• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.1
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• pp.46-51
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• 2015

Stainless steel is a popular structural materials for liquid-hydrogen storage containers and piping components for transporting high-temperature fluids because of its superior material properties such as high strength and high corrosion resistance at elevated temperatures. In general, tungsten inert gas (TIG) arc welding is used for bonding stainless steel. However, it is often reported that the thermal fatigue cracks or initial defects in stainless steel after welding decreases the reliability of the material. The objective of this paper is to clarify the characteristics of ultrasonic guided wave propagation in relation to a change in the initial crack length in the welding zone of stainless steel. For this purpose, three specimens with different artificial defects of 5 mm, 10 mm, and 20 mm in stainless steel welds were prepared. By considering the thickness of s stainless steel pipe, special attention was given to both the L(0,1) mode and L(0,2) mode in this study. It was clearly found that the L(0,2) mode was more sensitive to defects than the L(0,1) mode. Based on the results of the L(0,1) and L(0,2) mode analyses, the magnitude ratio of the two modes was more effective than studying each mode when evaluating defects near the welded zone of stainless steel because of its linear relationship with the length of the artificial defect.

• Journal of Korean Society of Steel Construction
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• v.21 no.5
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• pp.451-459
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• 2009

The purpose of this study was to evaluate the in-plane bending moment for T-joints made of cold-formed square hollow steel sections. In the previous studies, the T-joint was shown not to have an obvious peak load, and the failure mode was the main chord flange failure at the branch-width-to-chord-width ratio ($\beta$) of below 0.71. Based on the experimental results, including the tests conducted by Zhao, the deformation limit of 1% B was proposed for ${16.7{\leq}2{\gamma}(=B/T){\leq}33}$ and ${0.34{\leq}{\beta}(=b_{1}/B){\leq}0.71}$. Then, the ultimate in-plane bending strength was shown to be Mu=1.5${\cdot}$M1% B. The existing strength formulae for the original T-joint were investigated and were determined to be the main chord flange failure for the branch-squared T-joint. The bending strength formulae of CIDECT and other researchers were compared with the test results. Finally, a reasonably good agreement with Zhao's formula was found. Therefore, the design guidelines were presented based on Zhao's strength formula for T-joints.

• Journal of Korean Society of Steel Construction
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• v.26 no.6
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• pp.511-522
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• 2014

In this study, an innovative steel stair system is presented which enables rapid erection and high quality control in both residential and office building construction. This system features two lightweight steel stringers of box shape, bolted connections easy to absorb construction tolerance, and stair steps movable transversely (or sliding steps) such that the work space needed for concrete stairway wall could be easily provided. In this type of stairway system, other than providing robust connecting details, ensuring vibration performance is especially important since this system may be vibration-sensitive due to lightweight nature and/or probable low damping. To tackle these issues, a series of full-scale mock-up tests were conducted by using box-shape stringer members with or without concrete-fill. The connection system was shown to be sufficiently stiff and strong, or it remained elastic even under the 160% of service load level. Among the seven stringer alternatives, five exhibited satisfactory vibration performance according to the related North American and European acceptance criteria.

• Journal of Korean Society of Steel Construction
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• v.28 no.5
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• pp.373-382
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• 2016

Painting or thermally sprayed metal coating is often used in corrosion protection of steel structures. In recently, duplex coating system which combines thermally sprayed metals with paint is selected as a new generic type of coatings on steel structures under the highly corrosive environments. In this study, the structural steel specimens were surface treated, thermally sprayed with zinc, zinc-15%aluminum alloy, aluminum and aluminum-5%magnesium alloy, and finally sealing or painted with acrylic urethane. And as a reference specimens, steel specimens were painted with acrylic urethane after surface treatment. Circular defects with 1.0, 3.0 and 5.0 mm in diameters and line defect with 2.0 mm width, which reach the steel substrate were created on all specimens. The specimens were exposed into an environmental testing chamber controlled by the ISO 20340, which is a laboratory cyclic accelerated exposure test condition of spraying/UV/low temperature, for up to 175 days. Based on the corrosion tests, corrosion deterioration from the initial defects were evaluated and weathering performance of the specimens are compared.

• Journal of Veterinary Clinics
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• v.27 no.6
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• pp.652-662
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• 2010

The purpose of this experiment was to study the effects of demineralized bone matrix (DBM), calcium sulfate (CS), and calcium metaphosphate (CMP) on osteogenesis of unicortical 5-mm-diameter defects in canine femurs. Seventy-two femoral unicortical defects of nine adult beagles (eighteen femurs, four unicortical femoral defects were made in each femur) were made. Three bone graft substitutive materials such as CS, DBM, and CMP and the empty controls were compared each other. The postimplanted specimens were harvested at week 4, 8, and 24 for radiographic, biochemical and histomorphologic evaluation. In radiograph, CS group appeared to be absorbed rapidly and made new cortical bone. Defects of cortical bone was gradually filled with new bone around bone graft materials in DBM group. Bone graft substitutes weren't absorbed rapidly but, remained performing structural roles in cortical bone after 24 weeks in CMP group. Radiographic intensity of control group showed significantly (p < 0.05) lower compared to that of experimental group. Defects treated with either CS, DBM or CMP had more bone formation than the untreated defects (p < 0.05). The results of analysis in the cortical bone region were deduced the conclusions as follows. Three bone graft materials seemed to accelerate the formation of new bone compared with controls for 24 weeks. CMP group having more or less large particle space was more adequate than DBM group, as well as more compact CS group was more pertinent than CMP group as the glues for bones.

• Journal of Korea Water Resources Association
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• v.42 no.6
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• pp.505-511
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• 2009

When replacing deteriorated pipes, it is important to select pipe diameters of new pipes for improving the long-term reliability of a water distribution system. However, as the use of larger diameter pipes brings cost increase, it is required to evaluate the improvement of the reliability by the use of larger diameter pipes. In this study, we propose a methodology to evaluate the improvement of the reliability by the use of different pipe diameters. For this purpose, we rely on the segment-based minimum cutset method with the success mode approach to evaluate the reliability of a water distribution system and determine which pipes and their diameters will be replaced to improve the reliability using GA, After the suggested method is applied to a real water distribution system, the optimized pipe diameters produces higher reliability of the system than the current ones with the same construction cost. However, compared to the increase rate of the construction cost, the improvement of the reliability is not significant. Thus, in addition to the use the different pipe diameters, the structural modification or adding new valves to the system is necessary to improve the reliability efficiently.

• Geophysics and Geophysical Exploration
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• v.13 no.3
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• pp.235-242
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• 2010

Two moderate earthquakes with local magnitude 4.9 and 5.0 at the Yellow Sea area occurred successively around Hong island on March 22, 2003 and Baengnyeong island on March 30, 2003, respectively, close to the Korean Peninsula. Focal mechanisms by the waveform inversion analysis are strike slip faulting with a thrust component for the March 22 event, and normal faulting for the March 30 event. The direction of P-axes of two events were ENE-WSW which were similar to previous studies on that of P-axes in and around the Korean Peninsula. Moment magnitudes determined by the waveform inversion analysis were 4.7 and 4.5, respectively, whereas those determined by spectral analysis were 4.8 and 4.6, respectively. As regards the March 22 event, regional stress by combined tectonic forces from compressions of plates colliding to the Eurasian plate, rather than mere local stress, was indicated. However, it was estimated that the March 30 event took place when the weak zone generated from the existing collision zone was reactivated when subjected to local stress in the tensile direction. This seismological observation indirectly supports the idea that the collision zone may extend to the Korean Peninsula.

• Journal of the Korea Concrete Institute
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• v.13 no.5
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• pp.430-437
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• 2001

Recently, there have been increased much concerns about repair and rehabilitation works for aged concrete structures. It is in particular known that due to repeated overburden vehicles, there are significantly increasing number of aged concrete bridge slabs, which are strongly needed to construct and rehabilitate by innovative construction method. The objective of this research is to develop the new construction method of concrete slab in bridge superstructure, which can contribute to minimize a traffic congestion during repair and rehabilitation works of aged concrete slab, and can sufficiently assure the quality through the minimization of in-situ works at the site. I-beams with punch holes, which are substituted instead of main reinforcing steels in concrete slabs, can be manufactured in accordance with the specification in the factory, and be preassembled into the panel. After erecting the preassembled panels in the site, concrete will be poured into the slab panel. This research is to investigate mechanical properties of I-beam with punch holes itself, and then to investigate structural properties of assembled I-beam panels through static test, of which result can be utilized for the development of the new constructional method for concrete slab in bridge superstructure.

• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.529-537
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• 2007

The purpose of this study is to discuss how strength and ductility of each system in low-rise reinforced concrete buildings composed of extremely brittle, shear and flexural failure lateral-load resisting systems have influence on seismic capacities of the overall system, which is based on nonlinear seismic response analyses of single-degree-of-freedom structural systems. In order to simulate the triple lateral-load resisting system, structures are idealized as a parallel combination of two modified origin-oriented hysteretic models and a degrading trilinear hysteretic model that fail primarily in extremely brittle, shear and flexure, respectively. Stiffness properties of three models are varied in terms of story shear coefficients, and structures are subjected to various ground motion components. By analyzing these systems, interaction curves of demand strengths of the triple system for various levels of ductility factors are finally derived for practical purposes. The result indicates that demand strength levels derived can be used as a basic information for seismic evaluation and design criteria of low-rise reinforced concrete buildings having the triple lateral-load resisting system.

• Ocean and Polar Research
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• v.33 no.4
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• pp.473-483
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• 2011

In the recent WTO/DDA negotiations, discussions are progressing to forbid fishery subsidies which have negative effect on the natural environment and the fishery resources and to lower or to eliminate the tariff/non-tariff barriers that distort trade liberalization. As a result, linking to the weak structural environment of Korea's fishing villages; such a scheme has jeopardized the livelihood of fishermen who settle down in local fishing harbors. Against this backdrop, the government is attempting to positively respond to changes in the fishing environment in a number of different ways: promotion of fishing tourism, fishing harbor reinforcement in function, developing fishing villages, and harbors. With respect to investment by priority in fishing harbor development, it is very important to appropriately select investment targets based on objective criteria. A small number of harbors are chosen and investment plans by harbor are systematically devised, economic feasibility and the effects of investment are analyzed and reviewed in relation to each target harbor. This paper is designed to review and assess objective evaluation methods and the degree of importance for the designation of target harbors, dealing with local harbors in Chung Nam Do as a model. Each local government has tried to reorganize existing harbors and develop new harbors, considering a fall in the number of fishing vessels and the expansion of maritime leisure activities. In order to overcome the limit of existing harbors in function, to raise the income of fishermen, and to activate tourism, they have shifted their focus from simple functions such as vessel evacuation and anchoring to harbor beautification, which can work as a basis for fishing tourism. This paper points out that the AHP analysis method for prioritizing local harbors in Chung Nam Do should help to be chosen target harbors in other cities and provinces. Each local government has attempted to reorganize existing harbors and to develop new harbors, taking into consideration the decline in the number of fishing vessels and the expansion of maritime leisure activities. In order to overcome the limited number of functional harbors, to raise the income of fishermen, and to boost tourism, they have shifted their focus from simple functions, such as vessel evacuation and anchoring, to harbor beautification, which can work as a basis for fishing tourism. This paper shows that the AHP analysis method for prioritizing local harbors in Chungcheongnam-do could aid in the effective selection of target harbors in other cities and provinces.