Admissible Stress Research Articles

Three-dimensional fracture modes decoupling by means of invariant integrals in wood under mixed mode loading

This paper addresses the determination of the energy release rate in an orthotropic elastic material such as wood with a three-dimensional view of the problem. The mixed mode loading associated with the anisotropy of the material required mode decoupling by isolating the energy release rates in mode I, mode II and in mode III. These energy release rates are calculated using the invariant integral M of Linear Elastic Fracture Mechanics (LEFM). This decoupling has necessitated the introduction of kinetically and statically admissible three-dimensional virtual displacement and stress fields in the vicinity of the crack front. The fracture mode decoupling strategy is presented and implemented through finite element modelling of a Mixed Mode Crack Growth (MMCG) specimen. Different thicknesses are investigated to highlight the 3D effects. The modelling highlighted the effect of Mode II at the edges of free surfaces for mixed loadings including mode III (mode III, mode (II+III) and mode (I+II+III)), while mode III was the predominant at the middle of the specimen. In cases of mixed mode (I+II), the energy release rate GI was highest at the middle of the specimen and lowest at the edges of the free surfaces, regardless of the degree of mixing for a given thickness. The correlation between the results obtained using the proposed approach and the non-dependence of the integration domain, as well as with the usual approaches employed in the literature, is demonstrated.

Passive earth pressure on vertical rigid walls with negative wall friction coupling statically admissible stress field and soft computing

It is well known that the roughness of a wall plays a crucial role in determining the passive earth pressure that is exerted on a rigid wall. While the effects of positive wall roughness have been extensively studied in the past few decades, the study of passive earth pressure with negative wall friction is rarely found in the literature. This study aims to provide a precise solution for negative friction walls under passive wall conditions. The research is initiated by adopting a radial stress field for the cohesionless backfill and employs the concept of stress self-similarity. The problem is then formulated in a way that a statically admissible stress field be developed throughout an analyzed domain using a two-step numerical framework. The framework involves the successful execution of numerical integration, which leads to the exploration of the statically admissible stress field in cohesionless backfills under negative wall friction. This, in turn, helps to shed light on the mechanism of load transfer in such situations so that reliable design charts and tables be provided for practical uses. The study continues with a soft computing model that leads to more robust and effective designs for earth-retaining structures under various negative wall frictions and sloping backfills.

Additive effect of admission hyperglycemia on left ventricular stiffness in patients following acute myocardial infarction verified by CMR tissue tracking

BackgroundStress hyperglycemia occurs frequently in patients following acute myocardial infarction (AMI) and may aggravate myocardial stiffness, but relevant evidence is still lacking. Accordingly, this study aimed to examine the impact of admission stress hyperglycemia on left ventricular (LV) myocardial deformation in patients following AMI.MethodsA total of 171 patients with first AMI (96 with normoglycemia and 75 with hyperglycemia) underwent cardiac magnetic resonance (CMR) examination were included. AMI patients were classified according to admission blood glucose level (aBGL): < 7.8 mmol/L (n = 96), 7.8–11.1 mmol/L (n = 41) and ≥ 11.1 mmol/L (n = 34). LV strains, including global radial/circumferential/longitudinal peak strain (PS)/peak systolic strain rate (PSSR)/peak diastolic strain rate (PDSR), were measured and compared between groups. Further, subgroup analyses were separately conducted for AMI patients with and without diabetes. Multivariate analysis was employed to assess the independent association between aBGL and LV global PS in AMI patients.ResultsLV global PS, PSSR and PDSR were decreased in radial, circumferential and longitudinal directions in hyperglycemic AMI patients compared with normoglycemic AMI patients (all P < 0.05). These differences were more obvious in patients with diabetes than those without diabetes. AMI patients with aBGL between 7.8 and 11.1 mmol/L demonstrated significant decreased radial and longitudinal PS, radial PSSR, and radial and longitudinal PDSR than those with aBGL < 7.8 mmol/L (all P < 0.05). AMI patients with aBGL ≥ 11.1 mmol/L showed significantly decreased PS, PSSR and PDSR in all three directions than those with aBGL < 7.8 mmol/L, and decreased longitudinal PSSR than those with aBGL between 7.8 and 11.1 (all P < 0.05). Further, aBGL was significantly and independently associated with radial (β = − 0.166, P = 0.003) and longitudinal (β = 0.143, P = 0.008) PS.ConclusionsHyperglycemia may exacerbate LV myocardial stiffness in patients experienced first AMI, leading to reduction in LV strains. aBGL was an independent indicator of impaired LV global PS in AMI patients. Blood glucose monitoring is more valuable for AMI patients with diabetes.

A Toolkit for Delirium Identification and Promoting Partnerships Between Carers and Nurses: A Pilot Pre–Post Feasibility Study

BackgroundDelirium is frightening for people experiencing it and their carers, and it is the most common hospital-acquired complication worldwide. Delirium is associated with higher rates of morbidity, mortality, residential care home admission, dementia, and carer stress and burden, yet strategies to embed the prevention and management of delirium as part of standard hospital care remain challenging. Carers are well placed to recognize subtle changes indicative of delirium, and partner with nurses in the prevention and management of delirium.ObjectiveTo evaluate a Prevention & Early Delirium Identification Carer Toolkit (PREDICT), to support partnerships between carers and nurses to prevent and manage delirium.DesignA pre–post-test intervention and observation study.Main MeasuresChanges in carer knowledge of delirium; beliefs about their role in partnering with nurses and intended and actual use of PREDICT; carer burden and psychological distress. Secondary measures were rates of delirium.ParticipantsParticipants were carers of Indigenous patients aged 45 years and older and non-Indigenous patients aged 65 years and older.InterventionNurses implemented PREDICT, with a view to provide carers with information about delirium and strategies to address caregiving stress and burden.Key ResultsParticipants included 25 carers (43% response rate) (n = 17, 68% female) aged 29–88 (M = 65, SD = 17.7 years). Carer delirium knowledge increased significantly from pre-to-post intervention (p = < .001; CI 2.07–4.73). Carers’ intent and actual use of PREDICT was (n = 18, 72%; and n = 17, 68%). Carer burden and psychological distress did not significantly change. The incidence of delirium in the intervention ward although not significant, decreased, indicating opportunity for scaling up.ConclusionThe prevention and management of delirium are imperative for safe and quality care for patients, carers, and staff. Further comprehensive and in-depth research is required to better understand underlying mechanisms of change and explore facets of nursing practice influenced by this innovative approach.

A new yield criterion based constitutive model for porous materials

In the present work, a new explicit expression of macroscopic yield criterion is derived for porous materials, such as soil, rock and cement-based materials. To consider the asymmetric behavior between tensile and compression loading, the matrix is assumed to obey to a Drucker–Prager local criterion. The influence of porosity and the effect of matrix properties are well taken into account by this criterion. By using the stress variational approach with a suitable statically admissible stress field, a new more accurate estimation with a simple expression has been obtained for the case of purely deviatoric loading. The exact solutions can be retrieved by this criterion in the case of hydrostatic loading. It also resolves the problem of discontinuity between tension and compression. The weaknesses of the main existing criteria have been overcome by this new yield criterion. By comparing with the finite element numerical results with a wide range values of porosity and frictional parameter of the matrix, the proposed macroscopic yield criterion has a great accuracy and improves the existing ones. Based on this yield criterion, a complete constitutive model is constructed and implemented. This micro-mechanics based model is then applied to describe the mechanical behavior of porous sandstone, and validated by the comparisons with experimental results at different confining pressures.

Passive earth pressure in sand on inclined walls with negative wall friction based on a statically admissible stress field

Passive earth pressure in sand on inclined walls with negative wall friction based on a statically admissible stress field

Enhanced earth pressure determination with negative wall-soil friction using soft computing

Estimating active earth pressure in cohesionless backfill behind rigid retaining walls has been significantly improved through the application of cutting-edge soft computing techniques in this paper. This study delves into the intricate interplay of negative wall-soil friction with load transfer mechanisms, underpinned by a comprehensive dataset obtained from a conservative solution that leverages statically admissible stress fields. Utilizing a Bayesian regularization backpropagation neural network, we construct an explicit function for active earth pressure estimation, ensuring the model's reliability through its remarkable alignment with measured values. Furthermore, feature importance analysis and advanced mathematical modeling enrich the study, providing a practical tool for retaining wall design and analysis. This tool is adept at addressing complex scenarios, including those involving negative wall-soil friction, thereby advancing the state-of-the-art in geotechnical engineering.

Limit analysis of axisymmetric masonry domes under vertical loads: parametric studies and statically admissible stress fields

Limit analysis of axisymmetric masonry domes under vertical loads: parametric studies and statically admissible stress fields

Rail Wear Evolution on Small-Radius Curves under Mixed Traffic Conditions, In-Field Investigations

This paper’s aim is to assess the rail wear evolution of railway tracks under mixed traffic conditions for sharp curves. Field investigations were conducted over a period of five years, at 800 points on a rail track, for two curves that underwent maintenance interventions: sleeper and rail replacements during measurements. Lateral and vertical wear measurements were monitored with mechanical instruments, and Prokon and Sap simulations were performed in order to determine the bearing capacity of the rail at different stages of wear. The results obtained after five years of investigation show wear speed propagation on the outer rail of small-radius curves as well as the bending moments and admissible stress variation. At more than 18% of the studied points, lateral wear exceeded the maximum admissible limit, showing a faster propagation speed on the outer rail compared to the vertical wear rate.

Revisiting Active and Passive Earth Pressure Problems using Three Stability Factors

This paper presents rigorous plasticity solutions to the classical active and passive earth pressure problems. The primary method adopted is a conventional equation based on the soil property and three stability factors (Fc, Fs, and Fγ), that are analogous to Terzaghi’s bearing capacity factors (Nc, Ns, and Nγ) of strip footings. The proposed method is considered as a practical yet smart approach to the determination of earth pressures and is one of the main novelties in this study. To achieve this, the finite element limit analysis (FELA) of upper and lower bounds solutions, a powerful tool in studying the behaviour of soil stability, is employed to compute the three stability factors for a wide range of soil internal friction angles, wall roughness, and surcharge pressures. In addition, analytical solutions based on statistically admissible stress fields are adopted to validate the proposed FELA solutions. The validation satisfactorily demonstrated the accuracy and reliability of the proposed solutions. It follows that the numerical results are presented in the form of tables, figures, and several examples provided to demonstrate the practical use of the three factors in estimating active and passive earth pressures with various backfill soils, wall roughness, and surcharge pressure. The study should, therefore, be of value to practitioners.

An isogeometric collocation method for the static limit analysis of masonry domes under their self-weight

A novel isogeometric collocation method is proposed for the static limit analysis of axially-symmetric masonry domes subject to their self-weight. A shell-based static formulation is employed, alongside Heyman’s assumptions on masonry, to characterize the equilibrated and statically admissible stress states in the dome. As a distinctive feature of the approach, a vector stress function is introduced, generating point-wise self-equilibrated shell stress resultants in the dome. Accordingly, the classical minimum-thrust problem is formulated in terms of the unknown vector stress function, and the static admissibility conditions are enforced as the only optimization constraint. NURBS-based isogeometric analysis is adopted to accomplish the need for an accurate geometric description of the dome and a high-order continuous interpolation of the vector stress function. A discrete minimum-thrust problem is derived as a linear programming problem, with the static admissibility conditions checked at suitable collocation points. Instrumental to its solution is the computation of a particular solution of the equilibrium equations, which is obtained by an isogeometric collocation method. By a mechanical interpretation of the dual optimization problem, the settlement mechanism of the dome corresponding to its minimum-thrust state is also computed. Numerical results, dealing with a thorough convergence analysis, parametric analyses on spherical and ogival domes with parameterized geometry, and the real case of the Taj Mahal central dome are presented to prove the computational merit of the proposed approach.

FEATURES OF THE CALCULATION OF ROLLS ON THE FATIGUE STRENGTH

On modern rolling mills, manufacturers have the possibility to use a wide range of materials with technologically determined properties, which allows for effective use of rolls and improvement of technical and economic indicators of production processes. Reasonable choice of materials and properties of rolls is impossible without reliable methods of calculating the strength and predicting the service life of the rolls. In particular, increasing of the reliability of methods for calculating the fatigue strength of rolls is an urgent task, both for scientists and for technologists and specialists of rolling mills.&#x0D; The purpose of the work is to study the features of fatigue calculation of rolls based on the predicted number of load cycles. The work solves the problem of assessing the possibility of applying a known method of determining the predicted number of load cycles and studying the features of such a method for rollsofrolling mills.&#x0D; The method of calculation based on the approximation of Woehler curves for the roll material by Beskin's power dependence within the zone of high cycle fatigue, which was determined by the number of cycles from 1·103 to 5·106, was considered. It has been proven that such a technique can be used for rolls into account the identified features. The main features of the calculation of rolls for fatigue strength include: a symmetrical cycle of changes in bending stresses and a pulsating cycle of changes in torsional stresses; mandatory consideration of working conditions due to the modified endurance limit of the material; compliance with the condition that the working stresses exceed the modified endurance limit, but are less than the admissible stresses for the roll material; taking into account the stress concentration depending on the shape of the grooves that form the passes. Consider influence the effect of stress concentration in the grooves of the rolls requires clarification based on empirical data of a certain rolling mill.&#x0D; The application of the fatigue calculation method for rolls, with considerthe identified features, will allow to increase the accuracy of determining the predicted terms of operation of the rolls and determining their consumption.

Coupling physics-informed neural networks and constitutive relation error concept to solve a parameter identification problem

Identification of material model parameters using full-field measurement is a common process both in industry and research. The constitutive equation gap method (CEGM) is a very powerful strategy for developing dedicated inverse methods, but suffers from the difficulty of building the admissible stress field. In this work, we present a new technique based on physics-informed neural networks (PINNs) to implement a CEGM optimization process. The main interest is to easily construct the admissible stress thanks to automatic differentiation (AD) associated with PINNs. This new method combines the high quality of the CEGM with the numerical effectivity of the PINNs and realizes the identification of material properties in a more concise way. We compare two variants of the developed method with the classical identification strategies on simple two-dimensional (2D) cases and illustrate its effectiveness in three-dimensional (3D) problems, which is of interest when dealing with tomographic images. The results indicate that the proposed method has good performance while avoiding complex calculation procedures, showing its great potential for practical applications.

Modeling and design of concrete hinges under general loading

AbstractDespite their successful applications in practice for over a century, the design of concrete hinges still entails considerable modeling uncertainty. Their dimensioning still relies on semi‐empirical recommendations originally proposed for admissible stress design, based on limited experimental data and generalized with engineering judgment. This presumably results in overly conservative designs in many cases, particularly when applied with modern design codes based on partial safety factors. This paper addresses these issues by revisiting the analytical modeling for one‐way Freyssinet concrete hinges under general loading based on approaches compatible with current design codes. A cross‐sectional analysis with confined concrete properties is proposed for the behavior under axial forces and bending moments, where the strength of the triaxially compressed concrete in the hinge throat is determined with a discontinuous stress field. The hinge resistance to shear forces is investigated with failure mechanisms inspired by failure modes observed in experiments. Based on the shear strength, a simple approach to estimate the torsional resistance of the throat is proposed. Remarks are also made on the analysis of combined actions. The predictions of the proposed models are validated against a wide range of test data, including a series of recently conducted own experiments. Overall, the proposed models agree better with the available experimental data than the existing approaches, potentially allowing for a more efficient design of new and assessment of existing concrete hinges.

Statically Admissible Stress Fields in Conical Sand Valleys and Heaps: A Validation of Haar–von Kármán Hypothesis

The usage of the Haar–von Kármán hypothesis for circumferential stress in axisymmetric problems is still questionable. This study aims to reveal statically admissible stress fields in conical sand valleys and heaps by applying the Haar–von Kármán hypothesis to rigid-plastic material obeying the Mohr–Coulomb criterion. The original boundary-value problem reduces to a pair of ordinary differential equations by employing the self-similarity assumption in conjunction with the condition of incipient failure everywhere. The pair of governing equations are numerically integrated with the fifth-order adaptive Runge–Kutta method. The shooting method is employed to numerically convert the boundary-value problem to the initial-value problem. Moreover, the singularities that occurred in the integrations are coped with by numerical perturbation of the initial boundary conditions. A line of stress discontinuity together with the stress jump condition is imposed to link the stress solution between the rigid and plastic regions. Admissible stress fields in various axisymmetric geometries are successfully achieved whereby the load transfer mechanisms in the conical sand heaps and valleys are elucidated. The arch action that occurred in bulk solid is observed. The effect of the circumferential stress hypotheses, that is, Haar–von Kármán hypothesis and Lévy’s flow rule, on the results of rigid-plastic solution is demonstrated; therefore, the advantages and disadvantages of both the hypotheses are elucidated. This study rigorously justifies the validity of the Haar–von Kármán hypothesis, thus a guideline on determining the value of hoop stress using the Haar–von Kármán hypothesis is proposed.

The impact of maternal ACEs on obstetric outcomes and psychosocial wellbeing during pregnancy

Adverse childhood experiences (ACE) are traumatic events, such as physical or emotional abuse/neglect, sexual abuse, and household dysfunction, that confer an increased lifetime risk of chronic disease. We examined the relationship between maternal ACEs and adverse obstetric and psychosocial outcomes. This is a secondary analysis of a larger clinical trial (CRADLE study) that compared group vs individual prenatal care on pregnancy outcomes. The Behavioral Risk Factor Surveillance System ACE questionnaire and psychosocial measures (Center for Epidemiological Studies-Depression Screen, Prenatal Anxiety Screen, and Prenatal Distress Questionnaire) were administered to all participants. Pregnancy outcomes were obtained via chart abstraction; the primary outcome was a composite of preterm birth (PTB, < 37 weeks), low birth weight (LBW, < 2,500g), and intrauterine fetal demise (IUFD). Secondary outcomes included 1) composite of maternal morbidity (BMI >35, hypertensive disorders of pregnancy, gestational diabetes), 2) NICU admission, and 3) psychosocial measures or new diagnosis of anxiety/depression. Multivariable logistic regression models were performed. 2221 patients were included; 40.1% Black, 36.5% White, 21.4% Hispanic, and 1.3% Other. 96.4% were Medicaid eligible and 65.9% reported an unintended pregnancy. There was no relationship between ACE scores and PTB, LBW, IUFD, or the composite (p >0.10). Higher ACE scores were associated with increased risk of composite maternal morbidity (p< 0.01) and NICU admission (p< 0.01). Higher ACE scores were also associated with positive CES-D, prenatal anxiety, prenatal distress, and a new depression and/or anxiety diagnosis during the study (p< 0.01). We did not identify an increased risk of PTB or LBW with ACE >5. Higher ACE scores were associated with maternal morbidity, NICU admission, and psychosocial stress during pregnancy. Future projects should seek avenues by which screening, supportive treatment or counseling could improve outcomes for women identified at risk, specifically those with ACE >5 at entry to prenatal care.View Large Image Figure ViewerDownload Hi-res image Download (PPT)

Limit analysis of axisymmetric masonry domes under vertical loads: parametric studies and statically admissible stress fields

Limit analysis of axisymmetric masonry domes under vertical loads: parametric studies and statically admissible stress fields

Effects of Tele-Counseling on Reducing Anxiety Levels of COVID-19 Patients in Isolation Wards: An Observational Study.

COVID-19 causes psychological distress and anxiety due to fear of infection and the possibility of worsening symptoms leading to mortality. Public health measures like contact tracing and lockdowns further increase the panic among infected patients and the public. We intended to assess the effect of telecounseling in reducing anxiety in patients admitted to isolation wards. In this multi-center observational study, we administered a Generalized Anxiety Disorder-7 (GAD-7) scale before and after telecounseling. The study group consisted of participants who gave consent for telecounseling, and those who did not give consent constituted the control group. The telecounseling was based on the Psychological First Aid model, due to its simplicity. There was a statistically significant decrease in anxiety after telecounseling in the study group (P value ≤ 0.001, effect size = 0.484). There was a statistically significant decrease in anxiety in the study group compared to the control group (P value ≤ 0.001). Telecounseling contributed to the reduction in anxiety in COVID-19 patients in isolation wards. Several other factors like severity of the infection, comorbid medical illness, pre-existing mental health issues, individual's level of coping with stress, and duration and place of admission may have affected the anxiety levels in the patients.

An exact solution of active earth pressures based on a statically admissible stress field

Static lateral earth pressure problems are a central and long-standing topic in geotechnical engineering, but their exact solutions are lacking. This study is dedicated to providing an exact solution for active earth pressure exerted against rigid retaining walls with various wall geometries, backfill geometries, and wall roughness. A numerical model based on the rigid plastic analysis, namely a fully plastic solution, has been successfully developed to search out statically admissible stress fields in the backfills. In particular, Sokolovski’s theory coupled with the Mohr-Coulomb criterion has been adopted to enable the statically admissible stress fields to be developed. Robust numerical frameworks based on the fifth-order adaptive Runge-Kutta method, and a shooting technique has demonstrated efficacy in coping with the stress singularity that appeared in the analyzed domain, thus the admissible stress fields have been successfully figured out. The accuracy of the proposed solution is satisfactorily verified and validated by comparing the obtained results with exact values and those of experimental results available in the literature. The admissible stress fields explored in the backfills of rigid walls elucidate the load transfer mechanism of cohesionless materials in the backfills; the potential effects of various parameters e.g., wall geometries, backfill geometries, and wall roughness on the active earth pressure coefficients have been disclosed thereof. In essence, this study provided a conservative answer for the static active earth pressure problems whereby the exact values of active earth pressure coefficients are tabulated and provided for engineering practice.

Impact of admission and early persistent stress hyperglycaemia on clinical outcomes in acute pancreatitis.

BackgroundTo determine the impact of glucose levels at admission and during first week (early phase) on clinical outcomes in patients with acute pancreatitis (AP) and to investigate the relationship between stress hyperglycaemia (SHG) and hypertriglyceridaemia (HTG).MethodsTwo independent and prospective databases were retrospectively analysed (n = 1792). Patients admitted with pain of less than 48 hours and confirmed AP were included. SHG was defined as admission blood glucose ≥ 10.00 mmol/L (non-diabetic) or ≥ 16.67 mmol/L (diabetic). Blood glucose records for the first week were inspected to determine whether SHG lasted ≥ 48 hours (persistent) or < 48 hours (transient). Clinical outcomes were compared between designated patient groups using multivariate and trend analyses. The correlation between SHG and HTG (serum triglyceride ≥ 5.65 mmol/L) was also analysed.ResultsOn admission, SHG was present in 27.8% (499/1792) patients; during the first 48 hours of admission, transient and persistent SHG was found in 31% (556/1792) and 8.0% (144/1792) patients, respectively. Admission SHG was associated with higher incidence of persistent organ failure, acute necrotic collection, major infection, and mortality as well as prolonged length of hospital stay (all P < 0.05). Duration of SHG was also associated with worsened clinical outcomes (all P < 0.05). In HTG-AP patients, more severe clinical outcomes were observed in those who concomitantly had SHG (P < 0.05). ConclusionsAdmission and persistent SHG during the first week of admission worsens clinical outcomes of AP patients. These effects are more pronounced when admission HTG co-existed.