Applied Mechanics and Materials Vols. 166-169

Abstract: Time dependency of chloride transport has been studied and an improving chloride penetration model has been established. Based on reliability theory, a durability analysis model has been build up and sensitivity analysis of steel corrosion probability has been performed. The analytical results show that age factor, cover depth and diffusion coefficient are key influence factors for corrosion probability of steel bar. Furthermore, influences on corrosion probability of temperature and relative humidity are significant quietly and must be considered in practical engineering.

Abstract: In order to investigate the resistance mechanism of steel frame structure in progressive collapse, an advanced finite element model(FEM) is presented based on fiber beam-column element. Using this FEM, non-linear static pushdown analysis of a ten-story structure was carried out by the alternate load path method, in the two cases that two different columns are removed respectively. Analytical results show that residual structure has the different resistance mechanism for the different column removal case. In the initial stage, bending resistance mechanism can provide dominate resistance capacity in the structural progressive collapse, after both middle and side columns are removed. However, when the bending resistance is out of work, the catenary action is induced in the case of the middle column removal only, which is not developed after the side column is removed. It can be seen that steel frame structure has higher collapse risk in the case of the side column removal than in the case of the middle column removal.

Abstract: The theory of statistical inferences is the base of the reliability analysis. The results of inferences can not be believed unquestionably because the data sample could not involve whole information about the parent distribution. In engineering, it is reasonable to estimate the precision of inference results concerning the reliability index. Therefore, the randomness of reliability index is discussed in this paper. The confidence interval, which is one of the most important concepts in statistics, is employed to express the precision of the reliability index.

Abstract: In this article, a few testing methods of sulfate-attack resistance are discussed. The merits and demerits of every method are commented, the existent problems are pointed out, and a suggestion of study on testing method of sulfate-attack resistance in future is put forward.

Abstract: There are two problems frequently encountered in the risk analysis of foundation pit through the probability based reliability method. One is the large amount of calculation and the other is insufficient statistic field information. To solve these problems, uniform experiment design (UD), non-parametric regression (NPR) and Bootstrap simulation (BS) techniques are introduced based on the concept of response surface (RS). UD and NPR are used to construct more efficient RS, based on which, the failure probability is calculated through field information and BS. Combined with a practical project, the probability distributions calculated by BS based on field observation datum, and those calculated by Monte Carlo simulation (MCS) based on assumed probability distribution are compared. The results show that the probability distributions obtained through BS and MCS are the same in most cases, but BS is more suitable for the case of small sample datum. The RS methods based on UD and NPR can provide higher accuracy with less computation while containing more uncertain parameters.

Abstract: A self-anchored suspension bridge is analyzed for its structural system reliability, and the bridge reliability is relatively high under vehicular load. Through seeking the distinct structural system fault modes the relatively weak structural elements can be identified, which can be the basis on its reasonable design and offer the reference to the analysis for the similar bridge structures. The results verify that the global -Unzipping method and the improved difference equivalent recursion algorithm is efficient and applicable for system reliability evaluation of the complex structures such as self-anchored suspension bridges.

Abstract: Concerning the issue of high dimensions and low failure probabilities including implicit and highly non-linear limit state function (LSF), the approach of reliability simulation combing Kriging and Monte Carlo Radius-Outside Importance Sampling (MCROIS) is presented, and the Kriging model is to approximate the unknown LSF, then calculate the initial sampling radius of the sphere, and the optimal radius is gained through the iterative algorithm. As such, the joint probability density function of importance sampling is constructed, which ensures that sampling domain is restricted to values outside the sphere located in the design point, and the efficiency is improved. The numerical example of space structure latch demonstrates the efficiency, accuracy and robustness compared with Crude Mote Carlo (CMC), which is validated that the method is of particular interest in applications with a low failure probability of failure, and it realizes the comprehensive design of reliability and wear lifetime on-orbit, and makes contributions to the exploration of reliability and lifetime analysis for the complex aerospace equipment

Abstract: Stress constraints have a significant impact on the stress-strain fields of the crack front. In this paper, the weight function method is used to calculate the stress intensity factor K and constraint parameter T-stress at the crack front of pressure pipeline with a axial semi-elliptical surface crack. Based on the R6 procedure and considering the influence of stress constraint on fracture toughness, a modified failure assessment curve(FAC) and a computational formula are proposed to predict the fracture probability. In the end, a typical numerical example is presented to illustrate the proposed methodology and analyze the influences of crack geometry and axial stress on the failure probability of pipeline,where the crack size, material property parameter and load follow certain probability distribution.

Abstract: Degradation of mechanical properties of electric explosive device fuse-head was serious in different temperature and humidity environments. The objective of this study was to examine the effects of temperature and humidity aging on the damage evolution behavior of fuse-head used for electric explosive device. In this paper, the experimental studies were presented to appreciate the influence of humidity and temperature on the corrosion damage and firing of electric explosive device. The damage mechanisms and failure modes were determined through nondestructive evaluation. The explosive broken and corrosion damage on lead induced by temperature and humidity aging were the main factors affecting the firing probability. At last, the evolution rule of corrosion damage in the environment of different relative humidity and temperature was discussed.

Abstract: The strength of the aging structure deteriorates mainly as a result of corrosion and fatigue damage. In this paper, the life prediction methods of corroded and corrosion fatigued aluminum alloy structure were proposed. The stress multiplication of aluminum alloy structure subjected to corrosion damage was simulated by ANSYS software. We proposed the AFGROW software simulation method to predicate the numerical simulation of corrosion fatigue crack growth. At last, the life cycles of structures subjected to corrosion damage and corrosion fatigue were estimated, and a very good performance of the proposed methods are achieved after validation with the experimental data.