• Journal of Korean Tunnelling and Underground Space Association
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• v.11 no.1
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• pp.47-56
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• 2009

Rock bolts and shotcrete play a crucial role as a main support system in the underground space. Thus, the safety of the underground space may be affected by the defect of rock bolts. In order to evaluate the rock bolt integrity by using non-destructive technique, the transmission method of the guided ultrasonic waves, which are generated by using the piezo disk elements has been successfully performed. The energy generated by the piezo disk elements, however, is not enough for the rock bolts in the field. In addition, the piezo disk elements should be installed at the end of the steel bar during construction of the rock bolts. The purpose of this study is the devolvement of the reflection method, which may generate enough energy, and the application in the field rock bolts. Both laboratory and field tests are carried out. The guided ultrasonic waves with high energy are generated by the hammer impact with the center punch, and the AE sensor is used to measure the reflected guided waves. The received guided waves are analyzed by the wavelet transform. The peak value of the wavelet transform produces the energy velocity, which is used for the evaluation of the rock bolt integrity. The energy velocity increases with an increase in the defect ratio in both laboratory and field rock bolts. This study demonstrates that the hammer-impact reflection method may be a suitable method for the evaluation of the rock bolt in the field.

• Journal of Practical Engineering Education
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• v.15 no.2
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• pp.243-258
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• 2023

The purpose of this study is to examine the mediating effect of organizational commitment in the relationship between transformational and transactional leadership and innovative behavior and demonstrate the moderated mediating effect of job satisfaction. To this end, 4,133 cases from the 『2021 Public Servant Life Survey』 conducted to general public servants belonging to central administrative agencies and metropolitan governments by the Korea Institute of Public Administration were used for the analysis, and SPSS 21.0 and Mplus 8.4 programs were used to test the research hypotheses. As a result of the analysis, it was confirmed that transformational and transactional leadership had a positive effect on organizational commitment and innovative behavior, and organizational commitment had a positive effect on innovative behavior. In addition, it was confirmed to have a significant mediating effect in the relationship between transformational and transactional leadership and innovative behavior. Finally, it was confirmed that the mediating effect of transformational and transactional leadership on innovative behavior through organizational commitment was moderated by the level of job satisfaction, and all the proposed hypotheses were adopted. Based on theses findings, theoretical and practical suggestions and future research suggestions were discussed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.5
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• pp.120-129
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• 2023

Hanger cable tension is a major response that can determine the integrity and safety of suspension bridges. In general, the vibration method is used to estimate hanger cable tension on operational suspension bridges. It measures natural frequencies from hanger cables and indirectly estimates tension using the geometry conditions of the hanger cables. This study estimated the hanger cable tension of the Palyeong Bridge using a vision-based system. The vision-based system used digital camcorders and tripods considering the convenience and economic efficiency of measurement. Measuring the natural frequencies for high-order modes required for the vibration method is difficult because the hanger cable response measured using the vision-based system is displacement-based. Therefore, this study proposed a back analysis technique for estimating tension using the natural frequencies of low-order modes. Optimization for the back analysis technique was performed by defining the difference between the natural frequencies of hanger cables measured in the field and those calculated using finite element analysis as the objective function. The direct search method that does not require the partial derivatives of the objective function was applied as the optimization method. The reliability and accuracy of the back analysis technique were verified by comparing the tension calculated using the method with that estimated using the vibration method. Tension was accurately estimated using the natural frequencies of low-order modes by applying the back analysis technique.

• Journal of the Korean Institute of Gas
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• v.27 no.4
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• pp.62-69
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• 2023

The use of low-grade coal is continuously increasing with the development of combustion technology and cost reduction for coal used in thermal power plants . During combustion, the latent heat of evaporation due to moisture is large, and there is a risk of spontaneous combustion and dust explosion during the process of storing and pulverizing coal. This study compared and evaluated the minimum explosive concentration and explosive strength of four types of coal dust-fine, coal dust-coarse, wood pallet+organic dust, and wood chip with coal powder collected from domestic power plant D. The minimum explosive concentration of coal dust was measured according to JIS Z 8818:2002, and the explosion strength was tested according to ASTM E1226 using a Siwek 20 L Chamber Apparatus. As a result of the minimum explosive concentration test, it was found that coal dust-fine has a risk of dust explosion, and since an explosion occurs at a dust concentration of 130 g/m³ of wood chips, it was found that there is a risk of explosion at the lowest dust concentration. According to the dust explosion class standard, Kst is less than 200 bar m/s, and all samples fall under the explosion class St 1, and the dust has a low risk of explosion.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.3
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• pp.91-99
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• 2024

Piping systems are crucial facilities used in various industries, particularly in areas related to daily life and safety. Piping systems are fixed to the main structures of buildings and facilities but do not support external loads and serve as non-structural elements performing specific functions. Piping systems are affected by relative displacements owing to phase differences arising from different behaviors between two support points under seismic loads; this can cause damage owing to the displacement-dominant cyclic behavior. Fittings and joints in piping systems are representative elements that are vulnerable to seismic loads. To evaluate the seismic performance and limit states of fittings and joints in piping systems, a high-stroke actuator is required to simulate relative displacements. However, this is challenging because only few facilities can conduct these experiments. Therefore, element-level experiments are required to evaluate the seismic performance and limit states of piping systems connected by fittings and joints. This study proposed a method to evaluate the seismic performance of an elbow specimen that includes fittings and joints that are vulnerable to seismic loads in vertical piping systems. The elbow specimen was created by connecting straight pipes to both ends of a 90° pipe elbow using flexible groove joints. The seismic performance of the elbow specimen was evaluated using a cyclic loading protocol based on deformation angles. To determine the margin of the evaluated seismic performance, the limit states were assessed by applying cyclic loading with a constant amplitude.

• The Korea Journal of Herbology
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• v.39 no.3
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• pp.107-114
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• 2024

Objective : Cicadae Periostracum (CP), which is the discarded shell of the Cryptotympana atrata (Fabricius, 1775), is a recognized component of oriental medicine for treatment sore throat, itching, shock, sedation, edema. However, the safety and toxicity of CP have not yet been established. It has been reported that symptoms of addiction or side effects may occur in patients who take high doses of CP or who are hypersensitive to it. Therefore, we investigated the acute toxicity of an CP extracts in Sprague-Dawley (SD) rats. Methods : To study acute toxicity, five SD rats of each sex per group were treated with CP extracts at single doses of 0, 500, 1000, or 2000 mg/kg administrated by oral gavage, and body weight, clinical signs, and mortality were observed after dosing. At the end of 14-day observation period, all animals were sacrificed and complete hematological and macroscopic examinations were performed. Results : There were no dead animal and test article-related effects on body weight change or the gross finding. No toxicologically significant results were observed between control and treated groups in hematology. Although salivation related to stress at the highest dose was observed in clinical signs immediately after administration, it is considered to have no toxicological significance. Conclusion : As the results, we did not find any adverse effect at the dose levels of 500, 1000, or 2000 mg/kg in rats. The minimal lethal dose was considered to be over 2000 mg/kg body weight in rats.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.3
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• pp.163-171
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• 2024

Structural health monitoring for ships and offshore structures is important in various aspects. Ships and offshore structures are continuously exposed to various environmental conditions, such as waves, wind, and currents. In the event of an accident, immense economic losses, environmental pollution, and safety problems can occur, so it is necessary to detect structural damage or defects early. In this study, structural response data of multi-linked floating offshore structures under various wave load conditions was calculated by performing fluid-structure coupled analysis. Furthermore, the order reduction method with distortion base mode was applied to the structures for predicting the structural response by using the results of numerical analysis. The distortion base mode order reduction method can predict the structural response of a desired area with high accuracy, but prediction performance is affected by sensor arrangement. Optimization based on a genetic algorithm was performed to search for optimal sensor arrangement and improve the prediction performance of the distortion base mode-based reduced-order model. Consequently, a sensor arrangement that predicted the structural response with an error of about 84.0% less than the initial sensor arrangement was derived based on the root mean squared error, which is a prediction performance evaluation index. The computational cost was reduced by about 8 times compared to evaluating the prediction performance of reduced-order models for a total of 43,758 sensor arrangement combinations. and the expected performance was overturned to approximately 84.0% based on sensor placement, including the largest square root error.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.1
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• pp.39-45
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• 2024

Seismic safety of expansion joints for piping systems has been underscored by water pipe ruptures and leaks resulting from the Gyeongju and Pohang earthquakes. Metal bellows in piping systems are applied to prevent damage from earthquakes and road subsidence in soft ground. Designed with a series of corrugated segments called convolutions, metal bellows exhibit flexibility to accommodate displacements. Several studies have examined variations in convolution shapes and layers based on the intended performance to be evaluated. Nonetheless, the research on the seismic performance of complex bellows having multiple corrugation heights is limited. In this study, monotonic loading tests, cyclic loading tests, and fatigue tests were conducted to evaluate the shear performance in seismic conditions, of metal bellows with variable convolution heights. Single- and triple-layer bellows were considered for the experimentation. The results reveal that triple-layer bellows exhibit larger maximum deformation and fatigue life than single-layer bellows. However, the high stiffness of triple-layer bellows in resisting internal pressure poses certain disadvantages. The convolutions are less flexible at lower displacements and experience leakage at a rate related to the variable height of the convolutions in certain conditions. At lower deformation rates, the fatigue life is rated higher as the number of layers increase. It converges to a similar fatigue life at higher deformation rates.

• Archives of Plastic Surgery
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• v.51 no.1
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• pp.42-51
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• 2024

Background Increasing concerns regarding the safety of textured surface implants have resulted in surgeons transitioning from textured tissue expanders (TEs) to smooth TEs. Given this change has only recently occurred, this study evaluated outcomes between smooth and textured TEs. Methods Women who underwent two-stage breast reconstruction using TEs from 2013 to 2022 were included. TE-specific variables, perioperative information, pain scores, and complications were collected. Chi-squared, t-test, and linear regression analyses were performed. Results A total of 320 patients received a total of 384 textured and 152 smooth TEs. Note that 216 patients received bilateral reconstruction. TEs were removed in 9 cases. No significant differences existed between groups regarding comorbidities. Smooth TEs had a higher proportion of prepectoral placement (p < 0.001). Smooth TEs had less fills (3±1 vs. 4±2, p < 0.001), shorter expansion periods (60±44 vs. 90±77 days, p < 0.001), smaller expander fill volumes (390±168 vs. 478±177 mL, p < 0.001), and shorter time to exchange (80±43 vs. 104±39 days, p < 0.001). Complication rates between textured and smooth TEs were comparable. Smooth TE had a greater proportion of TE replacements (p = 0.030). On regression analysis, pain scores were more closely associated with age (p = 0.018) and TE texture (p = 0.046). Additional procedures at time of TE exchange (p < 0.001) and textured TE (p = 0.017) led to longer operative times. Conclusion As many surgeons have transitioned away from textured implants, our study shows that smooth TEs have similar outcomes to the textured alternatives.

• Tunnel and Underground Space
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• v.34 no.2
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• pp.89-103
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• 2024

In the disposal environment, gases can be generated at the interface between canister and buffer due to various factors such as anaerobic corrosion, radiolysis, and microbial degradation. If the gas generation rate exceeds the diffusion rate, the gas within the buffer may compress, resulting in physical damage to the buffer due to the increased pore pressure. In particular, the rapid movement of gases, known as gas breakthroughs, through the dilatancy pathway formed during this process may lead to releasing radionuclide. Therefore, understanding these gas generation and movement mechanism is essential for the safety assessment of the disposal systems. In this study, an experimental apparatus for investigating gas migration within buffer was constructed based on a literature review. Subsequently, a gas injection experiment was conducted on a compacted bentonite block made of Bentonile WRK (Clariant Ltd.) powder. The results clearly demonstrated a sharp increase in stress and pressure typically observed at the onset of gas breakthrough within the buffer. Additionally, the range of stresses induced by the swelling phenomenon of the buffer, was 4.7 to 9.1 MPa. The apparent gas entry pressure was determined to be approximately 7.8 MPa. The equipment established in this study is expected to be utilized for various experiments aimed at building a database on the initial properties of buffer and the conditions during gas injection, contributing to understanding the gas migration phenomena.