• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.3
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• pp.298-304
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• 2017

The corrosion of reinforcements embedded in concrete causes some durability problems in reinforced and prestressed concrete structures. The epoxy coated reinforcements are one of the effective and reliable methods to prevent corrosion of reinforcements. However, it has been known that the epoxy coating reduces the bond capacity of reinforcement to concrete. This paper investigates the bond behaviors of epoxy coated reinforcements experimentally using direct pull-out test. Bond behaviors of epoxy coated bars for various reinforcement diameters of 10, 19 and 29mm and thicknesses of cover concrete of 1, 2, 3, and $4.5c/d_b$ (ratio of cover to bar diameter) are examined. Total 66 specimens were manufactured and tested according to the RILEM standard method. As the diameters of the epoxy coated reinforcements increase, the difference of bond strength between epoxy coated reinforcements and uncoated bars also increases. Epoxy coated bars showed more than 85% bond performance compared to those of uncoated bars. A new formular for estimating basic development length of epoxy coated reinforcement based on equilibrium equation is proposed using this experimental result.

• Composites Research
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• v.31 no.4
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• pp.139-144
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• 2018

Long Fiber-reinforced composites have advantages of excellent production efficiency and formability of complex shapes compared to conventional continuous fiber reinforced composite materials. However, if we need to make complicated composite shapes or to assemble parts made of different materials, a variety of joining methods are needed. In general, long fiber prepreg sheet (LFPS) contains mold release agent to facilitate demolding after thermoforming. Therefore, mechanical fastening is required in addition to the adhesive bonding to get proper joining strength. In this study, we proposed a stainless steel insert for co-cure bonding which cures LFPS and bonds the stainless steel insert through thermoforming process. The wing of the insert which is spread during the thermoforming process induces adhesion and mechanical wedging effect and serves as a hook to resist the pulling force. The burn-out method was used to confirm the unfolded state of the stainless steel insert wings inserted into the composite material. The static pull-out test was performed to quantitatively evaluate the joining strength. From these experimental results, the condition which guarantees the most appropriate joining strength was derived.

• The Journal of Engineering Geology
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• v.17 no.4
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• pp.525-534
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• 2007

The peculiarity of end-expanded soil nailing method(EESNM) is in fixing the wedge-type steel body spreaded by collars and grouting its surroundings by cement milk within soils, after extending hole bottom over drilling hole diameter with top drill bit. The present study was done to establish the effect of this method. Laboratory model test were carried out to investigate the behavior characteristics with the performance of the pull-out test and failure experiment, after preparing soil test box having 1,300mm length, width 1,000mm, and height 1,100mm, and the same experimental condition was set up to compare with the general soil nailing method(GSNM). The pull-out force of about 23 percentage was increased, and the horizontal displacements 1.2 from 9.1 percentage in soil-nailed wall decreased in EESNM compare with GSNM. The axial force acting on nail increased considerably at load level over 7 ton in EESNM and 5 ton in GSNM. The predicted failure line from the maxima analyzed by axial tensile strain located at long distance from soil-nailed wall in EESNM. The EESNM demonstrated the superiority of reinforcement effect in comparison with GSNM from the results above mentioned.

• The Journal of Korean Academy of Prosthodontics
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• v.45 no.6
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• pp.717-723
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• 2007

Statement of problem. Unreasonable distal cantilevered implant-supported prosthesis can mask functional problems of reconstruction temporarily, but it can cause serious strain and stress around its supported implant and surrounding alveolar bone. Purpose. The purpose of this study was to evaluate strain of implants supporting distal cantilevered fixed prosthesis with two different cantilevered length under distal cantilevered static load. Material and methods. A partially edentulous mandibular test model was fabricated with auto-polymerizing resin (POLYUROCK; Metalor technologies, Stuttgart, Swiss) and artificial denture teeth (Endura; Shofu inc., Kyoto, Japan). Two implants-supported 5-unit screw-retained cantilevered fixed prosthesis was made using standard methods with Type III gold alloy (Harmony C&B55; Ivoclar-vivadent, Liechtenstein, Germany) for superstructure and reinforced hard resin (Tescera; Ivoclar-vivadent, Liechtenstein, Germany) for occlusal material. Two strain gauges (KFG-1-120-C1-11L1M2R; KYOWA electronic instruments, Tokyo, Japan) were then attached to the mesial and the distal surface of each standard abutment with adhesive (M-bond 200; Tokuyama, Tokyo, Japan). Total four strain gauges were attached to test model and connected to dynamic signal conditioning strain amplifier (CTA1000; Curiotech inc., Paju, Korea). The stepped $20{\sim}100$ N in 25 N increments, cantilevered static load 8mm apart (Group I) or 16mm apart (Group II), were applied using digital push-pull gauge (Push-Pull Scale & Digital Force Gauge, Axis inc., Seoul, Korea). Each step was performed ten times and every strain signal was monitored and recorded. Results. In case of Group I, the strain values were surveyed by $80.7{\sim}353.8{\mu}m$ in Ch1, $7.5{\sim}47.9{\mu}m/m$ in Ch2, $45.7{\sim}278.6{\mu}m/m$ in Ch3 and $-212.2{\sim}718.7{\mu}m/m$ in Ch4 depending on increasing cantilevered static load. On the other hand, the strain values of Group II were surveyed by $149.9{\sim}612.8{\mu}m/m$ in Ch1, $26.0{\sim}168.5{\mu}m/m$ in Ch2, $114.3{\sim}632.3{\mu}m/m$ in Ch3, and $-323.2{\sim}-894.7{\mu}m/m$ in Ch4. Conclusion. A comparative statistical analysis using paired sample t-test about Group I Vs Group II under distal cantilevered load shows that there are statistical significant differences for all 4 channels (P<0.05).

• 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 Korean Tunnelling and Underground Space Association
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• v.26 no.1
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• pp.19-37
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• 2024

Rockbolts are the primary-supports in NATM tunnels and are widely used at tunnel construction sites. Among the rockbolts methods applied in domestic tunnel design, fully grouted rockbolts are the most representative and frequently used. Fully grouted rockbolts exhibit relative behavior between the bolt and the ground due to the grout material. However, during numerical analysis for tunnel design, fully grouted rockbolts are often modeled in a way that does not reflect their behavior characteristics. This may result in underestimating or overestimating the force of the supports. Based on a literature review, it was analyzed that fully grouted rockbolts are modeled using truss element or cable element. To analyze the effect of grout properties of cable elements on rockbolts behavior, this paper compared the behavior of rockbolts in two models: one estimating grout properties based on rockbolt pull-out test data, and another assuming complete adhesion between the rockbolts and the ground by applying large grout properties. Under identical tunnel conditions, the numerical analysis was conducted by modeling the fully grouted rockbolts differently using truss and cable elements, and the tunnel behavior was analyzed. The research results suggest that modeling fully grouted rockbolts as a function of the interface effect between the bolts and the ground, specifically considering grout, is desirable. The use of pull-out test data to simulate the behavior of actual fully grouted rockbolts was considered as a valid approach.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.12 no.1
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• pp.11-16
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• 2016

Fuel assembly's mechanical characterization test facility (FAMeCT) in KAERI was constructed with upgraded functional features such as increased loading capacity, underwater vibration testing and severe earthquake simulation for extended fuel design guideline. This facility is designed and developed to provide out-pile fuel data for accident analysis model and fuel licensing. Functional tests of FAMeCT were performed to confirm functionality, structural integrity, and validity of newly-built fuel assembly mechanical test facility. Test program includes signal check of data acquisition system, load delivering capacity using real-sized fuel assemblies and a standard loading cylindrical rigid specimen. Fuel assembly's lateral bending test was carried out up to 30 mm of pull-out displacement. Limit case axial compression loading test up to 33 kN was performed to check structural integrity of UCPS (Upper Core Plate Simulator) support frame. Test results show that all test equipment and measurement system have acceptable range of alignment, signal to noise ratio, load carrying capacity limit without loss of integrity. This paper introduces newly constructed fuel assembly's mechanical test facility and summarizes results of functional test for the mechanical test equipment and data acquisition system.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.647-652
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• 1999

The purpose of this study is to find the bond properties of deformed bars in hign-strength concrete by experimental and analytical method. In this study the following variables were adopted, i.e. (1) the compressive strength of concrete : 270, 400 and 600kg/$\textrm{cm}^2$ (2) the corrosion the bars : corroded and normal bars (3) the mixing ratio of natural and smashed fine aggregate : 7 : 3 and 5 : 5 (natural sand : smashed sand) For analytical method, the finite element analysis is performed. And the Pull-out test is performed as the experimental method.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.234-237
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• 2003

Previous researches about headed reinforcement have not been concerned about bond failure which is quite important is some cases. In this paper, failure mechanism including bond failure was presented in order to define the contribution of bond stress at the time failure occurs. Examined with design codes and test results, it is proved to be rational to consider the contribution of bond stress in determining the ultimate pull-out capacity of headed reinforcement. Direct adaptation of design code for anchor bolt without modification for the contribution of bond stress will lead to underestimate the capacity of headed reinforcement.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1997.04a
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• pp.343-353
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• 1997

This study had been performed to estimate for vibration characteristics of the Power Motor Coaches with Diesel-Hydraulic Drive and to secure a dynamic characteristic construction technology of another rolling stock. Air bags, springs and dampers of Bogie are carefully reviewed in order to improve ride quality. Dynamic analysis had been performed using VAMPIRE program, which had been developed by BRR, and the analysis results had been compared with test data to verify.