in mitigating local member buckling as stipulated in the latest seismic design specifications. However, existing steel moment frame buildings with beams that lack the adequate slenderness ratios set forth for new buildings are vulnerable to local member buckling and thereby system-wise instability prior to reaching the required plastic rotation capacities specified for new buildings. This paper presents results from a research study investigating the cyclic behavior of steel I-beams modified by a welded haunch at the bottom flange and reinforced with glass fiber reinforced polymers at the plastic hinge region. Cantilever I-sections with a triangular haunch at the bottom flange and flange slenderness ratios higher then those stipulated in current design specifications were analyzed under reversed cyclic loading. Beam sections with different depth/width and flange/web slenderness ratios (FSR/WSR) were considered. The effect of GFRP thickness, width, and length on stabilizing plastic local buckling was investigated. The FEA results revealed that the contribution of GFRP strips to mitigation of local buckling increases with increasing depth/width ratio and decreasing FSR and WSR. Provided that the interfacial shear strength of the steel/GFRP bond surface is at least 15 MPa, GFRP reinforcement can enable deep beams with FSR of 8-9 and WSR below 55 to maintain plastic rotations in the order of 0.02 radians without experiencing any local buckling.