• KSCE Journal of Civil and Environmental Engineering Research
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• v.7 no.1
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• pp.43-54
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• 1987

Cumulative damage characteristics of concrete, on which rapetitive loads are applied, are investigated. Preliminarily, a series of uniaxial compression tests on cylindrical specimens of plain concrete is carried out to find out that, among various factors, stress levels of repetitive loadings and loading order are the most governing factors of cumulative damage of concrete. Based on this preliminary study, fatigue tests are carried out applying two levels of stresses, stepwisely. As a result, it is found that characteristics of cumulative damage of concrete are governed by nonlinear relationships and do not follow Miner's linear theory. It is also observed that cumulative damage characteristics and static strengths of concrete vary with loading history of stresses. Empirical equations which may be useful in predicting fatigue characteristics and remaining life of concrete stuctures are proposed for concrete subjected two stress levels.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.8
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• pp.1623-1630
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• 2002

Recently, much attention is imposed on the design of the fuel assemblies in the Pressurized Light Water Reactor (PWR). Spacer grid is one of the main structural components in a fuel assembly. It supports fuel rods, guides cooling water, and maintains a coolable geometry from the external impact loads. In this research, a new shape of the spacer grid is designed by the axiomatic approach. The Independence axiom is utilized for the design. For conceptual design, functional requirements (FRs) are defined and corresponding design parameters (DPs) are found to satisfy FRs in sequence. Overall configuration and shapes are determined in this process. Detail design is carried out based on the result of the axiomatic design. For the detail design, the system performances are evaluated by using linear and nonlinear finite element analysis. The dimensions are determined by optimization. Some commercial codes are utilized for the analysis and design.

• Computers and Concrete
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• v.21 no.5
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• pp.547-557
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• 2018

This paper measures the mechanical response of precast pavement joints under moving axle loads using the finite-element method, and the models were validated with results of field tests. In order to increase the ability to use the non-linear FE analysis for design and assessment of precast pavement subjected to moving axle load, this paper investigated the effects of different load transfer between the slabs using the ABAQUS finite-element package to solve the nonlinear explicit model equations. The assembly of the panels using dowels and groove-tongue keys has been studied to assess the efficiency of keyway joint system. Concrete damage plasticity model was used to calculate the effects of permanent damages related to the failure mechanisms. With aggregate interlock as the only load transferring system, Load transfer efficiency (LTE) is not acceptable when the axle load reaches to slab joints. The Finite-element modelling (FEM) results showed that keyway joints significantly reduced tensile stresses developed at the mid-slab. Increasing the thickness of the tongue the LTE was improved but with increasing the height of the tongue the LTE was decreased. Stresses are transferred to the adjacent slab efficiently when dowels are embedded within the model. When the axle load approaches joints, tensile damage occurs sooner than compressive damage, but the damage rate remains constant, then compressive damage increases significantly and become the major form of distress under the dowels.

• Journal of Aerospace System Engineering
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• v.11 no.5
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• pp.13-19
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• 2017

In this study, the bending analysis of composite laminates using the classical laminated theory is investigated. A piece-wise linear incremental approach is employed to describe the nonlinear mechanical behavior of the composite laminates, and a 2D strain-based interactive failure theory is employed to predict the ultimate flexural loads. The 3-point bending tests are performed for cross-ply and quasi-isotropic laminates. The analysis results with the failure theory are verified by comparing the analysis findings to the experimental outcome.

• Structural Engineering and Mechanics
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• v.80 no.6
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• pp.711-726
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• 2021

This paper presents a multiple parameters-based recursive methodology for the reliability quantification of civil structures subjected to meteorological disasters. Recognizing the challenge associated with characterizing at a single stroke all the meteorological disasters that may hit a structure during its service life, the proposed methodology by contrast features a multiparameter recursive mechanism to describe the meteorological demand of the structure. The benefit of the arrangements is that the essentially inevitable deviation of the practically observed meteorological data from those in the existing model can be mitigated in an adaptive manner. In particular, the implications of potential climate change to the relevant reliability of civil structures are allowed for. The application of the formulated methodology of recursive reliability quantification is illustrated by first considering the reliability quantification of a linear shear frame against simulated strong wind loads. A parametric study is engaged in this application to examine the effect of some hyperparameters in the configured hierarchical model. Further, the application is extended to a nonlinear hysteretic shear frame involving some field-observed cyclone data, and the incompleteness of the relevant structural diagnosis data that may arise in reality is taken into account. Also investigated is another application scenario where the reliability of a building envelope is assessed under hailstone impacts, and the emphasis is to demonstrate the recursive incorporation of newly obtained meteorological data.

• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.5
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• pp.381-388
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• 2003

In this paper, the IED(Intelligent Electronic Devices) with the consideration of harmonic problems is discussed, With significant development of power electronics technology, the proliferation of a nonlinear load has more deteriorated power quality, As continuous harmonic current makes for a shortening lifetime, overheat and abnormal operation, it should be considered to improve these problems. However, the conventional digital protective relay which eliminates harmonic elements with orthogonal filter has a defect on actually implementation. The prototype IED is constructed with Digital Signal Processor(TMS320C32) and Complex Programmable Logic Device. According to the experiment and simulation results, it is proved that the proposed system has good performance of measuring harmonic factors and protecting electrical equipment.

• The Transactions of the Korean Institute of Power Electronics
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• v.16 no.4
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• pp.317-325
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• 2011

In this paper a robust voltage controller for a single-phase UPS inverter is newly presented. The voltage controller is designed using ${\mu}$-based robust control scheme to simultaneously guarantee robust stability and robust tracking performance in the presence of load variations. Firstly the robust performance of the resulting controller is theoretically confirmed via ${\mu}$-analysis. Then simulations and experiments for the single-phase inverter system with linear and nonlinear loads demonstrate feasibility of the proposed control method providing improved performance - good regulation and fast dynamic response.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.1007-1015
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• 2013

A stochastic probability model based on the non-homogeneous Poisson process is represented that can correctly analyze the time-dependent linear and nonlinear behaviors of total damage over the occurrence process of loads. Introducing several types of damage intensity functions, the probability of failure and the total damage with respect to mean time to failure has been investigated in detail. Taking particularly the limit state to be the random variables followed with a distribution function, the uncertainty of that would be taken into consideration in this paper. In addition, the stochastic probability model has been straightforwardly applied to the rubble-mound breakwaters with the definition of damage level about the erosion of armor units. The probability of failure and the nonlinear total damage with respect to mean time to failure has been analyzed with the damage intensity functions for armor units estimated by fitting the expected total damage to the experimental datum. Based on the present results from the stochastic probability model, the preventive management for the armor units of the rubble-mound breakwaters would be suggested to make a decision on the repairing time and the minimum amounts repaired quantitatively.

• Journal of Korean Society of Steel Construction
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• v.14 no.1
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• pp.59-67
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• 2002

The ultimate strength testing of a two-story, single-bay, and sway allowed space steel frame was performed. Considering a majority of large-scale frame tests in the past, only two-dimensional frames were experimentally studied. Therefore, three-dimensional experiment is needed to extend the knowledge of this field. The steel frame subjected to non-proportional vertical and horizontal load was tested. The load-displacement curve of the test frame is provided. The experiment results are useful for verification of the three-dimensional numerical analysis. The results obtained from 3D non-linear analysis using ABAQUS were compared with experimental data.

• Journal of Korean Society of Steel Construction
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• v.15 no.3
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• pp.313-320
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• 2003

The governing equation of the post-buckling of shear-deformable uniform columns under a combined load consisting of a uniformly distributed axial load and a concentrated load at a free end was derived and the post-buckling analysis was investigated by using differential transformation. The loads were obtained for various end-slopes. The results obtained by the present method agree well with published results. In this paper, the differential transformation method was illustrated through its application to the non-linear differential equation of the post-buckling. It is expected that applications of the method to more challenging problems will are expected follow in future to ensue.