Heecheul Kim

3-Aminopropyltriethoxysilane Effect on Thermal and Mechanical Properties of Multi-walled Carbon Nanotubes Reinforced Epoxy Composites

Diglycidyl ether of bisphenol A nanocomposites with unmodified multi-walled carbon nanotubes (u-MWCNTs) and silanized multi-walled carbon nanotubes (si-MWCNTs) were prepared by cast molding method. The effects of 3-aminopropyltriethoxysilane functionalization of MWCNTs on the thermal and mechanical properties of the nanocomposites were examined. The nanocomposites were characterized by thermogravimetric analysis, dynamic mechanical thermal analysis, and flexural testing. The results showed that epoxy composites based on si-MWCNTs showed better thermal stability, glass transition temperature, and flexural properties than the composites based on u-MWCNTs. These results prove the effect of silane functionalization on the interfacial adhesion between epoxy and MWCNTs. This was further confirmed by morphology study of fractured surfaces of nanocomposites by scanning electron microscopy.

Thermal and Mechanical Properties of Epoxy/Carbon Fiber Composites Reinforced with Multi-walled Carbon Nanotubes

Multi-scale hybrid composite laminates of epoxy/carbon fiber (CF) reinforced with multi-walled carbon nanotubes (MWCNTs) were fabricated in an autoclave. For laminate fabrication, 0.5 wt% of pristine MWCNTs or silane-functionalized MWNCTs (f-MWCNTs) were dispersed into a diglycidyl ether of bisphenol-A epoxy system and applied on the woven carbon fabric. The neat epoxy/CF composite and the MWCNTs-reinforced epoxy/CF hybrid composites were characterized by thermogravimetric analysis (TGA), thermomechanical analysis (TMA), tensile testing, and field emission scanning electron microscopy (FE-SEM). A significant improvement in initial decomposition temperature and glass transition temperature of epoxy/CF composite was observed when reinforced with 0.5 wt% of f-MWCNTs. The coefficient of thermal expansion (CTE), measured by TMA, diminished by 22% compared to the epoxy/CF composite, indicating an improvement in dimensional stability of the hybrid composite. No significant improvement in tensile properties of either MWCNTs/epoxy/CF composites was observed compared to those of the neat epoxy/CF composite.

An Experimental Study on Shear Behaviors for Reinforced Concrete Beams Embedded with GFRP Plate with Openings

Architectural Engineering, Kyung Hee University, Yongin 446-701,KoreaABSTRACT The purpose of this study is to experimentally investigate the shear behavior of reinforced concrete beams embed-ded with GFRP (glass fiber reinforced polymer) plate with openings. In this study, the parameters include the shape of rein-forcement, reinforcement area, and thickness and width of reinforcements. The test was performed on 9 specimens with shear span-to-depth ratio of 2.8. When the reinforcement area was varied, the GFRP plate showed 3.6 times greater shear strength than steelstirrup. The test result showed that shear strength increased as reinforcement area increased. Also, when the shape of a par-allelogram GFRP plate was used, it showed higher shear strength than that with rectangular shape. Effect of thickness and widthof reinforcement showed that shear capacity increased as width increased. For a comparison study, a calculation of the shearstrength of reinforced beams with GFRP plate based on the ACI 318M-08 was compared with the test results. The test results werecompared with the maximum shear reinforcement areas required by ACI 318M-08, CSA-04, and EC2-02 provision.Keywords : GFRP, stirrup, reinforced concrete beam, maximum shear reinforcement

Thermal and Tensile Properties of Epoxy Nanocomposites Reinforced by Silane-functionalized Multiwalled Carbon Nanotubes

Epoxy nanocomposites with unmodified multiwalled carbon nanotubes (u-MWCNTs) and silanized multiwalled carbon nanotubes (si-MWCNTs) were prepared by a cast molding method. The effects of 3-aminopropyltriethoxysilane functionalization of MWCNTs on thermal, tensile, and morphological properties of the nanocomposites were examined. The nanocomposites were characterized by thermogravimetric analysis, dynamic mechanical thermal analysis, and tensile testing. The results showed that epoxy composites based on si-MWCNTs showed better thermal stability, glass transition temperature, and tensile properties than the composites based on u-MWCNTs. These results prove the effect of silane functionalization on the interfacial adhesion between epoxy and MWCNTs. This was further confirmed by morphology study of fractured surfaces of nanocomposites by field emission scanning electron microscopy.

Experimental study on bond strength of fiber reinforced polymer rebars in normal strength concrete

The bond behavior of reinforcing bars is an important issue in the design of reinforced concrete structures and the use of fiber reinforced polymer (FRP) rebars is a promising solution to handle the problems of steel reinforcement corrosion. This study investigates the bond characteristics of carbon and aramid FRP (CFRP and AFRP) bars embedded in normal strength concrete. A pullout test was performed on 63 normal strength concrete specimens reinforced with FRP and steel rebars with different embedment lengths and bar diameters. The average bond stress versus slip curve is plotted for all specimens and their failure modes are identified. The effects of the embedment length and diameter of an FRP rebar on its bond strength are examined in this work. The bond strengths obtained from the test results are compared with the predictions by the bond strength equation proposed by Okelo and Yuan (2005), and its validity is evaluated.

Evaluation of Shear Capacity According to Transverse Spacing of Wide Beam Shear Reinforced with Steel Plate with Openings

Abstract In this paper, transverse shear spacing and effective depth of wide beams were considered as parameters to evaluate the shear capacity of wide beam according to transverse spacing of steel plates with openings in experimental way. The eight specimens were composed of: five specimens of shear reinforced by steel plates with openings and three non-reinforced specimens. Crack, failure mode, strain and load-displacement curve of specimens were analysed. Shear contribution of shear reinforcement is evaluated and maximum transverse spacing of shear reinforcement was proposed. Shear strength of the specimen that reinforced with three stirrup legs was higher than shear strength of the specimen that reinforced with two stirrup legs. And as the effective depth increased, shear strength was increased. Keywords :steel plate with openings, wide beam, shear reinforcement, transverse spacing, effective depth † Corresponding author: Tel: +82-31-201-2542; E-mail: kimhc@khu.ac.krReceived January 19 2015; Revised March 6 2015Accepted March 18 2015Ⓒ2015 by Computational Structural Engineering Institute of KoreaThis is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http://creativecommons. org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Evaluation of Shear Strength for Reinforced Flat Plates Embedded with GFRP Plates

Abstract In this study, The purpose of this study is to experimentally investigate the shear behavior of reinforced flat plate embedded with GFRP(glass fiber reinforced polymer) plate with openings. The GFRP shear reinforcement is manufactured into a plate shape with several openings to ensure perfect integration with concrete. The test was performed on 7 specimens. the parameters include the type of reinforcement and amount of the shear reinforcement., From the test, we analysed the crack, failure mode, Strain, load-displacement graph. a calculation of the shear strength of reinforced flat plate with GFRP plate based on the ACI 318-11 was compared with the test results. The results of the experiment indicate that GFRP plate is successfully applied as a shear reinforcement in the flat plate under punching shear. Keywords :shear reinforcement, flat plate, glass fiber reinforced polymer(GFRP), shear strength. † Corresponding author: Tel: +82-31-201-2542; E-mail: kimhc@khu.ac.krReceived March 13 2014; Revised March 27 2014;Accepted March 28 2014Ⓒ2014 by Computational Structural Engineering Institute of KoreaThis is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http://creativecommons. org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Experimental Study on the Temperature Dependency of Full Scale Low Hardness Lead Rubber Bearing

Abstract Rubber laminated bearings with lead core are highly affected by changes in temperature because key materials which are rubber and lead have temperature dependencies. In this study, two full scale LRB(D800, S=5) are manufactured and temperature dependency tests on shear properties are accomplished. The shear properties at the 3rd cycle are used at -10℃, 0℃, 10℃,20℃, 30℃, 40℃ respectively. The double shear configuration, simultaneously testing two pieces, is applied for compression shear test in order to minimize the friction effects due to the test machine, described in ISO 22762-1:2010. Characteristic strength, post-yield stiffness, effective stiffness, equivalent damping ratio are estimated and presented coefficient due to the temperature changes. Keywords :lead rubber bearing, temperature dependency, low hardness rubber, nuclear power plants † Corresponding author: Tel: +82-41-620-3431; E-mail: parkjy@uet.co.krReceived November 9 2012; Revised November 28 2012;Accepted November 28 2012Ⓒ2012 by Computational Structural Engineering Institute of KoreaThis is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License(http://creativecommons. org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Phase Separation in Poly(Methyl Methacrylate)-Epoxy Blend

Diglycidyl ether of bisphenol A (DGEBA) epoxy resin was modified with high molecular weight poly(methyl methacrylate) (PMMA). Morphological variations of a 2 wt% PMMA-modified epoxy mixture were studied by optical microscopy and scanning electron microscopy (SEM). A PMMA-epoxy blend cured at 100°C revealed that a secondary phase morphology was observed in both epoxy and PMMA phases from the early stages of the phase separation process. A morphology consisting of a rough striated continuous phase along with large smooth regions was observed by SEM, confirming the secondary phase separation. The dynamic mechanical thermal analysis showed that the PMMA modification of epoxy at such a low PMMA concentration of 2 wt% has no major influence on the glass transition temperature of the epoxy-rich phase. The PMMA-epoxy blend showed a slight increase in the flexural properties and the fracture toughness.

Experimental investigation of deck plate system with non-welding truss type deformed steel wires (tox deck plate slab)

On the bases of a decreased construction period and convenience of construction, the steel deck plate system has been widely used in the construction field in Korea. In particular, due to its good stiffness and economic considerations, the steel-wire-integrated deck plate system (or truss deck plate system) has become very popular in recent years. But while it offers many advantages, the truss deck plate system has a critical defect: rust forms in the welding joints between the lattice steel wire and the deck plate, resulting in the cracking of these welding joints and water leakage. To address these problems, the TOX deck plate system, a new type of truss deck plate system that does not require welding and does not rust, is proposed in this paper. Tests have been conducted on 15 specimens to evaluate the structural safety of the proposed deck plate system during the construction stage. The test parameters were as follows: the depth of the slab, the length of the span, the diameters of the top, bottom, and lattice steel wire, and the material properties of the zinc-coated steel sheets. The test results show that the TOX deck plate system can guarantee structural safety owing to its deflection and strength.