• Journal of Welding and Joining
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• v.28 no.2
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• pp.32-38
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• 2010

In shipbuilding industry, welding position are usually flat and vertical position at the erection stage. Application of SAW and EGW for these positions makes it possible to achieve enhanced productivity and high quality. But owing to their large size and weight it is difficult to apply these techniques in short and narrow regions. To overcome this problem, our company developed light weight and compact size 4-axis welding carriage which perform 3D weaving. The purpose of this study is to explain the development and application of intelligent welding carriage using 3D weaving pattern that can fill a large amount of welds and thereby making it possible to achieve high quality of welding. This study shows 3D weaving pattern, development of weaving database, and skill of adaptive control response for the variable gap. Also, it shows the results of procedure qualification test for the AH-grade steel when applied to the intelligent welding carriage.

• Resources Recycling
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• v.30 no.1
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• pp.83-91
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• 2021

Ladle furnace slag is a byproduct of the steel-making process, and it contains the mineral β-C2Sandtherapid-settingmineral (dependingonwhichreducingagenthasbeenused). Ladle furnace slag is often treated through slow cooling, which causes the slag to lose its reactivity. In this study, the properties of air-quenched CAC and pulverized ladle furnace slag containing gypsum were evaluated, and the optimal mixing ratio was determined for broadening their usage. Consequently, the properties of CAC aredemonstrated by the dissolution of gypsum after a period of three hours and the content of gypsum after a period of one day. The optimal mixing ratio of anhydrate and hemihydrate gypsum is found to be within 30% and that of dihydrate gypsum is found to be higher than 35%. Furthermore, based on the results of CAC with dihydrate gypsum, the applicability of the by-product dihydrate gypsum has been verified.

• Journal of the Earthquake Engineering Society of Korea
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• v.25 no.3
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• pp.103-110
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• 2021

A shake table test is conducted for the three-story reinforced concrete building structure using 0.28 g, 0.5 g, 0.75 g, and 1.0 g of seismic input motions based on the Gyeongju earthquake. Computational efforts are made in parallel to explore the mechanical details in the structure. For engineering practice, the elastic modulus of concrete and rebar in the dynamic analysis is reduced to 38% and 50%, respectively, to calibrate the structure's natural frequencies. The engineering approach to the reduced modulus of elasticity is believed to be due to the inability to specify the flexibility of the actual boundary conditions. This aspect may lead to disadvantages of nonlinear dynamic analysis that can distort local stress and strain relationships. The initial elastic modulus can be applied directly without the so-called engineering adjustment with infinite element models with spring and spring-dashpot boundary conditions. This has the advantage of imposing the system flexibility of the structure on the sub-boundary conditions of springs and damping devices to control its sensitivity in a serial arrangement. This can reflect the flexibility of realistic boundary conditions and the effects of system damping (such as the gap between a concrete footing and shake table, loosening of steel anchors, etc.) in scalar quantities. However, these spring and dashpot coefficients can only be coordinated based on experimental results, making it challenging to select the coefficients in-prior to perform an experimental test.

• Steel and Composite Structures
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• v.31 no.6
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• pp.541-558
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• 2019

In Special Concentrically Braced Frames (SCBFs), vertical and horizontal components of the brace force must be resisted by column and beam, respectively but normal force component existing at the gusset plate-to-column and beam interfaces, creates out-of-plane action making distortion in column and beam faces adjacent to the gusset plate. It is a main concern in Hollow Structural Section (HSS) columns and beams where their webs and gusset plate are not in the same plane. In this paper, a new gusset plate passing through the HSS columns and beams, named as through gusset plate, is proposed to study the force transfer mechanism in such gusset plates of SCBFs compared to the case with conventional gusset plates. For this purpose, twelve SCBFs with diagonal brace and HSS columns and twelve SCBFs with chevron brace and HSS columns and beams are considered. For each frame, two cases are considered, one with through gusset plates and the other with conventional ones. Based on numerical results, using through gusset plates prevents distortion and out-of-plane deformation at HSS column and beam faces adjacent to the gusset plate helping the entire column and beam cross-sections to resist respectively vertical and horizontal components of the brace force. Moreover, its application increases energy dissipation, lateral stiffness and strength around 28%, 40% and 32%, respectively, improving connection behavior and raising the resistance of the normal force components at the gusset plate-to-HSS column and beam interfaces to approximately 4 and 3.5 times, respectively. Finally, using such through gusset plates leads to better structural performance particularly for HSS columns and beams with larger width-to-thickness ratio elements.

• Explosives and Blasting
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• v.37 no.1
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• pp.34-47
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• 2019

This case study is concerned with the project of the explosive demolition for the DCRE Incheon plant located in Hakik district in Incheon city. The building was severely aging due to the high temperature and sea winds of hundreds of degrees emitted by chimney-shaped steel structures inside the building. Due to this, the concrete of the column and the beam fell off and rusted rebar were exposed, and some of the slabs were severely damaged, making it difficult for workers to access the structure. Therefore, it is not possible to apply a mechanical demolition method in which heavy equipment enters the interior of the building, and an explosive demolition method was applied to allow the building to be demolished without dismantling the internal facilities of the building. The order of blasting proceeded in the order of (1) building ${\rightarrow}$ (2) chimney 2 ${\rightarrow}$ (3) chimney 1. A total of 406 electronic detonators (Unitronic 600) was used to sequentially initiate the explosives installed at appropriate in building and chimneys.

• Journal of the Economic Geographical Society of Korea
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• v.21 no.4
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• pp.409-424
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• 2018

Since the 1950s, many of the traditional industrial cities of advanced economies in Europe and North America were affected by a series of de-industrialization. The de-industrialization process, characterized by company shut-downs and massive lay-offs, has resulted in high unemployment rates and massive redundancies in physical infrastructure. Since the 1980s, many of the old industrial cities have attempted to overcome such problems. However, it has been found that not many of the cities are found to be successful. The City of Dortmund, one of the core cities of the large German industrial conurbation of the past, the Ruhr, is found to be an exceptional case demonstrating a clear success in overcoming deindustrialization problems. The City in fact strategically pursued transforming backbone of its economy from steel-making, coal-mining and beer-brewery to high-technology and future-oriented industries, based on microsystems, biomedical, electronic logistics and information technology. This paper attempts to analyse the processes and outcomes of transforming Dortmund beginning from the 1980s to articulate the roles of the agencies contributing to the success.

• Journal of Ocean Engineering and Technology
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• v.33 no.5
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• pp.486-494
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• 2019

Recently, the interest in marine leisure activities has been growing rapidly with the work-life balance trend. In response to this demand, the Korean government is supporting fostering and revitalizing the relevant industries and facilities. In particular, a marina has been making efforts to change itself into a resort with multiple amenities instead of a simple mooring facility. However, the facilities in a marina for the transport of marine leisure equipment mostly consist of cranes and boat-lifts using ropes, which can result in incidents such as damage and accidents during lifting or movement. This paper proposes the equipment and support system for the safe transportation of marine leisure ships. Aluminum transport equipment was designed by performing a structural analysis to achieve a lighter weight than the existing steel products. In addition, a safety support system with alarms for tilting or obstacles and a slope monitoring system was developed to enhance the safety during operation and transportation. The safety support system developed in this study was implemented and installed in the transport system, and verified through commissioning on land.

• Journal of Powder Materials
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• v.28 no.6
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• pp.483-490
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• 2021

A new Fe-Cr-Mo-B-C amorphous alloy is designed, which offers high mechanical strength, corrosion resistance as well as high glass-forming ability and its gas-atomized amorphous powder is deposited on an ASTM A213-T91 steel substrate using the high-velocity oxygen fuel (HVOF) process. The hybrid coating layer, consisting of nanocrystalline and amorphous phases, exhibits strong bonding features with the substrate, without revealing significant pore formation. By the coating process, it is possible to obtain a dense structure in which pores are hardly observed not only inside the coating layer but also at the interface between the coating layer and the substrate. The coating layer exhibits good adhesive strength as well as good wear resistance, making it suitable for coating layers for biomass applications.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.523-530
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• 2022

The problem in the construction of seawall reinforcing the seawall where there is seawater flow is the outflow of materials. Gravity-type pouring of concrete is difficult to fill the voids smoothly, and the cement of concrete that has not hardened is likely to be dispersed in seawater. This phenomenon not only reduces the reliability of quality after concrete hardening, but can also adversely affect the surrounding environment. Therefore, there is a need for a gel-like injection material that can be injected, In this study, the initial strength and durability improvement effect of seawater immersion were evaluated by using electrofurnace reduction slag and blast furnace slag with acute properties. As a result of the experiment, it was possible to prepare a gel-like injection material having flowability through reaction with silica-based chemical liquid. The flowability of the gel is 105~143 mm depending on the formulation, and the on-site simulation test can fill the voids without external leakage, confirming its on-site applicability.

• Transactions of Materials Processing
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• v.31 no.2
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• pp.51-56
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• 2022

In this study, finite element analyses were performed by applying a stress ring and split die design to relieve the tensile stress acting on the die due to high surface pressure during warm-closed forging. The applied material was a yield-ratio-control-steel (YRCS). It was used without quenching or tempering after forging. In the case of stress rings design, the number of stress rings and the tolerance for shrink fit were different. Vertical and horizontal splits were applied for insert die split design. Case 5 die with three stress rings, 0.2 % shrink fit tolerance, and vertical split was selected as an effective die design for tensile stress reduction. Based on die stress reduction analyses, Case 5 die for warm-closed forging was produced and smooth forgeability was secured, making it possible to manufacture forging product of yoke with the required geometry. In addition, controlled cooling using warm forging heat was applied to secure mechanical properties of yokes. When oil cooling was used for direct controlled cooling after warm-closed forging, a relatively uniform Rockwell hardness distribution and high mechanical properties could be obtained.