• Journal of Korean Tunnelling and Underground Space Association
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• v.24 no.4
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• pp.317-326
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• 2022

This research performed single fiber pull-out test to evaluate the effect between fineness modulus of cement composites and the fiber bond performance (bond strength and pull-out energy). A synthetic fiber (polypropylene) and a steel fiber (hooked ends type) were inserted in the middle of dog bone shape specimens which were designed with fine aggregates of F. M. 1.96, 2.69, 3.43. The experiment results showed bond strength and pullout energy of synthetic fiber are improved as fineness modulus of cement composites increases. It is considered that the frictional resistance between synthetic fiber and cement composite increases as fineness modulus of cement composite increases and consume more energy while pull out the fiber from cement composite. However bond performance of steel fiber which resist pull out by mechanical behavior is less effected on fineness modulus of cement composite. It is considered that the mechanical fixedness of hooked ends exerts a greater effect on the pullout resistance than the frictional resistance between the cement composite and the steel fiber so F. M. of fine aggregate has a relatively small effect on the pullout resistance with the steel fiber.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1354-1359
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• 2009

Ground anchor should not be used in soft clay, because anchor resistance can not be guaranteed. However, there is a way to increase the capacity of anchors. The anchor is an underreamed anchor by using high voltage electric discharge energy. In this study, a series of field test were carried out in order to find ultimate load of underreamed anchors in weathered soil at the new apartment construction site located in Inchon, Korea. Data were analyzed in order to define a relation between ultimate load and the number of electric discharge.

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.411-420
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• 2007

The applicability of headed bars in exterior beam-column joints under reversed cyclic loading was investigated. A total of ten pullout tests were first performed to examine pullout behavior of headed bars subjected to monotonic and cyclic loading with test variables such as connection type between head and bar stem (weld or no weld), loading methods (monotonic or cyclic loading), and head shape (small or large circular head and square head). Two full-scale beam-column joint tests were then performed to compare the structural behavior of exterior beam-column joints constructed using two different reinforcement details: i.e. $90^{\circ}$ standard hooks and headed bars. Both joints were designed following the recommendations of ACI-ASCE Committee 352 for Type 2 performance: i.e. the connection is required to dissipate energy through reversals of deformation into inelastic range. The pullout test results revealed that welded head to the stem did not necessarily result in increased pullout strength when compared to non-welded head. Relatively large circular head resulted in higher peak load than smaller circular and square head. Both beam-column joints with conventional $90^{\circ}$ hooks and headed bars behaved similarly in terms of crack development, hysteresis curves, and peak strengths. The joint using the headed bars showed better overall structural performance in terms of ductility, deformation capacity, and energy dissipation. These experimental results demonstrate that the headed bars using relatively small head can be properly designed far use in external beam-column joint.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.1107-1112
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• 2009

Ground anchor should not be used in soft clay, because anchor resistance can not be guaranteed. However, there is a way to increase the capacity of anchors. The pulse powered anchor is an underreamed anchor by using high voltage electrokinetic pulse energy. In this study, a series of field test were carried out in order to find expansion rate related in number of pulse charge. and Anchor pull-out tests were performed at the Geotechnical Experimentation Site at Sungkyunkwan University in Suwon, Korea. Data were analyzed in order to define a relation between expansion rate and ultimate pullout load.

• Computers and Concrete
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• v.31 no.5
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• pp.433-442
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• 2023

This study presents the visually observed behavior of fibers embedded in concrete samples that were subjected to a flexural bending test. Three types of fibers such as macro polypropylene, macro polyethylene, and the hybrid of steel and polyvinyl alcohol were mixed with cement by a designated mix ratio to prepare a total of nine specimens of each. The bending test was conducted by following ASTM C1609 with a net deflection of 2, 4, and 7 mm. The X-ray computed tomography (XCT) was carried out for 7 mm-deflection specimens. The original XCT images were post-processed to denoise the beam-hardening effect. Then, fiber, crack, and void were semi-manually segmented. The hybrid specimen showed the highest toughness compared to the other two types. Debonding based on 2D XCT sliced images was commonly observed for all three groups. The cement matrix near the crack surface often involved partially localized breakage in conjunction with debonding. The pullout was predominant for steel fibers that were partially slipped toward the crack. Crack bridging and rupture were not found presumably due to the image resolution and the level of energy dissipation for poly-fibers, while the XCT imaging was advantageous in evaluating the distribution and behavior of various fibers upon bending for fiber-reinforced concrete beam elements.

• Journal of the Korean Geotechnical Society
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• v.25 no.7
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• pp.5-10
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• 2009

The ground anchor is not usually used in soft clay and loose sand, because the pullout resistance of anchors can not be guaranteed. However, there is a method to increase the capacity of anchors using electric discharge geotechnical technologies, which are also known as pulse discharge and electric-spark technologies. The pulse-discharge anchor has a bulbed (or underreamed) bond length that is expanded by high voltage electrokinetic pulse energy. 24 anchors were installed in the weathered soil and sandy clay at the Geotechnical Experimentation Site at Sungkyunkwan University in Suwon, Korea. In this study, in order to define a relation between expansion rate of the anchor diameter and ultimate load, anchor load tests were carried out in accordance with testing procedures by AASHTO (AASHTO 1990) and FHWA (Weatheb 1998). And then several anchors were exhumed to measure the diameter of the pulse discharge anchors.

• Journal of the Korean GEO-environmental Society
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• v.10 no.4
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• pp.49-57
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• 2009

The governmental investment to SOC facilities currently has increasedthe construction of new roads and the consistent extension of already-existing roads or the line-shape revision of those roads. As a result, the road cut slopes have been increasingrapidly. Unfortunately, human-life damages and property damages frequently occur due to the rockfall and the landslide every year. To reduce those damages, many studies have been performed. The present regulation regarding rockfall protection facilities follows the "Guide for Installation and Management of Road Safety Facilities" issued by MLTM (the Ministry of Land, Transport, and Maritime Affairs) that indicates the standard size of facilities and energy absorbing efficiencies. Most domestic road slopes use standardized rockfall protection facilities based on the regulation. However, there have been doubted about the effectiveness of rockfall protection facilities and the damages caused by rockfalls havebeen increasedevery year. Thus, it seems that relevant studies are necessary on the rockfall protection net being capable of supporting rockfall energies. Accordingly, this study reviews previous literature to investigate the function and the feature of rockfall protection nets and analyzetheir limitations by each type. After that, by using the pullout test device for a rockfall protection net, an experiment on the PVC coating net and the expanded metal is performed under the exact same condition. Finally, the features of the Expended metal is explained with the comparison analysises of load-variation and the confirmation of damaged forms. As a result, there have been founded the problemsof net breaking down and not being able to support due to PVC coating net's material property of disintegration. On the other hand, the Expanded Metal might be expected as a substituteof rockfall protection net according to its capability of support and integration.

• International Journal of Concrete Structures and Materials
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• v.5 no.1
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• pp.3-10
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• 2011

Theoretical models for prediction of the mechanical properties of cement mortar are developed based on the morphology and interactions of cement hydration products, capillary pores and microcracks. The models account for intermolecular interactions involving the nano-scale calcium silicate hydrate (C-S-H) constituents of hydration products, and consider the effects of capillary pores as well as the microcracks within the hydrated cement paste and at the interfacial transition zone (ITZ). Cement mortar was modeled as a three-phase material composed of hydrated cement paste, fine aggregates and ITZ. The Hashin's bound model was used to predict the elastic modulus of mortar as a three-phase composite. Theoretical evaluation of fracture toughness indicated that the frictional pullout of fine aggregates makes major contribution to the fracture energy of cement mortar. Linear fracture mechanics principles were used to model the tensile strength of mortar. The predictions of theoretical models compared reasonably with empirical values.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.1014-1021
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• 2008

Ground anchor should not be used in soft clay, because anchor resistance can not be guaranteed. However, there is a way to increase the capacity of anchors. The pulse powered anchor is an underreamed anchor by using high voltage electrokinetic pulse energy. In this paper, conceptual introduction of the pulse powered anchor was presented. Anchor pull-out tests were performed at the Geotechnical Experimentation Site at Sungkyunkwan University in Suwon, Korea. Data were analyzed in order to verify the performance of pulse powered anchors.

• Structural Engineering and Mechanics
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• v.41 no.5
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• pp.645-662
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• 2012

Deteriorative effects of steel corrosion on the structural response of reinforced concrete are simulated for varying degrees of corrosion. The simulation approach is based on a three-dimensional irregular lattice model of the bulk concrete, in which fracture is modeled using a crack band approach that conserves fracture energy. Frame elements and bond link elements represent the reinforcing steel and its interface with the concrete, respectively. Polylinear stress-slip properties of the link elements are determined, for several degrees of corrosion, through comparisons with direct pullout tests reported in the literature. The link properties are then used for the lattice modeling of reinforced concrete beams with similar degrees of corrosion of the main reinforcing steel. The model is successful in simulating several important effects of steel corrosion, including increased deflections, changes in flexural cracking behavior, and reduced yield load of the beam specimens.