• Journal of Korean Society of Steel Construction
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• v.24 no.6
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• pp.743-751
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• 2012

This paper investigates an experimental behavior of circular columns and beam-columns made of HSB600 high strength steel as a fundamental study to enhance the applicability of HSB steel. The applicability of the current Standard such as KBC and Eurocode 3 is also evaluated. A total of six specimens are fabricated and tested. The main parameters are slenderness ratio(KLe/r = 12, 14, 40, 65), diameter-to-thickness ratio(D/t = 25, 40), and eccentricity ratio(e/D = 0, 0.5). It is drawn from the experiment that both the KBC and Eurocode 3 can be used to predict the strength of circular columns and beam-columns made of HSB600 high strength steel.

• Tunnel and Underground Space
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• v.21 no.2
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• pp.93-102
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• 2011

In spite of being unable to take into the effect of intermediate principal stress, Mohr-Coulomb and Hoek-Brown criteria are very popular as rock failure criteria. The recent researches reveal that the influence of intermediate principal stress on the failure strength of rock is substantial, so that 3-D failure criteria in which the intermediate principal stress could be considered is necessary for the safe design of the important rock structures. In this study, the likely application of the 3-D failure criterion proposed by Jiang & Pietruszczak (1988) to the prediction of the true triaxial strength of rock materials is discussed. The failure condition is linear in the meridian plane of principal stress space and it is represented by the smooth surface contacting the corners of the Mohr-Coulomb surface. The performance of the Jiang & Pietruszczak's criterion is demonstrated by simulating the actual true triaxial tests on the rock samples of three different rock types.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.89-92
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• 2008

The seismic behavior of the lightly reinforced concrete frames (LRCFs) was controlled by the nonductile behavior of the critical regions. These critical regions require retrofit to improve the seismic behavior of the lightly reinforced concrete frames. Critical column end regions must be retrofit to increase the global ductility capacity. The objective of this research is to evaluate structural strengthening performance of lightly reinforced concrete frame with Strain hardening cement composite(SHCC) experimentally. The experimental investigation consisted of a cyclic load tests on 1/3-scale models of precast infill walls. Reinforcement detail of infill wall was variables in the experiment. The experimental results, as expected, show that the multiple crack pattern, strength, ductility and energy dissipation capacity are superior for specimen with SHCC infill wall due to bridging of fibers and stress redistribution in cement matrix.

• Convergence Security Journal
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• v.13 no.3
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• pp.33-38
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• 2013

Security between mobile nodes and efficient communication is one of the most important parts of the MANET. In particular, the wireless network is significantly higher for the attack threats because of collaborative structure for open communication media and communication. However, application of existing security mechanisms and intrusion detection system is not easy due to the characteristics of MANET. It is because collection and integration of adult data by the dynamic topology due to the mobility of nodes and many network sensors is difficult. In this study, we propose cooperative security system technique that can improve the reliability based on authentication assessing confidence about the whole nodes which joins to network and detect effectively this when intrusion occurs. Cluster head which manages the cluster performs CA role for the certificate issue and the gateway node performs role of intrusion detection system. Intrusion detection is performed by cooperating with neighboring nodes when attack is not detected in one intrusion detection node. The performance of the proposed method was confirmed through experiments comparing with the SRP technique.

• Journal of the Korea Society of Computer and Information
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• v.8 no.3
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• pp.179-187
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• 2003

This study investigate the reasons of organizational failure in detection and appropriate response to risk signal. The Crisis does not come true suddenly, there is some risk signals in crisis. If Organization detect the risk signals the crisis is come true opportunities, if not the crisis is come true disastrous outcome. This is use the system dynamics approach. System Dynamics assume the system as a collection of causal feedback loop, so we understand the dynamics around the problems. This investigate suggest that, the focus on growth is the a kind of promotional pressure and the pressure drive the organization to less attention the risk signal, so the risk is underestimate In proportion to real risk. Ultimate, the organization entrap the promotional climate and insensible to security. This study is a kind of hypothesis-discovering research, in the further study, the discovered hypothesis will be empirically tested.

• Journal of Korean Society of Steel Construction
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• v.10 no.1 s.34
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• pp.37-45
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• 1998

The relational database system on fatigue strength was constructed, and the properties of fatigue life distribution were examined to analyze reliability and safety of metallic materials. Data manipulations were efficiently performed in relational fatigue strength database system using dependency diagram. Regardless of the distribution of fatigue strength, the proposed method, the Robust method and the complementary error function method using probability distribution, successfully estimated parameters of the 3-parameter Weibull distribution. The proposed criterion for estimating non-failure probability showed good results regardless of censoring time. The fatigue life distribution function described as a function of parameters of the Weibull distribution and applied stress ratio produced P-S-N characteristics reasonably.

• Tunnel and Underground Space
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• v.17 no.3 s.68
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• pp.175-185
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• 2007

When filling material such as clay is included along the discontinuity, it may cause instability on a slope even if the direction of discontinuity works in a positive way. In the study area, slope sliding occurred at the boundary between a clay filling material and weathered soil because the physical properties differ across the boundary; and this is very similar to the situation where foliation in a rock works as a weak zone during a structural behavior, causing an inter-layer slip. In most analysis, if there exists a clay filling material, a single discontinuity is assumed to perform analysis. In those cases, the discontinuity is modeled as a slip surface within clay. Therefore, the characteristics of the boundary are not considered in the analysis, so that ultimately the physical property of clay usually prevails. The result of evaluating the slope stability affected by clay filling material shows the significant difference in the safety level due to the strength parameter depending on the failure type of the discontinuity by a filling material.

• Journal of the Korean Society for Nondestructive Testing
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• v.28 no.4
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• pp.352-357
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• 2008

The detection of micro cracks in materials at the early stage of fracture is important in many structural safety assurance problems. The nonlinear ultrasonic technique (NUT) has been considered as a positive method for this, since it is more sensitive to micro crack than conventional linear ultrasonic methods. The basic principle is that the waveform is distorted by nonlinear stress-displacement relationship on the crack interface when the ultrasonic wave transmits through, and resultantly higher order harmonics are generated. This phenomenon is called the contact acoustic nonlinearity (CAN). The purpose of this paper is to prove the applicability of CAN experimentally by detection of micro fatigue crack artificailly initiated in Aluminum specimen. For this, we prepared fatigue specimens of Al6061 material with V-notch to initiate the crack, and the amplitude of second order harmonic was measured by scanning along the crack direction. From the results, we could see that the harmonic amplitude had good correlation with COD and it can be used to detect the crack depth in more accurately than the common 6 dB drop echo method.

• Fire Science and Engineering
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• v.20 no.4 s.64
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• pp.33-41
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• 2006

Nowadays in Korea, KS F 2271(Testing method for incombustibility of internal finish material and element of buildings) has been using for the evaluation of fire safety performance of sandwich panels. The test method in Japan and in Korea was based on the same way. When the Japanese standard building code was revised in 2000, the test method in the ISO 5660-1 was adopted for the test method for combustion performance of internal finishing materials and elements of buildings. According to this, the revision version of draft substituting the test method in the KS F 2271 for one in the ISO 5660-1(Cone Calorimeter method) is informed in Korea. In this study, combustion properties of sandwich panels were tested using the cone calorimeter method. Ignition time, peak heat release rate and total heat released of four sandwich panels and four core materials (thermal insulation material), which are widely used in Korea, were tested. Test results were analyzed for each specimen. Finally, test results were classified by Japanese standard building code and Canadian NBC revised.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.11
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• pp.127-134
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• 2015

Tissue stimulation technique using ultrasound has been continuously studied and developed. Recently, as a increment of interests for obesity treatment and cosmetic care, a various studies on ultrasonic fat emulsification has been conducted. In this study, the fat emulsification adapted ultrasonic transducer was designed. And using designed transducer, the simulation for the shape of focal area and thermal degradation region was conducted. The dimensions were verified by the simulation results. And the effectiveness was confirmed by evaluating measured radiation characteristic and heating characteristic. In addition, we estimated the ultrasonic heating characteristics in composite structure medium. The shape of focal point and heating characteristic of the proposed transducer were determined to be sufficient to emulsify the fat. The results of this study are considered to be used as basic research in more efficient and safe ultrasonic fat removal.