• 한국방재학회:학술대회논문집
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• 2008.02a
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• pp.477-480
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• 2008

Hydraulic experiment was executed to identify the souring range of bride pier. The experiment categorized three kind of bridge pier shape, that is composed of circle shape, square shape and the special shape. Measured scouring data was compared with the results by empirical CSU formula which was generally used in practice. As empirical formula could not consider backfill, measured scouring range is by far smaller than results of CSU formula. Therefore in case of design anti-scouring structure, there is the possibility of overestimation in case of using empirical formula.

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.5
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• pp.40-47
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• 1998

This paper report sthe design, fabrication and characterization of an AlGaAs/GaAs HBT (heterojunction bipolar transistor) with an air-bridge isolation structure which is made to improve high frequency characteristics for the application to the mobile communication system in the next genration. We found that the size, shape and structure of HBT have an effect on the high frequency operation. The measured dc and ac characteristics of the four type HBTs were compared and analyzed. An E-type HBT with an air-bridge structure by undercut etching exhibited .beta.=56, $V_{off-set}$ = 0.3 V, B $V_{CEO}$=7.0V with $f_{T}$=40 GHz and $f_{max}$=45GHz at a collector current density of 7.1*10$^{4}$ A/c $m^{2}$.>.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.1040-1047
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• 2006

Bridges are exposed to constantly changing weather conditions and temperature. The temperature change is induced by a change in atmospheric temperature and solar radiation. Atmospheric temperature change acts on the whole structure. Thus, it is relatively easy to consider in the design. Solar radiation, however, causes un-uniform temperature distribution in the structure, depending on the shape of the structure and its shadows. Un-uniform temperature distribution causes a torsional moment in bridge section and a deformation of bridge. A deformation can make differences of dynamic and static behavior of bridge. In this study, the method for analysis of static and dynamic behavior considering deformation and changes of material properties due to temperature variation was developed. By this method, it is found from dynamic analysis results that the change of frequency in analysis model is similar with test results of public used cable-stayed bridge. When a temperature goes down, a frequency goes up. And it is found that the change of frequency is affected by the change of material properties.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.10a
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• pp.321-329
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• 2002

Artificial neural network has been used for damage assessment by many researchers, but there are still some barriers that must be overcome to improve its accuracy and efficiency. The major problems with the conventional neural network are the necessity of many training patterns for neural network teaming process and ambiguity in the relationship of neural network structure to the convergence of solution. In this paper, the PNN is used as a pattern classifier to detect the damages of the railway bridge using dynamic response. The comparison between the mode shape and the natural frequency of structure as training pattern is investigated for approriate selection of the training pattern in the damage detection of railway bridge using the PNN.

• Journal of the Korean Institute of Telematics and Electronics
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• v.22 no.5
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• pp.1-9
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• 1985

In this paper, a new methods which decomposes the handwritten-Hangout shape panerns into subpatterns and recognizes the decomposed subpatterns are proposed. the feature vcfices arc detected by searching boundary of the shape pattern and a topolo-gical structure is represented by a bridge links and contact links between the feature vertices. From the tpcological structure, Hangout shape patterns are decomposed into the subpatterns of 44-Korean alphabet. The 학obol and the local attributes are extracted from the subpattrrns and the subpatterns are recognized by matching those attributes with the dictionary. It is assured that this method is more effect and reasonable for deformed handwrioen Hangout shape patterns. Experimental results show that recognition rate is 99(%) and recogni-tion time is also reduced as those using the thinning process.

• International Journal of Highway Engineering
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• v.15 no.1
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• pp.1-9
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• 2013

PURPOSES: The purpose of this study is to evaluate physical properties, durability, fatigue resistance, and long-term performance of poly-urethane concrete (PU) which can be possible application of thin layer on long-span orthotropic steel bridge and to check structural stability of bridge structure. METHODS : Various tests of physical properties, such as flexural strength, tensile strength, bond strength and coefficient of thermal expansion tests were conducted for physical property evaluation using two types of poly urethane concrete which have different curing time. Freezing and thawing test, accelerated weathering test and chloride ion penetration test were performed to evaluate the effect of exposed to marine environment. Beam fatigue test and small scale accelerated pavement test were performed to assess the resistance of PU against fatigue damage and long-term performance. Structural analysis were conducted to figure out structural stability of bridge structure and thin bridge deck pavement system. RESULTS: The property tests results showed that similar results were observed overall however the flexural strength of PUa was higher than those of PUb. It was also found that PU materials showed durability at marine environment. Beam fatigue test results showed that the resistances of the PUa against fatigue damage were two times higher than those of the PUb. It was found form small scale accelerated pavement test to evaluate long-term performance that there is no distress observed after 800,000 load applications. Structural analysis to figure out structural stability of bridge structure and thin bridge deck pavement system indicated that bridge structures were needed to increase thickness of steel deck plate or to improve longitudinal rib shape. CONCLUSIONS: It has been known that the use of PU can be positively considered to thin layer on long-span orthotropic steel bridge in terms of properties considered marine environment, resistance of fatigue damage and long-term performance.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.169-170
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• 2009

CFT structure has many advantages compared with the ordinary structural member made of steel or reinforced concrete. Because of increases in ductility, stiffness and load carrying capacity of overall structure owing to confinement effect of steel box and concrete, CFT structure is widely used to columns. Recently, the utilization of CFT member has been expanded to bridge structure as a girder member. The purpose of this study is to develop the analytical model and propose design method for CFTA girder bridge consisting of CFT structure, arch shape and tendons.

• Smart Structures and Systems
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• v.8 no.4
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• pp.399-412
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• 2011

This study compares the performance of two smart isolation systems that utilize superelastic shape memory alloys (SMAs) for seismic protection of bridges using energy balance concepts. The first isolation system is a SMA/rubber-based isolation system (SRB-IS) and consists of a laminated rubber bearing that decouples the superstructure from the bridge piers and a SMA device that provides additional energy dissipation and re-centering capacity. The second isolation system, named as superelastic-friction base isolator (S-FBI), combines the superelastic SMAs with a flat steel-Teflon bearing rather than a laminated rubber bearing. Seismic energy equations of a bridge structure with SMA-based isolation systems are established by absolute and relative energy balance formulations. Nonlinear time history analyses are performed in order to assess the effectiveness of the isolation systems and to compare their performance. The program RSPMatch 2005 is employed to generate spectrum compatible ground motions that are used in time history analyses of the isolated bridge. Results indicate that SRB-IS produces higher seismic input energy, recoverable energy and base shears as compared to the S-FBI system. Also, it is shown that combining superelastic SMAs with a sliding bearing rather than rubber bearing significantly reduce the amount of the required SMA material.

• Smart Structures and Systems
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• v.4 no.5
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• pp.629-640
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• 2008

A new algorithm is proposed to determine optimal accelerometer locations (OAL) when a structure is identified by frequency domain system identification (SI) method. As a result, a guideline is presented for selecting OAL which can reflect modal response of a structure properly. The guideline is to provide a minimum number of necessary accelerometers with the variation in the number of measurable target modes. To determine OAL for SI applications effectively, the modal sensitivity effective independence distribution vector (MS-EIDV) is developed with the likelihood function of measurements. By maximizing the likelihood of the occurrence of the measurements relative to the predictions, Fisher Information Matrix (FIM) is derived as a function of mode shape sensitivity. This paper also proposes a statistical approach in determining the structural parameters with a presumed parameter error which reflects the epistemic paradox between the determination of OAL and the application of a SI scheme. Numerical simulations have been carried out to examine the proposed OAL algorithm. A two-span multi-girder bridge and a two-span truss bridge were used for the simulation studies. To overcome a rank deficiency frequently occurred in inverting a FIM, the singular value decomposition scheme has been applied.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.3
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• pp.409-420
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• 2002

This paper proposed a technique of structural re-analysis for the evaluation of dynamic responses of bridge structure under moving loads using experimental modal results. For successful structural re-analysis, it is required to have accurate estimation techniques of the modal characteristics of bridge structures. The natural frequencies and mode shapes were identified by direct fourier analysis techniques and damping ratios by the random decrement method, respectively. An interpolation method was also proposed for the extension of mode shape measured on limited DOFs. Second, the structural reanalysis was performed using moving mass model and identified modal parameters. The results from the reanalysis show that the proposed technique is very reasonable to evaluate the actual behavior of bridge structures under moving loads.