• Structural Engineering and Mechanics
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• v.81 no.2
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• pp.205-217
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• 2022

The thermodynamic properties of shaft lining concrete (SLC) are important evidence for the design and construction, and the spatial variability of concrete materials can directly affect the stochastic thermal analysis of the concrete structures. In this work, an array of field experiments of the concrete materials are carried out, and the statistical characteristics of thermophysical parameters of SLC are obtained. The coefficient of variation (COV) and scale of fluctuation (SOF) of uncertain thermophysical parameters are estimated. A three-dimensional (3-D) stochastic thermal model of concrete materials with heat conduction and hydration heat is proposed, and the uncertain thermodynamic properties of SLC are computed by the self-compiled program. Model validation with the experimental and numerical temperatures is also presented. According to the relationship between autocorrelation functions distance (ACD) and SOF for the five theoretical autocorrelation functions (ACFs), the effects of the ACF, COV and ACD of concrete materials on the uncertain thermodynamic properties of SLC are analyzed. The results show that the spatial variability of concrete materials is subsistent. The average temperatures and standard deviation (SD) of inner SLC are the lowest while the outer SLC is the highest. The effects of five 3-D ACFs of concrete materials on uncertain thermodynamic properties of SLC are insignificant. The larger the COV of concrete materials is, the larger the SD of SLC will be. On the contrary, the longer the ACD of concrete materials is, the smaller the SD of SLC will be. The SD of temperature of SLC increases first and then decreases. This study can provide a reliable reference for the thermodynamic properties of SLC considering spatial variability of concrete materials.

• Earthquakes and Structures
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• v.22 no.2
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• pp.147-155
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• 2022

Regarding the importance of seismic pounding, the available standards and guidelines specify minimum separation distance between adjacent buildings. However, the rules in this field are generally based on some simple assumptions, and the level of confidence is uncertain. This is attributed to the fact that the relative response of adjacent structures is strongly dependent on the frequency content of the applied records and the Eigen frequencies of the adjacent structures as well. Therefore, this research aims at investigating the separation distance of the buildings through a probabilistic-based algorithm. In order to empower the algorithm, the record-to-record uncertainties, are considered by probabilistic approaches; besides, a wide extent of material nonlinear behaviors can be introduced into the structural model by the implementation of the hysteresis Bouc-Wen model. The algorithm is then simplified by the application of the linearization concept and using the response acceleration spectrum. By implementing the proposed algorithm, the separation distance in a specific probability level can be evaluated without the essential need of performing time-consuming dynamic analyses. Accuracy of the proposed method is evaluated using nonlinear dynamic analyses of adjacent structures.

• Geomechanics and Engineering
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• v.36 no.6
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• pp.601-618
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• 2024

The joint probability distribution of uncertain geomechanical parameters of geotechnical strata is a crucial aspect in constructing the reliability functional function for roof structures. However, due to the limited number of on-site exploration and test data samples, it is challenging to conduct a scientifically reliable analysis of roof geotechnical strata. This study proposes a Copula method based on small sample exploration and test data to construct the intensity characteristics of roof geotechnical strata. Firstly, the theory of multidimensional copula is systematically introduced, especially the construction of four-dimensional Gaussian copula. Secondly, data from measurements of 176 groups of geomechanical parameters of roof geotechnical strata in 31 coal mines in China are collected. The goodness of fit and simulation error of the four-dimensional Gaussian Copula constructed using the Pearson method, Kendall method, and Spearman methods are analyzed. Finally, the fitting effects of positive and negative correlation coefficients under different copula functions are discussed respectively. The results demonstrate that the established multidimensional Gaussian Copula joint distribution model can scientifically represent the uncertainty of geomechanical parameters in roof geotechnical strata. It provides an important theoretical basis for the study of reliability functional functions for roof structures. Different construction methods for multidimensional Gaussian Copula yield varying simulation effects. The Kendall method exhibits the best fit in constructing correlations of geotechnical parameters. For the bivariate Copula fitting ability of uncertain parameters in roof geotechnical strata, when the correlation is strong, Gaussian Copula demonstrates the best fit, and other Copula functions also show remarkable fitting ability in the region of fixed correlation parameters. The research results can offer valuable reference for the stability analysis of roof geotechnical engineering.

• Smart Structures and Systems
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• v.20 no.2
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• pp.207-217
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• 2017

Because of the inevitable uncertainties such as structural parameters, external excitations and measurement noises, the effects of uncertainties should be taken into consideration in structural damage detection. In this paper, two probabilistic structural damage detection approaches are proposed to account for the underlying uncertainties in structural parameters and external excitation. The first approach adopts the statistical moment-based structural damage detection (SMBDD) algorithm together with the sensitivity analysis of the damage vector to the uncertain parameters. The approach takes the advantage of the strength SMBDD, so it is robust to measurement noise. However, it requests the number of measured responses is not less than that of unknown structural parameters. To reduce the number of measurements requested by the SMBDD algorithm, another probabilistic structural damage detection approach is proposed. It is based on the integration of structural damage detection using temporal moments in each time segment of measured response time history with the sensitivity analysis of the damage vector to the uncertain parameters. In both approaches, probability distribution of damage vector is estimated from those of uncertain parameters based on stochastic finite element model updating and probabilistic propagation. By comparing the two probability distribution characteristics for the undamaged and damaged models, probability of damage existence and damage extent at structural element level can be detected. Some numerical examples are used to demonstrate the performances of the two proposed approaches, respectively.

• Journal of applied mathematics & informatics
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• v.40 no.1_2
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• pp.351-370
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• 2022

The design of mechanical structures aims to meet criteria, together with the safety of operators and lives in the vicinity of the equipment. Thus, there are several cases that meeting the desired specification causes the mechanical device to perform unstable and, sometimes, chaotic behavior. In these cases, control methods are applied in order to stabilize the device when in operation, aiming at the physical integrity of the component and the device operators. In this work, we will develop a study about the influence of a controller applied in a non-ideal capsule system operating with uncertain parameters, being non-existent in the literature. For this, two initial conditions were used: one that the capsule starts from rest and another that it is already in motion. Thus, the effectiveness of the controller can be assessed in both initial conditions, restricting the movement of the internal vibration-impact system to the capsule.

• Journal of Ocean Engineering and Technology
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• v.12 no.1
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• pp.58-64
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• 1998

An analysis method for the reliability of ceramic structures subjected to thermal shocks is presented. Flaws with the size of given probability distribution function are assumed to be distributed at random with a certain density per unit volume in the structures. Criterions for crack instability are derived for brittle solids under general thermal stresses. A probabilistic failure model is presented to study the probability of crack instability for brittle solids containing cracks with uncertain size. The reliabilities of brittle structures are evaluated based on the weakest-link hypothesis, which states that a structure fails when the cracks in any differential volume become unstable. A numerical example is given to demonstrate the application of the proposed method.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.334-338
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• 1995

In recent years, the prediction of the deterioration rate of concrete structures has become major research interest. However, there are still many uncertain factors in the deterioration process and the relation between deterioration and durability of structures. This is mainly due to various uncertainties involved in the construction process and the environmental conditions which affect the rate of deterioration of concrete structures. In this study a limit state model in terms of random crack width due to applied dead and live loads is proposed for the assessment of crack damage of reinforced concrete structures. The AFOSM reliability method is used for the reliability evaluation of the crack durability of concrete bridges. The proposed model for crack durability of concrete bridges is applied to the Seoul interior circuit elevated expressway. The sensitivity analyses are performed for the proposed model.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1996.11a
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• pp.954-958
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• 1996

An analysis method for the reliability of ceramic structures subjected to thermal shocks is presented, Flaws with the size of given probability distribution function are assumed to be distributed at random with a certain density per unit volume in the structures. Criterions for crack instability are derived for brittle solids under general thermal stresses. A probabilistic failure model is presented to study the probability of crack instability for blittle solids containing cracks with uncertain crack size. The reliabilities of brittle structures are evaluated based on the weakest-link hypothesis, which states that a structure fails when the cracks in any differential volume become unstable. A numerical example is given to demonstrate the application of the proposed method.

• Geomechanics and Engineering
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• v.22 no.5
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• pp.433-439
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• 2020

Tunnels are one of the most important constructions in civil engineering. The damage to these structures caused enormous costs. Therefore, the safe and economic design of these structures has long been considered. However, both applied loads on the tunnels as well as the resistance of the structural members are naturally uncertain parameters, hence, the design of these structures requires considering the probabilistic approaches. This study aims to determine the load and resistant factors of lining tunnels concerning the earthquake extreme events limit state function. For this purpose, tunnels that have been designed according to the previous design codes (AASHTO Tunnel LRFD 2017) and using reliability analysis, the optimum reliability of these structures for different loading scenarios is determined. In this paper, the tunnel is considered circular. Finally, the proper load and resistance factors are calculated corresponding to the obtained target reliability. Based on the performed calibration earthquake extreme events limit state function, the result of this study can be recommended to AASHTO Tunnel LRFD 2017.

• Structural Engineering and Mechanics
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• v.18 no.3
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• pp.331-342
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• 2004

The vibration control problem of structures with random parameters is discussed, which is approximated by a deterministic one. A method for calculating the standard deviations of eigenvalues of the closed-loop systems is presented by using the random perturbation. The method presented in this paper will not require the distribution function of the random parameters of the systems other than their means and variances. Similarly, the distribution function of the random eigenvalues will not be computed other than their means and variances. The standard deviations of eigenvalues of the uncertain closed-loop systems can be used to estimate the stability robustness. The present method is applied to a vibration control system to illustrate the application. The numerical results show that the present method is effective.