• Structural Engineering and Mechanics
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• v.84 no.4
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• pp.531-546
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• 2022

Headed bars are often used when there is insufficient space for a straight or curved bar to be fully developed to ensure the transference of forces between steel and concrete in several types of connections between structural members. In such cases, the concrete breakout strength of the headed bars can be a critical point of the design and must be considered appropriately. This paper evaluates the tensile strength of headed bars embedded in reinforced concrete members, failing due to concrete breakout. Four experimental tests on headed bars embedded in slender concrete members are presented and discussed, showing that strength previsions from the design codes can be significantly conservative as they ignore the contribution from the flexural reinforcement. 3D finite element models were developed using Abaqus Unified FEA to simulate the tested specimens, and it was observed that they were able to reproduce the formation of the concrete cone accurately, besides the response and resistance observed in tests. Furthermore, the experimental, numerical, and design code resistances are compared and discussed. A new equation to evaluate the concrete cone strength of the tested headed bars is proposed, which takes into account parameters not explicitly considered in the current design equations.

• Journal of the Korean Society of Hazard Mitigation
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• v.4 no.2 s.13
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• pp.29-34
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• 2004

The time to ignition, heat release rate characteristics, and carbon monoxide yield of fiber reinforced and sandwich phenol resin were investigated with cone calorimeter. The fire characteristics of unsaturated polyester, mostly being applied to the existing passenger train, and phenolic resin were compared. DSC & TGA was used to monitor the degree of thermal decomposition and weight loss for the phenolic resin. According to the cone calorimeter data, the time to ignition was shorter, heat release rate, and CO yield was higher as the external heat flux increased. Under the same heat flux, the time to ignition of sandwich type phenolic resin was shorter than that of laminated. The result of comparison between unsaturated polyester and phenolic resin was that phenolic resin was shown to have better fire resistance than unsaturated polyester.

• Journal of the Korean Geosynthetics Society
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• v.18 no.3
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• pp.1-9
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• 2019

In this study, the effect of ground improvement was to be verified by granular compaction pile from the ground reclaimed with Fly Ash landfill site. The depth and strength parameters of the Fly ash layer was determined using the ground investigation and cone penetration test. And the STONE C program was used to predict the strength parameter, bearing capacity and settlement of the improved ground. As a result of the plate bearing test, the bearing capacity of improvement ground was higher than the design load and the settlement was smaller than the reference value. After the construction, the improvement effect by the cone penetration test was confirmed. The cone penetration resistance value($q_c$) increased by 250% to 500% and the effect was excellent.

• Restorative Dentistry and Endodontics
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• v.48 no.1
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• pp.10.1-10.9
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• 2023

Objectives: This study compared the buckling resistance of 3 nickel-titanium (NiTi) retreatment file systems and the torque/force generated during retreatment. Materials and Methods: The buckling resistance was compared among the D-RaCe (DR2), HyFlex Remover, and Mtwo R25/05 retreatment systems. J-shaped canals within resin blocks were prepared with ProTaper NEXT X3 and obturated by the single-cone technique with AH Plus. After 4 weeks, 4 mm of gutta-percha in the coronal aspect was removed with Gates-Glidden drills. Retreatment was then performed using DR1 (size 30, 10% taper) followed by DR2 (size 25, 4% taper), HyFlex Remover (size 30, 7% taper), or Mtrwo R25/05 (size 25, 5% taper) (15 specimens in each group). Further apical preparation was performed with WaveOne Gold Primary. The clockwise torque and upward force generated during retreatment were recorded. After retreatment, resin blocks were examined using stereomicroscopy, and the percentage of residual filling material in the canal area was calculated. Data were analyzed using 1-way analysis of variance with the Tukey test. Results: The HyFlex Remover files exhibited the greatest buckling resistance (p < 0.05), followed by the Mtwo R25/05. The HyFlex Remover and Mtwo R25/05 files generated the highest maximum clockwise torque and upward force, respectively (p < 0.05). The DR1 and DR2 files generated the least upward force and torque (p < 0.05). The percentage of residual filling material after retreatment was not significantly different between file systems (p > 0.05). Conclusions: NiTi retreatment instruments with higher buckling resistance generated greater clockwise torque and upward force.

• Fire Science and Engineering
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• v.24 no.3
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• pp.52-57
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• 2010

Fire protection countermeasure were considered on the straw thatched roof and wooden structure. For the fire resistant treatment, rice straw was soaked in the fire resistant liquid with different soaking time. After treatment, some rice straw sample was washed with water then the rice straws were tested to check the fire resistance performance. And the wood was soaked in the fire resistant liquid at an atmospheric pressure, vacuum-pressure condition and painted with brush on the surface. To analyse the fire resistant performance of rice straw, ignition delay time was measured under the radiant heat flux of cone heater. And the fire resistant performance of wood samples were tested with 45 degree fire resistant test apparatus and cone heater. Based on the cone heater test, the rice straw which most easily ignitable material shows the longer ignition delay time than not treated ones and even in the water washed straw show a longer ignition delay time than not treated ones. And fire resistant treated woods of vacuum-pressure treated sample showed the most excellent performance on fire resistance. And the fire resistant treated by brush and soaking showed a longer ignition delay time than not treated ones. From this experiment, it was found that a fire resistant treatment of rice straw and wood of the house can be protected from the fire spread.

• Journal of the Korean Geotechnical Society
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• v.25 no.2
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• pp.45-54
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• 2009

The electrical characteristics of soils have been used for investigating soil properties. The purpose of this study is the development and application of the electrical resistivity cone probe (ERCP) for the evelation of the porosity in the field with high precision. The shape of the probe tip is a cone shape to minimize the disturbance during penetration. In addition, the four terminal pair configuration is adopted to minimize the electrical interference. The electrical resistances are continuously measured during penetration of the ERCP using penetration rigs with 0.33 mm/sec penetration rate at Incheon and Busan sites. With the measured resistance profile and electrical resisivity of electrolyte of undisturbed samples, soil porosity profiles are obtained by using Archie's law. The empirical coefficients for the Archie's law are obtained based on the electrolyte extracted from the undisturbed samples. The estimated porosity profiles show similar trends to those of in-situ penetration tests such as SPT, CPT, and DMT. This study suggests that the ERCP may be an effective tool for the porosity estimation in the field with minimum disturbance.

• Journal of Environmental Health Sciences
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• v.47 no.3
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• pp.292-301
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• 2021

Objectives: Wearing medical masks has been recommended since the declaration of coronavirus disease-19 (COVID-19) as a pandemic disease. Certified medical masks are evaluated according to filtration efficiency and facial inhalation resistance. However, some people use non-certified common masks. This study aimed to evaluate various non-certified commercial masks based on the certification criteria for medical masks. Methods: Twenty mask products (three anti-droplet, three disposable dental, eight fashion, three cotton, and three children's masks) were selected. For performance evaluation, filtration efficiency and facial inhalation resistance tests were conducted. The evaluation method followed the certification method for KF-certified masks of the Ministry of Food and Drug Safety (MFDS) and the N95 respirator of the National Institute for Occupational Safety and Health (NIOSH). Results: None of the 20 masks met the KF94 certification standard set by the MFDS. Four and three masks respectively met the KF80 certification standard and the N95 standard of NIOSH. Filtration efficiency was significantly higher in three-layer masks than in single layer masks. Pleated-type masks had higher filtration efficiency than cone-type masks. There was no correlation between the structure of masks and facial inhalation resistance. Conclusion: While no masks complied with the KF94 certification standard, a few masks met the KF80 and the N95 certification standards of NIOSH. Although some people wear non-certified commercial masks, protection from aerosols is not guaranteed by such masks. Evaluation of the protection efficiency of non-certified mask against microbiological infection is needed for the prevention of infectious disease.

• 한국지구물리탐사학회:학술대회논문집
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• 2005.09a
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• pp.125-153
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• 2005

It has been widely known that the seismic piezo-cone penetration test (SCPTU) is one of the most useful techniques for investigating the geotechnical characteristics including dynamic soil properties. As the practical applications in Korea, SCPTU was carried out at two sites in Busan and four sites in Incheon, which are mainly composed of alluvial or marine soil deposits. From the SCPTU waveform data obtained from the testing sites, the first arrival times of shear waves were and the corresponding time differences with depth were determined using the cross-over method, and the shear wave velocity profiles (VS) were derived based on the refracted ray path method based on Snell's law and similar to the trend of cone tip resistance (qt) profiles. In Incheon area, the testing depths of SCPTU were deeper than those of conventional down-hole seismic tests. Moreover, for the application of the conventional CPTU to earthquake engineering practices, the correlations between VS and CPTU data were deduced based on the SCPTU results. For the empirical evaluation of VS for all soils together with clays and sands which are classified unambiguously in this study by the soil behavior type classification Index (IC), the authors suggested the VS-CPTU data correlations expressed as a function of four parameters, qt, fs, $\sigma$, v0 and Bq, determined by multiple statistical regression modeling. Despite the incompatible strain levels of the down-hole seismic test during SCPTU and the conventional CPTU, it is shown that the VS-CPTU data correlations for all soils clays and sands suggested in this study is applicable to the preliminary estimation of VS for the Korean deposits and is more reliable than the previous correlations proposed by other researchers.

• Composites Research
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• v.33 no.4
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• pp.177-184
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• 2020

Flame retardant(FR) clothes prohibit additional fire diffusion and make the personnel do their tasks without a hitch in a flammable environment. The existing FR clothes, however, are heavy and give high thermal fatigue. Therefore, it is strongly demanded to develop a light, convenient, and eco-friendly clothes. Recently, many works have been reported to make FR fabrics with phosphorus compounds, but their performance could not satisfy the specified criteria in appraisal standards of domestic and American FR clothes or combat uniforms. In this paper, two kinds of phosphorus compounds were applied to cotton fabric. Graphene oxide functionalized with a phosphorus-rich deep eutectic solvent and ammonium polyphosphate were coated on cotton fabric by eco-friendly padding procedure. The coated fabrics were analyzed with thermogravimetric analysis, vertical flame resistance test(ASTM D6413), cone calorimeter test(ISO 5660-1), and method of test for limited flame spread(ISO 15025). It was revealed that the as-made cotton with those two materials simultaneously had better flame resistance than the cottons with each one. Furthermore, an additional coating for hydrophobicity on the FR cotton was tried for better washing fastness.

• Geophysics and Geophysical Exploration
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• v.19 no.4
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• pp.187-199
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• 2016

In order to delineate the soft ground distribution, an integrated geostatistical analysis was performed using the MASW (Multichannel Analysis of Surface Wave) which has the information of overall region and CPTu (Piezo Cone Penetration Test) which provides the direct information of the measuring point of the ground. MASW results were known to have close relationship with the ground stiffness. This correlation was confirmed through the comparison of MASW data obtained from two survey lines to the laboratory test with extracted soil samples. 3D physical property distribution in the study area was acquired by geostatistical integrated analysis with the data of tip resistance ($q_c$) and pore pressure (u) from the CPTu obtained at 6 points within the study area. The integrated analysis was conducted by applying the COSGSIM (Sequential Gaussian Co-Simulation) technology which can carry out the simulation in accordance with the spatial correlation between the MASW results and both tip resistance and pore pressure. Besides the locations of CPTu, borehole investigations were also conducted at two different positions. As a result, the N value of SPT and borehole log could be secured, so these data were used for the analysis of the geotechnical engineering accuracy of the integrated analysis result. For the verification of reliability of the 3D distribution of tip resistance and pore pressure secured through integrated analysis, the geotechnical information gained from the two drilling areas was compared, and the result showed extremely high correlation.