• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.1
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• pp.148-156
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• 2020

The paper is a summary of the results of the basic pullout test which is conducted to evaluate the anchorage capacity of high strength headed bars that is mechanical anchored vertically on steel fiber reinforced concrete members. The main experimental parameters are volume fraction of steel fiber, concrete strength, anchorage length, yield strength of headed bars, and shear reinforcement bar. Both sides of covering depth of the specimen are planned to double the diameter of the headed bars. The hinged point is placed at the position of each 1.5𝑙_dt and 0.7𝑙_dt around the headed bars, and the headed bars are drawn directly. As a result of pullout test experiment, concrete fracture and steel tensile rupture appear by experimental parameters. The compressive strength of concrete is 2.7~5.4% higher than that of steel fiber with the same parameters, while the pullout strength is 20.9~63.1% higher than that of steel fiber without the same parameters, which is evaluated to contribute greatly to the improvement of the anchorage capacity. The reinforcements of shear reinforcements parallel to the headed bars increased 1.7~7.7% pullout strength for steel fiber reinforced concrete, but the effect on the improvement of the anchorage capacity was not significant considering the increase in concrete strength. As with the details of this experiment, it is believed that the design formula for the anchorage length of KCI2017and KCI2012 are suitable for the mechanical development design of SD600 head bar that is perpendicular to the steel fiber reinforced concrete members.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.3
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• pp.314-320
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• 2022

The function of reinforcing fibers used in building materials is to maintain resistance to bending loads and to function for cracking caused by drying shrinkage. High-density fiber-cement composites are mainly used for linear plates and are used to increase bending resistance. Therefore, tensile properties, bonding strength with cement hydrate, alkali resistance, and the like are required. Recently, as the non-combustible performance has been strengthened, a function to minimize the occurrence of sparks during high-temperature heating has been added. Therefore, the use of organic fibers is limited. In this study, a study was conducted to replace polypropylene used as reinforcing fiber with hemp fiber with excellent heat resistance. Hemp fibers have excellent heat resistance, good affinity with cement, and excellent alkali resistance. Based on the total volume of polypropylene fibers used in the existing formulation, the non-combustible performance was compared and evaluated by using hemp fibers instead of the polypropylene fibers, and basic physical properties such as flexural strength were tested. As a result of conducting a non-combustibility and physical property test using hemp fibers with a fiber length of 7 mm using 2 % and 3 % by weight, it was found that there is no remaining time of the flame, and the flexural strength can be secured at 95 % level of the existing polypropylene fiber.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.46-49
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• 2003

Cu have been widely used as signal transmission materials for electrical electronic components owing to its high electrical conductivity. However, it's size have been limited to small ones due to its poor mechanical properties, Until now, strengthening of the copper at toy was obtained either by the solid solution and precipitation hardening by adding alloy elements or the work hardening by deformation process. Adding the at toy elements lead to reduction of electrical conductivity. In this aspect, if carbon nanofiber is used as reinforcement which have outstanding mechanical strength and electric conductivity, it is possible to develope Cu matrix nanocomposite having almost no loss of electric conductivity. It is expected to be innovative in electric conduct ing material market. The unidirectional alignment of carbon nanofiber is the most challenging task developing the copper matrix composites of high strength and electric conductivity In this study, the unidirectional alignment of carbon nanofibers which is used reinforced material are controlled by drawing process in order to manufacture the intermediary materials for the carbon nanofiber reinforced Cu matrix nanocomposite and align mechanism as well as optimized drawing process parameters are verified via experiments and numerical analysis. The materials used in this study were pure copper and the nanofibers of 150nm in diameter and of $10~20\mu\textrm{m}$ In length. The materials have been tested and the tensile strength was 75MPa with the elongation of 44% for the copper it is assumed that carbon nanofiber behave like porous elasto-plastic materials. Compaction test was conducted to obtain constitutive properties of carbon nanofiber. Optimal parameter for drawing process was obtained by experiments and numerical analysis considering the various drawing angles, reduction areas, friction coefficient, etc Lower reduction areas provides the less rupture of cu tube is not iced during the drawing process. Optimal die angle was between 5 degree and 12 degree. Relative density of carbon nanofiber embedded in the copper tube is higher as drawing diameter decrease and compressive residual stress is occurred in the copper tube. Carbon nanofibers are moved to the reverse drawing direct ion via shear force caused by deformation of the copper tube and alined to the drawing direction.

• Geotechnical Engineering
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• v.12 no.3
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• pp.127-148
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• 1996

Recently, foundations of heavy structures such as bridge abutments have been built on slopes or near the crest of slopes at an increasing rate. Because the bearing capacity of such foundations is considerably lower than the bearing capacity of the same soil on a level ground, deep footings such as piles and caissons are often used. However, the costs of such methods are generally very high. One of the new techniques to overcome the problem is to place reinforcing members such as geosynthetics or metal strips horizontally at some depths beneath the footings. Rational methods of analysis to predict the bearing capacity of footings in reinforced slopes are therefore needed. This paper proposes an analytical method for estimating the increase in bearing capacity gained from the included horizontal strips or ties of tensile reinforcing in the foundation soil below the footing built near the crest of a slope. A failure mechanism, including the concept of'wide slab effect', adopted in the present study for analyzing the bearing capacity of foundations in reinforced slopes, is established through the observed model test behaviors described by Binquet SE Lee and Huang et al, and the Boussinesq solutions. The analytical results are then compared with the experimental data described in the paper by Huang et al. Also in order to properly evaluate the soil reinforcement interaction, typical pullout test values of the apparent friction coefficient, which usually vary with depths owing to both the increase of the shearing volume and the increase in local stress caused by soil dilatancy, are analyzed and related functionally. Furthermore, analytical parametric studies are carried out to investigate the effect and significance of various pertinent parameters associated with design of reinforced slope foundations. Keywords : Bearing capacity, Reinforced slope, Slab effect, Friction coefficient.

• Composites Research
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• v.29 no.5
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• pp.282-287
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• 2016

p-DCPD (poly dicyclopentadiene) is the resin that the versatile mechanical properties can be changeable via the control of inner monomer and catalysts. In this work, to improve the strength of composites, surface treated MGF (milled glass fiber) was used as an reinforcement in p-DCPD by molybdenum (Mo) catalyst matrix. The optimum concentration of surface treatment was obtained and the cohesion of MGF themselves increased with concentration. In case of 0.2 wt% silane concentration, the maximized mechanical properties of MGF/p-DCPD composite exhibited because of minimized MGF cohesion. When butyl silane showing minimizing cohesion was used as the optimized alkyl length, high tensile and flexure strength exhibited due to the steric hindrance effect among MGFs. Mechanical and their fractured surfaces of MGF/p-DCPD composites was compared for 4 different chemical functional groups. Norbornene functional groups containing similar chemical structure to DCPD matrix exhibited higher interfacial adhesion between MGFs and DCPD matrix.

• Journal of the Korea Concrete Institute
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• v.15 no.2
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• pp.234-245
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• 2003

Most of the concrete bridge structures are exposed to damage due to the excessive traffic loading and the aging of the structure. The damage of concrete causes the further deterioration of the function in the concrete structure due to corrosion of the reinforced bars and decohesion between the concrete and the reinforced bar. The quick rehabilitation of the damaged concrete structures has become of great importance in the concrete structural system in order to avoid the further deterioration of the structures. Recently fiber sheets are used for strengthening the damaged concrete structures due to its many advantages such as its durability, non-corrosive nature, low weight, ease of application, cost saving, control of crack propagation, strength to thickness ratio, high tensile strength, serviceability and aesthetic. However, the lack of analytical procedures for assessing the nominal moment capacity by the fiber sheet reinforcement leads to difficulties in the effective process of decisions of the factors in the strengthening procedure. In this work, flexural strengthening effects by fiber sheets bonded on bottom face of the member are studied for the reinforced concrete T beam. In addition, auxiliary flexural strengthening effects by U-type fiber sheets bonded on bottom and side faces of the member to prevent delamination of the bottom fiber sheet are theoretically investigated. The analytical solutions are compared with experimental results of several references to verify the proposed approach. It is shown that the good agreements between the predicted results and experimental data are obtained.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.3
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• pp.160-170
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• 2010

Steel Fiber Reinforced Concrete (SFRC) beams has greater shear strength than typical reinforced concrete beams due to the high tensile strength of steel fibers. In this research, an experiment has been conducted to investigate the shear behavior of SFRC beams, and especially, the portion of shear resistance by uncracked compressive concrete section has been measured. Based on the test results in this study and 87 test data collected from literature, the accuracy of the existing equations for the estimation of shear strength has been evaluated. The shear strength of SFRC beams increased as more steel fibers were mixed. However, it is considered that the most efficient amount of steel fiber for enhancement of shear strength would be between 1% and 2% in that the specimen with 0.5% of steel fibers were abruptly failed after inclined cracking, and that the specimen with 2.0% of steel fibers showed a relatively low efficiency in increasing shear strength. The portion of shear resistance by the uncracked compressive concrete section was measured to be greater than 21%, and the equation proposed by Oh et al. provided the best accuracy on the estimation of shear strength of SFRC beams among the approaches evaluated in this study.

• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.5
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• pp.173-181
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• 2021

Reinforced concrete structures are exposed to various environments, resulting in reinforcement corrosion due to moisture and ions penetration. Reinforced concrete corrosion causes a decrease in the durability performance of reinforced concrete structures. One solution to mitigate such issues is using FRP rebars, which offer several advantages such as high tensile strength, corrosion resistance, and light-weight than conventional rebars, in reinforced concrete instead of conventional steel rebars. The FRP rebar used should be examined at the limit state because FRP reinforced concrete has linear behavior until its fracture and can generate excessive deflection due to the low elastic modulus. It should be considered while designing FRP reinforced concrete for flexure. In the ultimate limit state, the flexural strength of FRP reinforced concrete as per ACI 440.1R is significantly lower than the flexural strength by applying both the environmental reduction and strength reduction factors accounting for the material uncertainty of FRP rebar. Therefore, in this study, the experimental results were compared with the deflection of the proposed effective moment of inertia referring to the local and international standards. The experimental results of GFRP and BFRP reinforced concrete were compared with the flexural strength as determined by ACI 440.1R and Fib bulletin 40. The flexural strength obtained by the experimental results was more similar to that obtained by Fib bulletin 40 than ACI 440.1R. The flexural strength of ACI 440.1R was conservatively evaluated in the tension-controlled section.

• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.6
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• pp.73-81
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• 2022

Recently, as the service life of structures increased, the load-carrying capacity of deteriorated reinforced concrete, where corrosion of reinforcing bars occurs due to various causes, is frequently decreased. In order to address this problem, many studies on the bond characteristic of FRP (Fiber Reinforced Polymer) bars with corrosion resistance, light weight and high tensile strength have been conducted, however there are not many studies on the bond characteristic of grid-typed CFRP embedded in concrete. Therefore, in order to evaluate the bond characteristics of grid-typed CFRP and its usability as a substitute for steel rebar, a pull-out test is performed using the longitudinal bond length and transverse grid length of the grid-typed CFRP as variables. Through the pull-out test, the bond load-slip curve of the grid-typed CFRP is derived, and the bond behavior is analyzed. The total bond load equation is proposed as the sum of the bond force of the longitudinal bond length and the shear force of the grid in the transverse direction. Also, expressing the area of the bond load-slip curve as total work, the change in dissipated energy with respect to the slip is analyzed to examine the effect of the tranverse grid on the bond force.

• Journal of the Korea Concrete Institute
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• v.19 no.1
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• pp.121-130
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• 2007

To investigate the enhancement in strength and deformation capacities of concrete confined by FRP composites, tests under axial loads were carried out on three groups of thirty six short columns in circular section with diverse GFRP confining reinforcement. The major test variables considered include fiber content or orientation, wrap or tube type by varying the end loading condition, and continuous or discontinuous confinement depending on the presence of vortical spices between its two halves. The circumferential FRP strains at failure for different types of confinements were also investigated with emphasis. Various analytical models capable of predicting the ultimate strength and strain of the confined concrete were examined by comparing to observed results. Tests results showed that FRP wraps or tubes provide the substantial increase in strength and deformation, while partial wraps comprising the vertical discontinuities fail in an explosive manner with less increase in strength, particularly in deformation. A bilinear stress-strain response was observed throughout all tests with some variations of strain hardening. The failure hoop strains measured on the FRP surface were less than those obtained from the tensile coupons in all tests with a high degree of variation. In overall, existing predictive equations overestimated ultimate strengths and strains observed in present tests, with a much larger scatter related to the latter. For more accuracy, two simple design- oriented equations correlated with present tests are proposed. The strength equation was derived using the Mohr-Coulomb failure criterion, whereas the strain equation was based on entirely fitting of test data including the unconfined concrete strength as one of governing factors.