• Journal of Ocean Engineering and Technology
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• v.22 no.5
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• pp.94-99
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• 2008

Three types of salt resistant concrete beams reinforced with glass fiber reinforced polymer-ribbed bars (GFRP-ribbed bars) were selected, and their applicable properties were investigated with the goal of improving the problem of capacity deterioration in marine structures due to sea water corrosion. In this study, the structural behaviors were similar to RC beams in relation to the development of the strength and stiffness up to the generation of the initial crack. After the growth of this initial crack, the structural properties decreased owing to a sudden loss of bond strength. Also these beams showed the trends of brittle failure. As a result, it was confirmed that a GFS beam replaced with Fly Ash (20%) and Silica Fume (5%) has the best application as a marine structural element.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.04a
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• pp.107-112
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• 1993

The objective of this experimental investigation is to examine the feasibility and the usefulness of the complementary crosstie in the current ACI 318-89 code for rienforced concrete columns subjected to constant axial load and lateral load reversals. Tests were conducted on1/3 scaled four columns with the length of 1.9m and the cross section of 20$\times$20 cm. The main parameters of specimens were the magnitude of axial load applied and the configuration of transverse reinforcements . From the experimental results, it can be seen that while the column subjected to lower axial load represented considerable ductility behaviors, the column subjected to higher axial load showed the brittle failure

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.653-660
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• 1998

Bond strength of reinforcing bar to high-performance concrete using belite cement is explored using beam end test specimen. The key parameters for the bond test are slump of concrete, top bar effect, and strength of concrete in addition to concrete covers. Specimen failed in the typical brittle bond failure splitting the concrete cover as the wedging action. The test results show that the specimens with belire cement concrete show higher bond strength than those with portland cement concrete. Bond strength of the top bar is less than bond strength of bottom bar, but the top bar factor satisfies the modification factor for top reinforcement. The results also show that the bond strength is function of the square root of concrete compressive strength and cover thickness. The recently developed high-strength and high-slump concrete with belite cement performs well in terms of bond strength to reinforcing steel.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.327-332
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• 2001

It is generally observed that steel fiber reinforced concrete with traditional straight steel fibers overcomes brittle nature of plain concrete by failure mechanisms by fiber pull-out rather than fiber rupture resulting from fiber yielding or concrete fracture at failured surface. Ring type steel fibers in concrete which is confined in concrete matrix and has better orientation, thus, lead to fiber yielding and concrete fracture as well as increase of flexural behavior of concrete more efficiently, Comparative experimental study is performed in order to measure the relative efficiencies of steel fiber reinforced concrete reinforced with two different fibers. It is found that better toughness is obtained from the ring type steel fiber reinforced concrete than from straight steel fiber reinforced concrete under flexural loading.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.853-858
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• 2001

Experimental studies were peformed to investigate variations in ductility of shear wall with length of boundary confinement. Eight specimens containg different lengths of confinment zone, which model compressive zone in plastic regions of shear walls, were tested against eccentric vetical load. Stress-strain model for confined concrete was used to predict strength and ductility of the specimens, which was compared to the test results. The results obtained show that failure of the compressive zone occurs in a brittle manner when the stress of unconfined zone softened after the ultimate strength were reached. To enhance the ductility of shear walls with concentrated confinement zone such as barbell-type walls, the ultimate strength of the confinement zone needs to be increased, and for shear walls with distributed confinement zone the length of the confinement zone needs to be extended.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2001.10a
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• pp.57-60
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• 2001

In order to extend the life time of building and civil infra-structure, nowadays, patch type fibrous composite materials are widely used. Retrofitted concrete columns and beams gain the stiffness and strength, but they lose toughness and show brittle failure. Usually, the cracks of concrete structures are visible with naked eyes and the status of the structure in the life cycle is estimated with visible inspection. After retrofitting of the structure, crack visibility is blocked by retrofitted composite materials. Therefore, structural monitoring after retrofitting is indispensible and self diagnosis method with optical fiber sensor is very useful. In this paper, We try to detect peel out effect and find the strain difference between main structure and retrofitting patch material when they separate each other.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.4
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• pp.106-113
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• 2000

One of the recent changes in machining technology is rapid application of micro- and high precision grinding processes. A fine groove generation is necessary for the fabrication of optics, electronics and semiconductor parts. Slot grinding is very efficient for the generation of micro ordered groove with hard and brittle materials. In the process of slot grinding, chipping at the sharp edges and microcracks of the ground grooves are inevitable defects. Chipping should be reduced for the improvement of surface integrity. Mechanical contact with diamond grits causes microcracks at the grooves. This damage resides subsurface, and can be the cause of failure of the punch die. This paper deals with chipping generation at the sharp edges, surface integrity of side groove and fracture strength is related to the microcracks in the slot grinding.

• Transactions of Materials Processing
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• v.20 no.2
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• pp.173-178
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• 2011

Environmental Stress Cracking(ESC) is one of the most common causes of unexpected brittle failure of thermoplastic polymers. The exposure of polymers to liquid chemicals tends to accelerate the crazing process, initiating crazes at stresses that are much lower than the stress causing crazing in air. In this study, ESC of acrylonitirile butadiene styrene(ABS) was investigated as a function of the molding conditions such as injection velocity, packing pressure, and melt temperature. A constant strain was applied to the injection molded specimens through a 1.26% strain jig and a mixture of toluene and isopropyl alcohol was used as the liquid chemical. In order to examine the effects of the molding conditions on ESC, an experimental design method was adopted and it was found that the injection velocity was the dominant factor. In addition, predictions from numerical analyses were compared with the experimental results. It was found that the residual stress in the injection molded part was associated with the environmental stress cracking resistance (ESCR).

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.110-113
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• 2004

Aluminum and CFRP tube is light-weight material representatively but collapse mechanism is different under axial loading. Aluminum tube absorbs energy by stable plastic deformation under axialloading. While CFRP(Carbon Fiber Reinforced Plastics)tube absorb synergy by unstable brittle failure but its specific strength and stiffness is higher than that of aluminum tube. In this study, for complement of detect and synergy effect by combination with the advantages of each member, the axialcollapsetests were performed for combined aluminum CFRP tubes which are composed of aluminum tubes wrapped with CFRP out side aluminum square tubes. Collapsecharacteristics were analyzed for combined square tubes which have different CFRP orientation angle and thickness. Test results were compared with that of aluminum tubes and CFRP tubes.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.65-70
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• 2001

The compression toe of structural wall is designed to resist the axial compression and shear force caused by wind or earthquake. The performance of shear wall used in tall building is highly influenced by combined shear and axial force. For this reason, it is possible to result in local brittle failure because of concentrated damage in the potential plastic hinge region under severe earthquake. Thus, it is necessary to establish the lateral confinement details at the plastic hinge of shear wall so that shear wall can behave a ductile manner, The objective of this study is to evaluate the seismic performance of L-shaped walls with different confinement details. For this purpose, three wall specimens were tested experimentally and also analyzed using Nonlinear FEM package.