• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.6
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• pp.1150-1155
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• 1992

The cooling characteristics of a hot steel plate by a laminar impinging water bar were investigated experimentally. The dynamic parameters investigated were nozzle height L between nozzle and the hot plate, flow rate Q, and initial cooling temperature. Because the boiling phenomena on a hot steel plate are unsteady and change discontinuously, it is difficult to analyze the cooling characteristics directly. In this study the cooling efficiency was estimated by using the temperature decay rates and expansion speed of the water cooling zone. Temperature in the water cooling zone decreased rapidly and the radius of the water cooling zone expanded nearly in proportion to square root of the cooling time. With increasing initial temperature of a hot steel plate, the cooling efficiency became descendent. The cooling curve in the case of L/D = 30 showed the largest temperature decay rate and excellent cooling performance.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.4
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• pp.48-54
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• 2009

The demand for formable high-strength steel (HSS) sheets has recently increased to reduce the weight of automotive bodies. The 340MPa (Tensile Strength) grade steel sheets are widely used for body inner and outer panels. Especially, super formable 340MPa grade steel sheets with high r-value have an excellent deep drawability compared with the other 340MPa grade steel sheets. It is very available for a part such as rear floor, center floor and dash panels used conventional mild steels up to now. We developed a super formable HSS by optimization of chemical composition, texture control and heat treatment control. It has good mechanical properties with excellent formability (tensile strength: 343MPa, elongation: 41.1% and $\bar{r}=2.1$).

• Earthquakes and Structures
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• v.12 no.2
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• pp.201-211
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• 2017

This paper experimentally investigates the effect of yield strength of reinforcing bars and stirrups on the seismic performance of reinforced concrete (RC) circular piers. Reversed cyclic loading tests of nine-large scale specimens with longitudinal and transverse reinforcement of different yield strengths (varying between HRB335, HRB500E and HRB600 rebars) were conducted. The test parameters include the yield strength and amount of longitudinal and transverse reinforcement. The results indicate that the adoption of high-strength steel (HSS) reinforcement HRB500E and HRB600 (to replace HRB335) as longitudinal bars without reducing the steel area (i.e., equal volume replacement) is found to increase the moment resistance (as expected) and the total deformation capacity while reducing the residual displacement, ductility and energy dissipation capacity to some extent. Higher strength stirrups enhance the ductility and energy dissipation capacity of RC bridge piers. While the product of steel yield strength and reinforcement ratio ($f_y{\rho}_s$) is kept constant (i.e., equal strength replacement), the piers with higher yield strength longitudinal bars are found to achieve as good seismic performance as when lower strength bars are used. When higher yield strength transverse reinforcement is to be used to maintain equal strength, reducing bar diameter is found to be a better approach than increasing the tie spacing.

• Structural Engineering and Mechanics
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• v.61 no.6
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• pp.711-719
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• 2017

This study investigates the effects of reinforcing bar diameter and cover depth on the shrinkage behavior of restrained ultra-high-performance fiber-reinforced concrete (UHPFRC) slabs. For this, twelve large-sized UHPFRC slabs with three different rebar diameters ($d_b=9.5$, 15.9, and 22.2 mm) and four different cover depths (h=5, 10, 20, and 30 mm) were fabricated. In addition, a large-sized UHPFRC slab without steel rebar was fabricated for evaluating degree of restraint. Test results revealed that the uses of steel rebar with a large diameter, leading to a larger reinforcement ratio, and a low cover depth are unfavorable regarding the restrained shrinkage performance of UHPFRC slabs, since a larger rebar diameter and a lower cover depth result in a higher degree of restraint. The shrinkage strain near the exposed surface was high because of water evaporation. However, below a depth of 18 mm, the shrinkage strain was seldom influenced by the cover depth; this was because of the very dense microstructure of UHPFRC. Finally, owing to their superior tensile strength, all UHPFRC slabs with steel rebars tested in this study showed no shrinkage cracks until 30 days.

• Journal of Construction Engineering and Project Management
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• v.3 no.2
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• pp.13-20
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• 2013

Construction industry has become a larger and highly competitive industry. A successful construction project cannot be achieved only by efficient and fast construction techniques but also reasonable material cost and adequate transferring time of materials to installation. The steel industry in East Asia has become the mainstream in overall steel industries in over the world during the middle of the 21st century. China, Japan and Korea has been the main exportation countries. However, even though the international economic failure, China has increased the exportation amount and became an only exporting country which must be considered a serious problem regarding competitiveness in the international steel exportation industry. Thus, this study analyses the factors affecting the supply and demand amount of reinforced bars in the domestic field and moreover suggesting a unit cost prediction model using the System Dynamics simulation methodology, one of powerful prediction tools using cause-effect relationships. It is expected that this study contributes to the domestic steel industry growth in competitiveness in the international industry. In addition, the methodology used in this paper presents the frameworks for appropriate tools for market trend analysis and prediction of other markets.

• Journal of Korean Society of Steel Construction
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• v.12 no.4 s.47
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• pp.445-455
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• 2000

This study proposed to beam-column joint model consisting of different type structural member to develop new structural system in the structural viewpoint as to a method to overcome various problem according to change of construction environment. This study promoted rigidity and capacity to stiffen reinforced concrete for steel structure end to increase rigidity of long spaned steel beam, and welt to steel flange to anchor U-shaped main bar of SRC structure end to easy stress flow between the different type structure. Through the series of experiments, proposed to possibility of this joint model, and investigated joint rigidity and capacity.

• Steel and Composite Structures
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• v.27 no.2
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• pp.243-253
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• 2018

In recent years, concrete-filled box or tubular columns have been commonly used in high-rise buildings. However, a number of fire test results show that there are significant differences between high strength concrete (HSC) and normal strength concrete (NSC) after being subjected to high temperatures. Therefore, this paper presents an investigation on the fire resistance of HSC filled steel tubular columns (CFTCs) under combined temperature and loading. Two groups of full-size specimens were fabricated to consider the effect of type of concrete infilling (plain and reinforced) and the load level on the fire resistance of CFTCs. Prior to fire test, a constant compressive load (i.e., load level for fire design) was applied to the column specimens. Thermal load was then applied on the column specimens in form of ISO 834 standard fire curve in a large-scale laboratory furnace until the set experiment termination condition was reached. The results demonstrate that the higher the axial load level, the worse the fire resistance. Moreover, in the bar-reinforced concrete-filled steel tubular columns, the presence of rebars not only decreased the spread of cracks and the sudden loss of strength, but also contributed to the load-carrying capacity of the concrete core.

• KCI Concrete Journal
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• v.11 no.3
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• pp.181-189
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• 1999

An experimental study was performed on the Pull-out behavior of 90-deg standard hooks from the exterior beam-column connections. the effects of the number of hooked bars and fiber reinforcement of the joint area were investigated with the following conclusions : (1) Under the pull-out action of hooked bars. the damage and cracking of joint area the number of hooks pulling out from a joint increases; (2) Substitution of the transverse column (confining) reinforcement with steel fibers at the joint region effectively reduces the extent of cracking in exterior joints caused by the pull-out of hooked bars; (3) The pull-out strength and post-peak ductility of hooked bars are adversely influenced by the increase in number of hooks pulling out from an exterior joint. Current hooked bar anchorage design guidelines may be improved by considering the effect of the number of hooked bars on anchorage conditions at the exterior joints; and (4) The strength and ductility of hooked bars under pull-out forces are positively influenced by substituting the conventional confining reinforcement of exterior joints with steel fibers . The application of steel fibers to the exterior joints is an effective technique for improving the anchorage conditions of hooked bars, and also for reducing the congestion of reinforcement in the beam-column connections.

• Journal of Korea Foundry Society
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• v.22 no.3
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• pp.137-143
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• 2002

Silica sand, zircon sand, and steel shots were used as mold packing materials in lost foam casting of the aluminum alloy bar. Vibration acceleration in three directions and temperatures in the casting and mold were measured, and packing and cooling characteristics of these materials were investigated. Packing densities increased with increase in vibration magnitude and time, and were $1.41{\sim}1.49g/cm^2$ for silica sand, $2.54{\sim}2.86g/cm^2$ for zircon sand, and $3.92{\sim}4.52g/cm^2$ for steel shots. Sound castings were obtained only without evacuation of the flask during pouring. Solidification time became faster in order of silica sand, zircon sand and steel shot packing because steel shot has the highest cooling capacity of them. Solidification time of steel shot packing was shortened to about 1/2 of silica sand packing. Cooling capacity of sand mold was generally evaluated by heat diffusivity of the mold, however could be simply evaluated with specific heat per unit volume of the packing material in lost foam casting.

• Computers and Concrete
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• v.24 no.3
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• pp.237-247
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• 2019

The key issue for the finite element analysis (FEA) of section steel reinforced concrete (SRC) structure is how to consider the bond-slip performance. However, the bond-slip performance is hardly considered in the FEA of SRC structures because it is difficult to achieve in the finite element (FE) model. To this end, the software developed by Python can automatically add spring elements for the FE model in ABAQUS to considering bond-slip performance. The FE models of the push-out test were conducted by the software and calculated by ABAQUS. Comparing the calculated results with the experimental ones showed that: (1) the FE model of SRC structure with the bond-slip performance can be efficiently and accurately conducted by the software. For the specimen with a length of 1140 mm, 3565 spring elements were added to the FE model in just 6.46s. In addition, different bond-slip performance can also be set on the outer side, the inner side of the flange and the web. (2) The results of the FE analysis were verified against the corresponding experimental results in terms of the law of the occurrence and development of concrete cracks, the stress distribution on steel, concrete and steel bar, and the P-S curve of the loading and free end.