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Reliability assessment of ductile frame structures in a systematic manner has remained a challenging issue because of the difficulties in searching for important failure modes and evaluating the system probability of failure stemmed from these important modes. In this paper, based on the Box-Cox transformation, a new failure mode independent performance function with the probability distribution of weak non-normality is proposed for the system reliability assessment of ductile frame structures. An efficient approach is then developed for estimating the failure probability of the proposed performance function, which includes two steps: first, the point-estimate method based on hybrid dimension-reduction integrated with structural limit analysis is developed to evaluate the first four central moments (i.e., mean, standard deviation, skewness, and kurtosis) of the proposed performance function; next, the system probability of failure corresponding to the proposed performance function is then estimated using the moment-based reliability method. Three numerical examples are presented to demonstrate the efficiency and accuracy of the proposed method, where the method of subset simulation is employed for comparison. It can be concluded that the developed methodology successfully overcomes the two difficulties including the identification of important failure modes and the evaluation of system probability of failure stemmed from these important modes in system reliability assessment of ductile frame structures.

Mechanical heterogeneity is a major characteristic of the organic-rich shale. The relation between mechanical heterogeneity and formation in-situ stress has been seldomly addressed but important to understand hydraulic fracture propagation, wellbore stability, and hydrocarbon flow. In this paper, the grid nanoindentation technique was used to characterize the heterogeneity of the mechanical properties of Longmaxi organic-rich shales from various burial depths and in-situ stress. The measured elastic modulus and hardness of each sample are deconvolved into three phases including soft phase, medium stiff phase and stiff phase according to mineral category. As the burial depth and corresponding in-situ stress increase, the overall elastic modulus and hardness of the sample enhance. Simultaneously, the percentage of soft minerals decreases, and the probability distribution tends to concentrate through 95% confidence interval evaluation which demonstrates weakened heterogeneity. Furthermore, SEM images provide evidence that extended cracking, initiated cracking, crushing and ductile deforming always occur around indentation imprints. This confirms that even under deep buried depth and high in-situ stress, brittle fracture and ductile deformation can exist synchronously. This paper demonstrates the influence of in-situ stress on the heterogeneity of shale micromechanics.

On-site observations show that several damages have occurred in CRTS II slab-type ballastless track system, such as crack and interface debonding between different structural layers, which will trigger the occurrence of some failure modes of CRTS II track slab. As the damages are the prior for specific failure modes, time-dependent reliability of CRTS II track slab should be conducted considering the uncertainties associated with both the failure mode and the damage, which is defined as the conditional time-dependent reliability in this study. To appropriately express the causal relationship among the failure modes and prior damages, a conditional limit state function (LSF) model is proposed with explicit expressions provided. With the aid of the proposed model, conditional time-dependent reliability of CRTS II track slab for two individual failure modes are investigated, which are the steel yielding failure mode under longitudinal cracking, and the vertical instability failure mode under interface debonding. Furthermore, conditional time-dependent system reliability of the track slab has also been analyzed considering four safety failure modes. The advantage of the proposed method is that prior damages have been accounted in establishing the failure criteria and incorporated in the formulation of time-dependent reliability, which provides a general formwork for structural reliability involving the causal relationship among the failure modes and damages.

The service life of reinforced concrete structures is significantly affected by the chloride-induced corrosion of reinforcing steel. This paper presents a comprehensive study on the influence of the corrosion environment and other parameters on the corrosion rate of reinforcing steel in concrete. Comparative tests were carried out on concrete block and beam specimens subjected to accelerated corrosion in indoor and outdoor environments for a period of 1.5 years. The experimental variables considered included the chloride content, depth of concrete cover, type of reinforcing steel and water-to-cement (w/c) ratio. The test results indicated that the corrosion rate of the reinforcing steel increases with the increase in the w/c ratio, chloride content, temperature and relative humidity, while it is reduced when the thickness of the concrete cover increases. Furthermore, an empirical model for predicting the corrosion rate of reinforcing steel in concrete is proposed using the experimental data, which offers a good prediction of the corrosion rate.

In this paper, a total of 70 experimental flexural tests of corroded post-tensioned prestressed concrete (PC) beams were gathered from the published literatures. Using the experimental data, a comprehensive databank of flexural capacity of the corroded PC beams was established. Meanwhile, four existing empirical models for calculating the residual flexural strength of the corroded PC beams were also gleaned and contrasted with each other based on the databank. It turns out that three of the four existing empirical models underestimate the flexural capacity. To deeply analyze the factors affecting the flexural capacity, numerous factors were discussed, e.g., the corrosion ratio, beam width, effective height of the beam section, concrete compressive strength, and the ratio of strength between the tensile reinforcement (including prestressed and non-prestressed reinforcement) and concrete. It is found that the corroded post-tensioned PC beams’ residual flexural capacity is affected most by the corrosion ratio. In the end, a better empirical model is proposed for computing the residual flexural capacity of corroded PC beams, which provides accurate and effective predictions in a wide range of corrosion ratio for engineering practice.

This paper introduces an efficient methodology for evaluating the first four central moments of performance functions in structural reliability assessment. The procedure of the proposed method is d...

The interface damage is one of the main concerns for high-speed railway ballastless track structures during its whole service life, as it would affect the reliability of track structures or even cause the high-speed train accident. In this paper, various existing cohesive zone models (CZMs) were identified and compared regarding the performance in modeling the interface behaviors of ballastless track structures. The results show that the existing CZMs cannot accurately represent the nonlinear relationship of the ascending and descending sections in the interface traction-separation curve concurrently. Therefore, a new CZM was proposed in this study, and the feasibility of the proposed model was examined by the experimental results. It indicates that the proposed model can reasonably describe the nonlinear behaviors of the ascending and descending sections in the traction-separation curve by introducing exponential coefficients. The proposed CZM also exhibits higher accuracy in predicting the normal and tangential cracking behaviors of the interlayer interface of the ballastless track structures in comparison with the existing models, with the coefficients of determination (R2) in the fitting results all above 0.85. As a result, this model can be used for the analysis of the interface behaviours of ballastless track structures.

Background The interaction between tumor microenvironment (TME) and tumors offers various targets in mounting anti-tumor immunotherapies. However, the prognostic biomarkers in endometrial carcinoma (EC) are still limited. Here, we aimed to analyze the TME features and identify novel prognostic biomarkers for EC. Methods ESTIMATE, CIBERSORT, protein-protein interaction (PPI) network, univariate and multivariate Cox regression, and functional enrichment analysis were performed to identify immune- and survival-related hub genes as well as possible molecular mechanisms. The limma package and deconvolution algorithm were adopted to estimate the abundance of tumor-infiltrating immune cells (TICs) and their relationship with the target gene. In the validation section, tissue microarrays (TMAs) of EC and multiplex immunohistochemistry (m-IHC) were evaluated to validate the expression of TNFRSF4, and its correlation with immune markers, including CD4, CD8, and FOXP3. Besides, the receiver operating characteristic (ROC) curve was plotted to determine the diagnostic performance of TNFRSF4, CD4, CD8, and FOXP3 in EC. Results Two genes, TNFRSF4 and S1PR4, were screened out from 386 intersection differential expression genes (DEGs) shared by ImmuneScore and StromalScore in EC. Highlighted by TNFRSF4, we found that it was not only positively correlated with the TICs (mainly CD4+ T cells, CD8+ T cells, and Tregs) but significantly related to the prognosis in patients of EC, both verified by data from The Cancer Genome Altas (TCGA)-EC database and clinical samples. At the same time, the expression trend of TNFRSF4 was further confirmed by an integrated meta-analysis based on six microarrays from the Gene Expression Omnibus database (GEO). Conclusions Collectively, TNFRSF4, a previously unrecognized key player in EC, could serve as a potential biomarker for prognosis prediction and immunomodulation of EC.

Bayesian updating of the reliability of deteriorating engineering structures based on inspection data has been attracting a lot of attention recently because it can provide more accurate es...

In this study, a total of 177 flexural experimental tests of corroded reinforced concrete (CRC) beams were collected from the published literature. The database of flexural capacity of CRC beam was established by using unified and standardized experimental data. Through this database, the effects of various parameters on the flexural capacity of CRC beams were discussed, including beam width, the effective height of beam section, ratio of strength between longitudinal reinforcement and concrete, concrete compressive strength, and longitudinal reinforcement corrosion ratio. The results indicate that the corrosion of longitudinal reinforcement has the greatest effect on the residual flexural capacity of CRC beams, while other parameters have much less effect. In addition, six available empirical models for calculating the residual flexural strength of CRC beams were also collected and compared with each other based on the established database. It indicates that though five of six existing empirical models underestimate the flexural capacity of CRC beams, there is one model overestimating the flexural capacity. Finally, a newly developed empirical model is proposed to provide accurate and effective predictions in a large range of corrosion ratio for safety assessment of flexural failure of CRC beams confirmed by the comparisons.

The existing theoretical models for the analysis of concrete-filled steel tube (CFST) columns are mainly limited to circular specimens. This paper is aimed at developing a unified theoretic...

The concept of system reliability will be described in this chapter. A moment-based method for assessing the system reliability of series and non-series structures is investigated, with emphasis on series systems. The reliability index is directly calculated based on the first few moments of the system performance function of a structure. It requires neither the reliability analysis of the individual failure modes nor the iterative computation of derivatives, the computation of the mutual correlations among the failure modes, and any design points. As a practical topic, the evaluation of system reliability for ductile frame structures using methods of moment is introduced in the final part of this chapter. The difficulty in both failure mode identification and failure probability computation is still hard to overcome when using the traditional method for the system reliability assessment of ductile frame structures. To avoid the difficulties, a failure mode independent performance function with weak non-normality is introduced. The method of moments is then utilized to estimate the failure probability of ductile frame structures corresponding to the general performance function. From the numerical examples, it can be concluded that the introduced methodology successfully overcomes the two difficulties including the identification of significant failure modes and the computation of overall failure probabilities contributed from these significant modes in system reliability evaluation of ductile frame structures.

Because of the vulnerability of roof sheathing panel to wind load, light-frame wood low-rise buildings often suffer from serious destructions in typhoon hazards. Efficient assessment of the...

The corrosion of steel strands due to the chloride contamination is one of the most common causes for the degradation of prestressed concrete infrastructure. In this paper, an experimental study was performed to investigate the bond behaviors between steel strands and concrete after suffered the chloride corrosion. Total twenty central and off-center pull-out specimens with different corrosion levels were prepared and tested, in which the electrochemical acceleration method was employed to induce various corrosion levels. The effects of corrosion rate, stirrup configuration and holding condition of concrete to the steel strands on the bond behaviors of steel strands were studied and compared, in terms of the failure mode, bond-slip relationship, bond strength, and bond toughness. The results show that both the ultimate bond strength and characteristic bond strength decreased with the increase of corrosion degree. The presence of stirrups can significantly enhance the bond performance, indicating the more ductile failure characteristic and increased bond toughness. Moreover, the prediction results using empirical and analytical models are also compared with the experimental results to verify their applicability and accuracies in predicting the bond strength of steel strands after corrosion.