• Proceedings of the Korean Geotechical Society Conference
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• 1997.10a
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• pp.65-72
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• 1997

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.656-661
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• 1998

This paper presents a method of statistical analysis and sensitivity analysis of creep and shrinkage effects in PSC box girder bridges. The statistical and sensitivity analyses are performed by using the numerical simulation of Latin Hypercube sampling. For each sample, the time-dependent structural analysis is performed to produce response data, which are then statistically analyzed. The probabilistic prediction of the confidence limits on long-term effects of creep and shrinkage is then expressed. Three measures are examined to quantify the sensitivity of the outputs to each of the input variables. These are rank correlation coefficient(RCC), partial rank correlation coefficient(PRCC) and standardized rank regression coefficient(SRRC) computed on the ranks of the observations. Probability band widens with time, which indicates an increase of prediction uncertainty with time. The creep model uncertainty factor and the relative humidity appear as the most dominant factors with regard to the model output uncertainty.

• Journal of the Korean Wood Science and Technology
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• v.34 no.2
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• pp.46-57
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• 2006

To estimate nondestructively strength performances of laminated woods, 3-ply parallel- and cross-laminated wood specimens exposed under atmosphere conditions after bending creep test were prepared for this study. The effects of density of species, arrangement of laminae and lamination types on dynamic MOE obtained by flexural vibration were investigated, and regression analyses were conducted in order to estimate static bending strength and bending creep performances. Dynamic MOE of parallel-laminated woods showed 1.0~1.2 times higher values than static bending MOE, and those of cross-laminated woods showed 1.0~1.4 times higher values than static bending MOE. The degree of anisotropy of dynamic MOE perpendicular to the grain of face laminae versus that parallel to the grain of face laminae was markedly decreased by cross-laminating. There were strong correlations between dynamic MOE by flexural vibration and static bending MOE (correlation coefficient r = 0.919~0.972) or bending MOR (correlation coefficient r = 0.811~0.947) of 3-ply laminated woods, and the correlation coefficient were higher in parallel-laminated woods than in cross-laminated woods. It indicated that static bending strength performances were able to be estimated from dynamic MOE by flexural vibration. Also, close correlations between the reciprocal of dynamic MOE by flexural vibration and initial compliance at 0.008 h of 3-ply laminated woods were found (correlation coefficient r = 0.873~0.991). However, the correlation coefficient between the reciprocal of dynamic MOE and creep compliance at 168 h of 3-ply laminated woods was considerably lower than those between dynamic MOE and initial compliance, and it was hard to estimate creep compliance with a high accuracy from dynamic MOE due to the variation of creep deformation.

• Tribology and Lubricants
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• v.23 no.6
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• pp.278-282
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• 2007

Friction characteristics of a low-steel friction material were examined to investigate creep groan phenomena. The amount of three ingredients (steel fiber, $ZrSiO_4$, cashew) were changed to produce test specimens using a constrained mixture design. Tribological properties of the friction material specimens were obtained by using a 1/5 scale dynamometer. Results showed that the amount of three different ingredients strongly affected the level of friction coefficient and the difference between the static friction coefficient and the kinetic friction coefficient $({\Delta}{\mu}).\;ZrSiO_4$ and steel fiber tended to increase the average friction coefficient and aggravated the stick-slip phenomena suggesting high creep groan propensity. On the other hand, cashew tended to decrease average friction coefficient and ${\Delta}{\mu}$.

• Journal of the Korean Society of Safety
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• v.21 no.1 s.73
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• pp.28-34
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• 2006

A procedure of estimating failure probability is demonstrated for a pressurized pipe of CrMo steel used at $538^{\circ}C$. Probabilistic fracture mechanics were employed considering variations of pressure loading, material properties and geometry. Probability density functions of major material variables were determined by statistical analyses of implemented data obtained by previous experiments. Distributions of the major variables were reflected in Monte Carlo simulation and failure probability as a function of operating time was determined. The creep crack growth life assessed by conventional deterministic approach was shown to be conservative compared with those obtained by probabilistic one. Sensitivity analysis for each input variable was also conducted to understand the most influencing variables to the residual life analysis. Internal pressure, creep crack growth coefficient and creep coefficient were more sensitive to failure probability than other variables.

• Multiscale and Multiphysics Mechanics
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• v.1 no.3
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• pp.261-270
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• 2016

The longitudinal velocity (forward speed) having significant importance in proper running of railway wheelset on track, depends greatly upon the adhesion ratio and creep analysis by implementation of suitable dynamic system on contamination. The wet track condition causes slip and slide of vehicle on railway tracking, whereas high speed may also increase slip and skidding to severe wear and deterioration of mechanical parts. The basic aim of this research is to design appropriate model aimed estimator that can be used to control railway vehicle forward velocity to avoid slip. For the filtration of disturbance procured during running of vehicle, the kalman filter is applied to estimate the actual signal on preferered samples of creep co-efficient for observing the applied attitude of noise. Thus error level is detected on higher and lower co-efficient of creep to analyze adhesion to avoid slip and sliding. The skidding is usually occurred due to higher forward speed owing to procured disturbance. This paper guides to minimize the noise and error based upon creep coefficient.

• Geomechanics and Engineering
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• v.7 no.3
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• pp.279-295
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• 2014

A series of one-dimensional consolidation tests and triaxial creep tests were performed on Nansha clays, which are interactive marine and terrestrial deposits, to investigate their time-dependent behaviour. Based on experimental observations of oedometer tests, normally consolidated soils exhibit larger secondary compression than overconsolidated soils; the secondary consolidation coefficient ($C_{\alpha}$) generally gets the maximum value as load approaches the preconsolidation pressure. The postsurcharge secondary consolidation coefficient ($C_{\alpha}$') is significantly less than $C_{\alpha}$. The observed secondary compression behaviour is consistent with the $C_{\alpha}/C_c$ concept, regardless of surcharging. The $C_{\alpha}/C_c$ ratio is a constant that is applicable to the recompression and compression ranges. Compared with the stage-loading test, the single-loading oedometer test can evaluate the entire process of secondary compression; $C_{\alpha}$ varies significantly with time and is larger than the $C_{\alpha}$ obtained from the stage-loading test. Based on experimental observations of triaxial creep tests, the creep for the drained state differs from the creep for the undrained state. The behaviour can be predicted by a characteristic relationship among axial strain rate, deviator stress level and time.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.4
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• pp.154-159
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• 2010

Recent concrete structures have been being constructed with higher strength concrete than normal strength concrete. Therefore, it is necessary to review the applicabilities of current design codes and models for the prediction of mechanical behaviors of concrete materials such as creep. To investigate the applicability of creep model with the consideration of the strength level of concrete, three current models (ACI 209R, CEB-FIP MC90 and EC2) were studied and compared with series of experimental results. It was shown that EC2 model which is the updated model of CEB-FIP MC90 better predicts creep coefficient for high strength level concretes and showed relatively good agreements with experimental data.

• Journal of Welding and Joining
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• v.23 no.6
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• pp.61-66
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• 2005

A probabilistic approach for evaluating failure risk is suggested in this paper. Probabilistic fracture analyses were performed for a pressurized pipe of a Cr-Mo steel reflecting variation of material properties at high temperature. A crack was assumed to be located along the weld fusion line. Probability density functions of major variables were determined by statistical analyses of material creep and creep crack growth data measured by the previous experimental studies by authors. Distributions of these variables were implemented in Monte Carlo simulation of this study. As a fracture parameter for characterizing growth of a fusion line crack between two materials with different creep properties, $C_t$ normalized with $C^*$ was employed. And the elapsed time was also normalized with tT, Resultingly, failure probability as a function of operating time was evaluated fur various cases. Conventional deterministic life assessment result was turned out to be conservative compared with that of probabilistic result. Sensitivity analysis for each input variable was conducted to understand the most influencing variable to the analysis results. Internal pressure, creep crack growth coefficient and creep coefficient were more sensitive to failure probability than other variables.

• Korean Journal of Metals and Materials
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• v.48 no.11
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• pp.965-973
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• 2010

The small punch creep (SPC) test has recently received much attention as a new alternative to the conventional uniaxial creep test because it needs only a miniature-sized specimen directly detached from an operating system or component without any serious sampling damages. However, it is difficult to obtain the equivalent uniaxial creep data directly from the SPC data. As a specimen is deformed by a punch in the SPC test, the test result is sensitive to the friction between them. Finite element analyses with various friction coefficients was performed and showed a tendency of increased SPC life with an increased friction coefficient. The necking position predicted by the SPC simulation with a proper friction coefficient showed good agreement with that observed from the real SPC test. Finally, a noble method to convert the SPC load and displacement rate into the equivalent uniaxial creep stress and strain rate, respectively, was established in this study.