• Korean Journal of Metals and Materials
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• v.46 no.8
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• pp.495-505
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• 2008

With the high proportion of zinc coated steels in body-in-white assembly, newly developed surface roughness textured galvannealed steel sheets have been introduced. In this study, zinc coated and surface roughness textured steel sheets were welded by resistance spot welding to investigate its weldability including electrode wear test. Based on the results of tensile-shear test, nugget diameter changes, and electrode tip growth test, it was clear that both surface roughness textured steels (GA-T and GA-E) showed good weldability. Also, there was no large difference in weldability and electrode wear behavior between GA-T and GA-E steels which have different surface roughness morphology. An analysis of electrode degradation showed Fe and Zn penetration through the electrode tip surface at 2400 welds reached $55{\sim}60{\mu}m$ and $75{\sim}80{\mu}m$, respectively. Therefore, there is no significant effect of surface roughness morphology on spot weldability of surface roughness textured galvannealed steel sheets. However, slight difference in thickness of alloying layers existing on electrode tip was found between GA-T and GA-E steels.

• Journal of the Korean Society for Heat Treatment
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• v.34 no.2
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• pp.66-74
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• 2021

Cladding material, which can selectively obtain excellent properties of different metals, is a composite material that combines two or more types of dissimilar metals into one plate. The titanium-copper cladding material between titanium which has excellent corrosion resistance and copper which has high thermal and electrical conductivity, are highly valuable composite materials. It can be used as heat exchangers with high conductivity under severe corrosion conditions. In order to apply the clad plate to the heat exchanger, it must be manufactured in the form of a tube and additional welding is required. It is important to select the cladding material manufacturing process and the welding process. The process of manufacturing the cladding material includes extrusion, rolling, and explosive bonding. Among them, the explosive bonding process is suitable for additional welding because no heat-affected zone is formed. In this study TIG welding of the explosive-bonded dissimilar clad plates was successfully performed by butt welding. The microstructures and bonding interface of the welded part were observed, and the effect of the bonding layer at the welding interface and the intermetallic compounds on the mechanical properties and tensile plastic deformation behaviors were analyzed. And also the integrity of TIG-welded dissimilar part was evaluated.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3A
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• pp.375-381
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• 2008

This paper deals with the shear capacity of corrugated rib as the shear connector in composite structures. Corrugated rib is modified as perfobond rib shear connector type to evaluate the shear capacity. A total 12 push-out specimens with stud, perfobond rib, and corrugated rib connector were fabricated. Then, the influences of hole-crossing bars, concrete dowel, depth of corrugated panel and height of rib on the shear capacity were evaluated experimentally. As the results of these tests, the failure mechanisms of corrugated rib and perfobond rib specimens were associated with the bearing failure of the concrete slabs, but the failure of weld zone did not occur. The shear capacity of corrugated rib specimens improved as high to 96% compared to the perfobond rib shear connectors. Also, the hole-crossing bars were effective on the improvement of concrete dowel action, and consequently, shear capacity increased by 48%. It was also proven that the increment of the depth of corrugated panel and the height of rib increased the concrete bearing resistance, therefore increasing the shear capacity.

• Journal of Korean Society of Steel Construction
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• v.26 no.4
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• pp.299-309
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• 2014

HSA800 is a new high strength steel (HSS) plate for building structures developed by POSCO and RIST in 2011. It has upper and lower bounds for yield ($F_y$) and tensile ($F_u$) strength as of 650-770MPa and 800-950MPa, respectively, with yield ratio ($F_y/F_u$) limit as of 0.85 which make steel quality more reliable and enhance the seismic resistance of structures. As made by TMCP, it has a good weldability without increasing carbon percentage. The objective of this study is to provide alternative design of mega-structural members of the Lotte World Tower (555m, 123 story), a first super-tall building in Korea, using HSS considering structural safety, constructability, and cost-effectiveness. Steel outrigger trusses, belt-trusses and steel exterior columns were selected and analyzed to evaluate the structural performance between original and alternative designs using HSS. The results show that HSS can be applied to the members which do not affect lateral stiffness of a building and, in this study, approximately 1100tons of steel were saved. It implies that HSS can save overall construction costs - manufacturing, delivery, and erection costs - by reducing mega structural member size. HSA800 was very first applied to the Lotte World Tower based on the results of this study.

• Journal of the Korea Concrete Institute
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• v.26 no.2
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• pp.151-157
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• 2014

Since recently developed Ultra-High-Performance-Concrete (UHPC) provides very high strength, stiffness, and durability, many studies have been made on the application of the UHPC to bridge decks. Due to high strength and stiffness of UHPC bridge deck, the structural contribution of top flange of steel girder composite to UHPC deck would be much lower than that of conventional concrete deck. At this point of view, this study proposes a inverted-T shaped steel girder composite to UHPC deck. This girder requires a new type of shear connector because conventional shear connectors are welded on top flange. This study also proposes three different types of shear connectors, and evaluate their ultimate strength via push-out static test. The first one is a stud shear connector welded directly to the web of the girder in the transverse direction. The second one is a puzzle-strip type shear connector developed by the European Commission, and the last one is the combination of the stud and the puzzle-strip shear connectors. Experimental results showed that the ultimate strength of the transverse stud was 26% larger than that given in the AASHTO LRFD Bridge Design Specifications, but a splitting crack observed in the UHPC deck was so severe that another measure needs to be developed to prevent the splitting crack. The ultimate strength of the puzzle-strip specimen was 40% larger than that evaluated by the equation of European Commission. The specimens combined with stud and puzzle-strip shear connectors provided less strength than arithmetical sum of those. Based on the experimental observations, there appears to be no advantage of combining transverse stud and puzzle-strip shear connectors.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.39-40
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• 2010

The demands for longer span and reduction of story height have greatly increased as building structures become much larger and higher in recent years. Although the development of flexural members for reducing story height or making long span has been studied by many researchers and engineers, there is still a lack of efficient systems that meet these two demands simultaneously. This study aimed at developing a new composite beam system suitable for long span and reduction of story height, and proposed a prestressed composite beam with corrugated web. It has great resistance against non-symmetric construction load due to its strong out-of-plane shear strength with relatively small member height as well as good constructability and economic efficiency by removing/minimizing form work. The corrugated webs also make accordion effect introducing larger effective prestressing force to top and bottom flanges, which causes larger upward camber reducing the member deflection. Five full-scale specimens with key test parameters, which are web sectional shapes and number of drape points, were tested to understand their flexural behavior and to verify the performance of the proposed method. The experimental test results showed that the proposed prestressed composite beam had greater flexural strength and stiffness than the ordinary non-prestressed composite beam.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.10 no.2
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• pp.105-115
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• 2012

Necessity of demonstration test to evaluate the structural integrity of a basket for accident conditions arose during license approval procedure for the WSPP's dry storage facility named MACSTOR/KN-400. A drop test facility for demonstration was constructed in KAERI site and demonstration tests for basket drop were conducted. As the upper welding region of a loaded basket was collided with a dropped basket during the drop test, the welding in this region was fractured and leakage happened after the drop test. The enhancement of basket design was needed since the existing basket design was not able to satisfy the performance requirement. The directions for design modification were determined and six enhanced designs were derived based on these directions. Structural analyses and specimen tests for each enhanced design were conducted. By evaluating structural analysis results and test results, one among six enhanced designs was decided as a final design for revision. The final design was the one to reduce the height of central post of a basket and to decrease the impact velocity with a dropped basket. Test basket models were fabricated with accordance with the final enhanced design. Additional demonstration test was performed for this test model and all the performance requirements were satisfied.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.7
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• pp.25-32
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• 2019

Welded joints and mechanical joints using bolt connection have been used as a pile-to-pile connecting method for PHC piles. These PHC pile joint methods may have difficulty in securing connecting quality and connecting performance in PHC pile joining process. Therefore, this study proposes a non-welded connection plate type mechanical PHC pile joint to improve the disadvantages of existing PHC pile connection methods and to secure the connection performance of PHC pile joint. Its connection performance was evaluated from nonlinear FE analysis and loading tests for actual PHC piles with suggested pile joints. From nonlinear FE analysis for the proposed PHC pile joint, it was evaluated to have sufficient connection performance under flexural, compressive, tensile, shear, and eccentric compressive load condition. PHC piles connected by the suggested connection plate type mechanical PHC pile joint show that they show stable linear behaviors for the crack moment and the flexural moment level of the PHC pile. Therefore, the proposed a non-welded connection plate type mechanical PHC pile joint can secure sufficient connection performance in PHC pile.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.2
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• pp.153-161
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• 2009

After several PWSCCs were found in Bugey(France), Ringhals(Sweden), Tihange(Belgium), Oconee, Arkansas, Crystal Fever, Davis-Basse, VC Summer(U.S.A.), Thuruga(Japan), USNRC and PNNL started the research on PWSCC, that is, PINC project. The aim of this project is to fabricate and obtain representative NDE mock-ups with flaws to simulate tight PWSCC cracks, to identify and quantitatively assess NDE methods for accurately detecting, sizing and characterizing tight cracks such as PWSCC, to document the range of locations and crack morphologies associated with PWSCC and observed responses and to incorporate findings from other ongoing PWSCC research programs, as appropriate. By participating in PINC project, Korean morphology technique about PWSCC and NDE technique have improved and become similar lever with other advanced country. Therefore, the evaluation technique of integrity for nickel alloy component has been improved by cooperation with university, research institute and industries.

• Journal of the Korea Concrete Institute
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• v.21 no.1
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• pp.37-45
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• 2009

An objective of this study is to evaluate the structural performance of the weak axis SRC column-RC beam joints by experiments. Although one of common joint types is the connection with standard hooks, it has been required to examine its safety and to settle problems of the joint among practical engineers. Specimen types are classified into two categories, namely the type of standard hook and the type of shape improvement. The first one is consisted of three specimens which are reference type, development length modification type, and development length supplement type. Three specimens for shape improvement were made with variations on the arrangement of longitudinal reinforcements and the development length. Test results based on cyclic loadings were discussed with load-deflection curves, maximum strengths, strength degradations beyond the maximum. It was found that the standard hook types showed premature failures and consequent strength degradations due to splitting of joint concrete. However, satisfactory performance was obtained with the shape improvement type with wing-plate welding. No premature failures and strength degradations were detected with the specimens.