• Journal of the Korea Concrete Institute
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• v.22 no.3
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• pp.381-388
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• 2010

In this study, characteristics of the seismic response of the non-earthquake resistant reinforced concrete (RC) frame were identified. The test building is designed to withstand only gravity loads and not in compliance with modern seismic codes. Smooth bars were utilized for the reinforcement. Members are provided with minimal amount of stirrups to withstand low levels of shear forces and the core concrete is virtually not confined. Columns are slender and more flexible than beams, and beam-column connections were built without stirrups. Through the modeling of an example RC frame, the feasibility of the fiber elementbased 3D nonlinear analysis method was investigated. Since the torsion is governed by the fundamental mode shape of the structure under dynamic loading, pushover analysis cannot predict torsional response accurately. Hence, dynamic response history analysis is a more appropriate analysis method to estimate the response of an asymmetric building. The latter method was shown to be accurate in representing global responses by the comparison of the analytical and experimental results. Analytical models without rigid links provided a good estimation of reduced stiffness and strength of the test structure due to bond-slip, by forming plastic hinges closer to the column ends. However, the absence of a proper model to represent the bond-slip poased the limitations on the current inelastic analysis schemes for the seismic analysis of buildings especially for those with round steel reinforcements. Thus, development of the appropriate bond-slip model is in need to achieve more accurate analysis.

• Journal of Korean Society of Steel Construction
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• v.26 no.5
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• pp.407-418
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• 2014

As a continuing work of previously conducted standard tension tests, full-scale flexural tests were conducted in this study to assess the structural performance the CJP groove welded joints connecting thick HSA800 plates. Two welding electrodes were available at the time of this experimental research; one was GMAW-based electrode A and the other FCAW-based electrode B. Three full-scale box-type beam specimens with single bevel- and V-groove CJP welded joints were fabricated from 60mm and 25mm thick HSA800 plates according to the AWS-prequalified groove welded joint details. In designing the specimens, all possible limit states like local and lateral torsional buckling were carefully controlled in order to induce flexural plastic yielding or eventual joint fracture. All the CJP joints made by both welding electrodes showed satisfactory performance and were able to transfer the tensile flange forces higher than that corresponding to the measured tensile strength of HSA800 flange plates. However, it should be noted that, during fabrication, serious concerns about the welding efficiency and workability of the GMAW-based electrode were raised by a certified welder. The fracture occurred at the unbeveled (or vertical) interface between the weldment and the base metal when the GMAW-based electrode was used in the single-bevel joint, implying the possibility of insufficient melting. Thus, the FCAW-based electrode B is again recommended as the choice of welding electrode for HSA800 plates. The limited test data of this study implies that the V-groove CJP joint should be used in favor of the single bevel CJP joint, if possible.

• Journal of Korean Society of Steel Construction
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• v.20 no.4
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• pp.519-528
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• 2008

A simple steel-concrete composite deck is developed for preventing the lateral torsional buckling of girders that are under construction and for reducing the term of works using H-shaped rolled beams as bridge girders. A new type of shear connectors is also developed for the composite behavior between a simple steel-concrete composite deck and the rolled beams by the connecting conditions between the deck and the girders. One is a connector bolt that is lengthened and split or tightened with two nuts and the other is an I-shaped rolled beam welded on a steel plate with a number of holes punched through the web. In this study, to estimate the shear strength of those shear connectors the push-out tests are performed and the test results are compared with that of the previous studies and the codes. The result of the push-out tests of the connector bolts showed that the shear performance is similar to that of the stud connector and revealed that the equation for the shear strength in the Korean Specification of Highway Bridge overestimates the shear capacity of the connector bolt whose diameter is larger than 19mm. From the push-out tests of punched I-shaped rolled beams with varying welding amounts, with the small amount of welding, shear capacity is governed by the shear capacity of welding. On the other hand, shear capacity is governed by the size of the punched I-shaped rolled beams, regardless of the amount of welding.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.74-79
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• 2019

The military vehicle produces electric power through an engine-integrated serial hybrid generator that is connected to the engine and does not have a separate generator installation space. However, depending on the mechanical characteristics of the connection between the generator and the engine, iron oxide for internal rusting and lubrication grew scattered. The iron oxide is adhered to the starter to deteriorate the starting performance, and there is a problem that the noise of the leg due to wear of the gear is increased. To solve this problem, the connection spline material and the surface treatment of the engine were improved and the shape was changed to a grease sealing type to prevent the generation of iron oxide inside. As the shape of the generator connector composing the shafting system was changed, the integrity of the structure was confirmed through the torsional endurance test. In addition, through the actual vehicle load test, it was verified that no corrosion occurred during the target life span without internal corrosion. It was confirmed that the anti-scattering structure of the grease effectively suppresses the generation of iron oxide, thereby reducing the noise generated from the generator. In this paper, we propose a fundamental solution to the degradation of the starter and the noise generation by preventing the back corrosion caused by the serial hybrid generator installed between the engine and the transmission.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.6A
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• pp.1013-1022
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• 2006

Although the cable-stayed bridges with two I-type girders inherently do not have good aerodynamic characteristics, a lot of the bridges with this type girders are constructed in Korea recently because of an economical merit. This paper investigated the aerodynamic characteristics of the cable-stayed bridges with two I-type girders. Section model tests were conducted in order to investigate the aerodynamic behaviors of this section with varying of the angles of attack, turbulence intensity and damping ratios. Two deck section configurations with different torsional stiffness were studied under construction and after completion respectively. Three types of the fairings were investigated to improve the aerodynamic characteristics of the bridges. The result of this study showed that the traditional section model test in uniform flow estimates the aerodynamic behavior rather pessimistically. The wind induced responses of the bridges were severely varied in accordance with the turbulence intensity and the structural damping ratio. The proposed fairing reduced the magnitude of the vortex-shedding vibrations and buffeting responses. It also increased the wind speed at which flutter occurs. It is expected that these investigations would provide a lot of information for the design of the cable stayed bridges with two I-type girders regarding wind resistance.

• Journal of Korean Society of Steel Construction
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• v.23 no.4
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• pp.417-428
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• 2011

Depending on the plastic deformation capacity required, structural steel design under the current codes can be classified into three categories: elastic, plastic, and seismic design. Most of the current steel codes explicitly forbid the use of a steel material with a yield strength higher than 450 MPa in the plastic design because of the concerns about its low plastic deformation capacity as well as the lack of test data on local and lateral torsional buckling behavior. In this study, flexural tests on full-scale H-shape members built with SM490A (ordinary steel or benchmark material) and HSB800 (high-strength steel) were carried out. The primary objective was to investigate the appropriateness of extrapolating the local buckling criterion of the current codes, which was originally developed for normal-strength steel, to the case of high-strength steel. All the SM490A specimens performed consistently with the current code criteria and exhibited sufficient strength and ductility. The performance of the HSB800 specimens was also very satisfactory from the strength perspective; even the specimens with a noncompact and slender flange developed the plastic moment capacity. The HSB800 specimens, however, showed an inferior plastic rotation capacity due to the premature tensile fracture of the beam bottom flange beneath the vertical stiffener at the loading point. The plastic rotation capacity that was achieved was less than 3 (or the minimum level required for a plastic design). Although the test results in this study indicate that the extrapolation of the current flange local-buckling criterion to the case of high-strength steel is conservative from the elastic design perspective, further testing together with an associated analytical study is required to identify the causes of the tensile fracture and to establish a flange slenderness criterion that is more appropriate for high-strength steel.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.85-94
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• 2005

Post-tensioned Precast concrete System(PPS) consists of U-shaped precast wide beams and concrete column. The continuity of beam-column joint is provided with floor concrete cast on the PC shell beam and post-tensioning. The purpose of this paper is to evaluate the response of PPS interior beam-column joint subjected to cyclic lateral loading. To this end, an experimental investigation was performed with three half-scale specimens of interior connection. The design parameters are the amount of beam reinforcement placed inside the joint core. The test results showed that cracks were distributed well without my significant degradation of strength and ductility. Also, it was found that the prestressing may affect to alter the torsional crack angle. And the specimens sufficiently resist up to limiting drift ratio of 0.035 in accordance with the provisional by ACl of acceptance criteria for concrete special moment frames.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.7
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• pp.743-749
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• 2014

In this study, a noncircular drawing (NCD) sequence for manufacturing high-strength and high-ductility pearlitic steel wires was investigated. Multipass NCD was conducted up to the 12th pass at room temperature with two processing routes (defined as the NCDA and NCDB), and compared with the wire drawing (WD). During the torsion test, delamination fracture in the drawn wire was observed in the 10th pass of the WD whereas it was not observed until the 12th pass of the NCDB. From X-ray diffraction, the circular texture component that increases the likelihood of delamination fracture of the drawn wire was rarely observed in the NCDB. Thus, the improved ability of the multipass NCDB to manufacture high-strength pearlitic steel wires with high torsional ductility compared to the WD (by reducing the likelihood of delamination fracture) was demonstrated.

• Journal of Korean Society of Steel Construction
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• v.25 no.5
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• pp.555-567
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• 2013

Slim floor system using deep decks has been developed and employed in Europe to reduce the floor height of steel structures. Although long span buildings involving the issue of reducing floor height are being increasingly built in Korea, employing deep decks in more than 7m long span structures is likely to cause problems associated with excessive deflection. This study is applied to the long-span concrete casting of the deep deck plate usability of deflection due to bending and torsional instability of open cross-section, as a way to improve the problem of cap plates are suggested, and the optimum length of reinforcement and location are derived from theoretic estimation. The cap plates are placed on the deep decks with regular intervals to overcome the instability of open sections, improve the stiffness of the sections and control the deflection at the centers. The improvement in flexural capacity associated with the location of the cap plates and the length of reinforcement are verified through analysis and test.

• Journal of the Korean Geotechnical Society
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• v.24 no.5
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• pp.117-127
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• 2008

The volumetric pressure plate extractor (VPPE) was modified for the measurement of shear wave velocity ($V_s$) at various levels of matric suction as well as soil water characteristic curve (SWCC). A non-destructive technique with a pair of bender element (BE) was employed in order to measure the $V_s$ and the corresponding maximum shear modulus ($G_{max}$) of unsaturated soil specimens. Three types of soil were collected from different road construction sites in Korea. For all test soils, the variations in $G_{max}$ with the various levels of water content and matric suction were investigated using the developed apparatus. Compared with the preceding results from the suction-controlled torsional shear (TS) testing system and in-situ seismic tests, the feasibility fur evaluating modulus characteristics of unsaturated compacted soils with the developed VPPE-BE system was assessed. It was confirmed that the newly developed system would be potentially helpful in modeling seasonal variation of modulus.