Search

Hydraulic structures are typically subjected to long-term hydraulic loading, and concrete—the main material of structures—may suffer from cracking damage and seepage failure, which can threaten the safety of hydraulic structures. In order to assess the safety of hydraulic concrete structures and realize the accurate analysis of the whole failure process of hydraulic concrete structures under the coupling effect of seepage and stress, it is vital to comprehend the variation law of concrete permeability coefficients under complex stress states. In this paper, several concrete samples were prepared, designed for loading conditions of confining pressures and seepage pressures in the first stage, and axial pressures in the later stage, to carry out the permeability experiment of concrete materials under multi-axial loading, followed by the relationships between the permeability coefficients and axial strain, and the confining and seepage pressures were revealed accordingly. In addition, during the application of axial pressure, the whole process of seepage–stress coupling was divided into four stages, describing the permeability variation law of each stage and analyzing the causes of its formation. The exponential relationship between the permeability coefficient and volume strain was established, which can serve as a scientific basis for the determination of permeability coefficients in the analysis of the whole failure process of concrete seepage–stress coupling. Finally, this relationship formula was applied to numerical simulation to verify the applicability of the above experimental results in the numerical simulation analysis of concrete seepage–stress coupling.

Context Individuals with type 2 diabetes mellitus (DM) have an increased risk of pneumonia and septic shock. Traditional glucose-lowering drugs have recently been found to be associated with a higher risk of infections. It remains unclear whether sodium-glucose cotransporter 2 inhibitors (SGLT2is), which have pleiotropic/anti-inflammatory effects, may reduce the risk of pneumonia and septic shock in DM. Methods MEDLINE, Embase, and ClinicalTrials.gov were searched from inception up to May 19, 2022, for randomized, placebo-controlled trials of SGLT2i that included patients with DM and reported outcomes of interest (pneumonia and/or septic shock). Study selection, data extraction, and quality assessment (using the Cochrane Risk of Bias Assessment Tool) were conducted by independent authors. A fixed-effects model was used to pool the relative risk (RRs) and 95% CI across trials. Results Out of 4568 citations, 26 trials with a total of 59 264 patients (1.9% developed pneumonia and 0.2% developed septic shock) were included. Compared with placebo, SGLT2is significantly reduced the risk of pneumonia (pooled RR 0.87, 95% CI 0.78-0.98) and septic shock (pooled RR 0.65, 95% CI 0.44-0.95). There was no significant heterogeneity of effect size among trials. Subgroup analyses according to the type of SGLT2i used, baseline comorbidities, glycemic control, duration of DM, and trial follow-up showed consistent results without evidence of significant treatment-by-subgroup heterogeneity (all Pheterogeneity > .10). Conclusion Among DM patients, SGLT2is reduced the risk of pneumonia and septic shock compared with placebo. Our findings should be viewed as hypothesis generating, with concepts requiring validation in future studies.

The deformation instability of surrounding rock and the collapse of rock blocks are two common failure modes observed during the construction of underground caverns. Therefore, a comprehensive safety evaluation method (CSEM) of surrounding rock for application during underground cavern construction is presented in this paper. The method can be used to evaluate the deformation stability of surrounding rock and predict the collapse of rock blocks, rapidly. First, a deformation stability prediction and evaluation method (DSPEM) for rock mass is established. It combines the safety evaluation method based on a deformation statistical analysis and an inverse deformation prediction method using measured deformation data of surrounding rock. This approach possesses the unique characteristics of complementary and mutual verification. In addition, a comprehensive early-warning index system (CWIS) for assessing the deformation stability of surrounding rock is presented. It consists of three types of warning indicators and three levels of warning values. The early-warning values can be adjusted reasonably by the prediction correction method according to the measured displacements. For the collapse of rock blocks controlled by structural surfaces, a rapid prediction method of rock block collapse (RPMBC) based on the block theory is then presented. Finally, combining the DSPEM, RPMBC, and CWIS, the CSEM of surrounding rock for assessing the safety of cavern construction is established. It can provide technical support for decision making on the safety of surrounding rock during the construction of underground caverns.

Cracking behavior in massive concrete structure is inescapable. Cracks would impair the thermal conduction ability of concrete and indirectly induce temperature redistributions, which, in this study, is termed “Crack Thermal Resistance (CTR) effect”. In order to evaluate the influence of CTR on massive concrete structure, a specific thermo-mechanical (TM) coupled model at room temperature, featuring with the evolution of concrete thermal conductivity during material fracture, is proposed based on the thermodynamic principle and concrete damage plastic model. This coupled model is coded as subroutines in ABAQUS and the implementation validated by an uniaxial cyclic test of a single element and a double edge notched specimen (DENS) test. In the DENS numerical test, it is observed that CTR effect can cause heat flux turbulences around cracking area, leading to redistributions of temperature. As a consequence, the stress field and crack opening change around the cracking area as well. In the end, this model is applied to investigate the influence of CTR on the TM coupled behavior of a gravity dam under a long term operation period thermal load. The comparison between the simulations with and without CTR effect demonstrates that (a) CTR effect has a negative effect on structure interior crack propagation, because thermal resistances near dam toe protect the dam from the downstream environment temperature shock; (b) CTR effect can induce redistributions of stress field around the crack area, but the difference in stress field does not affect the compressive stress state on dam-foundation interface.

Introduction: Computational pressure-flow dynamics derived fractional flow reserve (caFFR) is an angiographic-derived index to determine the fractional flow reserve (FFR) in patients with stable coronary artery disease (CAD), without the need of invasive pressure wire and hyperaemic stimulus in FFR. Although the safety of FFR-guided deferral of revascularization in non-ischemic lesions is well-established, clinical events still occur. The aim of the study is to investigate the prognostic implications of caFFR in those without significant ischemia. Methods: 513 stable CAD patients (mean age=64.3±11.1, 57.7% male) with all lesions being nonischemic, defined by caFFR>0.75, without undergoing revascularization were recruited. The study population was divided into high (n=240) and low (n=273) caFFR groups, according to the median value of caFFR (0.89). The primary endpoint was 3-year major adverse cardiac events (MACE), defined as a composite of all-cause mortality, myocardial infarction (MI), target vessel revascularization (TVR) and hospitalization for heart failure. Results: A total of 44 composite events occurred, including 17 all-cause mortality, 2 MI, 8 TVR and 17 hospitalization for heart failure. Following multivariate adjustment, patients in low caFFR group had a significantly higher risk of MACE than those in high caFFR group (adjusted hazard ratio [HR], 3.02; 95% confidence interval [Cl], 1.19-7.71; P=0.02). Every 0.01 decrease in caFFR was associated with a higher risk of MACE (adjusted HR, 1.12; 95%Cl, 1.03-1.21; P Conclusions: In stable CAD patients without significant functional ischemia, caFFR provides valuable prognostic information on adverse cardiac outcomes. This novel index could enhance risk stratification in stable CAD patients with nonischemic lesions.

Introduction: Computational pressure-flow dynamics derived fractional flow reserve (caFFR) has emerged for non-invasive assessment of fractional flow reserve (FFR) in patients with stable coronary artery disease (CAD), without the need for hyperaemic induction and guidewire placement in conventional FFR. The clinical value of caFFR in diabetic patients, who are at risk of microvascular dysfunction, has not been validated. The aim of the study is to evaluate the use of caFFR in diabetic patients with stable CAD. Methods: A total of 212 stable CAD patients with diabetes (mean age=67.6±10.6, 66.5% male) were included. Patients were said to be adherent to caFFR if all ischemic vessels, defined by caFFR≤0.8 were treated with PCI and all nonischemic vessels, defined by caFFR>0.8 were not. Otherwise, they were considered to be non-adherent to caFFR. The primary endpoint was 3-year major adverse cardiac events (MACE), defined as a composite of cardiovascular mortality, non-fatal myocardial infarction (MI), stroke and unplanned revascularization. Results: Among the 212 patients, PCI was performed in 62.3% of them. A total of 26 composite events occurred, including 5 cardiovascular mortality, 5 non-fatal MI, 2 strokes and 14 unplanned revascularization. The incidence rate of MACE was significantly lower in adherent patients than in non-adherent patients (5.4% vs 15.8%; P=0.01). After multivariate adjustment, adherent patients had a significantly lower risk of MACE than non-adherent patients (adjusted hazard ratio [HR], 0.33; 95% confidence interval [Cl], 0.13-0.83; P=0.02). Conclusions: In stable CAD patients with diabetes, caFFR-guided revascularization significantly reduces the risk of MACE in 3 years. The findings support the potential use of caFFR in treatment guidance of diabetic patients.

Introduction: Increasing number of heart failure (HF) patients diagnosed with dementia due to improved treatment and aging population. Data relating to the association of statin use on the risk of dementia incidence among patients with HF are sparse. Hypothesis: The use of statin is associated with lower risk of new- onset dementia in HF population. Methods: Using a previously validated territory-wide clinical information registry, statin use was ascertained among all eligible patients with HF (N=241,995) from 1996 to 2019. Propensity score matching was used to balance baseline covariates between statin nonusers (167,738 patients) with statin users (74,257 patients). Competing risk regression with Cox proportional-hazard models was performed to estimate the risk of incident dementia associated with statin use. Results: Of all eligible subjects, the mean age was 76.5±13.0 years, 115,371(47.7%) was male. Over a median follow-up of 2.7 years (interquartile range [IQR]: 0.6 to 6.7), 13,482 (5.6%) patients were diagnosed with dementia including Alzheimer's disease (N=5,253), senile dementia uncomplicated (N=4,273), arteriosclerotic dementia (N=3,262), and others (N=694). Statin use (vs. none) was associated with a 58% lower risk of dementia incidence (multivariable-adjusted sub-distribution hazard ratio [SHR]=0.42; 95% Confidence Interval [CI], 0.38 to 0.46) after accounting for death as a competing risk. Moreover, the male gender was associated with a 51% lower risk of dementia incidence (multivariable-adjusted SHR=0.59; 95%CI (0.54-0.65) compared with females. Conclusions: Our study suggests that there is substantial sex difference in the incidence of dementia among HF patients. Moreover, statin use is associated with a significantly lower risk of incident dementia in HF.

The mechanical responses of steel fiber–reinforced concrete (SFRC) thermally damaged at high temperature needs a deeper evaluation via a mesoscopic model that explicitly treats the fibers. ...

PURPOSE: Gestational diabetes mellitus (GDM) is a growing public health problem worldwide and its etiology remains unclear. The pathophysiology of GDM is similar to that of type 2 diabetes (T2DM) and insulin resistance (IR) is the main reason for the development of GDM. Carnitine palmitoyltransferase 1A (CPT1A) is a candidate gene for metabolic disorders; however, the association of the CPT1A gene and GDM has not yet been studied. We aimed to explore whether single-nucleotide polymorphisms (SNPs) of the CPT1A gene could influence the risk of GDM. METHODS: We examined 18 single-nucleotide polymorphisms (SNPs) in the CPT1A gene and the risk of GDM in a nested case-control study of 334 GDM patients and 334 controls. The controls who had no GDM were randomly selected through matching to cases by age and residence. RESULTS: After adjusting the family history of diabetes, pre-pregnancy body mass index, and multiple comparison correction, the CPT1A rs2846194 and rs2602814 were associated with reduced GDM risk while rs59506005 was associated with elevated GDM risk. Moreover, the GGAC haplotype in the CPT1A gene (rs17399246 rs1016873 rs11228450 rs10896396) was associated with a reduced risk of GDM. CONCLUSION: Our study provides evidence for an association between genetic polymorphisms in the CPT1A and the risk of GDM.

AIM The aim is to examine the association between seven candidate single nucleotide polymorphisms in AMPKα1 and gestational diabetes in Chinese people. METHOD We used a matched nested case-control study design, individuals including 334 participants with gestational diabetes and 334 healthy pregnant women. Confirmed 334 gestational diabetes cases and maternal age and district of residence matched controls (1:1) were enrolled. We examined seven candidate single nucleotide polymorphisms in AMPKα1 gene and the risk of gestational diabetes. The associations were estimated in Co-dominant, Dominant, Recessive, and Alleles models. The odds ratios (ORs) and their 95% confidence intervals (95% CI) were estimated by unconditional logistical regression as a measure of the associations between genotypes and gestational diabetes adjusting for maternal age, prepregnancy body mass index (BMI), fetal sex and parity. RESULT At the gene level, we found that AMPKα1 was associated with gestational diabetes (p = 0.008). After adjusting the covariates and multiple comparison correction, AMPKα1 (rsc1002424, rs10053664, rs13361707) polymorphisms were associated with the risk of gestational diabetes. In addition, gestational diabetes was related to the AAGGA haplotype comprising rs1002424, rs2570091, rs10053664, rs13361707 and rs3805486 in the haplotype models (p = 0.011). CONCLUSIONS This study provides evidence that the AMPKα1 genotypes (rs1002424 G/A, rs10053664 A/G, rs13361707 A/G) and the haplotype (AAGGA) are relevant genetic factors in a Chinese population with gestational diabetes.

Exposure to air pollutants may be associated with preterm birth (PB) through oxidative stress, metabolic detoxification, and immune system processes. However, no study has investigated the interactive effects of maternal air pollution and genetic polymorphisms in these pathways on risk of PB. The study included 126 PB and 310 term births. A total of 177 single nucleotide polymorphisms (SNPs) in oxidative stress, immune function, and metabolic detoxification-related genes were examined and analyzed. The China air quality index (AQI) was used as an overall estimation of ambient air pollutants. Among 177 SNPs, four SNPs (GPX4-rs376102, GLRX-rs889224, VEGFA-rs3025039, and IL1A-rs3783550) were found to have significant interactions with AQI on the risk of PB (Pinteraction were 0.001, 0.003, 0.03, and 0.04, respectively). After being stratified by the maternal genotypes in these four SNPs, 1.38 to 1.76 times of the risk of PB were observed as per interquartile range increase in maternal AQI among women who carried the GPX4-rs376102 AC/CC genotypes, the GLRX-rs889224 TT genotype, the VEGFA-rs3025039 CC genotype, or the IL1A-rs3783550 GT/TT genotypes. After adjustment for multiple comparisons, only GPX4-rs376102 and AQI interaction remained statistically significant (false discovery rate (FDR)=0.17). After additional stratification by preeclampsia (PE) status, a strongest association was observed in women who carried the GPX4-rs376102 AC/CC genotypes (OR, 2.26; 95% CI, 1.41–3.65, Pinteraction=0.0002, FDR=0.035) in the PE group. Our study provided the first evidence that association between maternal air pollution and PB risk may be modified by the genetic polymorphisms in oxidative stress and immune function genes. Future large studies are necessary to replicate and confirm the observed associations.

The risk management of cascade reservoir systems (CRSs) is a major public challenge, and the establishment of risk criteria is critical to solving this issue. In this paper, an approach is presented to establish risk criteria of for CRSs in China based on statistical data (reservoir dam break accidents; fatalities due to reservoir dam breaks; the construction date of defective reservoirs; and the current situation of CRSs), F–N curves, F–E curves, F–I curves, and the as low as reasonably practicable (ALARP) principle. This paper has some innovations in the following aspects. First, the characteristics of CRSs are revealed for the first time. Second, risk criteria for CRSs are suggested. Third, the engineering safety level, risk exposure level, and risk level of CRSs in China are determined. The research results of this paper provide abundant information for the operation management, maintenance and reinforcement of CRSs in China.

Explosive thermal spalling behavior during fire exposure is one of the major issues in the design of modern reinforced concrete structures. Previous experience on fire disasters indicates that spalling of concrete can have serious structural and economic consequences and must be taken into account in the design for fire. However, spalling mechanisms and their interaction still remain in dispute in the scientific community. In order to shed some light on this phenomenon, a discrete hygro-thermal model of concrete at high temperature called DTemPor3 is proposed and a full coupling scheme between DTemPor3 and the Lattice Discrete Particle Model (LDPM) is performed. The proposed multi-physical coupled model features the effect of pore pressure and temperature on the mechanical response as well as the impact of cracking on moisture mass transport and heat transfer. Simulations of typical spalling experiments show good agreements with data gathered from the literature for both high-performance concrete and ordinary concrete, demonstrating the accuracy of the proposed approach. Cracking localization is found to significantly impede the local pore pressure build-up due to the increase of pore or crack volume. The numerical simulations demonstrate that the spalling phenomenon can be successfully reproduced, only when the effect of thermal stresses is taken in account along with the effect of pore pressure on crack initiation.

The Impact Echo (IE) method is a widely used method for the detection of concrete structures. The signal has non-stationary characteristics. Empirical mode decomposition (EMD) is one of the typical ways of dealing with non-stationary signals. Due to EMD having mode overlap and a breakpoint effect, Variational Mode Decomposition (VMD) has been proposed to overcome these problems. In this study, VMD is introduced into the analysis of the concrete component detection signals, and the impact echo analysis method based on VMD and marginal spectrum is established. The proposed method to solve the marginal spectrum is used in order to analyze the numerical simulation model’s IE signal. This method is able to correctly obtain the main frequency. When compared with the traditional Fourier spectrum, the marginal spectrum that is based on the VMD method shows that the band width that is present in the main frequency is narrow. Even in the presence of a highly noisy background, the method is able to correctly obtain the main frequency. At last, through the detection signal analysis of the non-defective concrete specimen and the concrete specimen with the circular hole, the results show that the proposed method can distinguish the signal in the different defective states of the concrete structures, which has obvious advantages compared with the Fourier spectrum.

The representative volume element (RVE) plays an important role in the study of concrete properties. Meanwhile, RVE size determination itself is an issue that needs further study. For the first time, the problem of determining RVE size based on several factors is regarded as a multi-objective decision-making problem. A new method, the entropy weight–grey correlation model, is proposed, by comprehensively considering the influence of coarse aggregate content, aggregate average particle size and the aggregate fineness modulus. A two-dimensional concrete aggregate specimen, randomly generated by numerical simulation with an aggregate size of 5–20 mm, is taken as a case study, and the RVE size is determined as 6–7 times the maximum aggregate size. Then the finite-element method is used to verify its mechanical properties. This new method has the advantage of depending less on variable data compared to the traditional method, indicating a wider range of applicability. Additionally, the model is applied to determine the RVE size of three-dimensional concrete, which is similar to two-dimensional concrete. It provides a new comprehensive insight for the study of concrete RVE size, which could also be extended to apply to determining the RVE of other composite materials.

A hysteretic model for concrete structure subjected to cyclic tension and tension–compression reversals is presented. The proposed model was intended to predict the complex hysteretic behavior of concrete under cyclic loading in a simple and practical way. Based on the analysis of the characteristic hysteretic behavior of concrete, the residual deformation in tension was considered principally due to the incomplete closure of the opening cracks. The mechanism for the hysteretic behavior of concrete under tension–compression reversals was suggested as the crack closing and opening. Considering the application within different numerical approaches, dimensionless stress-deformation coordinates was adopted to perform the hysteretic model. The unloading and reloading paths have been derived from the crack closing and opening mechanism and were represented as straight lines in the model. Partial unloading and reloading were considered in both cyclic tension and tension–compression reversals. The proposed model has been validated by comparison with available experimental results and the seismic response of a SDOF system with the hysteretic model has been analysed.

The present work proposes a closed-form solution based on refined beam theories for the static analysis of fiber-reinforced composite and sandwich beams under simply supported boundary conditions. The higher-order beam models are developed by employing Carrera Unified Formulation, which uses Lagrange-polynomials expansions to approximate the kinematic field over the cross section. The proposed methodology allows to carry out analysis of composite structure analysis through a single formulation in global-local sense, i.e. homogenized laminates at a global scale and fiber-matrix constituents at a local scale, leading to component-wise analysis. Therefore, three-dimensional stress/displacement fields at different scales can be successfully detected by increasing the order of Lagrange polynomials opportunely. The governing equations are derived in a strong-form and solved in a Navier-type sense. Three benchmark numerical assessments are carried out on a single-layer transversely isotropic beam, a cross-ply laminate [Formula: see text] beam and a sandwich beam. The results show that accurate displacement and stress values can be obtained in different parts of the structure with lower computational cost in comparison with traditional, enhanced as well as three-dimensional finite element methods. Besides, this study may serve as benchmarks for future assessments in this field.

This study examines the effects of hydraulic pressure and tectonic stress on fracture initiation in rock flaws by using the finite element method. A square domain with double flaws is analyzed under vertical load, different horizontal loads (modeling tectonic stresses), and various hydraulic pressures.

Concrete meso-structure significantly affects its mechanical property, as crack generally starts and develops basically along the interface between aggregate and mortar on the meso-scale. The cracking path is highly dependent on the interface structure, the main component of concrete meso-structure. Since the interface is formed due to aggregate distributing in mortar mix, the relation between aggregate surface area and interface perimeter could be considered as a representative index of concrete meso-structure. As it is too complicated to adopt traditional methods to represent this relation, in order to better understanding the influence of meso-structure change on mechanical property, fractal theory is introduced to explore the relationship, with the main focus on the characteristics of the concrete meso-structure and its influence on mechanical property. Results show that the specimen size has great impact on meso-structure and mechanical property, while the influence of aggregate volume fraction can be neglected. It is more obvious in larger specimen size that aggregate volume fraction increase could contribute a lot to bearing capacity improving and whole stress level descending. Besides, aggregate volume fraction increase could improve the local cracking stress, but reduce the cracking strain, resulting in cracking brittleness.

The mesoscopic thermal cracking behavior in steel fiber reinforced concrete (SFRC) caused by high-temperature load can result in a substantial reduction of effective thermal conductivity (ETC) at macroscale level. In this study, a multiscale homogenization method for identifying the ETC of thermally damaged SFRC is proposed. This new method is characterized by the consideration of crack thermal resistance effect rather than using temperature-dependent thermal conductivities of components in cementitious composite. A series of experiments on thermal conductivity of mortar, plain concrete, and SFRC heated at various temperatures is performed. The method predictions satisfy the experimental results extremely well when the interfacial thermal resistance (ITR) coefficient is assumed to increase linearly with temperature. The numerical and experimental results show that the ITR effect makes approximately 50%, 36%, and 7%–12% contributions to the overall thermal conductivity reductions in the mortar, plain concrete, and SFRC heated up to 600 ∘ C , respectively. Moreover, it is found that the trend and magnitude of ETC reduction caused by heating increase with the increase in particle content and particle-matrix thermal conductivity ratio due to the synergistic effect of heat bridge and ITR.

The pronounced decrease of Effective Thermal Conductivity (ETC) due to the cracking behavior of concrete changes the temperature profile in concrete structures, indirectly inducing the redistribution of thermal stresses. To study this phenomenon, a mini-scale numerical method within the framework of finite element method is proposed for both tensile and compressive cracked concrete and this method is applied to obtain quantitative relationships between tensile or compressive strain and ETC. Results show that (a) for tensile dominated failure, concrete ETC decreases by 23% during the plastic stage whereas little decrease is found at complete failure; (b) for compressive dominated failure, ETC decreases by 30% during the plastic stage, and then becomes stable afterwards. In the softening stage ETC linearly decreases with the increase of compressive strain; (c) it is the interfacial thermal resistances induced by the micro-cracks between aggregates and mortar rather than the macro-cracks that play the dominant role in this phenomenon; (d) concrete ETC becomes anisotropic when cracks appear. The experiments show that compressive cracked concrete's ETC vertical to cracks dramatically decreases by 20–25% at plastic drop stage and then becomes stable at the plastic steady stage. The numerical results are used to determine the interfacial thermal resistance factor in Wang Jiajun model. The proposed formulation provides results that are in excellent agreement with experiments.

Low strain dynamic testing is an important nondestructive testing method in the engineering. However, the pile foundation material is usually assumed as having a uniform elastic modulus in low strain simulations. In this paper, we consider the elastic modulus of concrete as having an inhomogeneous elastic modulus that is described by the Weibull distribution model. An explicit algorithm was adopted in order to solve the model. The finite element method (FEM) was used to simulate the low strain dynamic test of a 3D pile. The response velocity characteristics of different shape parameters were obtained using this method, and the Daubechies wavelet transform was used to analyze the characteristics of the wavelet modulus. The result shows that simulation response velocity has a correlation with the different homogeneity of the elastic modulus.

The scale of cascade reservoir systems is increasing rapidly along with the development of hydroelectric projects in these systems. Related security problems are receiving increasing public attenti...

The drying process of concrete is a complex unsteady heat and mass transfer process that is greatly affected by the drying temperature. The influence of the drying process on the drying cha...

This paper investigates the free vibration of a homogeneous Euler–Bernoulli beam with multiple transverse cracks under non-symmetric boundary conditions. The differential equation is formulated by introducing Dirac’s delta function into the uniform flexural stiffness, and the close-form solution of mode shapes is then derived by applying the Laplace transform technique. The proposed method is validated against existing experimental method for damaged cantilever beams. With the validated method, a parametric study is performed to study the effect of crack numbers, damage parameters and crack locations on the natural frequencies and mode shapes for three non-symmetric boundary conditions (pinned–clamped, clamped–free shear and pinned–free shear).

Compared with conventional time-frequency analysis method, synchrosqueezing wavelet transformation (SST) exhibits high resolution capability and good application effect. In this study, SST is introduced to ground-penetrating radar (GPR) processing. This method is applied to analyze a continuous electromagnetic signal. SST can obtain a higher resolution and a better processing effect than conventional wavelet transform and short-time Fourier analysis. In the application of GPR forward analysis data, the transform can correctly distinguish different interfaces and objects. Its resolution increases as frequency increases. However, compression wavelet modulus gradually decays as frequency increases. The proposed method is applied to detect tunnel lining under actual conditions and in a strong noise background. Indeed, the method can efficiently identify interfaces and abnormalities.

The principal means of conserving water and utilizing hydropower in China is to exploit the use of a series of reservoirs in a cascade. This method and its inherent engineering safety problems are receiving increasing attention nowadays. In the field of engineering safety analysis, much work has focused on single reservoir projects in the past few years, but there is little research available on the safety risk analysis of cascade reservoirs, either within China or internationally. Therefore, a framework for risk analysis on the cascade reservoir system based on the theory of system engineering is constructed in this article. A cascading failure model is established and the connection degree factor discussed. In addition, the importance degree of the subsystem, which can be calculated by combining the analytical hierarchy process and the entropy weight method, is explained. According to brittleness theory of a complex system, brittle risk entropy is proposed as a performance index for measuring the collapse uncertainty of the cascade reservoir system. In addition, the brittle risk of the cascade reservoir system is predicted, which provides a reference for safety analysis in water conservation and hydropower construction projects in China.

The mechanical properties and damage cracks of concrete, especially the former in non-elastic phase, are obviously discrete and random. One important influencing factor is the aggregate distribution, but its quantitative characterization is a tricky issue. At mesoscale, the numerical specimen of concrete is established by assuming the concrete as three-phase composite material, which is composed of aggregate, mortar matrix, and the interfacial transition zone (ITZ) between them. The uniaxial tensile mechanical behaviors of 36 groups of concrete specimens with different aggregate distribution are performed numerically to gain the mesoscopic damage crack paths. Successively, the box dimension and multifractal spectrum are employed to quantitatively characterize the aggregate and crack distribution. It is found that the multifractal spectrum shows a better performance for the local detail features characterization than that of box dimension, which thus is turned out to be a new method for quantitative study of aggregate distribution. Furthermore, the correlations among multifractal spectrum width of aggregate distribution, peak stress, brittleness, and box dimension of crack distribution are analyzed statistically. The results show a negative relation of multifractal spectrum width of aggregate distribution and box dimension of crack distribution with peak stress and brittleness, but positive relation of multifractal spectrum width of aggregate distribution with box dimension of crack distribution. This implies that lower multifractal spectrum width of aggregate distribution, indicator of more uniform of aggregate distribution, will result in higher tensile strength and brittleness, and lower box dimension of crack distribution, representative of more regular of crack propagation. These results provide valuable information for in-depth understanding of the mechanical properties and damage cracking of concrete.

Single shear tests performed to study the debonding between the concrete and the FRP plate of 2 mm thickness are presented. Specimens with five different bond lengths have been tested. In order to investigate the debonding mechanism and measure the complete strain distribution, digital image correlation (DIC) method was applied. The shear stress and slip distribution curves were calculated from the strain distribution functions fitted from measured strain data. Based on the features of the shear stress transfer zone under different load levels, the whole loading process has been divided into four stages: (1) elastic stage; (2) cracking stage; (3) debonding stage; (4) failure stage. According to the relationship between the relative bearing capacity and bond length, a concept of efficient bond length was suggested. A bi-linear bond stress-slip model was calibrated by the constitutive parameters of the experimental shear stress-slip curves. Based on the bi-linear bond stress-slip relationship, a numerical model of FRP plate-concrete interface was built using the bonded-particle model (BPM) and the debonding process was numerically analyzed. The numerical results present good agreement with the experimental results in the load-slip response and the shear stress distribution along the bond length. The comparison between the experimental and the numerical results shows that BPM can effectively simulate the debonding process of the FRP plate-concrete interface.

In order to test vehicle shift-feel, establish key models of automotive power transmission such as automotive engines, torque converters, transmissions, clutches, and vehicle loads. Build up the simulink model of the whole vehicle power transmission system, simulate the vehicle accelerates, observe the variety of the speed of the Turbine speed of hydraulic torque converter and the output shaft torque.

The pronounced decrease of effective thermal conductivity (ETC) due to cracking behavior of concrete will change the temperature profile in concrete structures, indirectly inducing the redistribution of thermal stresses. To evaluate this phenomenon, this paper presents a mesoscopic numerical method that is capable of quantitatively evaluating the effect of cracking behavior on concrete ETC. With this method, the development of ETC during uniaxial tension test of concrete is investigated and main conclusions are drawn as follows: (a) the ETC decreases greatly when micro-cracks initiate, and then becomes anisotropic when micro-cracks further propagate; (b) the cracked concrete ETC and its decrease rate nonlinearly increase with aggregate volume fraction (AVF); (c) the drop of ETC in specimens made by circle aggregates is greater than that in specimens made by arbitrary polygon aggregates, and their difference becomes more pronounced with the increase of AVF; (d) these numerical results can be utilized to determine uncertain parameters when estimating cracked concrete ETC using a recommended semi-theoretical model.

The fracture parameters (the fracture energy and the effective length of the fracture process zone for an infinitely large specimen) in the size effect model of concrete exhibit a large scatter as measured in most of the experimental studies. This phenomenon is ubiquitous and has presented a great challenge to characterize the structural failure over the last decade. In order to remove the perplexing issue, this paper develops two models to predict the two fracture parameters using the artificial neural network (ANN) methodology. The proposed models are verified by using 77 experimental data collected from the literature. The results demonstrate that the two ANN-based size effect model models (ANN-I and ANN-II) are viable for predicting the fracture parameters and yield more accurate results than those obtained from the conventional regression formulations. Additionally, a parametric study is employed to evaluate the impact of each independent material parameter on the fracture parameters.

The dynamic model of the hydraulic control system of the shift clutch is established through the flow equation of the valve port, the flow continuity equation and the balance equation of the valve core force, the piston motion of clutch cylinder is divided into three stages. And simulate the dynamic curves of the hydraulic pressure of the hydraulic inlet of the hydraulic cylinder during different stages.

The low efficiency of feedback analysis is one of the main shortcomings in the construction of underground cavern engineering. With this in mind, a method of intelligent autofeedback and safety early-warning for underground cavern is proposed based on BP neural network and FEM. The training sample points are chosen by using uniform test design method, and the autogeneration of FEM calculation file for ABAQUS is realized by using the technique of file partition, information grouping, and orderly numbering. Then, intelligent autoinversion of mechanics parameters is realized, and the automatic connection of parameter inversion, subsequent prediction, and safety early-warning is achieved. The software of intelligent autofeedback and safety early-warning for underground cavern engineering during construction is developed. Finally, the applicability of the proposed method and the developed software is verified through an application example of underground cavern of a pumped-storage power station located in Southwest China.