• Journal of the Korean Society of Safety
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• v.29 no.3
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• pp.1-7
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• 2014

In this study, for the evaluation of the static and fatigue joining strength of the joint, the geometry of the cross-tension specimen was adopted. The specimens were produced with optimal joining force and fatigue life of the clinch joint specimens was evaluated. The material selected for use in this study was cold rolled mild steel (SPCC) with a thickness of 0.8 mm. The maximum tensile load was 708 N for the specimen with single point. The fatigue endurance limit (=42.6 N) per point approached to 6% of the maximum tensile strength at a load ratio of 0.1, suggesting that the joints are vulnerable to cross-tension loading during fatigue. Compared to equivalent stress and maximum principal stress, the SWT fatigue parameter and equivalent strain can properly predict the current experimental fatigue life. The SWT parameter can be expressed as $SWT=2497.5N^{-0.552)_f$.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.9 no.6
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• pp.82-88
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• 2000

The effect of the welding for the offshore structure in the TMCP steel on the fatigue crack propagation rate and crack opening-and-closure behavior was examined. The welding anisotropy of the TMCP steel and crack propagation characteristics of the excessive loading were reviewed. (1) It seemed that a heat which was generated by the welding made a compressive residual stress over the base metal, so fatigue crack propagation rate was placed lower than in case of the base metal. (20 In the base metal, an effect of the anisotropy which has an effect of fatigue crack propagation rate of the excessive load and the constant amplitude laos was not found but in the welding material case, fatigue crack propagation rate of the excessive load in the specimen of the width direction was located in the retard side as compared with a specimen rolling direction. (3) A crack opening ratio of the used TMCP stel in this study was not changed after excessive loading but a retard phenomenon of crack propagation was observed. Consequently, it was thought that all of the retard phenomenon of crack propagation did not only a cause of the crack opening-and-closure phenomenon.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.1
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• pp.147-156
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• 2004

The Rehabilitation and repair of structurally deteriorated, reinforced concrete structures will be highly demanded in the near future. The purpose of this study is to investigate whether damaged beams that crack and deflection are developed by bending moment are restored to the former state. In conclusion, when specimens strengthened with Steel Plate, CFS(Carbon Fiber Sheet) and CFRP-Grid(Carbon Fiber Reinforced Plastic-Grid) are compared with standard specimen, flexural capacity is increased and ductility and energy absorbtion capacity are similar with undamaged specimen. Therefore Steel Plate, CFS(Carbon Fiber Sheet) and CFRP-Grid (Carbon Fiber Reinforced Plastic-Grid) have highly efficiency as material of flexural strengthening.

• Journal of Korean Association for Spatial Structures
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• v.21 no.3
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• pp.69-76
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• 2021

Precast concrete (PC) modules have been increased its use in modular buildings due to their better seismic performance than steel modules. The main issue of the PC module is to ensure structural performance with appropriate connection methods. This study proposed a PC modular beam system for simple construction and improved structural and splicing performance. This modular system consisted of modules with steel plates inserted, and it is easy to construct by bolted connection. The steel plates play the role of tensile rebar and stirrup, which has the advantage of structural performance. The structural performance of the proposed PC modular beam system was evaluated by flexural test on one reinforced concrete (RC) beam specimen consisting of a monolithic, and two PC specimens with the proposed PC modular beam system. The results demonstrated that the proposed PC modular beam system achieved approximately 86% of the structural performance compared to the RC monolithic specimen, with similar ductility of approximately 1.06 fold greater.

• Journal of the Korean Society for Heat Treatment
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• v.34 no.3
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• pp.130-136
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• 2021

With the development of the industry, bearings that require higher durability and efficiency are required, and various methods to reduce friction and wear of bearings are being studied. In this study, a wear test was conducted for STB2, a bearing steel material, by machining a micro-line pattern on the race surface of the bearing by machining. The pattern pitch of the specimens was processed to 40㎛, 80㎛, and 150㎛, and the coefficient of friction characteristics were investigated for the unpatterned specimen and the specimen with a DLC thin film deposited on the surface. As a result of the wear test, the pattern pitch showed the smallest coefficient of friction at 40㎛, and it was confirmed that the smaller the pattern pitch, the better the tribology characteristics.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.11
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• pp.11-18
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• 2018

In this study, seven R/C beams, designed by the steel fiber with ground granulated blast furnace slag and recycled fine aggregate were constructed and tested under monotonic loading. In the material development, micromechanics was adopted to properly select the optimized range of the composite based on steady-state cracking theory and experimental studies on the matrix and interracial properties. Experimental programs were carried out to improve and evaluate the structural performance of the test specimens: the load-displacement, the failure mode, the maximum strength were assessed. Test results showed that test specimens (BSSR-20, 40, 60, 80) were increased the maximum load carrying capacity by 2~9% and the ductility capacity by 10~22% in comparison with the standard specimen (BSS) respectively. And the specimens (BSSR-100) was decreased the maximum load carrying capacity by 5% and the ductility capacity by 44% in comparison with the standard specimen (BSS) respectively.

• Steel and Composite Structures
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• v.43 no.5
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• pp.553-564
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• 2022

Many existing reinforced concrete (RC) structures need to be strengthening for reason such as poor construction quality, low ductility or designing without considering seismic effects. One of the strengthening methods is strengthening technique with eccentrically braced frames (EBFs). The characteristic element of these systems is the link element and its length is very important in terms of seismic behavior. The link element of Y shaped EBF systems (YEBFs) is designed as a short shear element. Different limits are suggested in the literature for the link length. This study to aim experimentally investigate the effect of the link length for the suggested limits on the behavior of the RC frame system and efficiency of strengthening technique. For this purpose, a total of 5 single story, single span RC frame specimens were produced. The design of the RC frames was made considering seismic design deficiencies. Four of the produced specimens were strengthened and one of them remained as bare specimen. The steel YEBFs were used in strengthening the RC frame and the link was designed as a shear element that have different length with respect to suggested limits in literature. The length of links was determined as 50mm, 100mm, 150mm and 200mm. All of the specimens were tested under cyclic loads. The obtained results show that the strengthening technique improved the energy consumption and lateral load bearing capacities of the bare RC specimen. Moreover, it is concluded that the specimens YB-2 and YB-3 showed better performance than the other specimens, especially in energy consumption and ductility.

• Journal of Korean Association for Spatial Structures
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• v.22 no.4
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• pp.23-30
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• 2022

It is effective to apply hybrid damping device that combine separate damping device to cope with various seismic load. In this study, HRS hybrid damper(hybrid rubber slit damper) in which high damping rubber and steel slit plate are combined in parallel was proposed and structural performance tests were performed to review the suitability for seismic performance. Cyclic Loading tests were performed in accordance with criteria presented in KDS 41 17 00 and MOE 2019. As a result of the test, the criteria of KDS 41 17 00 and MOE2019 was satisfied, and the amount of energy dissipation increased due to the shear deformation of the high-damping rubber at low displacement. Result of performing the RC frame test, the allowable story drift ratio was satisfied, and the amount of energy dissipation increased in the reinforced specimen compared to the non-reinforced specimen.

• Korean Journal of Materials Research
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• v.33 no.6
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• pp.251-256
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• 2023

This study aims to examine the correlation between microstructures and the mechanical properties of two high-strength API X70 linepipe steels with different specimen directions and Moaddition. The microstructure of the Mo-added steel has an irregularly shaped AF, GB matrix with pearlite because of the relatively large deformation in the non-recrystallization temperature region, while that of the Mo-free steel shows a PF matrix with bainitic microstructure. In the Mo-added steel, the M/A (martensite-austenite) in granular bainite (GB) and pearlite act as crack initiation sites with decreased upper shelf energy and an increased ductile to brittle transition temperature (DBTT). Regardless of Mo addition, all of the steels demonstrate higher strength and lower elongation in the T direction than in the L direction because of the short dislocation glide path and ease of pile-up at grain boundaries. In addition, the impact test specimens with T-L direction had a lower impact absorbed energy and higher DBTT than those with the L-T direction because the former exhibit shorter unit crack path compared to the latter.

• Journal of Korean Association for Spatial Structures
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• v.23 no.4
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• pp.35-42
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• 2023

The purpose of this study is to experimentally analyze the seismic performance of column with RSB (Replaceable Steel Brace), a steel brace system with slot length as a variable. To evaluate the seismic performance of the RSB, three specimens were manufactured and subjected to cyclic loading tests. The length of the sliding slots were considered to be 5 mm and 10mm to enable the brace to resist the load from the initiation of flexural crack and shear crack. As a result of the test, the specimen reinforced with the RSB showed improved maximun load and effective stiffness, and energy dissipation capacity compared to the non-reinforced specimens. The specimens with 5mm sliding slot showed little difference in test result compared to the specimen with a 10mm sliding slot, indicating that the length of sliding slot has little influence on the effectiveness of RSB.