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Cho, Tae-Jun Korean Society for Railway 2010 International Journal of Railway Vol.3 No.1
The initiation and growth process of cyclic ice body in porous systems are affected by thermo-physical and mass transport properties as well as by gradients of temperature and chemical potentials. Furthermore, the diffusivity of deicing chemicals reaches a significantly higher value under cyclic freeze-haw conditions. Moreover, disintegration of concrete structures is aggravated by marine environments, higher altitudes, and northern areas. A serious concern for concrete engineers is that the property of cyclic freeze-haw with crack growth and the deterioration, caused by accumulated damages hard to be identified by testing. The input variables employed in the analytical predictions are selected as random variables for the limit state functions, followed by reliability analyses. For this purpose, a linear adaptive weighted response surface method (LAW-RSM) has been developed. The verification exhibits a reasonably good correlation with the exact solution of MCS. The important parameters for cyclic freeze-haw-deterioration of concrete structures as water to cement ratio, entrained air pores, and the number of cycles of freezing and thawing are used to construct the limit state function of LAW-RSM. The regression equation fitted to the important deterioration criteria such as accumulated plastic deformation, relative dynamic modulus and equivalent plastic deformations served as the probabilistic evaluation of the performance to resist the structural degradation. The composed improved response surfaces could be utilized to predict the equivalent plastic strains, relative dynamic modulus and residual strains during the cycles of freeze-haw with the probability of failure as changing input random variables. Hence, it is possible to evaluate the life cycle management of concrete structures by the proposed prediction method in consideration of the accumulated damage due to cyclic freeze-thaw.
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A Numerical Model for the Freeze-Thaw Damages in Concrete Structures
Cho Tae-Jun Korea Concrete Institute 2005 콘크리트학회논문집 Vol.17 No.5
This paper deals with the accumulated damage in concrete structures due to the cyclic freeze-thaw as an environmental load. The cyclic ice body nucleation and growth processes in porous systems are affected by the thermo-physical and mass transport properties, and gradients of temperature and chemical potentials. Furthermore, the diffusivity of deicing chemicals shows significantly higher value under cyclic freeze-thaw conditions. Consequently, the disintegration of concrete structures is aggravated at marine environments, higher altitudes, and northern areas. However, the properties of cyclic freeze-thaw with crack growth and diffusion of chloride ion effects are hard to be identified in tests, and there has been no analytic model for the combined degradations. The main objective is to determine the driving force and evaluate the reduced strength and stiffness by freeze-thaw. For the development of computational model of those coupled deterioration, micro-pore structure characterization, pore pressure based on the thermodynamic equilibrium, time and temperature dependent super-cooling with or without deicing salts, nonlinear-fracture constitutive relation for the evaluation of internal damage, and the effect of entrained air pores (EA) has been modeled numerically. As a result, the amount of ice volume with temperature dependent surface tensions, freezing pressure and resulting deformations, and cycle and temperature dependent pore volume has been calculated and compared with available test results. The developed computational program can be combined with DuCOM, which can calculate the early aged strength, heat of hydration, micro-pore volume, shrinkage, transportation of free water in concrete. Therefore, the developed model can be applied to evaluate those various practical degradation cases as well.
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Zhaodonglong,Chotaejun 한국유통과학회 2013 KODISA ICBE (International Conference on Business Vol.2013 No.-
For further exploring the differences of incentive factors of university teachers with different professional title and different age, analyzing the incentive factors preference of university teachers with different characteristics, and accurately grasping university teachers' incentive factors, so as to provide theory basis and empirical support for attracting, retaining and stimulating college teachers. This paper takes LinYi university as the sample, exert the grey theory to empirically analyze the college and university teachers incentive factors, aim at teachers with different characteristics to make comparative study, adopt questionnaire method and the grey correlation degree analysis method to explore the incentive differences of university teachers between different titles and different age, and attempt to get realistic significance conclusion of university human resources management on theoretical and empirical aspects. At last, practical implications of the result is discussed.
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