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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.

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...

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.

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...

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...

Reinforcement corrosion exhibits an adverse effect on the shear strength of reinforced concrete structures. In order to investigate the effects of chloride-induced corrosion of reinforcing steel on the shear behavior and failure pattern of reinforced concrete beams, a total of 24 reinforced concrete beams with different concrete strength grades and arrangements of stirrups were fabricated, among which 22 beams were subjected to accelerated corrosion to achieve different degrees of reinforcement corrosion. The failure pattern, crack propagation, load–displacement response, and ultimate strength of these beams were investigated under a standard four-point loading test in this study. Extensive comparative analysis was conducted to investigate the effects of the concrete strength, shear span-to-depth ratio, and stirrup type on the shear behavior of the corroded reinforced concrete beams. The results show that increasing the stirrup yielding strength is more effective in improving the shear strength of corroded reinforced concrete beams than that of concrete compressive strength. In terms of three types of stirrups, the shear strength of the beams with deformed HRB-335 is least sensitive to stirrup corrosion, followed by the beams with smooth HPB-235 and the beams with deformed HRB-400. The effect of the different stirrups on the shear strength depends on the corrosion degree of stirrup and shear span-to-depth ratio of the beam. The predicted results of shear strength of corroded reinforced concrete beams by a proposed analytical model are well consistent with the experimental results.

A total of 158 experimental tests of shear behavior of corroded reinforced concrete (CRC) beams under action of concentrated load, published in the literature were collected and compiled into a shear strength database. This database was firstly used to discuss important parameters which affect the shear strength of CRC beams. The results show that the effect of stirrups’ corrosion on shear capacity of CRC beams is greater than that of longitudinal reinforcement corrosion. The shear span-to-depth ratio is also an important factor on shear strength of CRC beams. Total 9 available empirical models for predicting the residual shear strength are evaluated and compared based on the test database. It is found that eight of the nine models underestimate the shear strength of CRC beams while the other model gives the overestimated results. It is in this regard that a new empirical model for predicting the residual shear strength of CRC beams is proposed, in which a reduction coefficient is incorporated with the consideration of the effect of stirrups’ corrosion as well as shear span-to-depth ratio. The comparison studies demonstrate that the new proposal can provide an effective and accurate prediction of the shear capacity of CRC beams with a wide range of reinforcement corrosion damages.

In this paper, a new analytical formula is proposed to determine the mean outcrossing rate of nonstationary non-Gaussian performance functions. The performance function is firstly transform...

Structural reliability analysis involving highly nonnormally distributed performance functions or relatively small failure probabilities is still a challenging problem in engineering practi...

Structural reliability analysis without the exclusion of random variables with unknown distributions has attracted increasing attention, and many endeavors have been devoted to this aspect....

In determining structural responses under random excitation using the Monte Carlo method, simulation of non-Gaussian processes is always a challenge. Various methods have been developed to ...

The light-frame low-rise buildings widely used for residential and industrial purposes are very vulnerable to high winds. Postdisaster surveys indicated that envelope components such as win...

The effects of erosion mode, erosion age, and concentration of sulfate solution on mechanical properties of concrete were investigated. The dimensionless relationship model of the stress-strain of concrete on the basis of randomness was proposed. The variation of the elasticity modulus and Poisson’s ratio of the concrete surface attacked by sulfate was studied, and a novel method of using a superficial parameter to characterize the performance change of the concrete surface was recommended. The results showed that the dimensionless relationship model of stress-strain of concrete could be used to represent the variations of mechanical properties of concrete. The differences of load-displacement of concrete before and after sulfate attack were reflected as the change of curve’s slope and ultimate bearing capacity, and the slope of a straight section of the lateral and longitudinal strain curves of concrete surface also varied. The increment rates of ultimate bearing capacity of concrete attacked by 1% and saturated sulfate solution were about 30% and 10%, respectively. However, the decreasing ratio of the ultimate bearing capacity of concrete attacked by saturated sulfate solution was approximately 25%. The damage factor of the elasticity modulus of the concrete surface of C20 and C40 was 0.185 and −0.19, respectively. The obtained results could provide a support for investigating the variations of stress-strain relationship and mechanical performance of concrete under a sulfate environment.

In this article, an analytical moment-based procedure is developed for estimating the first passage probability of stationary non-Gaussian structural responses for practical applications. In the procedure, an improved explicit third-order polynomial transformation (fourth-moment Gaussian transformation) is proposed, and the coefficients of the third-order polynomial transformation are first determined by the first four moments (i.e. mean, standard deviation, skewness, and kurtosis) of the structural response. The inverse transformation (the equivalent Gaussian fractile) of the third-order polynomial transformation is then used to map the marginal distributions of a non-Gaussian response into the standard Gaussian distributions. Finally, the first passage probabilities can be calculated with the consideration of the effects of clumping crossings and initial conditions. The accuracy and efficiency of the proposed transformation are demonstrated through several numerical examples for both the “softening” responses (with wider tails than Gaussian distribution; for example, kurtosis > 3) and “hardening” responses (with narrower tails; for example, kurtosis

The corrosion rate of reinforcing steel is an important factor to determine the corrosion propagation of reinforced concrete structures in the chloride-laden environments. Since the corrosion rate of reinforcing steel is affected by several coupled parameters, the efficient prediction of which remains challenging. In this study, a total of 156 experimental data on corrosion rate from the literature were collected and compared. Seven empirical models for predicting the corrosion rate were reviewed and investigated using the collected experimental data. Based on the investigations, a new empirical model is proposed for predicting the corrosion rate in corrosion-affected reinforced concrete structures considering parameters including concrete resistivity, temperature, relative humidity, corrosion duration and concrete chloride content. The comparison between the experimental data and those predicted using the new empirical model demonstrates that the new model gives a good prediction of the corrosion rate. Furthermore, the uncertainty and probability characteristics of these empirical models are also investigated. It is found that the probability distributions of the model errors can be described as lognormal, normal, Weibull or Gumbel distributions. As a result, the new empirical model can provide an efficient prediction of the corrosion rate of reinforcing steel, and the model error analysis results can be utilized for reliability-based service life prediction of reinforced concrete structures under chloride-laden environments.

So far, the loading path effect on the compressive strength of confined concrete has been poorly investigated. To clarify the compressive strength of confined concrete in concrete-filled steel tube (CFT) columns, experimental tests with a total of 18 specimens are conducted to investigate the loading paths of confined concrete in concrete loaded CFT stub columns. The parameters that are varied in the experiment include the steel strength, the unconfined concrete strength and the D/t ratio. Two evaluation indices, namely the laterally dominant index and the effect index, are proposed to characterize the loading path and its effect on the compressive strength of confined concrete, respectively. A detailed parametric study is conducted on the loading paths and the corresponding effects on compressive strength. The results suggest that the loading paths of confined concrete in CFT column are affected by the column parameters. Depending on the loading paths by which the concretes are confined, the loading path effects on the compressive strength of the confined concrete in CFT columns could be totally different. Based on the test results, a compressive strength model incorporating the loading path effect is developed and good performance was found in comparison with the experimental results.

Analyzing the uncertainty of flutter propagated from different sources especially flutter derivatives is important for the risk assessment of long-span bridges. The uncertainty of flutter derivatives is often characterized based on the experimental data. Dependence and sampling error would therefore exist which may influence the onset prediction of bridges. This paper devotes to developing a framework towards the uncertainty analysis of bridge flutter considering the dependence and sampling error in flutter derivative measurements. In this framework, the dependence among different flutter derivatives is identified with Spearman’s rho instead of conventional Pearson’s product-moment correlation coefficient. A modified procedure based on bootstrap is proposed to characterize the sampling error by representing distribution parameters of flutter derivatives as interval variables. Regarding the probability-interval hybrid uncertainty, a double-layer analysis is employed. In the inner layer, probability of onset velocity is estimated using the point estimate-based probability analysis. In the outer one, the distribution envelope is obtained by the genetic algorithm-assisted interval analysis. Application of the framework to reliability assessment of bridge against flutter is also presented. In the numerical study, the influence of dependence and sampling error is verified in detail. By this framework, the distribution envelope of onset velocity or the interval of reliability index against flutter are expected to contain the true estimates. Consequently, the potential risk with respect to bridge flutter can be assessed in a conservative way.

The objectives of this paper is to investigate the mechanical behavior of steel reinforced concrete-filled square steel tubular (SRCFT) stub columns under axial loading through combined experimental and numerical studies. In total of six specimens are tested to investigate the effect of the concrete strength and steel ratio on the mechanical behavior of SRCFT stub columns. The ultimate bearing capacity, ductility, and confinement effects are discussed and clarified based on the experimental results. The inserted steel section can effectively prevent shear cracks in the core concrete from propagating quickly. The strength-weight-ratio of SRCFT stub column is larger than SCFT stub column. In addition, ABAQUS is used to establish the 3D finite element (FE) model and analyze the composite action of SRCFT stub columns under axial loading. Based on the experimental and numerical results, a simplified formula is proposed to estimate the ultimate bearing capacity of SRCFT stub columns using superposition method. The predicted results show satisfactory agreement with both experimental and FE results.

Background: Several previous studies have shown that snoring is associated with glucose metabolism and the development of diabetes, but rare study has shown the association between snoring frequency and prediabetes, particularly in China. We hypothesized that individuals who snore might have a higher risk of prediabetes. This study aimed to investigate the association between self-reported snoring and prediabetes in a Chinese population. Methods: A cross-sectional study was performed in three large communities of Beijing from December 2011 to August 2012 by recruiting individuals aged ≥40 years old. All participants were requested to complete a detailed questionnaire and undergo anthropometric measurements. A 75 g oral glucose tolerance test was performed in individuals without diabetes. Blood samples of all participants were collected; blood glucose and blood fat levels were measured. Multivariate logistic regression models were built to assess the association between snoring frequency and prediabetes. Results: A total of 13,592 participants (female: 66.56%; mean age: 56.8 ± 7.9 years; mean body mass index: 25.5 ± 3.4 kg/m2) were included in the final analysis. Of these, 30.9% were diagnosed with prediabetes, while 41.3% and 25.4% had occasional and habitual snoring, respectively. Habitual snoring was associated with an increased risk of prediabetes (odds ratio [OR]: 1.3, 95% confidence interval [CI]: 1.1–1.4, P < 0.001), after adjusting for diabetes and sleep-related confounders in the multivariable models. Habitual snoring was also associated with isolated impaired fasting glucose (IFG; OR: 1.3, 95% CI: 1.0–1.6; P < 0.001) and isolated impaired glucose tolerance (IGT; OR: 1.3, 95% CI: 1.2–1.5; P < 0.001), but not IFG + IGT (OR: 1.1, 95% CI: 0.9–1.4; P = 0.281). When stratified by total cholesterol (TC) levels, this association between habitual snoring and prediabetes was observed only in individuals with TC

The third-moment (3M) method has been considered to be one of the most reliable methods for calculating structural reliability with high computing efficiency. This paper proposes a new 3M reliabili...

Objective: To investigate the role of PSMA in the differential diagnosis of adrenocortical carcinoma samples (ACCs) and adrenocortical adenoma samples (ACAs), to validate the prognostic role of PSMA in patients with ACCs, and to explore the possibility that this marker can differentiate localized ACCs from adrenal metastases from other sites.Methods: PSMA protein expression in tissue samples from 50 ACCs, 90 ACAs (including 20 from patients who presented with Cushing's syndrome, 20 aldosterone-producing adenomas and 50 non-functional tumors) and 10 tissues that were metastases from other primary sites was assessed by immunohistochemistry. The clinical and pathological characteristics were compared, the intensity and density were analyzed, and the prognostic role was evaluated.Results: The analysis of clinical and pathological features revealed that the size of ACCs was greater than that of benign tissues and the ACC patients were older than the ACA patients (p < 0.01). The percentage of PSMA-positive vessels, the mean intensity and the degree of staining density were found to be significantly lower in ACAs than in ACCs (p < 0.01). In these 140 samples, 60% of the ACCs were grouped in the positive category. The samples were negative for metastases that were from other primary sites. The ENSAT stage and Ki-67 were correlated with PSMA expression. The survival distribution revealed that high PSMA expression did not show any prognostic relevance in the current ACCs series. Those samples with a score of > 3.5 were 75 times more likely to be malignant (OR = 75). We established a cut-off score of 3.5 (p < 0.05), which had 46% sensitivity and 99% specificity. Paralleling PSMA and Ki-67 maximized the area under the curve, with 72% sensitivity and 100% specificity.Conclusions: Our results strongly confirm that PSMA is helpful for distinguishing benign from malignant tumors and that its high expression levels correlate with a high ENSAT stage and high proliferation. The combination of PSMA and Ki-67 can be particularly useful. Furthermore, PSMA might be a useful tool for the identification of localized adrenal carcinoma and metastatic carcinoma.

Non-Gaussian processes beset many aspects of structural engineering analysis. To estimate non-Gaussian processes, various third-order Hermite polynomial models have been proposed and widely...

Evaluating the statistical moments of performance functions from the perspective of balancing accuracy and efficiency remains a challenge. This paper proposes an efficient algorithm for eva...

Previous studies suggested that the behaviors of confined concrete in concrete-filled steel tube (CFT) columns were dependent on their confining stress paths, which thus should be considered in order to well predict their behaviors. Several confining stress path dependent analytical models had been proposed, which, however, were all developed for fiber polymer (FRP) confined concretes. Although one of the existing models can also be applicable to CFT columns, it mainly focused on the specimens with normal strength concrete. Additionally, existing confining stress path dependent models may result in fluctuation issue of load-deflection curves for CFT specimens. This paper proposed a new confining stress path dependent analytical model that is applicable to normal, high and ultra-high strength concrete-filled steel tube columns. Experimental tests were collected to assess the performance of the proposed analytical model, and it was found that the proposed model performs quite well for normal, high and ultra-high strength concrete-filled steel tube columns and generally can avoid the fluctuation issue of load-deflection curves.

The fibre beam element (FBE) method has been widely used to investigate the behaviors of concrete-filled steel tube (CFT) columns for its high efficiency and accuracy. The existing models were generally developed or calibrated by using specimens with relatively small size, in which the size effects were ignored or poorly incorporated. Additionally, most existing FBE models focused on CFT stub columns. In this paper, a new FBE model for nonlinear analysis of concentrically loaded stub and slender columns was proposed, in which the size effects on the effective stress-strain relationships of steel tube and core concrete were well incorporated. The proposed FBE models were then used to develop an ultimate strength model for the design of both stub and slender columns. A total of 1029 specimens assembled from 72 previous studies were used to verify the proposed models. The results suggested that the proposed FBE model performs quite well for both small- and large- size CFT stub columns and predicts the behaviors of slender columns with reasonable accuracy. Moreover, the ultimate strength model developed based on the proposed FBE models was found to make satisfying prediction of test results.