Papers by Author: Young Moon Kim

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Authors: Cheol Min Yang, Young Moon Kim, Nag Ho Ko, Dong Pyo Hong
Abstract: This paper proposes a new semi-rigid detail used high-strength bolts for use in earthquake resistant structures. These specimens were single-side beam-to-column assemblies that are representative of exterior beam-to-column connections, and they were composed of identical beam and column but had the different connection details, respectively. All beam-to-column assembly required no welding. Specimen 1 (TSD) was standard Top-Seat-Double-web-angle but specimen 2 (MTSD) was made by modified shape. Two high-strength bolted steel semi-rigid connections were prepared and cyclic load was applied to each test specimen using displacement control. The cyclic load and displacements, moment-rotation plots, and the deformation pattern or failure modes for all the test cases are presented. The strength, stiffness, energy, and ductility of the tested connections are compared to each other.
Authors: Yong Hong, Byung Jin Kim, Dong Pyo Hong, Young Moon Kim
Abstract: Beam structures are a common form in many large structures, and therefore the real-time condition monitoring and active control of beams will improve the reliability and safety of many structures. However, the incipient damage, i.e. cracks, is not easy to be detected with using the traditional methods, such as modal analysis, etc. Piezoceramic (PZT) sensors offer special opportunities for the health monitoring of structures constructed by beams. The change of mechanical impedance of structures along with the occurrence of damage is sensitively indicated by the change of electro-impedance of PZT sensors. This paper presents work done on developing and utilizing PZT sensors to detect and quantitatively assess the extent and locations of cracks occurred in simulated structures. The PZT sensors are conducted particularly to generate the longitudinal wave along the beam specimen, and systematic experiments conducted on statistical samples of incrementally damaged specimens were used to fully understand the method, the cracks with different length and location are simulated to indicate the feasibility of the detection and assessment. To estimate the damage conditions numerically, in this paper, we propose the evaluation method of impedance peak frequency shift F and CC (Correlation Coefficient), Cov (Covariance). The results of experiments verify that the impedance peak frequency shift Δ F uniformly assesses the location of cracks, and as well CC. and Cov assesses the size of cracks efficiently. The study presents the method that is satisfied for much higher frequencies, alternate power, and minute damages.
Authors: Gao Ping Wang, Yong Hong, Byeong Hee Han, Dong Pyo Hong, Young Moon Kim
Abstract: The use of multi-type joints, such as rivet joints, adhesive joints, lap joints, L-shape joints, etc., has been driven by the need for stronger and lighter structures, particularly in bridges, aerospace structures, pipeline systems, automobiles industry. Among the multi-type joints, lap joints and L-shape joints possess a considerably important position. Moreover, in many real-field situations, it is not accessible to such joints, and thus it gives additional difficulties to detect damages. Fortunately, the electro-impedance method based on the use of smart sensors provides special opportunities for damage detection of such joints, which are not easy or impossible to be accessible. The piezoelectric-ceramic sensors which simultaneously act as an actuator and sensor are widely used for structural health monitoring. In the high frequency range, the electro-impedance-based technique using a piezoelectric-ceramic patch is very sensitive for the evaluation of the incipient and small damages. A large amount of experiments were executed and several conditions were imposed to simulate real-time damage, such as the bolt loosening and bolt absence. The different indices are discussed and executed to efficiently quantify the damage conditions. The theory behind this technique and the experimental investigations are presented in this paper. The analytical results strongly show the detectability and reliability of this method.
Authors: Young Moon Kim, Cheol Min Yang, Nag Ho Ko, Dong Pyo Hong
Abstract: This paper presents an experimental work on the cyclic behavior of bolted and welded beam-to-column connections in steel portal frame. Three types of connection were used; tests for each specimen were performed twice in order to maintain test reliability. Specimen 1 (DWA) had only a double web angle connection, specimen 2 (TSD) had a top and seat angles with double web angle connection, and specimen 3 (FW) had a fully welded connection. All specimens were tested under cyclic loading conditions in order to simulate the effects of earthquakes. We also conclude that with appropriate design and careful consideration of connection strength and stiffness, the steel project economy may be maximized.
Authors: Y.-J. Son, Y.G. Choi, Joon Chul Kwon, K.W. Cho, Young Moon Kim, Soon Young Kweon, Tae Whan Hong, Young Geun Lee, Sung Lim Ryu, Man Soon Yoon, Soon Chul Ur
Abstract: In an approach to acclimate ourselves to the recent ecological consciousness trends, a lead free piezoelectric material, bismuth sodium barium titanate (Bi0.5Na0.5)0.94Ba0.06TiO3 (BNBT), was considered as an environment-friendly alternative to the PZT system. A perovskite BNBT was synthesized by the conventional bulk ceramic processing technique.La2O3 as a dopant was incorporated into the BNBT system up to 0.025 mol, and the doping effects on subsequent piezoelectric and dielectric properties were systematically investigated. In the case of La2O3 addition, the formation of grain boundary coherency was remarkably increased, and the sintered density was increased with increasing La2O3 contents. Piezoelectric and dielectric properties were shown to have the maximum value at 0.02 mol of La2O3 addition. La3+ ions were believed to act as a softener in the BNBT system and to enhance dielectric and piezoelectric properties in this study.
Authors: Young Moon Kim, G.E. Jang, N.K. Kim, S.J. Yeom, Soon Young Kweon
Abstract: A 16Mb 1T1C FeRAM device was successfully fabricated with the lead-free BLT capacitors. The average value of the switchable polarization obtained in the 32k-array (unit capacitor size: 0.68 μm2) BLT capacitors was about 16 μC/cm2 at the applied voltage of 3V and the uniformity within an 8-inch wafer was about 2.8%. But random bit failures were detected during the measuring the bit-line signal of each cell. It was revealed that the grain size and orientation of the BLT thin film were severely non-uniform. Therefore, the grain size and orientation was optimized by varying the process conditions of nucleation step. The random bit failure issue was solved by adopting the optimized BLT film. The cell signal margin of the optimized FeRAM device was about 340 mV.
Authors: Yong Hong, Gao Ping Wang, Byeong Hee Han, Dong Pyo Hong, Young Moon Kim
Abstract: Beam structures are a common form in many large structures, and therefore the real-time condition monitoring and active control of beams will improve the reliability and safety of many structures. This paper presents a damage assessment method which combines the impedance method and guided wave method. The combination enabled to improve the damage detection efficiency. The impedance method is used first to detect whether the damage occurs or not and judge the damage extent. The guided wave then is introduced to accurately localize damages. The improved method provides possibility for more accurately identifying and localization damages compared to that conventional method. A powerful wavelet transform is used to extract the signals efficiently. Additionally, with using the general function generator to excite the piezoceramic (PZT) patches to generate the guided wave, the guided wave propagates along with the beam structures with PZT patches bonded, and the real-time signals are recorded. Damages are indicated by a change of response signals when compared with a template undamaged condition. The wave attenuation and mode conversion is sufficient to detect various types of defects. The results show considerable ability for identifying and localization of the simulated damages.
Authors: Ki Pyo You, Young Moon Kim, Cheol Min Yang, Dong Pyo Hong
Abstract: Wind-induced vibration of tall buildings have been of interest in engineering for a long time. Wind-induced vibration of a tall building can be most effectively controlled by using passive control devices. The tuned liquid damper(TLD) is kind of a passive mechanical damper, which relies on the sloshing liquid in a rigid tank. TLD has been successfully employed in practical mitigation of undesirable structural vibrations because it has several potential advantages: low costs, easy installation in existing structures, and effectiveness even against small-amplitude vibrations. Shaking table experiments were conducted to investigate the characteristics of the shallow water sloshing motion in a rectangular tank. To increase the damping ratio of the rectangular water tank, triangle sticks were installed at the bottom of water tank. This installation increased the damping ratio by amaximum of 40-70%.
Authors: Nag Ho Ko, Young Moon Kim, Ki Pyo You, Dong Pyo Hong
Abstract: The action of wind pressures is a major consideration in the design of cladding and its connections to building structures. Non-Gaussian environmental loads often may appropriately be reduced to Gaussian loads through the central limit theorem, e.g., integral loads on a building under wind loads. However, for the design load of cladding and its connections to building structures the Gaussian assumption is not valid and loads remain non-Gaussian, especially in separated flow regions. When the loads differ significantly from Gaussian distribution, they may lead to increase expected damage. In this study, the wind-induced high-cycle fatigue damage of a cladding fastener subjected to non-Gaussian local wind pressures and corresponding simulated Gaussian local wind pressures is estimated by using the rainflow cycle counting method and Miner’s rule. The fatigue damage is compared with each other in order to investigate the influence of non-Gaussian local wind pressures on the fatigue damage of a cladding fastener on the side face of a tall building.
Authors: Young Moon Kim, Nag Ho Ko, Cheol Min Yang, Ki Pyo You
Abstract: An appropriate choice of building shape and architectural modifications can result in the reduction of motion by altering the flow pattern around a building. Tapering which is one of aerodynamic devices has been known to be effective to reduce acrosswind response [1, 2]. The exterior wind loading patterns on claddings are sensitive to the building shape. When a building has a tapered cross section along the height, the influence of the exterior wind loading patterns on the wind-induced high-cycle fatigue damage of the cladding fastener of the tapered building needs to be found. In this study, the fatigue damage of the cladding fastener of a non-tapered building and two tapered buildings is estimated by using the rainflow cycle counting method and Miner’s rule. The fatigue damage is compared with one another in order to investigate the influence of the tapered cross section on the fatigue damage of cladding fasteners on side faces of tall buildings
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