• Computers and Concrete
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• v.9 no.2
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• pp.133-151
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• 2012

This paper presents an analytical procedure for the analysis of high strength steel fiber reinforced concrete members considering the cracking effect in the serviceability loading range. Modifications to a previously proposed formula for the effective moment of inertia are presented. Shear deformation effect is also taken into account in the analysis, and the variation of shear stiffness in the cracked regions of members has been considered by reduced shear stiffness model. The effect of steel fibers on the behavior of reinforced concrete members have been investigated by the developed computer program based on the aforementioned procedure. The inclusion of steel fibers into high strength concrete beams and columns enhances the effective moment of inertia and consequently reduces the deflection reinforced concrete members. The contribution of the shear deformation to the total vertical deflection of the beams is found to be lower for beams with fibers than that of beams with no fibers. Verification of the proposed procedure has been confirmed from series of reinforced concrete beam and column tests available in the literature. The analytical procedure can provide an accurate and efficient prediction of deflections of high strength steel fiber reinforced concrete members due to cracking under service loads. This procedure also forms the basis for the three dimensional analysis of frames with steel fiber reinforced concrete members.

• 한국태양에너지학회:학술대회논문집
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• 2008.11a
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• pp.280-287
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• 2008

In case of low pressure steam turbine used in power plant, it was operated in wet steam and high stress condition. Therefore, it is possible that the corrosion damage of low pressure was induced by this condition. According to previous study, about 30% of total blade failure correspond to corrosion fatigue or SCC(stress corrosion cracking) in low pressure turbine. Especially, LSB(last stage bucket) of low pressure turbine has a higher hardness to prevent erosion damage due to water droplet however, generally this is more dangerous for SCC damage. Therefore, to improve reliability of turbine blade. various methods for SCC evaluation has been developed. In this study, the crack found in LSB during in-service inspection was evaluated using microstructure analysis and stress analysis. From the stress analysis, the optimum size of fillet to remove the crack was proposed. And also, the reliability was evaluated for modified LSB using GOODMAN diagram.

• The KSFM Journal of Fluid Machinery
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• v.3 no.4 s.9
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• pp.7-14
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• 2000

This paper provides integrity evaluation and root cause analysis for defects observed at volute tongue, or cutwater, of the operating centrifugal pump in power plant. The cause of the cracks are analyzed and reviewed from the viewpoint of the operation and maintenance of the pumps, and the sample obtained from the cracked volute tongue of the pump are examined. At first, in-situ hardness test and microstructure examination were performed to understand the cause of cracking at volute tongue. The evaluation of structural integrity and the possibility of the crack propagation is also evaluated. Cracks were typical intergranular cracking and propagated along with prior austenite grain boundary. At easing volute tongue, the hardness was higher than ASTM requirement and a large amount of intergranular Cr carbide was precipitated. These were due to high C content in material. P content was also higher than ASTM requirement. Therefore, Cr carbide precipitation and P segregation at grain boundary, caused by higher C and P content in material, resulted in intergranular cracking of casing volute tongue. This procedure for integrity evaluation and root cause analysis is used to guide, and support the pump designer and manufacturer's material selection and process design to avoid a costly, unplanned outage of plant.

• Journal of the Korean Geotechnical Society
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• v.23 no.9
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• pp.29-37
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• 2007

The experiments have been conducted on Kaolinite in laboratory to investigate the development of shrinkage cracking and propose a simple model. Image analysis method consisting of control point selection(CPS) technique is used to process and analyze images of soil cracking captured by a digital camera. The distributions of crack length increment and crack area increment vary as a three-step process. These steps are regarded as stages of soil cracking. They are in turn primary crack, secondary crack and shrinkage crack stages. In case of crack area, the primary and secondary stages end at normalized gravimetric water content(NGWC) of 0.92 and 0.70 for different specimen thicknesses respectively. In addition, the primary stage in case of crack length also ends at NGWC of 0.92 while the secondary stage stops at NGWC of 0.79, 0.82, and 0.85 for the sample thicknesses of 0.5, 1.0, and 2.0 cm respectively Based on the experimental results, the distributions of crack length increment and crack area increment appear to be linear with a decrease of NGWC. Therefore, the development of shrinkage cracking is proposed typically by a simple model functioned by a combination of three linear expressions.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4A
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• pp.795-808
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• 2006

In this paper, an analytical method which can predict the occurrence of plastic shrinkage cracking on concrete slabs with sequential placement is proposed on the basis of the numerical model introduced in the previous study. The influence of many design variables on plastic shrinkage cracking such as the number of layers and the time interval between layers is quantitatively analyzed through parametric studies using the analytical method. In advance, two equations are introduced to take into account the effect of sequential placement on the plastic shrinkage cracking of concrete slab; The first one is to calculate the time at which the surface of concrete slab begins to dry, and the second one is to determine the critical time interval to prevent the surface drying of previously placed concrete layers. The timing of curing and the sequence of concrete placement, which are important for the prevention of plastic shrinkage cracking, can be effectively planned using the introduced both equations without any rigorous analysis.

• Journal of Welding and Joining
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• v.5 no.1
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• pp.34-41
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• 1987

To explore the possible application of thermal analysis technique as a probe for finding weld defects, Hydrogen trapping phenomena in Heat Affected Zone (HAZ) of the AISI 5160 spring steel were investigated. HAZ was divided into five parts, which were used as thermal analysis specimens. Two types of trap sites were found in HAZ, ferrite/cementin interface and microvoid. The thermal analysis peak due to the ferrite/cementite interface increased its height toward the weld deposit. The thermal analysis peak due to the microvoid was the highest where the grain size was the smallest. The correspondence between the cold cracking and hydrogen trap nature is also discussed.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.917-920
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• 2008

ECC is a special kind of high performance cementititous composite which exhibits typically more than 2% tensile strain capacity by bridging microcracks at a crack section. Therefore, micromechanics should be adopted to obtain multiple cracking and strain hardening behavior. This paper propose a linear elastic analysis method to simulate the multiple cracking and strain hardening behavior of ECC. In an analysis, the stress-crack opening relation modified considering the orientation of fibers and the number of effective fibers is adopted. Furthermore, to account for uncertainty of materials and interface between materials, the randomness is assigned to the tensile strength(${\sigma}_{fci}$), elastic modulus($E_{ci}$), peak bridging stress(${\sigma}_{Bi}$) and crack opening at peak bridging stress(${\delta}_{Bi}$), initial stress at a crack section due to chemical bonding, (${\sigma}_{0i}$), and crack spacing(${\alpha}_cX_d$). Test results shows the number of cracking and stiffness of cracked section are important parameters and strain hardening behavior and maximum strain capacity can be simulated using the proposed method.

• Advances in concrete construction
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• v.16 no.6
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• pp.277-290
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• 2023

In order to study the mechanical properties of basalt fiber reinforced ultra-fine fly ash concrete (BFUFARC), the effects of ultra-fine fly ash (UFA) content, basalt fiber content, basalt fiber length and water reducing agent content on the compressive strength, splitting tensile strength and flexural strength of the composite material were studied through experimental and theoretical analysis. Also, a scanning electron microscope (SEM) was employed to analyze the mesoscopic structure in the fracture surface of composite material specimens at magnifications of 500 and 3500. Besides, the energy release rate (G_c) and surface free energy (γ_s) of crack tip cracking on BFUFARC in different basalt fiber content were studied from the perspective of fracture mechanics. Further, the cracking resistance, reinforcement, and toughening mechanisms of basalt fibers on concrete substrate were revealed by surface free energy of BFUFARC. The experimental results indicated that basalt fiber content is the main influence factor on the splitting tensile strength of BFUFARC. In case that fiber content increased from 0 to 0.3%, the concrete surface free energy at the tip of single-sided crack showed a trend of increased at first and then decreased. The surface free energy reached at maximum, about 3.59 × 10^-5 MN/m. During the process of increasing fiber content from 0 to 0.1%, G_C-2_γS showed a gradually decreasing trend. As a result, an appropriate amount of basalt fiber can play a preventing cracking role by increasing the concrete surface free energy, further effectively improve the concrete splitting tensile performance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.3
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• pp.445-451
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• 2002

The refractory-lined pipe is used to protect the system from high-temperature of the internal flow. The property of the refractory has an effect upon the stress analysis for fluid catalytic cracking(FCC) unit piping design. The equivalent elastic modulus and density considering steel and refractory must be applied in the stress analysis of the system. In the research, the theoretical method to obtain the value of the equivalent property is introduced and then the parametric analysis is carried out to understand the characteristic of the material properties, and the stress analysis is performed with reactor, the part of FCC unit.

• Computers and Concrete
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• v.11 no.5
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• pp.399-410
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• 2013

A nonlinear finite element analysis of R/C hybrid deep T-beam with web opening subjected to pure torsion is presented. Hexahedral 8-nodes and space truss element were used for modeling concrete and reinforcement. The reinforcement was assumed perfectly bonded to the corresponding nodes of the concrete element. The constitutive relations for concrete and reinforcement are based on the modified field theory and elastic perfectly plastic. The smear crack approach was adopted for modeling the crack. The torque-twist angle relationship curve based on the finite element analysis was compared to the experimental results. The comparison shows that the curve of torque-twist angle predicted by the nonlinear finite element analysis is linear before cracking and close to the experimental result. After cracking, the curve becomes nonlinear and stiffer compared to the experimental result.