• Steel and Composite Structures
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• v.38 no.6
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• pp.617-635
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• 2021

This paper numerically investigated the behavior of built-up square concrete-filled steel tubular (CFST) columns under combined preload and axial compression. The finite element (FE) models of target columns were verified in terms of failure mode, axial load-deformation curve and ultimate strength. A full-range analysis on the axial load-deformation response as well as the interaction behavior was conducted to reveal the composite mechanism. The parametric study was performed to investigate the influences of material strengths and geometric sizes. Subsequently, influence of construction preload on the full-range behavior and confinement effect was investigated. Numerical results indicate that the axial load-deformation curve can be divided into four working stages where the contact pressure of curling rib arc gradually disappears as the steel tube buckles; increasing width-to-thickness (B/t) ratio can enhance the strength enhancement index (e.g., an increment of 1.88% from B/t=40 to B/t=100), though ultimate strength and ductility are decreased; stiffener length and lip inclination angle display a slight influence on strength enhancement index and ductility; construction preload can degrade the plastic deformation capacity and postpone the origin appearance of contact pressure, thus making a decrease of 14.81%~27.23% in ductility. Finally, a revised equation for determining strain εscy corresponding to ultimate strength was proposed to evaluate the plastic deformation capacity of built-up square CFST columns.

• Advances in materials Research
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• v.11 no.4
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• pp.251-277
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• 2022

Disposal of industrial waste in cities where municipal authorities permitting higher floor area ratio coupled with increasing living standards, a lot of demolition waste is being generated. Its disposal is a challenge particularly in megacities where no landfills are available. The ever-increasing cost of building construction materials also necessitates consuming demolition wastes in a useful manner to save fresh natural raw materials. In the present work, the crushed waste glass is used in high-strength concrete as a partial replacement of fine aggregate. The control concrete of grade M60 was proportioned following BIS 10262-2009. The crushed waste glass has been used as a partial replacement with varying percentages of 10, 20, 30, and 40% by weight of fine aggregate. Experimental tests were carried on the fresh and hardened state of the concrete. The effect of crushed waste glass on the workability of the concrete has been investigated. Non-destructive tests, acid attack tests, compressive strength, split tensile strength, and X-ray diffraction analysis was carried out for the control concrete and concrete containing crushed waste glass after 7, 28, and 270 days of normal curing. The results show that for the same w/c ratio, the workability of concrete increases with increasing replaced crushed waste glass content. However, the decrease in compressive strength of the concrete after 28 days of normal curing and further after 28 days of acid attacks, up to 30% replacement level of fine aggregate by the crushed waste glass is insignificant.

• Journal of the Korea Safety Management & Science
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• v.25 no.3
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• pp.31-36
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• 2023

The use of hanging scaffolding for exterior wall painting and cleaning in building construction and maintenance carries the inherent risk of fall accidents. While periodic rope replacement is crucial for preventing accidents resulting from rope breakage, current regulations lack specificity in determining appropriate disposal period for fiber ropes. This study analyzed the tensile strength of the most commonly used PP fiber ropes with different diameters (16 mm, 20 mm) in the domestic construction industry. Additionally, the effect of outdoor exposure was examined by measuring the tensile strength of new ropes and ropes exposing to outdoor conditions for 30 days and 90 days. The results showed that the new ropes and those exposed to outdoor for 30 days met the KS (Korean Standards) criteria for tensile strength. However, a significant decrease in tensile strength was observed in ropes exposed to outdoor for 90 days compared to both the new ropes and those exposed for 30 days. Furthermore, the ropes exposed for 90 days did not meet the KS criteria. These findings indicate the degradation of PP fiber ropes due to UV (Ultra Violet) radiation, highlighting the importance of considering this factor when determining the replacement period for fiber ropes used in scaffolding work.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.189-190
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• 2021

Recently, the spread of intense social distancing and untact culture due to COVID-19 has increased the time spent indoors. In addition, according to the International Cancer Institute, fine dust was classified as a first-class carcinogen, a substance found to be carcinogenic, such as asbestos and benzene. As a result, interest in indoor air quality is increasing, and many studies are underway to reduce air pollutants. This study is a basic experiment of a board made to improve indoor air quality. The basic characteristics of the board, flexural strength and compressive strength, are analyzed and the results of the test are as follows. Experiments have shown that flexural strength and compressive strength tend to decrease as the replacement rate of hydrocarbons increases. It is believed that the strength of the sludge has decreased due to the increase in internal voids due to the increase in non-surface area, volume and diameter of microfiber as it undergoes the carbonation process. In addition, it is believed that the amount of moisture needed for curing during the mixing process was reduced due to the absorption of hydrocarbons.

• Transactions of Materials Processing
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• v.31 no.3
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• pp.117-123
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• 2022

In this study, a commercial AZ61 magnesium alloy is extruded at 300 ℃ and 400 ℃ and the microstructures, mechanical properties, and high-cycle fatigue properties of the extruded materials are investigated. Both extruded materials have a fully recrystallized microstructure with no Mg₁₇Al₁₂ precipitates. The average grain size and maximum basal texture intensity of the extruded material increase with increasing extrusion temperature. The material extruded at 400 ℃ (AZ61-400) has higher tensile yield strength and lower compressive yield strength than the material extruded at 300 ℃ (AZ61-300) because of the stronger basal texture of the former. Because of coarser grain size, the tensile elongation of AZ61-400 is lower than that of AZ61-300. Despite the differences in microstructures and tensile/compressive properties, the two extruded materials have the same fatigue strength of 110 MPa. This is because the finer grain size of AZ61-300 causes an increase in fatigue strength, but its weaker texture causes a decrease in fatigue strength. In both extruded materials, fatigue cracks initiate at the surface of fatigue specimens at all stress amplitudes tested.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.309-310
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• 2023

Slag and ash generally have a higher powder degree than portland cement, so workability may deteriorate under the same unit quantity condition, and strength and durability decrease when the unit quantity is increased. At this time, if an aggregate having a low water absorption and an appropriate particle size is used to recover the loss of strength, it can contribute to reducing the unit quantity of the binder. Therefore, for the purpose of improving the workability and strength of non-sintered cement mortar using slag and ash, ferro nikel slag whose particle size was adjusted was used as an aggregate and its applicability was identified. In this experimental condition, it was confirmed that non-sintered cement mortar tends to improve workability and secure strength when ferro nikel slag having various particle size distributions is used as an aggregate. This can be analyzed as the effect of ferro nikel slag material properties including glassy properties and mixing conditions with a wide particle size distribution.

• Textile Coloration and Finishing
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• v.35 no.4
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• pp.189-195
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• 2023

In this study, as one of the eco-friendly dyeing methods, indigo, Phellodendron amurense and Caeasapinia sappan were complexed dyed on cotton fabric. For complexed dyeing, the cotton that was pre-dyed 5 times with indigo was dyed 1 ~ 2 times repeatedly with Phellodendron amurense and Caeasapinia sappan. Then the color, tensile strength, density, and color fastness of complexed dyed sample were analyzed and the following analysis results could be obtained. As a result of color difference measurement, the L* value was 22.7 in the sample in which the cotton was dyed 5 times and then the Phellodendron amurense was dyed 1 time, and the K/S value was 15 or higher in all samples. As a result of measuring the strength, cotton fabrics tended to have a slight decrease in tensile strength when complexed dyeing. As a result of measuring the density, the density decreased by 15 ~ 20% in all samples at the warp and increased by 20 ~ 30% in the weft due to the complexed dyeing of cotton fabric. Moreover, the fastness to washing and drycleaning showed good results of 2 ~ 3 or higher, and the light fastness was 4 or higher.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.11a
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• pp.181-182
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• 2023

This study is a study on the flexural adhesion performance of polymer cement composites(PCCs) repair section according to the crack depth, and the flexural adhesion strength was obtained through a flexural strength test of cement mortar that was filled into cracks and repaired to a certain thickness using PCCs made of ultra high-early strength cement and polymer dispersion of EVA. As a result of the study, the flexural adhesion performance according to the crack width and crack depth was expected to decrease the flexural adhesion strength as the crack depth increased at the crack width 3.0mm, but the crack width 2.0mm and 1.5mm did not show any tendency according to the crack depth. In addition, even in the final destruction, the fact that the cracks and bottoms filled with PCCs were not cut or dropped proves that PCCs have excellent adhesion and rich toughness.

• Advances in materials Research
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• v.1 no.2
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• pp.147-160
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• 2012

In the present study, diffusion bonding was carried out between AZ31B magnesium and AA2024 aluminium in the temperature range of $405^{\circ}C$ to $475^{\circ}C$ for 15 min to 85 min and 5MPa to 20 MPa uniaxial loads was applied. Interface quality of the joints was assessed by microhardness and shear testing. Also, the bonding interfaces were analyzed by means of optical microscopy, scanning electron microscopy, energy dispersive spectrometer and XRD. The maximum bonding and shear strength was obtained at $440^{\circ}C$, 12 MPa and 70 min. The maximum hardness values were obtained from the area next to the interface in magnesium side of the joint. The hardness values were found to decrease with increasing distance from the interface in magnesium side while it remained constant in aluminium side. It was seen that the diffusion transition zone near the interface consists of various phases of $MgAl_2O_4$, $Mg_2SiO_4$ and $Al_2SiO_5$.

• Design & Manufacturing
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• v.9 no.1
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• pp.27-30
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• 2015

The injection molding is used in more than 70% of total production of plastic products. Weld line in injection molded part is one of the defects in injection molding process. Weld line deteriorates not only appearance quality but also mechanical property. In this study, tensile strength about material such as ABS, PP, PA and PS was tested. as the results, the first result appears that weld's strength retention ratio's are 0.90, 0.84, 0.85, 0.76 and the second result apeears that weld depth decrease as processing temperature increased.