• Journal of Korean Society of Steel Construction
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• v.28 no.4
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• pp.231-242
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• 2016

Earthquake resistance of RC column-steel beam (RCS) joints with simplified details were studied. Simplified details are necessary for large columns to improve the productivity and constructability. To strengthen the beam-column joint, the effects of transverse beams, studs, and U-cross ties were used. Four 2/3 scale interior RCS connections were tested under cyclic lateral loading. The specimens generally exhibited good deformation capacity exceeding 4.0% story drift ratio after yielding of both beam and beam-column joint. Ultimately, the specimens failed by shear mechanism of the joint panel. The test strengths were compared with the predictions of existing design methods.

• Journal of Korean Association for Spatial Structures
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• v.8 no.2
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• pp.85-93
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• 2008

This study summarizes the results of a research project aimed at investigating the inelastic rotation capacity of beam-column joints of reinforced concrete special moment frames. All of the test specimens were classified as special moment frame (SMF), based on the design and detailing requirements of the ACI 318-02 provisions. The acceptance criteria, originally defined for steel moment frame connections in the 1997 edition of the AISC Seismic provisions, were used to evaluate the beam-column joints of the reinforced concrete moment frames. A total of 39 test specimens were examined in detail. Most of the joints that satisfy the design requirements for special moment frame structures were found to be ductile up to a plastic rotation of 3% without any major degradation in strength. This is mainly due to the stringent ACI 318-02 requirements for special moment frame joints. The presence of transverse beams increases confinement and shear resistance of joints, which results in better performance than for joints without transverse beams. All of the SMF connections that satisfy the ACI 318-02 limitations on joint shear stress turned out to meet the acceptance criteria.

• Geomechanics and Engineering
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• v.21 no.2
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• pp.207-213
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• 2020

Umbrella Arch Method (UAM) often employed in the tunnel construction under poor rock mass conditions in Korea. Insertion of steel pipes at the periphery of the tunnel and infiltration of grouts along the pipes into the rock masses increases tunnel stability. There are two major effects of grouts expected at the tunnel face: 1) increase of face stability by enhancing the frictional resistance of discontinuities and 2) decrease of permeability along the rock masses. Increase of resistance and decrease of permeability requires a certain curing time for the grout. In Korea, we require 24 hours for curing of grout, which means no progress of excavation for 24 hours after infiltration of grouts. This step delays the tunnel construction sequences. To eliminate such inefficiency, we propose MTG (Method for Tunnel construction using Grouting technology), which uses extended length of steel pipes (14 m) compared to conventional pipe roof method (12 m). The merit of MTG is the reduction of curing time. Because of the approximately 2 m extension of the length of steel pipe, blasting can be done after infiltration of grouting. For this paper, we conducted experiments on the shear strength behaviors of grout infilled rock joint with elapsing of curing time and blasting induced vibration. The results show that blasting induced vibration under MTG does not influence the mechanical features of grout material, which indicates no influence on the mechanical behaviors of grout, contributing to the stability of tunnels during excavation. This result indicates that MTG is a cost effective and fast construction method for tunneling in Korea.

• Journal of the Earthquake Engineering Society of Korea
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• v.4 no.3
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• pp.23-34
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• 2000

반복하중을 지지하는 4개의 2/3 크리 접합부 실험을 통하여 콘크리트 기둥 및 강재 보로 구성된 골조에 대한 외부 모멘트 접합부의 이력거동을 조사하였다. 주요 실험 변수는 접합부에 배치된 후프근의 수, 콘크리트만의 전단강도 발현응ㄹ 유도한 접합부 상세, 강재 보 플랜지 상, 하부에 스터드 형태의 전단키를 사용한 상세 등이다. 실험 시 관측된 균열양상, 파괴형상 및 다양한 계측결과에 근거하여 접합부 상세에 따른 각 시험체의 거동이 자세히 기술되었으며, 항복 후 보유강도, 강성저하 정도 및 에너지 소산능력 등이 분석되었다. 실험결과에 의하면, 이들 중 패널 및 인접 기둥 영역에 각각 2개의 후프근을 갖는 시험체 (CF3) 가 가장 우수한 이력응답을 나타냈으며, 이러한 형태의 접합부 상헤는 우리나와 같은 약진 지역에 적합할 것으로 판단되었다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.10
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• pp.1367-1375
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• 2010

In this study, optimization of the process parameters of the resistance spot welding of a sheet of aluminum-coated boron alloyed steel, 22MnB5, used in hot stamping has been performed by a Taguchi method to increase the strength of the weld joint. The process parameters selected were current, electrode force, and weld time. The heating temperature and heating time of 22MnB5 are considered to be noise factors. It was known that the variation in the thickness of the intermetallic compound layer between the aluminum-coated layer and the substrate, which influences on the formation of nugget, was generated due to the difference of diffusion reaction according to heating conditions. From the results of spot weld experiment, the optimum weld condition was determined to be when the current, electrode force, and weld time were 8kA, 4kN, and 18 cycles, respectively. The result of a test performed to verify the optimized weld condition showed that the tensile strength of the weld joint was over 32kN, which is considerably higher than the required strength, i.e., 23kN.

• Journal of the Korean GEO-environmental Society
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• v.9 no.4
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• pp.5-13
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• 2008

Just as infill material can reduce the shear strength of a rock joint, a layer of soft material between concrete and the surrounding rock socket can reduce pile shaft resistance of drilled shafts socketed in rocks. This can also result from construction methods that leave smeared or remoulded rock or drilling fluid residue on the sides of the rock sockets after concrete placement. The nature of the interface between the concrete pile shaft and the surrounding rock is critically important to the performance of the pile, and is heavily influenced by construction practice. Characteristics of the concrete-rock interface, such as roughness and the presence of the soft materials deposited during or after construction can significantly affect the shaft resistance response of the pile. In this study, we conducted the parametric study to examine the performance characteristics of drilled shafts socketed in smeared rock under the vertical load with the code of finite difference method of FLAC 2D. As the results of the current research, the parameters that affect the settlement of the pile head and the ultimate unit shaft resistance could be identified.

• International Journal of Highway Engineering
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• v.20 no.1
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• pp.87-95
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• 2018

PURPOSES : A geo-grid pavement, e.g., a stress-absorbing membrane interlayer (SAMI), can be applied to an asphalt-overlay method on the existing surface-pavement layer for pavement maintenance related to reflection cracking. Reflection cracking can occur when a crack in the existing surface layer influences the overlay pavement. It can reduce the pavement life cycle and adversely affect traffic safety. Moreover, a failed overlay can reduce the economic value. In this regard, the objective of this study is to evaluate the bonding properties between the rigid pavement and a SAMI by using the direct shear test and the pull-off test. The predicted fractural energy functions with the shear stress were determined from a numerical analysis of the moving average method and the polynomial regression method. METHODS : In this research, the shear and pull-off tests were performed to evaluate the properties of mixtures constructed using no interlayer, a tack-coat, and SAMI with fabric and without fabric. The lower mixture parts (describing the existing pavement) were mixed using the 25-40-8 joint cement-concrete standard. The overlay layer was constructed especially using polymer-modified stone mastic asphalt (SMA) pavement. It was composed of an SMA aggregate gradation and applied as the modified agent. The sixth polynomial regression equation and the general moving average method were utilized to estimate the interlayer shear strength. These numerical analysis methods were also used to determine the predictive models for estimating the fracture energy. RESULTS : From the direct shear test and the pull-off test results, the mixture bonded using the tack-coat (applied as the interlayer between the overlay layer and the jointed cement concrete) had the strongest shear resistance and bonding strength. In contrast, the SAMI pavement without fiber has a strong need for fractural energy at failure. CONCLUSIONS : The effects of site-reflection cracking can be determined using the same tests on cored specimens. Further, an empirical-mechanical finite-element method (FEM) must be done to understand the appropriate SAMI application. In this regard, the FEM application analy pavement-design analysis using thesis and bonding property tests using cored specimens from public roads will be conducted in further research.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.30 no.2
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• pp.147-151
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• 2004

This study aims at measuring electrical and rheological properties of cosmetic emulsions on the skin under shear flow. The effects of volume ratio and surfactants on structural changes of emulsions were examined by determining the changes of electrical resistance, viscosity, and morphology. As the ratio of the internal phase increased, the phase inversion occurred more quickly. The viscosity change was found to increase with increasing of the variation of electrical resistance of the emulsions. This phenomenon may be caused by decreased resistant force against the shear flow because of the breakdown of the internal phase. Surfactants a]so played a key ro]e on phase transition of emulsions. It is likely that polymeric surfactants anchoring on the emulsion surface reinforced the interfacial mechanical strength. As the concentration of surfactants increased, the phase transition occurred more slowly. It has been demonstrated that the phase changes of emulsions under shear flow can be monitored on the real-time basis by using a JELLI$\^$TM/ chip system, a combination of conductiometry and rheometry. Our approach is expected to a useful experimental tool for predicting the phase transition of the cosmetic products during skin application.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.170-175
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• 2018

For the seismic performance, it is necessary to prevent the destruction of the expansion joint device due to the appropriate deformation of the expansion joint device due to the seismic force. Recently, the hinge is installed on the fingering of the expansion joint device in Korea, New products are being developed. In this paper, we have experimentally evaluated the real scale resistance of the expansion joints with rotational finger joints against load at right angle to the bridge axis. Experimental results show that the maximum horizontal displacement is about 21.1mm for conventional stretch joints and 51.00mm for seismic stretch joints. It is presumed that the existing expansion joint test specimen is resistant to the load in a direction perpendicular to the throat axis, and then the bending and shear deformation of the finger are excessively generated and the fracture phenomenon is likely to occur. On the other hand, in the case of the seismic expansion joint, the deformation of the load due to the load is absorbed by the hinge of the finger with respect to the load in the direction perpendicular to the throat, so that only horizontal deformation in the direction of load action.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.7
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• pp.25-32
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• 2019

Welded joints and mechanical joints using bolt connection have been used as a pile-to-pile connecting method for PHC piles. These PHC pile joint methods may have difficulty in securing connecting quality and connecting performance in PHC pile joining process. Therefore, this study proposes a non-welded connection plate type mechanical PHC pile joint to improve the disadvantages of existing PHC pile connection methods and to secure the connection performance of PHC pile joint. Its connection performance was evaluated from nonlinear FE analysis and loading tests for actual PHC piles with suggested pile joints. From nonlinear FE analysis for the proposed PHC pile joint, it was evaluated to have sufficient connection performance under flexural, compressive, tensile, shear, and eccentric compressive load condition. PHC piles connected by the suggested connection plate type mechanical PHC pile joint show that they show stable linear behaviors for the crack moment and the flexural moment level of the PHC pile. Therefore, the proposed a non-welded connection plate type mechanical PHC pile joint can secure sufficient connection performance in PHC pile.