Papers by Author: Dong Pyo Hong

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Authors: Hyo Young Kim, Jung Jae Kim, Da Hoon Ahn, Dae Gab Gweon, Chan Gon Park, Dong Pyo Hong
Abstract: Flexure hinges have been widely used as mechanisms for high precision positioning stages that have a micrometer or nanometer resolution. This paper describes the analysis of a 3-DOF rotationally symmetric hinge for the vertical mask aligner stage. The vertical mask aligner stage was designed to overcome the bending of masks by gravity. In order to align the mask and the wafer, the vertical mask aligner stage has one linear motion and yaw rotating motions (Z, Θx, Θy). The new vertical mask aligner stage will try to use rotationally symmetric hinges. These rotationally symmetric hinges would act as guide mechanisms. However, the exact 6-DOF stiffness analysis of the rotationally symmetric hinge did not use these hinges as guide mechanisms. Therefore, this paper focuses on the stiffness analysis of the rotationally symmetric hinges.
Authors: Yong Hong, Seung Ho Hwang, Gao Ping Wang, Dong Pyo Hong
Abstract: This paper presents a primary study for a method of measurement using PZT sensors which is widely used for SHM. PZT sensor has many advantages when using smart material. It is easy to be shaped to various forms and can be embedded on the materials more conveniently. The development for a practical and quantitative technique for assessment of the structural health condition by PZT sensor associated with wave propagation is investigated. Two aluminum specimens bonded with PZT sensors tested for estimating characteristics of the wave propagate on specimens change by various damage condition cf. line crack, bolt loosening. To estimate condition of the specimens numerically, we suggest impedance and guided wave method in this paper.
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: Yong Hong, Gao Ping Wang, Seung Ho Hwang, Hyun Sik Kim, Dong Pyo Hong
Abstract: A piezoelectric ultrasonic sensing system based on an optical fiber has been developed for detection of various damages. The ultrasonic wave generated from a piezoelectric actuator is guided and propagated in the optical fiber and then sensed by a piezoelectric sensor located at the other end of the fiber. The sensed signal can be influenced by environmental and physical changes around the optical fiber. In this study, the sensitivity of the optical fiber sensor is experimentally studied. Various patterns of damage, such as cracks, loosen bolts, holes, are more common forms in real structures. In particular, detection method of the damage with respect to various depths of the crack is presented in this paper.
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.
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