• Structural Engineering and Mechanics
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• v.84 no.1
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• pp.101-111
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• 2022

It is widely known that axially loaded fiber-reinforced polymer (FRP) confined concrete presents significant and enhanced mechanical properties with reference to the unconfined concrete. Therefore, to predict the mechanical behavior of FRP-confined concrete two quantities-peak strength and ultimate strain are required. Despite the significant advances, the determination of the ultimate strain of FRP-confined concrete is one of the most challenging problems to be resolved. This is often attributed to our persistence in desiring the conventional methods as the sole technique to examine this phenomenon and the complex nature of the ultimate strain of FRP-confined concrete. To bridge the research gap, this study adopted two machine learning (ML) techniques-artificial neural network (ANN) and Gaussian process regression (GPR)-to analyze observations obtained from 627 datasets of FRP-confined concrete circular and non-circular sections under axial loading test. Besides, the techniques are also used to predict the ultimate strain of FRP-confined concrete. Seven parameters namely width/diameter of the specimens, corner radius ratio, the strength of concrete, FRP elastic modulus, FRP thickness, FRP tensile rupture strain, and the axial strain of unconfined concrete-are the input parameters used to predict the ultimate strain of FRP-confined concrete. The results of the current study highlight the merit of using AI techniques in structural engineering applications given their extraordinary ability to comprehend multidimensional phenomena of FRP-confined concrete structures with ease, low computational cost, and high performance over the existing empirical models.

• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.4
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• pp.295-306
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• 2010

Contrary to an intact rock, the jointed rock mass shows strain-dependent deformation characteristics (elastic modulus and damping ratio). The maximum elastic modulus of a rock mass can be obtained from an elastic wave-based exploration in a small strain level and applied to seismic analyses. However, the assessment and application of the non-linear characteristics of rock masses in a small to medium strain level ($10^{-4}{\sim}0.5%$) have not been carried out yet. A non-linear dynamic analysis module is newly developed for FLAC3D to simulate strain-dependent shear modulus degradation and damping ratio amplification characteristics. The developed module is verified by analyzing the change of the Ricker wave propagation. Strain-dependent non-linear characteristics are obtained from disks of cored samples using a rock mass dynamic testing apparatus which can evaluate wave propagation characteristics in a jointed rock column. Using the experimental results and the developed non-linear dynamic module, seismic analyses are performed for the intersection of a shaft and an inclined tunnel. The numerical results show that vertical and horizontal displacements of non-linear analyses are larger than those of linear analyses. Also, non-linear analyses induce bigger bending compressive stresses acting on the lining. The bending compressive stress concentrates at the intersection part. The fundamental understanding of a strain-dependent jointed rock mass behavior is achieved in this study and the analytical procedure suggested can be effectively applied to field designs and analyses.

• Korean Journal of Poultry Science
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• v.41 no.1
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• pp.69-75
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• 2014

This study was carried out to investigate the performance of laying period of A and B strains of Korean native ducks (KND). One hundred sixty eight ducks were used in this work and divided into A and B strains (6 replications/strain, 14 birds/replication). Ducks were fed with laying ducks' feedstuff (CP 15%, ME 2,900 kcal/kg) for the age of 20~80 wk old. There was no significant difference on body weight, feed intake and egg weight between A and B strains. Weekly body wt of KNDs was the lowest at the age of 40~48 wk old, and that of those was high at the age of 24~32 wk and 64~80 wk old (P<0.05). Weekly feed intake significantly decreased at the age of 36~48 wk and 68~72 wk old (P<0.05), but there was no significant difference at the age of 52~56 wk old. Weekly egg wt was the lowest at the age of 32~40 wk old. Egg production ratio of B strain was higher compared to that of A strain at the age of 24~28 wk, 60~64 wk and 20~80 wk old. Weekly egg production ratio was the highest at the age of 28~32 wk old, and was high maintained until the age of 48 wk old. However, weekly egg production ratio decreased from the age of 52 wk old to the age of 68 wk old. Number of egg of B strain (267.5) was higher than that of A strain (235.6) at the age of 20~80 wk old. There was no significant difference on feed conversion ratio between A and B strain at the age of 28~36 wk old, but feed conversion ratio of A strain was higher than that of B strain at the other weeks (P<0.05). These results provided the basic data on the record of laying period of Korean native ducks.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.4
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• pp.13-20
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• 2024

In this study, when subjected to in-plane shear such as a shear wall, the behavior characteristics of a concrete member using CFRP rebars were investigated when the longitudinal reinforcement ratio was kept constant at 2.96% and the transverse reinforcement ratio was changed from 0.30 to 2.98%. The evaluation was conducted based on MCFT theory and analyzed by comparison with the case of concrete members using steel rebars. When the reinforcement ratio ranged from 0.30 to 1.19%, concrete members employing CFRP rebars exhibited higher shear strength compared to those using steel rebars. In contrast, at high reinforcement ratios of 1.79 and 2.98%, it was observed that the shear strength of the member with CFRP rebar was lower compared to the member with steel rebar. Maximum shear strain was observed to be higher for members reinforced with steel rebars at lower reinforcing bar ratios, while for ratios of 0.97% and above, CFRP rebars resulted in higher maximum shear strain. As the reinforcement ratio increases, the use of CFRP rebar instead of steel rebar results in a greater increase in maximum shear strain. By analyzing the difference in strain in the reinforcing bar as well as the difference in principal strain in the element caused by differences in the mechanical properties of the steel rebar and CFRP rebar, the shear strength and shear strain when using steel rebar and CFRP rebar with different reinforcement ratios can be compared and analyzed.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1115-1122
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• 1993

Several yield criteria for porous materials are compared with each other, defining the apparent yield stress as the yield stress of the porous material in simple compression. It was found that the plastic Poisson's ratio is the parameter needed to define the yield criterion, rather than the relative density. The plastic Poisson's ratio is regarded as a material characteristic that is obtained from a simple compression test. A new form of yield criterion was suggested, and it was applied to hydrostatic compression as well as uniaxial strain compression of sintered Al-2024 powder. The crossover point in the mean stress vs volume change curves of the processes was predicted. It is presented that the flow stress of the fully densed material can be obtained from that of the porous material using relations obtained from the yield criterion.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.67-72
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• 2002

The purpose of this study is to investigate on the measurement of stress due to autogenous shrinkage of high strength concrete according to the W/C ratio at early age. The main parameters are as follows W/C ratio is 25, 30, 40%. The size of specimen is 10$\times$10$\times$150cm and the autogenous shrinkage strain is measured by the bonded strain gauge at the inside of the specimens. From the test, it is suggested that the autogenous shrinkage stress increased as W/C ratio decreased.

• Transactions of Materials Processing
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• v.12 no.3
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• pp.244-250
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• 2003

Sheets of aluminum alloy 1100 were asymmetrically cold rolled in a rolling mill with different roll speeds. In order to promote the shear deformation during asymmetrical rolling, cold rolling without lubrication was performed with a roll speed ratio of 1.5/l.0. The evolution of texture components during asymmetrical rolling was investigated by the calculation of the orientation distribution function (ODF) using the monoclinic sample symmetry. The strain state during asymmetrical rolling was tackled by means of FEM calculations. Asymmetrical rolling gave rise to the development of pronounced strain gradients throughout the thickness layers which resulted in the formation of strong texture gradients in the aluminum sheet.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.50-53
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• 2006

An experimental investigation on the behavior of reinforced concrete coupling beams is presented. The test variables are the span-to-depth ratio, the ratio of flexural reinforcement and the ratio of shear rebar. The distribution of arch action and truss action which compose the mechanism of shear resistance is discussed. This study proposes the deformation model for reinforced concrete coupling beams considering the bond slip of flexural reinforcement. The yielding of flexural reinforcements determines yielding states and the ultimate states of reinforced concrete coupling beam are defined as the ultimate compressive strain of struts and the degradation of compressive strength due to principal tensile strain of struts. It is expected that this model can be applied to displacement-based design methods.

• International Journal of Concrete Structures and Materials
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• v.9 no.4
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• pp.463-473
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• 2015

Three full-scale instrumented test slabs were constructed and tested using a heavy vehicle simulator (HVS) to evaluate the structural behavior of internally cured concrete (ICC) for use in pavements under Florida condition. Three mix designs selected from a previous laboratory testing program include the standard mixture with 0.40 water-cement ratio, the ICC with 0.32 water-cement ratio, and the ICC mixture with 0.40 water-cement ratio. Concrete samples were prepared and laboratory tests were performed to measure strength, elastic modulus, coefficient of thermal expansion and shrinkage properties. The environmental responses were measured using strain gages, thermocouples, and linear variable differential transformers instrumented in full-scale concrete slabs. A 3-D finite element model was developed and calibrated using strain data measured from the full-scale tests using the HVS. The results indicate that the ICC slabs were less susceptible to the change of environmental conditions and appear to have better potential performance based on the critical stress analysis.

• Journal of Welding and Joining
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• v.23 no.3
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• pp.34-39
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• 2005

It is required for the steel materials used in the sour environment to have sufficient resistance to hydrogen induced cracking(HIC). For line pipe steels, HIC resistance could be varied during pipe making process due to the large plastic deformation applied in the thick-wall pipe. In order to figure out such effect, HIC tests were performed not only in the plate condition but in the pipe condition and their results were compared in terms of cracking ratio. Test results demonstrated a detrimental effect of plastic deformation to HIC resulting in a substantial increase in the cracking ratio after pipe forming process. All of the cracks found in the pipe material were located in the outer layer of pipe where the tensile strain was resulted during pipe forming stage. In order to understand the HIC resistance of the pipe but in the plate condition, it was suggested to pre-strain the plate to some extent before the HIC test.