• Fire Science and Engineering
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• v.30 no.3
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• pp.79-85
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• 2016

Serious electrical problems, such as shorts, ground faults, or circuits, often cause fire events in the fire proof zone of nuclear power plants. These would be directed to the loss of safe shutdown capabilities performed by safety-related systems and equipment. The fire event can be treated with the basic design principle that safety systems should maintain their functions with redundancy and independency. In the case of a cable fire in the main control room, operators cannot perform their mission properly and can misjudge the situation because of spurious operation, incorrect indication or instrument. These would deteriorate the plant capabilities of safety shutdown and result in disastrous conditions. Therefore, during a main control room fire, 5 minutes of operator action time is very important to operate the safety shutdown components. This paper describes the cable functional failure temperature criteria and conducted a cable functional failure time evaluation using Fire Dynamic Simulator to obtain the operator action time for a main control room fire.

• Structural Monitoring and Maintenance
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• v.9 no.1
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• pp.29-42
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• 2022

In mountainous areas of China, concrete poles with connectors are widely employed in power transmission due to its convenience of manufacture and transportation. The bearing capacity of the poles must have degenerated over time, and most of the steel connectors have been corroded. Carbon fiber reinforced polymer (CFRP) offers a durable, light-weight alternative in strengthening those poles that have served for many years. In this paper, the bearing capacity and failure mechanism of CFRP sheet strengthened existing reinforced concrete poles with corrosion steel connectors were investigated. Four poles were selected to conduct flexural capacity test. Two poles were strengthened by single-layer longitudinal CFRP sheet, one pole was strengthened by double-layer longitudinal CFRP sheets and the last specimen was not strengthened. Results indicate that the failure is mainly bond failure between concrete and the external CFRP sheet, and the specimens fail in a brittle pattern. The cross-sectional strains of specimens approximately follow the plane section assumption in the early stage of loading, but the strain in the tensile zone no longer conforms to this assumption when the load approaches the failure load. Also, bearing capacity and stiffness of the strengthened specimens are much larger than those without CFRP sheet. The bearing capacity, initial stiffness and elastic-plastic stiffness of specimen strengthened by double-layer CFRP are larger than those strengthened by single-layer CFRP. Weighting the cost-effective effect, it is more economical and reasonable to strengthen with single-layer CFRP sheet. The results can provide a reference to the same type of poles for strengthening design.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.6
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• pp.73-83
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• 2016

Bearing stress near anchor plates is usually very high due to prestressing force in anchorage zone of concrete structure used post-tensioned prestressed method. In order to effective utilization of cross section and crack control, appropriate size of anchorage plates should be used to prevent crack initiation and failure of concrete structures eventually. This study aims to suggest equation for effective area of bearing plate of rectangle type and circular type by Highway Bridge Design Specification and PTI etc. A shape factor according to bearing plate shape is suggested based on numerical analysis, and it can be used suitability for design of special anchorage plate dimension.

• Advances in concrete construction
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• v.5 no.3
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• pp.221-240
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• 2017

The modeling of the mechanical behavior of quasi-brittle materials is still a challenge task, mainly in failure processes when fracture and plasticity phenomena become important actors in dissipative processes which occur in materials like concrete, as instance. Many homogenization-based approaches have been proposed to deal with heterogeneous materials in the last years. In this context, a computational homogenization modeling for concrete is presented in this work using the concept of Representative Volume Element (RVE). The material is considered as a three-phase material consisting of interface zone (ITZ), matrix and inclusions-each constituent modeled by an independent constitutive model. The Representative Volume Element (RVE) consists of inclusions idealized as circular shapes symmetrically and nonsymmetrically placed into the specimen. The interface zone is modeled by means of cohesive contact finite elements. The inclusion is modeled as linear elastic and matrix region is considered as elastoplastic material. A set of examples is presented in order to show the potentialities and limitations of the proposed modeling. The consideration of the fracture processes in the ITZ is fundamental to capture complex macroscopic characteristics of the material using simple constitutive models at mesoscopic level.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.668-674
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• 2002

Structural integrity assessment is indispensable for preventing catastrophic failure of industrial structures/components/facilities. This diagnosis of operating components should be done periodically for safe maintenance and economical repair. However, conventional standard methods for mechanical properties have the problems of bulky specimen, destructive and complex procedure of specimen sampling. Especially, the mechanical properties at welded zone including weldment and heat affected zone could not be evaluated individually due to their size requirement problem. So, an advanced indentation technique has been developed as a potential method for non-destructive testing of in-field structures. This technique measures indentation load-depth curve during indentation and analyzes the mechanical properties related to deformation such as yield strength, tensile strength and work-hardening index. Also indentation technique can evaluate a residual stress based on the concept that indentation load-depth curves were shifted with the direction and the magnitude of residual stress applied to materials. In this study, we characterized the tensile properties and welding residual stress of various industrial facilities through the new techniques, and the results are introduced and discussed.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.85-86
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• 2010

This study is aimed to investigate on the structural properties (like as strength, failure mode, ductility) of beams with web openings reinforced with steel tube of square. The main parameters are follows; 1) with and without web opening 2) the number of opening, 3) location of openings. In the quasi-static tests, structural properties of PFBS1A and PFBS2A were most superior. When the locations of opening are respectively maximal moment zone (M), shear (S), co-existence area of moment and shear (M+S), the specimen with web opening at maximal moment zone is not less than that without web opening in terms of strength and ductility.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.4
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• pp.117-123
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• 2002

X-ray diffraction observation of fracture surfaces yields useful information to analyze the causes of failure accidents of engineering structures. This experimental technique, named X-ray fractography, has been developed especially in metal and mechanical engineering fields. The distributions of the residual stress and the half value breadth of diffraction profiles beneath the fatigue fracture surface were measured with SNCM 439, HT100 and Ti-6Al-4V alloy. The size of the maximum plastic zone was successfully determined on the basis of the measured distributions. This size was correlated to maximum stress intensity factor. The distributions of the half value breadth of diffraction profiles on the fatigue fracture surfaces were measured with SNCM 439. HT100. The equations of x-ray parameter distribution were possible to estimated fracture parameters of fatigue fracture surfaces.

• Tribology and Lubricants
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• v.20 no.6
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• pp.322-329
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• 2004

Recently, a load/unload(L/UL) system is adopted to the hard disk drive(HDD) due to its advantages such as lower power consumption, larger data zone, simpler fabrication of disk due to no bumped parking zone, and rarer contact between slider and media. An analysis of the transient motion for the slider is very important to design an air bearing surface(ABS) of the slider to secure the stable performance of the system. During the L/UL process, however, there are several issues occurred such as contact or collision between slider and media. Sometimes this will cause the system failure. In this study, the dynamics of a pico slider during the loading process are investigated through numerical simulation using FEM analysis and experiment. Ramp profile and angular velocity of the swing arm actuator are very important parameters for the design of L/UL system to avoid collision between slider and disk.

• Steel and Composite Structures
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• v.26 no.1
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• pp.67-78
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• 2018

The application of rib stiffeners is common on steel connections, with regard to the stiffened angle connection, experimental results about the influence of stiffeners under monotonic and cyclic loading are very limited. Consequently, this paper presents the experimental investigation on four types angle connections with or without stiffener under static loading and another four type stiffened angle connections subjected to cyclic loading. The static experimental result showed that the rib stiffener weld in tension zone of the connection greatly enhanced its initial rotational stiffness and flexural strength. While a stiffener was applied to the compression zone of the connection, it had not obvious influences on the initial rotational stiffness, but increased its flexural strength. The moment-rotation curves, skeleton curves, ductility, energy dissipation and rigidity were evaluated under cyclic loading. Stiffened top-and-seat angle connections behaved as semi-rigid and partial strength, and rotation of all stiffened angle connections exceeded 0.04rad. The failure modes between monotonic and cyclic loading test were completely different and indicated certain robustness.

• Journal of Korean Society of Water and Wastewater
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• v.28 no.6
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• pp.699-711
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• 2014

This study was carried out to analyze water suspension in the water supply system through fault tree analysis. And quantitative factors was evaluated to minimize water suspension. Consequently the aim of this study is to build optimal planning by analyzing scenarios for water suspension. Accordingly the fault tree model makes it possible to estimate risks for water suspension, current risks is $92.23m^3/day$. The result of scenario analysis by pipe replacement, risks for water suspension was reduced $7.02m^3/day$ when replacing WD4 pipe. As a result of scenario analysis by water district connections, the amount of risk reduction is maximized when it is connecting to network pipe of D Zone. Therefore, connecting to network pipe for D Zone would be optimal to reduce risk for water suspension.