• Structural Engineering and Mechanics
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• v.30 no.6
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• pp.651-664
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• 2008

The purpose of this study is to develop a rehabilitation technique for heavily earthquake damaged masonry buildings. A full scale one storey masonry building with window and door openings was manufactured and tested on the shock table by applying increased amplitude free vibration up to the point where heavy earthquake damage was observed. Damaged test building was rehabilitated with vertical and diagonal steel straps and then tested again. The effectiveness of improvements obtained by the rehabilitation technique was investigated. Steel straps improved the lateral strength and stiffness of masonry walls and limited the lateral displacement of building. Stability of the masonry walls were also improved by the steel straps. Steel straps reduced the natural period of the earthquake damaged masonry building and prevented the failure of the building at the same amplitude of free vibration.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.6
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• pp.371-383
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• 2021

Steel-concrete single-leaf blast-resistant doors, having steel box and slab inside, are installed on the wall using supporting members such as hinges and latches. Several studies have been conducted on their deflection behavior in the same direction as that of the blast pressure, but studies on their deflection behavior in the opposite direction, that is, studies on negative deflection behavior are relatively insufficient. In this study, we conducted a parameter analysis using finite element analysis on blast-resistant doors, on their rebound behavior in the negative deflection phase. Results revealed that the plastic deformation of the door, and the change in momentum and kinetic energy during rebound, were major factors influencing the rebound behavior. Greater rebound force was developed on the supporting members in the impulsive region, than in the quasi-static region; due to the characteristics in the impulsive region, where the kinetic energy developed relatively greater than the strain energy. In the design process, it is necessary to consider excessive deformation that could occur in the supporting members as the rebound behavior progresses. Additionally, it was found that in the case of steel-concrete blast doors, the rebound force increased relatively more, when the effects of both rebound and negative blast pressure contributed to the negative deflection of the door. Since conditions for the occurrence of this superposition effect could vary depending on structural characteristics and explosion conditions, further investigation may be required on this topic.

• Journal of the Korean Society of Safety
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• v.26 no.3
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• pp.63-68
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• 2011

Access-control of hazard zone in a steel manufacturing industry is studied in terms of safety management. Based on the results of risk evaluation for hazard zone, three risk zones with low, middle and high level are categorized. These zones have different color door and locking shape depending on their risk levels. At the high level, red door and key-based locking system are employed to accessed-controled path. Furthermore, tagout, lockout, interlock system for emergency stop, warning and flashing are also introduced. New standardized procedure of access-control for various hazard zones, which could help to greatly contribute to the prevention of accidents in advance, is proposed considering the risk level and the condition of given hazard zones. The standardized procedure of access-management suggested in this study will take an effective role as one of safety guide lines for hazardous workshop of manufacturing industries.

• Wind and Structures
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• v.5 no.5
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• pp.463-478
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• 2002

Lighting and traffic signal columns are mainly stressed by excitation due to natural, gusty wind. Such columns typically have a door opening about 60 cm above ground level for the connection of the buried cable with the column's electric system. When the columns around this notch are inadequately designed, vibrations due to gusty winds will produce considerable stress amplitudes in this area, which lead to fatigue cracks. To give a realistic basis for a reliable and economic design of lighting and traffic signal columns, a number of experimental and theoretical investigations have been made. The proposed design concept allows the life of such columns to be assessed with a satisfactory degree of accuracy.

• International journal of steel structures
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• v.18 no.4
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• pp.1318-1324
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• 2018

This paper evaluates the effects of door opening, collar stiffener, and initial imperfection on the ultimate strength of a 10 MW wind tower. The lower segment of the tower was modeled to investigate the ultimate strength using steel cylindrical shell elements of finite element program ABAQUS. The wind tower was classified into three categories; without opening nor stiffener (C1), with opening but no stiffener (C2), and with opening and stiffener (C3). The C2 and C3 were further divided into long axis and short axis categories depending on the position of the opening. Result from linear and nonlinear analyses shows that the bigger the opening the bigger the reduction in strength and the same thing goes for the initial imperfection ratio or ovality of the shell. Also, there is a significant decreased in strength as the initial imperfection ratio increases by as high as 18.08%.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.7
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• pp.166-172
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• 2019

A case study was performed in order to develop well-designed of thin plate door impact beam. The conventional impact beam was consisted of steel-pipe welded two brackets on the both side, which causes low productivity and high cost. In order to overcome those disadvantage, it is necessary to develop a new type of door impact; thin plate impact beam. The thin plate impact beam was not needed a welding procedure, which can lead low cost and high productivity. In order to maximally resist from an external force, the cross-section design should be well designed. 6 different cross-section design were proposed based on engineer's experience. Three point bending test was simulated those 6 different impact beam and compared the reaction forces. Among them, one case was chosen and redesigned for detail design.

• Journal of Industrial Convergence
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• v.20 no.1
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• pp.63-68
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• 2022

In schools and corporate buildings, public WiFi Access Points are installed on the ceilings of hallways. In the case of an architectural structure in which a WiFi signal enters through a steel door made of a material with high signal attenuation, Internet connection is frequently cut off or fails when the door is closed. To solve this problem, our research implements an economical and portable WiFi extender using a Raspberry Pi and an auxiliary battery. Commercially available WiFi extenders have limitations in the location where the power plug is located, and WiFi extension using the WiFi hotspot function of an Android smartphone is possible only in some high-end models. However, because the proposed device can be installed at the position where the Wi-Fi reception signal is the best inside the door, the WiFi range can be extended while minimizing the possibility of damage to the original signal. Experimental results show that it is possible to eliminate the shadows of radio waves and to provide Internet services in the office when the door is closed, to the extent that web browsing and real-time video streaming for 720p are possible.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.11
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• pp.259-272
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• 2019

Steel-concrete single-leaf blast-resistant doors are protective structures consisting of a steel box and reinforced concrete slab. By the domestic blast-resistant doors, the structure is not designed efficiently because few studies have examined the effects of variables, such as the blast pressure, rebar ratio, and steel plate thickness on the structural behavior. In this study, the structural behavior of the doors was analyzed using the FE method, and the support rotation and ductility ratio used to classify the structural performance were reviewed. The results showed that the deflection changes more significantly when the plate thickness increases than when the rebar spacing is a variable. This is because the strain energy absorbed by the door is reduced considerably when the plate thickness increases, and as a result, the maximum deflection becomes smaller. According to a comparison of the calculated values of the support rotation and the ductility ratio, the structural performance of the doors could be classified based on the support rotation of one degree and ductility ratio of three. On the other hand, more explosion tests and analytical studies will be needed to classify the damage level.

• Transactions of Materials Processing
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• v.26 no.2
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• pp.87-94
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• 2017

Center pillar, which is installed in the center of flank of car body, supports roof and door and ensures the safety of driver by reducing the damage of car body caused by impact. Recently, high-strength steel is widely used to manufacture the center pillar due to high stiffness and fuel efficiency. In this study, material properties of the high-strength steel, whose tensile strength is more than 780MPa, were obtained to produce the center pillar. Stamping was performed by considering the design parameters (blank holder force, press stroke, blank size and pad pressure) used in the actual filed. The drawbeads were included in the stamping process to reduce the amounts of wrinkling and spring back. Using the commercial software, Autoform R5.2 and Minitab, effects of design parameters of the stamping process upon spring back were analyzed and applied to the design process. The restriking process meets the target of under 0.5mm in the amount of spring back.

• Korean Journal of Metals and Materials
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• v.56 no.11
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• pp.787-795
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• 2018

The effects of tempering condition on the microstructure and mechanical properties of 30MnB5 hot stamping steel were investigated in this study. Before the tempering, hot-stamped 30MnB5 steel was composed of only ${\alpha}^{\prime}$-martensite microstructure without precipitates. After the tempering at $180^{\circ}C$ for 120 min, nano-sized ${\varepsilon}$-carbides were precipitated in the ${\alpha}^{\prime}$-martensite laths. After tempering at $250^{\circ}C$ for 60 min, cementite was precipitated along the ${\alpha}^{\prime}$-martensite lath boundaries. The cementite was also observed in the specimens tempered at $350^{\circ}C$ for 30 min and $450^{\circ}C$ for 6 min, respectively. The globular ${\alpha}$-ferrite appeared at $350^{\circ}C-30min$ tempering, and the volume fraction of ${\alpha}$-ferrite increased when the tempering temperature was increased. The yield strength increased after tempering, and it reached a peak with the tempering condition of $180^{\circ}C-120min$, due to the nano-sized precipitates in the ${\alpha}^{\prime}$-martensite lath. After the tempering, the steel's ultimate tensile strength (UTS) was decreased due to the reduction in dislocation density and C segregation to lath boundaries. The highest elongation was observed at the $180^{\circ}C-120min$ tempering condition, due to the reduction of residual stress, and the lack of precipitates along the lath boundaries. The $180^{\circ}C-120min$ tempering condition was considered to have outstanding crash performance, according to toughness and anti-intrusion calculation results. In drop tower crash tests, the 30MnB5 door impact beam tempered at $180^{\circ}C$ for 120 min showed better crash performance compared to a 22MnB5 door impact beam.