• Computers and Concrete
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• v.8 no.1
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• pp.23-41
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• 2011

The behaviour of concrete confined by transverse reinforcement is a classical topic. Numerous studies have been conducted to establish the stress-strain relationships for concrete under various confining reinforcement arrangements. Many empirical and semi-empirical formulas exist. Simplified analytical models have also been proposed to evaluate the increase in the strength and ductility of confined concrete. However, relatively few studies have been conducted to utilise advanced computational models for a realistic simulation of the behaviour of concrete confined by transverse reinforcement. As a matter of fact, high fidelity simulations using the latest numerical solvers in conjunction with advanced material constitutive models can be a powerful means to investigating the mechanisms underlying the confining effects of different reinforcement schemes. This paper presents a study on the use of high fidelity finite element models for the investigation of the behaviour of concrete confined by stirrups, as well as the interpretation of the numerical results. The development of the models is described in detail, and the essential modelling considerations are discussed. The models are then validated by simulating representative experimental studies on short columns with different confining reinforcement schemes. The development and distribution of the confining stress and the subsequent increase in the axial strength are examined. The models are shown to be capable of reproducing the behaviour of the confined concrete realistically, paving a way for systematic parametric studies and investigation into complicated confinement, load combination, and dynamic loading situations.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.7
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• pp.185-197
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• 1996

We have adopted the strain compensated PBH(planar buried heterostructure) - LD in which the MQW active layer consisted of 1.4% compressively strained GainAsP (E$_{g}$ = 0.905eV) wells and 0.7% tensile strained GaInAsP(E$_{g}$ = 1.107eV) barriers grown by metal organic vapor phase epitaxy (MOVPE). We hav einvestigated effects of number of wells and the structure of the separate confinement heterostructure (SCH) layer in the strain-compensated MQW-PBH-LD. The threshold current, the external quantum efficiency, the transparency current density J$_{o}$, and the gain constant .beta. have been evaluated for uncoated MQW-PBH-LD. As the number of wells increases, the internal quantum efficiency and the transparency current density decreases, whereas the gain contant increases. The small width of the SCH layer shows the large internal quantum efficiency. The small internal loss and the large gain constant have been obtained by inserting the large bandgap SCH layer.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.5
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• pp.112-119
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• 2015

In this paper, the strengthening method was proposed for improving the seismic performance of the vulnerable structural frames. To improve the brittle characteristics of columns, aramid fiber sheet was used for the lateral confinement of columns. And to introduce the energy dissipation capacity, a steel damper with S-shaped struts was installed. By making the unreinforced and reinforced specimens with full size specimens were evaluated for lateral load resistance capacity. It was confirmed the strengthening effects by the evaluation of failure shape, strength, stiffness degradation, and energy dissipation capacity. Also from the FE analysis using ABAQUS, the hysteretic behavior of the specimens were predicted and evaluated.

• Structural Engineering and Mechanics
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• v.18 no.2
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• pp.167-194
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• 2004

In this paper axial loading tests on low strength concrete members, which were confined with various thickness of carbon fiber reinforced polymer (CFRP) composite sheets are described. Totally 46 specimens with circular, square and rectangular cross-sections with unconfined concrete compressive strengths between 6 and 10 MPa were included in the test program. During the tests, a photogrammetrical deformation measurement technique was also used, as well as conventional measurement techniques. The contribution of external confinement with CFRP composite sheets to the compressive behavior of the specimens with low strength concrete is evaluated quantitatively, in terms of strength, longitudinal and lateral deformability and energy dissipation. The effects of width/depth ratios and the corner radius of the specimens with rectangular cross-section on the axial behavior were also examined. It was seen that the effectiveness of the external confinement with CFRP composite sheets is much more pronounced, when the unconfined concrete compressive strength is relatively lower. It was also found that the available analytical expressions proposed for normal or high strength concrete confined by CFRP sheets could not predict the strength and deformability of CFRP confined low strength concrete accurately. New expressions are proposed for the compressive strength and the ultimate axial strain of CFRP confined low strength concrete.

• Advances in concrete construction
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• v.5 no.5
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• pp.539-561
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• 2017

In this study, the effects of initial damage of concrete columns on the post-repair performance of reinforced concrete (RC) columns strengthened with carbon-fiber-reinforced polymer (CFRP) composite are investigated experimentally. Four kinds of compression-damaged RC cylinders were reinforced using external CFRP composite wraps, and the stress-strain behavior of the composite/concrete system was investigated. These concrete cylinders were compressed to four pre-damaged states including low -level, medium -level, high -level and total damage states. The percentages of the stress levels of pre-damage were, respectively, 40, 60, 80, and 100% of that of the control RC cylinder. These damaged concrete cylinders simulate bridge piers or building columns subjected to different magnitudes of stress, or at various stages in long-term behavior. Experimental data, as well as a stress-strain model proposed for the behavior of damaged and undamaged concrete strengthened by external CFRP composite sheets are presented. The experimental data shows that external confinement of concrete by CFRP composite wrap significantly improves both compressive strength and ductility of concrete, though the improvement is inversely proportional to the initial degree of damage to the concrete. The failure modes of the composite/damaged concrete systems were examined to evaluate the benefit of this reinforcing methodology. Results predicted by the model showed very good agreement with those of the current experimental program.

• Asian-Australasian Journal of Animal Sciences
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• v.32 no.8_spc
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• pp.1296-1305
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• 2019

There have been recent advances concerning research of the feeding and nutrition of dairy goats in a wide array of areas. Ruminally emitted methane and supplementary feedstuffs to a lesser extent make appreciable contributions to the carbon footprint of dairy goats, with the former affected by type of production system and associated dietary characteristics. Unique behavior of goats necessitates careful consideration of the nature of confinement facilities to achieve optimal production by animals differing in social hierarchy. Physiological conditions such as nutritional needs and perhaps health status may influence diet selection by goats in both grazing and confinement settings. Some research suggests that low concentrations of protein and fat in milk of high-yielding dairy goat breeds could involve the type and nature of dietary ingredients as influencing end products of ruminal fermentation. With the relationship between milk urea nitrogen concentration and efficiency of dietary protein utilization, through future research the measure may be a useful tool for diet formulation as in dairy cattle. Effects of dietary inclusion of sources of fats and oils vary considerably depending on their nature, as is also true for byproduct feedstuffs and conventional ones being substituted for. Supplementation of dairy goats with sources of polyunsaturated fatty acids can affect oxidative stress and various feedstuffs influence antioxidant status; however, research addressing the significance of such changes under practical production settings would be beneficial.

• Structural Engineering and Mechanics
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• v.77 no.6
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• pp.705-720
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• 2021

Reinforced concrete (RC) columns are the primary type of vertical support used in building structures that sustain vertical loads. However, their strength may be insufficient due to fire, earthquake or volatile environments. The load demand may be increased due to new functional usages of the structure. The deformability of concrete columns can be greatly reduced under high axial load conditions. In response, a novel steel encasement that distinguishes from the traditional steel jacketing that is assembled by welding or bolt is developed. This novel strengthening method features easy installation and quick strengthening because direct fastening is used to connect the four steel plates surrounding the column. This new connection method is usually used to quickly and stably connect two steel components by driving high strength fastener into the steel components. The connections together with the steel plates behave like transverse reinforcement, which can provide passive confinement to the concrete. The confined column along with the steel plates resist the axial load. By this way, the axial load capacity and deformability of the column can be enhanced. Eight columns are tested to examine the reliability and effectiveness of the proposed method. The effects of the vertical spacing between adjacent connections, thickness of the steel plate and number of fasteners in each connection are studied to identify the critical parameters which affect the load bearing performance and deformation behavior. Lastly, a theoretical model is proposed for predicting the axial load capacity of the strengthened RC columns.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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• pp.409-416
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• 2000

This research aims at evaluating the seismic performance of the existing R/C bridge piers which were nonseismically or seismically designed in accordance with the provision of Korea Highway Design Specification. Further experimental investigations have been doing to figure out the retrofitting effects of nonseismic R/C bridge piers confined with glass fiber at the plastic hinge zone. Pseudo-dynamic tests have been carried out on nine scaled R/C column specimens to investigate their hysteretic behavior under earthquake loading, Test parameters are axial load input ground motion confinement steel ration glass fiber and etc,

• Proceedings of the Korea Concrete Institute Conference
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• 1999.10a
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• pp.521-524
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• 1999

Twelve column specimens were tested in compression, six were slab-column specimens and six were isolated column specimens. The slab column specimens were first tested to punching shear failure before the columns of the specimens were loaded axially. The effects of confinement from the surrounding slab on the axial capacity of the columns was investigated. Other parameters investigated were the placement of fiber-reinforced concrete in the slab and the concentration of flexural reinforcement in the column vicinity.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.39-42
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• 2003

We studied the vertical launch performance of the Laser-driven In-Tube Accelerator (LITA). This device is primarily characterized by accelerating a projectile in a tube. Owing to the confinement effect, the thrust performance is enhanced. The driver gas can be specified and its pressure be turned so that the impulse performance is optimized. In the experiments, a 3.0-gram projectile was vertically launched. The effects of the projectile exit condition, the laser beam incident direction and the driver gas species were experimentally studied.