• Journal of the Korea institute for structural maintenance and inspection
• /
• v.19 no.1
• /
• pp.100-108
• /
• 2015

The purpose of this study is to evaluate the effect of improvement on the impact resistance and strength properties of cement composites by surface modification of aramid fiber. For aramid fiber reinforced cement composites, therefore, dispersion capability and the bonding efficiency between the fibers and the cement composite material need to be improved. It is possible by modifying surface properties to hydrophobic, it is considered that oiling agent ratio of 1.2 % and improvement of performance is in need to be investigated. In this study, short aramid fibers were mixed by different fiber length and oiling agent ratio. And improvement of strength properties and impact resistance performance of hybrid cement composites were evaluated under the influence of steel fiber. As a result, strength properties of aramid fiber reinforced cement composites are different by mixing ratio of fiber, oiling agent ratio and length of fiber. In case of cement composites which have same volume fraction and fiber length, tensile strength and flexural strength were improved with increase of the emulsions throughput of the fiber surface. The results of evaluation on the static strength properties had effects on impact resistance performance by high-velocity impact. And it was observed that the scabbing of rear was suppressed with increase of the oiling agent ratio.

• Journal of Adhesion and Interface
• /
• v.17 no.1
• /
• pp.15-20
• /
• 2016

Fiber arrangement was important for fiber reinforced thermoplastic composites using injection fabrication. In this work, fiber arrangement in CF/PP was investigated to use electrical resistance (ER) method during injection times. There were 3 types of injection products of CF/PP with different ER change ratio by fiber arrangement. High ER change ratio case of injection CF/PP products had better increased tensile strength. This reason was due to the fiber arrangement of CF/PP by injection. Fractured surface and contact angle of CF/PP products were used to evaluate for injection product quality. Uniform fiber arrangement of CF/PP by injection type exhibited the uniform heat condition of melted CF/PP. Steady thermal transfer effect occurred from melted CF/PP to steel injection mold. Steady thermal transfer effect of CF/PP was transmitted to high ER change ratio of mold. Ultimately, good condition CF/PP product by injection molding method could be predicted by using ER method.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.19 no.2
• /
• pp.653-659
• /
• 2018

High-rise buildings and complex facilities are a representative urban system for the masses, and it requires an increasing role of commodity and safety. Smoke and toxic gasses can cause accidents due to fire in these systems. The purpose of this study is to develop a fiber screen material for emergency evacuation passages that can be avoided quickly and safely in cases of disasters. The fiber screen material is applicable to folding devices for emergency evacuation passages. The material is different from general steel material in that it is lightweight with less burden during storage for a long time in a roll form in a folding device. It also has an excellent secondary function in that it is less affected by radiant heat. Three kinds of fiber screen materials were selected that have good flame retardancy and post-processing characteristics. A performance evaluation was performed by a heat shrinkage test, contact heat test, combustibility test, flame retardancy test, tensile strength test, and tear strength test. As a result, the lightweight fabric shows excellent performance through post-processing, and silicone resin coating can secure safety of the pizza by the fiber screen material performance and radiant heat. The optimum post-treatment conditions were evaluated by performing a burning test after coating two kinds of glass fibers and four types of flame-retardant silicone resins with different weight and thickness.

• Korean Journal of Materials Research
• /
• v.28 no.12
• /
• pp.763-768
• /
• 2018

In this study, glass fibers are fabricated via a continuous spinning process using manganese slag, steel slag, and silica stone. To fabricate the glass fibers, raw materials are put into an alumina crucible, melted at $1550^{\circ}C$ for 2 hrs, and then annealed at $600^{\circ}C$ for 2 hrs. We obtain a black colored glass. We identify the non-crystalline nature of the glass using an XRD(x-ray diffractometer) graph. An adaptable temperature for spinning of the bulk marble glass is characterized using a high temperature viscometer. Spinning is carried out using direct melting spinning equipment as a function of the fiberizing temperature in the range of $1109^{\circ}C$ to $1166^{\circ}C$, while the winder speed is in the range of 100rpm to 250rpm. We investigate the various properties of glass fibers. The average diameters of the glass fibers are measured by optical microscope and FE-SEM. The average diameter of the glass fibers is $73{\mu}m$ at 100rpm, $65{\mu}m$ at 150rpm, $55{\mu}m$ at 200rpm, and $45{\mu}m$ at 250rpm. The mechanical properties of the fibers are confirmed using a UTM(Universal materials testing machine). The average tensile strength of the glass fibers is 21MPa at 100rpm, 31MPa at 150rpm, 34MPa at 200rpm, and 45MPa at 250rpm.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.25 no.5
• /
• pp.173-181
• /
• 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
• /
• v.26 no.6
• /
• pp.73-81
• /
• 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 Korean Society of Water and Wastewater
• /
• v.37 no.4
• /
• pp.215-229
• /
• 2023

In this study, non-destructive technologies that can be applied to evaluate the integrity of valve materials, safety against internal pressure caused by corrosion, and the blocking function of large-diameter water valves during operation without requiring specimen collection or manpower entering the inside of the valve were tested to assess the reliability of the technologies and their suitability for field application. The results showed that the condition of the graphite structure inside the valve body can be evaluated directly through the optical microscope in the field without specimen collection for large-diameter water butterfly valves, and the depth of corrosion inside the valve body can be determined by array ultrasound and the tensile strength can be measured by instrumented indentation test. The reliability of each of these non-destructive techniques is high, and they can be widely used to evaluate the condition of steel or cast iron pipes that are significantly smaller in thickness than valves. Evaluation of blocking function of the valves with mixed gas showed that it can be detected even when a very low flow rate of mixed gas passes through the disk along with the water flow. Finally, as a result of evaluating the field applicability of non-destructive technologies for three old butterfly valves installed in the US industrial water pipeline, it was found that it is possible to check the material and determine the suitability of large-diameter water valves without taking samples, and to determine the corrosion state and mechanical strength. In addition, it was possible to evaluate safety through the measurement results, and it is judged that the evaluation of the blocking function using mixed gas will help strengthen preventive response in the event of an accident.

• Geotechnical Engineering
• /
• v.12 no.4
• /
• pp.157-178
• /
• 1996

Current design methods for reinforced earth structures take no account of the magnitude of the strains induced in the tensile members as these are invariably manufactured from high modulus materials, such as steel, where straits are unlikely to be significant. With fabrics, however, large strains may frequently be induced and it is important to determine these to enable the stability of the structure to be assessed. In the present paper internal design method of analysis relating to the use of fabric reinforcements in reinforced earth structures for both stress and strain considerations is presented. For the internal stability analysis against rupture and pullout of the fabric reinforcements, a strain compatibility analysis procedure that considers the effects of reinforcement stiffness, relative movement between the soil and reinforcements, and compaction-induced stresses as studied by Ehrlich 8l Mitchell is used. I Bowever, the soil-reinforcement interaction is modeled by relating nonlinear elastic soil behavior to nonlinear response of the reinforcement. The soil constitutive model used is a modified vertsion of the hyperbolic soil model and compaction stress model proposed by Duncan et at., and iterative step-loading approach is used to take nonlinear soil behavior into consideration. The effects of seepage pressures are also dealt with in the proposed method of analy For purposes of assessing the strain behavior oi the fabric reinforcements, nonlinear model of hyperbolic form describing the load-extension relation of fabrics is employed. A procedure for specifying the strength characteristics of paraweb polyester fibre multicord, needle punched non-woven geotHxtile and knitted polyester geogrid is also described which may provide a more convenient procedure for incorporating the fablic properties into the prediction of fabric deformations. An attempt to define improvement in bond-linkage at the interconnecting nodes of the fabric reinforced earth stracture due to the confining stress is further made. The proposed method of analysis has been applied to estimate the maximum tensions, deformations and strains of the fabric reinforcements. The results are then compared with those of finite element analysis and experimental tests, and show in general good agreements indicating the effectiveness of the proposed method of analysis. Analytical parametric studies are also carried out to investigate the effects of relative soil-fabric reinforcement stiffness, locked-in stresses, compaction load and seepage pressures on the magnitude and variation of the fabric deformations.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.26 no.1
• /
• pp.73-80
• /
• 2022

In this study, details of NRC beam-column connections were developed in which beam and columns pre-assembled in factories using steel angles were bolted on site. The developed joint details are NRC-J type and NRC-JD type. NRC-J type is a method of tensile joining with TS bolts to the side and lower surfaces of the side plate of the NRC column and the end plate of the NRC beam. NRC-JD type has a rigid joint with high-strength bolts between the NRC beam and the side of the NRC column for shear, and with lap splices of reinforcing bar penetrating the joint and the beam main reinforcement for bending. For the seismic performance evaluation of the joint, three specimens were tested: an NRC-J specimen and NRC-JD specimen with NRC beam-column joint details, and an RC-J specimen with RC beam-column joint detail. As a result of the repeated lateral load test, the final failure mode of all specimens was the bending fracture of the beam at the beam-column interface. Compared to the RC-J specimen, the maximum strength of the specimen by the positive force was 10.1% and 29.6% higher in the NRC-J specimen and the NRC-JD specimen, respectively. Both NRC joint details were evaluated to secure ductility of 0.03 rad or more, the minimum total inter-story displacement angle required for the composite intermediate moment frame according to the KDS standard (KDS 41 31 00). At the slope by relative storey displacemet of 5.7%, the NRC-J specimen and the NRC-JD specimen had about 34.8% and 61.1% greater cumulative energy dissipation capacity than the RC specimen. The experimental strength of the NRC beam-column connection was evaluated to be 30% to 53% greater than the theoretical strength according to the KDS standard formula, and the standard formula evaluated the joint performance as a safety side.