• Journal of Korean Society of Steel Construction
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• v.26 no.5
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• pp.385-396
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• 2014

Traditionally, domestic steel design and construction practice has provided extra shear studs to moment frame beams even when they are designed as non-composite beams. In the 1994 Northridge earthquake, connection damage initiated from the beam bottom flange side was prevalent. The upward moving of the neutral axis due to the composite action between steel beam and floor deck was speculated to be one of the critical causes. In this study, full-scale seismic testing was conducted to investigate the side effects of the composite action in steel seismic moment frames. The specimen PN700-C, designed following the domestic connection and floor deck details, exhibited significant upward shift of the neutral axis under sagging (or positive) moment, thus producing high strain demand on the bottom flange, and showed a poor seismic performance because of brittle fracture of the beam bottom flange at 3% story drift. The specimen DB700-C, designed by using RBS connection and with the details of minimized floor composite action, exhibited superior seismic performance, without experiencing any fracture or concrete crushing, almost identical to the bare steel counterpart (specimen DB700-NC). The results of this study clearly indicate that the beams and connections in seismic steel moment frames should be constructed to minimize the composite action of a floor deck if possible.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.40 no.9
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• pp.631-637
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• 2003

We have evaluated structural and electric, ferroelectric properties of PZT(30/70) thick film prepared by using 1,3-propanediol based sol-gel method on Pt/Ti/SiO$_2$/Si substrates. Rapid thermal annealing (RTA) is used to reduce the thermal stress and final furnace annealing is processed at $650^{\circ}C$. As the results of SEM analysis, we find that we get 350 nm in thickness for one coating and 1 $\mu$m for three times of coating. In the results of C-D analysis at 1 kHz, dielectric constant ($\varepsilon$$_{r}$) and dissipation factor were 886 and 0.03, respectively. C-V curve is shaped as a symmetrical butterfly. Leakage current density at 200 kV/cm is 1.23${\times}$10$^{-5}$ A/cm$^2$ and in the results of hysteresis loops measured at 150 kV/cm, the remnant polarization (P$_{r}$) and the coercive field (E$_{c}$) are 33.8 $\mu$C/cm$^2$ and 56.9 kV/cm, respectively. PZT(30/70) thick film exhibits relatively good ferroelectric, electric properties.s..

• Journal of the Korean Magnetics Society
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• v.10 no.5
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• pp.225-231
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• 2000

The crystallographic and magnetic properties of the sample F $e_{0.8}$ $Co_{0.18}$(BN)$_{0.02}$ synthesized by microwave arc-melting with the maximum power of 3.5 kW have been studied by the methods of an X-ray diffraction and the measurement of the magnetic hysteresis using the vibrating sample magnetometer at room temperature. The samples were prepared in a form of pellet pressed under the pressure of 9,000 N/c $m^2$, rolled coldly, and treated with the different temperatures. The X-ray diffraction pattern of pelleted sample shows that the crystal structure of the sample is bcc as same as that of Fe with a good uniformity. The X-ray diffraction pattern shows that a residual stress, which exists in the sample, is eliminated by final 90$0^{\circ}C$ annealing. As rolling rate and heat treatment temperature increases, the saturation magnetization and the remanence of the samples increase whereas the coercivity of the samples shows decrease. Also the saturation magnetization and the remanence of the samples were affected by rolling rate and rolling direction than heat treatment temperature, but the coercivity of the samples was affected by rolling rate and direction as well as heat treatment temperature. This means that a domain wall motion is easy due to elimination of a residual stress and an inclusion which exists in the sample by rolling and heat treatment and a local induced-magnetization easy axis was also formed to parallel to the rolling direction due to creation of the like-atom pairs across the slip plane by rolling......

• Journal of Korean Society of Steel Construction
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• v.20 no.4
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• pp.483-491
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• 2008

There has been much focus on the strong axis steel moment connections after the Northridge earthquake in 1994. However, research studieson the seismic behavior of weak axis moment connections could be hardly found despite the fact that these connection details have been frequently used as seismic details of MRF in Korea. Therefore, the objective of this research is to provide better knowledge on the seismic behavior of weak-axis steel moment connections, which can be widely applicable to many structures with similar characteristics. For this purpose, an experimental program was designed and performed with twotypes of weak-axis steel moment connections, namely the bracket type and WUF-B type, based on the survey of existing field data and literatures. Using the experimental results obtained from the quasi-static cyclic testing of these specimens, structural performances of the joints such as hysteretic curves, maximum strength capacities and the strain of reinforced bars were investigated. From the test results, the bracket-type connection was shown to have more than a 5% story drift capacity, compared with the WUF-B type connection's 4%. These specimens were also shown to have higher strength capacities than the nominal design strength. The bracket-type connection showed a slow strength degradation after maximum strength was researched. However,the WUF-B type connection showed a rapid strength degradation that caused brittle behavior.

• Tunnel and Underground Space
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• v.33 no.1
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• pp.57-69
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• 2023

In this study, we simulated induced seismicity in the Groningen natural gas reservoir using 2D hydro-mechanical coupled discrete element modelling (DEM). The code used is PFC2D (Particle Flow Code 2D), a commercial software developed by Itasca, and in order to apply to this study we further developed 1)initialization of inhomogeneous reservoir pressure distribution, 2)a non-linear pressure-time history boundary condition, 3)local stress field monitoring logic. We generated a 2D reservoir model with a size of 40 × 50 km² and a complex fault system, and simulated years of pressure depletion with a time range between 1960 and 2020. We simulated fault system failure induced by pressure depletion and reproduced the spatiotemporal distribution of induced seismicity and assessed its failure mechanism. Also, we estimated the ground subsidence distribution and confirmed its similarity to the field measurements in the Groningen region. Through this study, we confirm the feasibility of the presented 2D hydro-mechanical coupled DEM in simulating the deformation of a complex fault system by hydro-mechanical coupled processes.

• Journal of the Korean earth science society
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• v.36 no.1
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• pp.1-15
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• 2015

In order to outline the kinematics and movement history of a new Quaternary fault, Jingwan Fault in Dangjin, West Korea, we analyzed the geometry of the fault zone composed of a few gouge zones, and made ESR dating for fault gouge materials. The $N55^{\circ}E$ striking Jingwan Fault is a normal fault and exhibits a gradual change in dip (gentle in the lower part, steep in the upper part), indicating a listric fault. As for the fault gouge zone, its thickness varies and reaches 2~3 cm in the lower part or between basement rocks, and 20~30 cm in the middle-upper part or between the basement and Quaternary deposit. It is observed in the latter case that more than three gouge zones develop with different colors, and branch out and re-merge, or they are partly superimposed, indicating different movement episodes. The cumulative displacement is estimated to be about 10 m using the geological cross-sections, from which it is inferred that the total length of fault may be about 2.5 km on the basis of the empirical relation between cumulative displacement and fault length. Therefore, a more study would be needed to verify the entire fault length. The results of ESR dating for three gouge samples at different spots along the fault yields ages of $651{\pm}47$, $649{\pm}96$, and $436{\pm}66ka$, indicating at least two movement episodes. Slickenlines observed on the fault planes indicate a pure dip slip (normal faulting), which suggests that the ENE-WSW trending Jingwan Fault was presumably moved under a NNW-SSE extensional environment.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.1
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• pp.67-76
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• 2024

In this paper, we present a DIP-MLS testing method that combines digital image processing with a rigid body-based MLS differencing approach to measure mechanical variables and analyze the impact of target location and image resolution. This method assesses the displacement of the target attached to the sample through digital image processing and allocates this displacement to the node displacement of the MLS differencing method, which solely employs nodes to calculate mechanical variables such as stress and strain of the studied object. We propose an effective method to measure the displacement of the target's center of gravity using digital image processing. The calculation of mechanical variables through the MLS differencing method, incorporating image-based target displacement, facilitates easy computation of mechanical variables at arbitrary positions without constraints from meshes or grids. This is achieved by acquiring the accurate displacement history of the test specimen and utilizing the displacement of tracking points with low rigidity. The developed testing method was validated by comparing the measurement results of the sensor with those of the DIP-MLS testing method in a three-point bending test of a rubber beam. Additionally, numerical analysis results simulated only by the MLS differencing method were compared, confirming that the developed method accurately reproduces the actual test and shows good agreement with numerical analysis results before significant deformation. Furthermore, we analyzed the effects of boundary points by applying 46 tracking points, including corner points, to the DIP-MLS testing method. This was compared with using only the internal points of the target, determining the optimal image resolution for this testing method. Through this, we demonstrated that the developed method efficiently addresses the limitations of direct experiments or existing mesh-based simulations. It also suggests that digitalization of the experimental-simulation process is achievable to a considerable extent.