• Journal of the Korean Institute of Gas
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• 제19권6호
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• pp.1-7
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• 2015

An ammonia fuel system is developed and applied to a 1 liter gasoline engine to use ammonia as primary fuel. Ammonia is injected separately into the intake manifold in liquid phase while gasoline is also injected as secondary fuel. As ammonia burns 1/6 time slower than gasoline, the spark ignition is needed to be advanced to have better combustion phasing. The test engine showed quite high variation in the power output to lead high increase in THC emission with large amount of ammonia, that is, higher than 0.7 ammonia-gasoline fuel ratios.

• Journal of Korean Society of Steel Construction
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• 제19권5호
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• pp.473-482
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• 2007

When the material strength and ductility of shear studs is sufficient to carry the interface shear force, the composite beam can behave safely without premature structural failure in the interface and without ultimate moment reduction. In this study, the influence of the deformation capacity of shear studs embedded in high-strength concrete on structural behavior and design condition of composite beam is analyzed using FEM. In the analysis, load type, degree of shear connection and arrangement of studs are considered as analysis parameters. According to analysis results, in the case of partial interaction,the deformation capacity of studs embedded in high-strength concrete should be considered together with material strength. Especially in the case of uniform arrangement of studs and uniformly distributed load, a minimum available degree of shear connection is restricted by the deformation capacity of studs. In this case,shear studs should be arranged in consideration of the distribution of shear force at the composite section.

• Tribology and Lubricants
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• 제17권4호
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• pp.267-275
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• 2001

Friction and wear properties of brake friction materials containing different metal fibers (Al, Cu or Steel fibers) were investigated. Based on a simple experimental formulation, friction materials with the same amount of metal fibers were tested using a pad-on-disk type friction tester. Two different materials (gray cast iron and aluminum metal matrix composite (MMC)) were used for disks rubbing against the friction materials. Results front ambient temperature tests revealed that the friction material containing Cu fibers sliding against gray cast iron disk showed a distinct negative $\mu$-v (friction coefficient vs. sliding velocity) relation implying possible stick-slip generation at low speeds. The negative $\mu$- v relation was not observed when the Cu-containing friction materials were rubbed against the Al-MMC counter surface. Elevated temperature tests showed that the friction level and the intensity of friction force oscillation were strongly affected by the thermal conductivity and melting temperature of metallic ingredients of the friction couple. Friction materials slid against cast iron disks exhibited higher friction coefficients than Al-MMC (metal matrix composite) disks during high temperature tests. On the other hand, high temperature test results suggested that copper fibers in the friction material improved fade resistance and that steel fibers were not compatible with Al-MMC disks showing severe material transfer and erratic friction behavior during sliding at elevated temperatures.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• 제17권3호
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• pp.301-309
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• 1999

Real-time kinematic (RTK) GPS surveying which allows centimeter level accuracy of three-dimensional coordinates without post-processing has become recognized as a major advance in GPS technology. Employing On-The-Fly initialization technique, the RTK system can escape from cycle slip problems that have affected as a main obstacle factor in traditional kinematic and static approaches. The objective of this research was to evaluate accuracy and effectiveness of the RTK-GPS surveying. First, the continuous RTK observation of a base line was conducted for the purpose of finding out the repeatability of the RTK surveying and the results which were then compared against results from static surveying showed RMS errors of $\pm{3mm}\;and\;\pm{13mm}$ for their respective horizontal and vertical components. On a test network of 30 stations covering the small area, the results of RTK testing were compared against those from not only post-processing kinematic and rapid-static surveyings but conventional surveyings and also the efficiency of RTK were analyzed. In addition, geoid heights which were derived by combination of GPS and spirit leveling about all of the points within the network were compared against those derived by the PNU95 and EGM96 models respectively.

• Journal of the Korean GEO-environmental Society
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• 제6권1호
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• pp.73-82
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• 2005

Generally, to evaluate a slope stability of the geosynthetic reinforced soil slope, the modified version of limit equilibrium method can be used. In most cases, resisting effects of reinforcement are dealt with considering an increased shear strength on the potential slip surface. However, it is not clear that the methods satisfy all three equilibrium equations. In this study, the new slope stability analysis method in which not only reinforcing effects of geosynthetics can be considered but also all three equilibrium equation can be satisfied is proposed. A number of illustrative examples, including published load test of large-scale reinforced retaining wall and centrifuge model tests on the geotextile reinforced soil slopes, are also analyzed. As a result, it is shown that the newly suggested method produces a relatively accurate factor of safety.

• Geomechanics and Engineering
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• 제13권5호
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• pp.715-742
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• 2017

Earth berms are often left in place to support retaining walls or piles in order to eliminate horizontal struts in excavations of soft soil areas. However, if the excavation depth is relatively large, an earth berm-supported retaining system may not be applicable and could be replaced by a multi-bench retaining system. However, studies on multi-bench retaining systems are limited. The goal of this investigation is to study the deformation characteristics, internal forces and interaction mechanisms of the retaining structures in a multi-bench retaining system and the failure modes of this retaining system. Therefore, a series of model tests of a two-bench retaining system was designed and conducted, and corresponding finite difference simulations were developed to back-analyze the model tests and for further analysis. The tests and numerical results show that the distance between the two rows of retaining piles (bench width) and their embedded lengths can significantly influence the relative movement between the piles; this relative movement determines the horizontal stress distribution in the soil between the two rows of piles (i.e., the bench zone) and thus determines the bending moments in the retaining piles. As the bench width increases, the deformations and bending moments in the retaining piles decrease, while the excavation stability increases. If the second retaining piles are longer than a certain length, they will experience a larger bending moment than the first retaining piles and become the primary retaining structure. In addition, for varying bench widths, the slip surface formation differs, and the failure modes of two-bench retained excavations can be divided into three types: integrated failure, interactive failure and disconnected failure.

• Journal of the Korea institute for structural maintenance and inspection
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• 제25권4호
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• pp.20-27
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• 2021

The present study presents a nonlinear finite element analysis (FEA) approach using the general program of Abaqus to evaluate the seismic response of unreinforced masonry walls strengthened with the steel bar truss system developed in the previous investigation. For finite element models of masonry walls, the concrete damaged plasticity (CDP) and meso-scale methods were considered on the basis of the stress-strain relationships under compression and tension and shear friction-slip relationship of masonry prisms proposed by Yang et al. in order to formulate the interface characteristics between brick elements and mortars. The predictions obtained from the FEA approach were compared with test results under different design parameters; as a result, a good agreement could be observed with respect to the crack propagation, failure mode, rocking strength, peak strength, and lateral load-displacement relationship of masonry walls. Thus, it can be stated that the proposed FEA approach shows a good potential for designing the seismic strengthening of masonry walls.

• Structural Engineering and Mechanics
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• 제71권4호
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• pp.433-444
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• 2019

Shear studs are often used to connect steel girders and concrete deck to form a composite bridge system. The application of precast concrete deck to steel-concrete composite bridges can improve the strength of decks and reduce the shrinkage and creep effect on the long-term behavior of structures. How to ensure the connection between steel girders and concrete deck directly influences the composite behavior between steel girder and precast concrete deck as well as the behavior of the structure system. Compared with traditional multi-I girder systems, a twin-I girder composite bridge system is more simplified but may lead to additional requirements on the shear studs connecting steel girders and decks due to the larger girder spacing. Up to date, only very limited quantity of researches has been conducted regarding the behavior of shear studs on twin-I girder bridge systems. One convenient way for steel composite bridge system is to cast concrete deck in place with shear studs uniformly-distributed along the span direction. For steel composite bridge system using precast concrete deck, voids are included in the precast concrete deck segments, and they are casted with cast-in-place concrete after the concrete segments are erected. In this paper, several sets of push-out tests are conducted, which are used to investigate the heavier of shear studs within the voids in the precast concrete deck. The test data are analyzed and compared with those from finite element models. A simplified shear stud model is proposed using a beam element instead of solid elements. It is used in the finite element model analyses of the twin-I girder composite bridge system to relieve the computational efforts of the shear studs. Additionally, a parametric study is developed to find the effects of void size, void spacing, and shear stud diameter and spacing. Finally, the recommendations are given for the design of precast deck using void for twin I-girder bridge systems.

• Journal of the Earthquake Engineering Society of Korea
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• 제23권5호
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• pp.239-248
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• 2019

In this study, the out-of-plane seismic resistance of lightly-reinforced existing walls strengthened with thick RC jacket was investigated. The thick RC jacket with a thickness of 500 mm was placed at one side of the thin existing wall with a thickness of 150 mm. At the interface between the wall and RC jacket, a tee-shaped steel section with a number of anchor bolts and dowel bars was used as the shear connector. To investigate the connection performance and strengthening effects, the cyclic loading tests of four jacketed wall specimens were performed. The tests showed that the flexural strength of the jacketed walls under out-of-plane loading was significantly increased. During the initial behavior, the tee shear connector transferred forces successfully at the interface without slip. However, as the cracking, spalling, and crushing of the concrete increased in the exiting walls, the connection performance at the interface was significantly degraded and, consequently, the strength of the jacketed walls was significantly decreased. The flexural strength of the jacketed walls with tee shear connector was estimated considering the full and partial composite actions of the tee shear connector.

• Journal of the Korean Recycled Construction Resources Institute
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• 제10권2호
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• pp.168-175
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• 2022

With the recent development of nanotechnology, its application in the field of construction materials is continuously increasing. However, until now, studies on the bond characteristics of concrete and rebar for applying high-strength lightweight concrete with a compressive strength of 50 MPa and a unit weight of 16 kN/m³ to structural members are lacking. Therefore, in this paper, 81 specimens of high-strength lightweight concrete with a compressive strength of 50 MPa and a unit weight of about 16 kN/m³ were fabricated and a direct pull-out tests were performed. The design code for the bond strength of ACI-408R and the experimental results are shown to be relatively similar, and as a result of the CEB-FIP and modified CMR bond behavior models through statistical analysis, it is shown to describe well on average.