• Structural Engineering and Mechanics
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• v.38 no.6
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• pp.803-823
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• 2011

In this paper, the three dimensional Parallel Realistic Failure Process Analysis ($RFPA^{3D}$-Parallel) code based on micromechanical model is employed to investigate the bonding behavior in FRP sheet bonded to concrete in single shear test. In the model, the heterogeneity of brittle disordered material at a meso-scale was taken into consideration in order to realistically demonstrate the mechanical characteristics of FRP-to-concrete. Modified Mohr-coulomb strength criterion with tension cut-off, where a stressed element can damage in shear or in tension, was adopted and a stiffness degradation approach was used to simulate the initiation, propagation and growth of microcracks in the model. In addition, a Master-Slave parallel operation control technique was adopted to implement the parallel computation of a large numerical model. Parallel computational results of debonding of FRP-concrete visually reproduce the spatial and temporal debonding failure progression of microcracks in FRP sheet bonded to concrete, which agrees well with the existing testing results in laboratory. The numerical approach in this study provides a useful tool for enhancing our understanding of cracking and debonding failure process and mechanism of FRP-concrete and our ability to predict mechanical performance and reliability of these FRP sheet bonded to concrete structures.

• Journal of the Earthquake Engineering Society of Korea
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• v.25 no.1
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• pp.1-9
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• 2021

Most commercial buildings among existing RC buildings in Korea have a multi-story wall-frame structure where RC shear wall is commonly used as its core at stairways or elevators. The members of the existing middle and low-rise wall-frame buildings are likely arranged in ordinary details considering building occupancy, and the importance and difficulty of member design. This is because there are few limitations, considerations, and financial burdens on the code for designing members with ordinary details. Compared with the intermediate or unique details, the ductility and overstrength are insufficient. Furthermore, the behavior of the member can be shear-dominated. Since shear failure in vertical members can cause a collapse of the entire structure, nonlinear characteristics such as shear strength and stiffness deterioration should be adequately reflected in the analysis model. With this background, an 8-story RC wall-frame building was designed as a building frame system with ordinary shear walls, and the effect of reflecting the shear failure mode of columns and walls on the collapse mechanism was investigated. As a result, the shear failure mode effect on the collapse mechanism was evident in walls, not columns. Consequently, it is recommended that the shear behavior characteristics of walls are explicitly considered in the analysis of wall-frame buildings with ordinary details.

• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.846-854
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• 2024

FEMAXI-ATF is being developed for fuel performance modeling of SiC cladded UO2 fuel with focuses on modeling pellet-cladding mechanical interactions (PCMI). The code considers probability distributions of mechanical strengths of monolithic SiC (mSiC) and SiC fiber reinforced SiC matrix composite (SiC/SiC), while it models pseudo-ductility of SiC/SiC and propagation of cladding failures across the wall thickness direction in deterministic manner without explicitly modeling cracks based on finite element method in one-dimensional geometry. Some hypothetical BWR power ramp conditions were used to test sensitivities of different model parameters on the analyzed PCMI behavior. The results showed that propagation of the cladding failure could be modeled by appropriately reducing modulus of elasticities of the failed wall element, so that the mechanical load of the failed element could be re-distributed to other intact elements. The probability threshold for determination of the wall element failure did not have large influence on the predicted power at failure when the threshold was varied between 25 % and 75 %. The current study is still limited with respect to mechanistic modeling of SiC failure as it only models the propagation of the cladding wall element failure across the homogeneous continuum wall without considering generations and propagations of cracks.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.5A
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• pp.611-617
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• 2000

Asynchronous mode W-CDMA system is kmown to be quite appropriate to the next generation mobile communication system, especially in a non-homogenious cellular architecture. In this case, however, each base station needs to use different spreading code for identification, so it is a demeanding task for a mobile terminal to find the best cell site and get an accurate code synchronization at the beginning of a communication. Since slow acquisition of a base station could mean the failure of initiation, a fast algorithm to accelerate the cell search process is essential. In this paper, a new cell search algorithm based on the binary code position modulation within the code block is proposed. Different cell sites are identified by different hopping code sequences, andeach position modulation is performed by the hopping code. The proposed algorithm is proved to make the cell search time in most places in a cell much shorter than the previous algorithms, and to make the receiver implementation simpler.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.9
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• pp.144-155
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• 2013

This paper presents a low-cost remote power-quality-failure monitoring system (RPMS) using Android App and TI MCU (micro-controller unit), which is appliable to a micro-grid. The designed RPMS testbed consists of smart nodes, a server, and Android APPs. Especially, the C2000-series MCU-based RPMS smart node that is low-cost compared to existing monitoring systems has both a signal processing function for power signal processing and a data transmission function for power-quality monitoring data transmission. The signal processing function implements both a wavelet-based power failure detection algorithm including sag, swell, and interruption, and a FFT-based power failure detection algorithm including harmonics such that reliable and real-time power quality monitoring is guaranteed. The data transmission function implements a low-complexity RPMS transmission protocol and defines a simple data format (msg_Diag) for power monitoring message transmission. We may watch the monitoring data in real time both at a server and Android phone Apps connected to the WiFi network (or WAN). We use RS-232 (or Bluetooth) as the wired (or wireless) communication media between a server and nodes. We program the RPMS power-quality-failure monitoring algorithm using C language in the CCS (Code Composer Studio) 3.3 environment.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.737-742
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• 1998

The tension stiffening effect is defined as the increase in stiffness in reinforced concrete member due to the stiffness provided by concrete between cracks. If this is disregarded in analysis of reinforced concrete members, especially at the level of service loads, member stiffnesses may be underestimated considerably. This paper presents on the failure behavior and tension stiffening of RC tension test with main variables such as concrete strength, rebar diameter and strength. The tension stiffening was analyzed from the load-displacement relationship by ACI code and the proposed by Collins & Mitchell. In summary, the effect of tension stiffening decrease rapidly as the rebar diameter increase, rebar strength increase, and concrete strength increase. The effect of tension stiffening on RC member is the biggest near the behavior of concrete cracking and decrease as the load close to the breaking point. Thus, the tension stiffening should be considered for the precise analysis near the load of concrete cracking.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.64 no.4
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• pp.251-255
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• 2015

Chiller system plays an important role of maintaining room temperature constantly by supplying chilled water to Heating, Ventilating and Air Conditioning(HVAC)or area room cooler equipment during plant normal operation or accident condition. Chiller failures are one of the most frequently occurring equipment failures. If the types of chiller failures are analyzed and grouped thoroughly, it would be helpful to make chiller maintenance strategy at the plants. That would enhance equipment reliability of chiller in the end. In this paper, chiller failure data during three years were analyzed and categorized by specific failure code. In addition, the various proposals to improve equipment reliability of chiller were suggested such as Preventive Maintenance Optimization(PMO) strategy and performance monitoring reinforcement and so on.

• Structural Engineering and Mechanics
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• v.23 no.4
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• pp.353-367
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• 2006

Two full-scale, precast, pretensioned box girders were subjected to shear-dominated loading, one under monotonic loads to failure and the other subjected to one-half million cycles of fatigue loads followed by monotonic ultimate loads. The number of cycles was selected to allow for comparison with previous research. The fatigue loads were applied in combination with occasional overloads. In the present study, fatigue loading reduced the shear capacity by only six percent compared to the capacity under monotonic loading. However, previous research on flexure-dominated girders subjected to the same number of repeated loads showed that fatigue loading changed the mode of failure from flexure to shear/flexure and the girder capacity dropped by 14 percent. The comparison of the measured data with calculated shear capacity from five different theoretical methods showed that the ACI code method, the compression field theory, and the modified compression field theory led to reasonable estimates of the shear strength. The truss model led to an overly conservative estimate of the capacity.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.471-474
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• 2005

Reliability-based durability model was developed to consider the uncertainty of analysis variables in durability model for harbor concrete structures. The durability analysis program based on Finite Element Method (FEM) was modified adopting the reliability concept to estimate the probability of durability failure. Water-cement ratio in the durability analysis is the most important factor influencing chloride diffusion coefficient, evaporable water, etc. The probability distribution of water-cement ratio was calculated converting standard deviations of compressive strength in Concrete Standard Code to those of water-cement ratio. Based on the Monte Carlo Simulation, the probabilities of penetration depth and durability failure were calculated.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.217-220
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• 2005

The designer has difficulty due to inadequacy of provisions in the domestic design code and lack of understanding for behavior of D-region. The reinforced concrete pier coping consists of various failure mechanisms as the crushing or splitting from compression concrete, and shearing failure under the loading plate. However, predicting those failure mechanisms is very difficult. In this study, reinforced concrete pier coping is analyzed and designed by using strut-tie model. Adequacy for the application of strut-tie model is verified by comparison with the way used in current design practice. The results show that strut-tie model can be a rational and an economical design than current conventional design methods.