Stress Reduction Factor Research Articles

Heterogeneous characteristics of stress transmission within finer fraction of gap-graded soils and its relevance to suffusion\\suffosion

The heterogeneous transmission of particle stress within the finer fraction has a critical effect on the development of suffusion\\suffosion in gap-graded soils, while quantitative evaluations on it are still needed. To this end, the stress transmission within the finer fraction of gap-graded soils with packing fabrics covering all the four typical packing fabrics under isotropic confining pressure were studied using discrete-element simulations. The finer particles with at least one contact, termed connected finer particles are classified into two groups that carry obviously different particle stress and have different contact features: primarily- and secondarily-stressed finer particles, which is well indicated by the gap in the particle stress contribution distribution of the connected finer particles, and meanwhile by the transition limitations of particle connectivity. The primarily-stressed finer particles always play a primary role in supporting the soil skeleton, while the role of the secondarily-stressed finer particles is closely related to the stress-reduction factor, α. The transition limit was found to be α = 0.146–0.191, over which the secondarily-stressed finer particles play a primary role in supporting the soil skeleton, while below which they play a secondary role. It also sets the borderline to identify the suffusion and suffosion susceptibility of gap-graded soils.

An improved CSM-based design method for H-section aluminium slender columns under eccentric compression

This study proposed an improved design method for predicting the load-carrying capacity of H-section aluminium alloy slender columns under eccentric compression based on CSM. Through eccentric compression tests and extensive numerical simulations, the study explored the influence of cross-sectional dimensions, member slenderness ratios, and initial geometric imperfections on the load-carrying capacity of columns. The proposed CSM-based design method utilized CSM limiting stress and CSM buckling reduction factors tailored to aluminium alloy columns, accounting for the specifics of their material behavior and geometric properties. The comparison and evaluation of the load-carrying capacities predicted from the proposed design method, European design code, and American design code, as well as with experimental and numerical results, were conducted. Meanwhile, the reliability analyses on these design method and codes were also performed, adopting the method provided by the AISC and EN 1990, Annex D. The comparison and reliability analyses results indicate that, compared to existing design codes, the proposed CSM-based design method could provide more accurate, consistent, and reliable load-carrying capacities of H-section aluminium alloy slender columns under eccentric compression.

Hydraulic heave in granular soils under hypergravity conditions

A series of discrete element method (DEM) simulations have been conducted to investigate the initiation and development of hydraulic heave for granular soils under hypergravity. During the development of hydraulic heave, local failure can occur when the stress-reduction factor (α) is less than 0.8, in which the particles are reorganized by the fluid and subsequently regain stability as particles settle down. However, if α is greater than 0.8, global failure occurs, causing the mobilization of the entire soil. The triggering mechanism of the hydraulic heave is the force equilibrium between the contact force and critical fluid force, which scales up proportionally with g-level. The non-linear variation of critical hydraulic gradient (icr) with g-levels is attributed to the non-linear relationship between fluid force and hydraulic gradient. Finally, an analytical model along with a fitting formula, is proposed to predict this non-linear relationship between icr and g-level.

Internal instability of cohesionless soils in upward and downward flow: an experimental verification of theory

Rigid-wall permeameter testing of two potentially unstable gradations established that the critical hydraulic gradient to trigger instability is smaller for upward flow than for downward flow. The experimental finding is explained with reference to the Skempton-Brogan stress reduction factor α in the finer fraction content of the soil. Theory uses the α-factor to define a hydro-mechanical envelope in gradient-stress space that is independent of flow direction, and the experimental results are found to be in good agreement with the theory. Testing with upward flow is recommended to determine the value of α for an internally unstable gradation because, in contrast to downward flow, there is no requirement for an outflow boundary.

Experimental Investigation on Fatigue Improvement of Orthotropic Steel Bridge Deck Using Steel Fiber Reinforced Concrete

AbstractThe high-performance topping concrete overlay would significantly reduce the fatigue stresses at susceptible details of orthotropic steel deck (OSD) and effectively improve the fatigue performance. Full-scale fatigue tests and numerical simulations were carried out to quantify the effects of steel fiber reinforced concrete (SFRC) topping pavement in reducing the OSD fatigue stresses based on a practical bridge design. Fatigue stress of the OSD critical details was measured from tests and cracking was observed in the SFRC overlay. Both an innovative pre-pump-pulse Brillouin optical time domain analysis (PPP-BOTDA) distributed optical fiber sensor and strain gauges were also used to measure the stress at OSD fatigue-prone details, including the crossbeam cut-out, rib-to-deck weld, rib-to-crossbeam weld and splice of U-rib. The corresponding three-dimensional (3-D) finite element model was then established and verified by the test results, and used to conduct a parametric study to obtain a quantitative expression of fatigue stress reduction factor, in terms of relative elastic modulus and thickness of overlay and steel deck plate. The proposed quantitative model of the fatigue stress reduction effect can guide the cost-effective design of composite bridge deck.

Study of shear induced stress redistribution in gap-graded soils by discrete element method

Combined effects of shear stress ratio, density, and fines content on stress redistribution during shearing and their implications for internal instability were investigated in this study using the discrete element method. The widely used stress reduction factor was modified in this study by introducing the Voronoi cell to account for the volume change during shearing. The response of stress in finer fraction and its relative contribution to the overall stress of the specimen as evaluated by the established stress reduction factor showed inconsistent trends. The relationship between the mean stress in finer fraction and the shear stress ratio of the entire specimen was found to be dependent on FC and density during pre-peak stress condition. At post-peak, the relationship was only governed by the soil load-bearing skeleton. The stress redistribution of dense transitional soils exhibited the most pronounced changes. The mean stress in finer fraction reached the peak and steady values quicker than the shear stress ratio. This could be attributed to the decrease in critical hydraulic gradient under a high shear stress ratio, as evidenced from previous experimental works. These nonsynchronous performances could be explained by the shift of contact force and volume change.

Discrepant Perceptions of Biopsychosocial and Active Care Recommendations Between Doctors of Chiropractic and Midlife and Older Adult Patients: A Descriptive Survey

ObjectiveThe purpose of this study was to assess perceptions about the inclusion of biopsychosocial and active care recommendations during chiropractic clinical encounters between doctors of chiropractic (DCs) and their midlife and older adult patients and to identify whether there were any discrepancies between their recollections. MethodsThis descriptive cross-sectional survey was part of a mixed-methods research project designed to gather information about the role of electronic health interventions for midlife and older adults who use chiropractic care. For this study, a convenience sample of 29 DCs and 48 chiropractic patients aged 50 years and older from 2 metropolitan areas in the United States completed online surveys between December 2020 and May 2021. The survey matched questions about components of chiropractic care discussed by patients and providers over 12 months. We used descriptive statistics to explore congruence in perceptions between groups and qualitative content analysis to describe DC perceptions of working with this population. ResultsDoctors of chiropractic and patients agreed (>90%) that pain management was the top reason midlife and older adults seek chiropractic care, yet differed in their prioritization of maintenance/wellness care, physical function/rehabilitation, and injury treatment as care drivers. While DCs reported frequent discussions about psychosocial recommendations, fewer patients reported talking about treatment goals (51%), self-care (43%), stress reduction (33%), or the impact of psychosocial factors (23%) and beliefs/attitudes (33%) on spinal health. Patients reported varied recollections about discussing activity limitations (2%) and exercise promotion (68%), being taught exercises (48%), or reassessing exercise progress (29%), which differed from higher levels reported by DCs. Qualitative themes from DCs included psychosocial considerations in patient education, importance of exercise/movement, role of chiropractic in lifestyle changes, and reimbursement limitations for older patients. ConclusionDoctors of chiropractic and their patients reported discrepant perceptions about biopsychosocial and active care recommendations during clinical encounters. Patients reported modest emphasis on exercise promotion and limited discussion on self-care, stress reduction, and psychosocial factors related to spine health compared to the recollections of DCs who reported frequent discussions of these topics.

Void states perspective for critical hydraulic gradient of internally unstable non-cohesive soils

The critical hydraulic gradient ([Formula: see text]) for internally unstable soils is observed to be significantly less than the [Formula: see text] given by Terzaghi's classical equation. The difference is due to the uneven stress contributions by fine and coarse fractions of internally unstable soils, and thus an empirical stress reduction factor ([Formula: see text]) was considered for [Formula: see text] predictions. Internally unstable soils are coarse fraction dominant with a void ratio of the fine fraction higher than the void ratio of overall internally unstable soil. The differential stress states lead to washout of the fines from the local voids of the coarse fraction at a hydraulic gradient of less than the [Formula: see text] given by the classical equation. This study presents a theoretical approach for predicting [Formula: see text] based on the notion of the effective stress of the fine fraction within the voids of a coarse fraction being equal to zero for internally unstable soils. A comparison of predicted [Formula: see text] based on the proposed approach and experimental observations obtained from the literature and the current study has demonstrated the validity of the proposed approach. The applicability of the proposed approach is also illustrated for the estimation of a critical hydromechanical envelope.

Static and fatigue performance of steel bridge decks strengthened with air-cured UHPC

Adding a thin layer of ultra-high performance concrete (UHPC) onto the steel deck plate is an effective approach to improve the fatigue performance of orthotropic steel decks (OSDs) through increasing structural stiffness and load-carrying capacity, but a wide industrial acceptance of the approach is hindered by heat curing of UHPC. In this study, air-cured UHPC with low shrinkage was adopted to fabricate the cast-in-situ topping layer for the composite decks. Experiments were carried out to investigate the structural behavior of the composite decks under static and fatigue loading. Experimental results showed that (1) UHPC with relatively high strengths and low shrinkage could be manufactured without any special curing regime; and (2) the composite decks had enough mechanical strengths and fatigue resistance to withstand service loads. Finite element analyses were performed to determine the contribution of air-cured UHPC on the fatigue performance of OSDs. Finally, a hot spot stress reduction factor was introduced to assess the long-term effectiveness of air-cured UHPC in improving the fatigue performance of OSDs. Results suggested that UHPC cracking and the associated degradation in structural stiffness had limited effects on the fatigue behaviors of composite decks.

Prediction Method for Fine Particle Loss Rate of Sandy Soil under Suffusion

In the process of seepage, the internally unstable fine particles of sandy soil are easy to be lost and form suffusion, which has a negative effect on the geotechnical building or foundation. The loss rate of fine particles is a key parameter for soil mechanical property degradation and stability analysis. In order to predict the loss rate of fine particles in sandy soil under suffusion, the internal stability evaluation criteria for determining whether soil will undergo suffusion is discussed first. Second this paper gives critical hydraulic gradient for erosion initiation and introduces the stress reduction factor. And then considering the difference of soil particles' forces, the stress reduction factor is modified, meanwhile the “erosion initiation probability of fine particles” is introduced to quantify the erosion initiation of fine particles. Next the migration process of fine particles in the pore network of soil is analyzed, and the probability of fine particles through constriction and the migration distance are given. Finally, the law of fine particle erosion and deposition are given according to the law of fine particle erosion initiation and migration, and the prediction method of fine particle loss rate was formed based on the law of mass conservation. The calculated results of fine particle loss by this prediction method are in good agreement with the numerical results, and the error is basically within 15%.

Assessing the Secondary Stress in a Pipe System With Circumferential Surface Crack Using Finite Element Modeling

Abstract In flaw evaluation criteria, the design limits for the secondary stresses are frequently different than the primary stresses. The evaluation procedure for primary stresses is load-controlled based which is independent of pipe deformation. The evaluation procedures for secondary stresses are displacement controlled which are dependent on pipe deformation. Certain stress components such as thermal expansion, thermal stripping, welding residual stress, misalignment/cold-springing, dynamic anchor motion are historically considered secondary stresses and their design limits are based on elastic stress analysis. In reality, there can be much more rotation/displacement of the pipe with nonlinear fracture behavior due to nonlinear material behavior and plasticity at the crack plane providing extra margins on the elastically calculated rotation values that come from uncracked-pipe design analyses. In assessing secondary stress margin, a secondary stress reduction factor is defined as the ratio of elastic-plastic moment to elastic moment. This is equivalent to another concept using a plastic reduction factor (PRF) as well as the inverse of structural (or safety) factor (SF) in ASME Section XI flaw evaluation criteria for various service levels. In this work, the secondary stress reduction factor was determined for a representative pipe system with multiple crack sizes, crack locations, and loading conditions. Nonlinear finite element (FE) analyses of a whole uncracked-pipe system were performed using abaqus® under various loading combinations to determine the critical locations for cracks in the pipe system. Next, FE analyses of the cracked-pipe system were carried out using cracked-pipe element—a methodology developed by the authors. Cracked-pipe system analyses were conducted for two loading conditions—one producing contained plasticity or single-hinge system and the other producing larger plasticity in the pipe system. Several analyses were conducted for each loading condition with a combination of two crack sizes at two key locations. Secondary stress reduction factors were then calculated for both loading conditions in the pipe system. Finally, the margin in secondary stress was assessed for the pipe system by comparing the secondary stress reduction factors with that for straight pipe sections (determined for experimental bend tests) as well as with the recommended equivalent PRF and the equivalent ASME secondary stress correction factors.

Energy Management Strategy for Hybrid Energy Storage Systems in Electric Vehicle –A Review

On board energy management system for Electric Vehicle (EV) defines the fuel economy and all electric range. Charging and discharging of energy storage devices take place during running as well as stand-still conditions. Battery-alone EV suffers from range anxiety, current drain during peak power demand and less battery life. It depends on the grid for charging and thus the increasing popularity of EV is increasing burden on the grid. Different energy storage devices are available which could be used on board to form a hybrid energy storage system. Batteries, Ultra-capacitors and fuel cells are some of them. Such a system will act as a stress reduction factor and increase the battery life. In this paper, a detail literature review of various energy storage devices that can be used in EV is presented. A comparative study of various topologies available for this purpose is also presented. Finally, a detailed review of Energy Management Strategy (EMS) is presented with current trends and research gaps i.e., challenges.

Reconstructing the microstructure of real gap-graded soils in DEM: Application to internal instability

This paper introduces a new technique that enables considering the impact of soil fabric on microstructure of internally unstable gap-graded soil. The influence of soil fabric on erodibility of fine particles was studied by transferring the real soil fabric from a micro-computed tomography (μCT) image to discrete element method (DEM) using a new image processing workflow. The pair correlation function (PCF), a two-point correlation between particles in images, was used as a microgeometrical parameter to assess the impact of image filters on the quality of the μCT image. Comparison between PCF and particle size distribution of the raw μCT and reconstructed images suggest that anisotropic diffusion and non-local mean filters reproduce the real soil fabric samples most effectively. DEM results showed lower coordination number but slightly higher stress reduction factor for the real fabric, indicating that the real contact geometry results in having fine particles more involved in force network.

Internal erosion: critical hydraulic gradient in one-dimensional vertical seepage and its relation to soil gradation

A hydromechanical envelope that governs the onset of soil erosion by seepage-induced internal instability is examined with reference to theoretical and laboratory stress-gradient paths for one-dimensional upward and downward seepage flow. The method is validated from permeameter test results on glass ballotini. Using the theory, analysis of a database of 22 gradations establishes a semi-empirical relation between attributes of a grain size distribution curve and a stress-reduction factor governing potential for internal erosion. The semi-empirical relation provides a screening tool for susceptibility of a soil to seepage-induced internal instability.

Prediction of rock mass quality index in the Q-system by multivariate regression using the most influential parameters

The extensive use of underground spaces is an index of development in countries. Choosing the right supporting system to achieve a safe and stable space is an important issue in tunnel construction. One of the methods used to classify rock masses is the Q-system. The Q-system depends on rock quality designation, joint strength, joint roughness, joint alteration, groundwater, and stress reduction factor, which are not always available. Sometimes it is not possible to access all the parameters of the Q-system due to time and cost. This paper aims to obtain the value of the rock quality index in the Q system using the most important parameters affecting it. Therefore, using the Pearson analysis method and SPSS software, the Q-system's most effective parameters are identified. In this regard, three models were selected to determine Q. The first and second models have three input parameters and one output parameter, and the third model has four input parameters and one output parameter. Using multivariate regression, a relationship to predict the Q-value using the most effective parameters is proposed. For this purpose, 140 experimental data were used, and 34 test data checked the results' accuracy. Determining the Q-value using three or four parameters instead of the six most effective parameters is the novelty of this paper. Comparing the results of the proposed relationship and the actual values obtained from the field measurements show that these results are in good agreement with each other. The results show that the second model with a correlation coefficient of 0.81 for the initial data and 0.8 for the test data and the root mean square error of 2.68 for the initial data and 2.55 for the test data has the best performance.

Modeling tomato root water uptake influenced by soil salinity under drip irrigation with an inverse method

The influence of soil salinity on plant root water uptake (RWU) must be considered in order to promote efficient irrigation management. However, due to challenges in parameterization, modeling RWU response to salinity is problematic. We set out to characterize the influence of soil salinity on tomato RWU under conditions of irrigation with high salinity water and to improve methods for optimizing parameters of RWU model. Experiments were conducted in a greenhouse over two seasons (2016 and 2017). Three irrigation water salinity treatments [0.4 (S1), 3.4 (S2) and 6.4 (S3) mg cm−3] were evaluated. The results showed that soil water content and salinity increased with the irrigation water salinity, especially in the top soil layers, and that RWU was reduced by the increased root zone salinity. An inverse method based on a one-dimensional equation of soil water movement was used to estimate the RWU rate distribution under drip irrigation and determined to be reliable. The parameter value of the normalized root length distribution (NRLD) function was fitted through the estimated RWU rate distributions for treatment S1 without the effect of salinity stress. The fitted NRLD function was used to optimize the parameters of the salinity stress reduction factor (β) through the measured soil moisture and salinity of treatments S2 and S3 in 2016. With the optimized parameters of β, the RWU rates of treatments S2 and S3 in 2017 were simulated. The simulated RWU rates based on the RWU model agreed well with the estimated RWU rates using the inverse method, with root mean squared error (RMSE) and normalized root mean squared error (NRMSE) less than 0.00067 cm3 cm−3 d−1 and 12.36%, and index of agreement (IA) higher than 0.94. These findings can be used to estimate the NRLD distribution and determine actual crop water requirements under saline conditions with no root distribution data required. This should contribute to efficient and sustainable irrigation scheduling.

Prepared and highly committed despite the risk of COVID-19 infection: a cross-sectional survey of primary care physicians\u2019 concerns and coping strategies in Singapore

BackgroundPrimary care physicians (PCPs) are first points-of-contact between suspected cases and the healthcare system in the current COVID-19 pandemic. This study examines PCPs’ concerns, impact on personal lives and work, and level of pandemic preparedness in the context of COVID-19 in Singapore. We also examine factors and coping strategies that PCPs have used to manage stress during the outbreak.MethodsTwo hundred and sixteen PCPs actively practicing in either a public or private clinic were cluster sampled via email invitation from three primary care organizations in Singapore from 6th to 29th March 2020. Participants completed a cross-sectional online questionnaire consisting of items on work- and non-work-related concerns, impact on personal and work life, perceived pandemic preparedness, stress-reduction factors, and personal coping strategies related to COVID-19.ResultsA total of 158 questionnaires were usable for analyses. PCPs perceived themselves to be at high risk of COVID-19 infection (89.9%), and a source of risk (74.7%) and concern (71.5%) to loved ones. PCPs reported acceptance of these risks (91.1%) and the need to care for COVID-19 patients (85.4%). Overall perceived pandemic preparedness was extremely high (75.9 to 89.9%). PCPs prioritized availability of personal protective equipment, strict infection prevention guidelines, accessible information about COVID-19, and well-being of their colleagues and family as the most effective stress management factors.ConclusionsPCPs continue to serve willingly on the frontlines of this pandemic despite the high perception of risk to themselves and loved ones. Healthcare organizations should continue to support PCPs by managing both their psychosocial (e.g. stress management) and professional (e.g. pandemic preparedness) needs.

New Stress Reduction Factor for Evaluating Soil Liquefaction in the Coastal Area of Catania (Italy)

In this paper, a study concerning the soil liquefaction potential in the city of Catania is presented. The stress-based liquefaction analysis framework for cohesionless soil includes a function that describes fundamental aspects of dynamic site response, i.e., the shear stress reduction coefficient, rd, which depends on several factors (depth; earthquake and ground motion characteristics; dynamic soil properties). Various relationships of rd are reported in literature because of the importance of assessment of CSR. Herein, new variations of rd with depth have been obtained using different deterministic earthquake scenarios as input motion. The relationships are based on large numbers of site response analyses for different site conditions. The new relationships obtained have been used for the evaluation of the liquefaction potential in the area of the Catania Harbour. The liquefaction resistance has been evaluated by the horizontal stress index (KD) from seismic dilatometer Marchetti tests (SDMTs). Various correlations were developed to estimate the CRR from KD, expressed in form of CRR-KD curves to differentiate between liquefiable and non-liquefiable zones. In this study three different CRR-KD curves have been used.

Effect of fire exposure on residual stresses relief in welded high strength Q690 steel sections

Welding induced residual stresses in steel sections can be reduced by high temperatures in fire conditions and thus affect the load bearing capacity and stiffness of structural steel members. This paper presents effect of high temperature exposure on residual stresses relief in welded high-strength Q690 steel sections by experimental and numerical studies. The distribution and magnitude of the residual stresses in three Q690 steel H-sections and three Q690 steel box-sections after exposure to 600 °C and 800 °C were investigated by cutting method. In the numerical studies, finite element analysis software ANSYS was employed to simulate residual stress generation and relief in the entire welding and high temperature exposure stages, including the heating and cooling phases. The predicted results of the residual stresses after an exposure to high temperature obtained by the finite element analysis agree well with the test results. Parametric studies were conducted to investigate the influence of exposed temperature, high temperature duration, and creep strain in steel on residual stresses after being exposed to high temperature. For welded Q690 steel H- sections and box-sections, equations to evaluate the corresponding residual stress reduction factor at elevated temperatures and after high temperature exposure were proposed based on the results of finite element analysis.

Centrifuge modeling of geosynthetic-encased stone column-supported embankment over soft clay

Geosynthetic-encased stone column (GESC) has been proven as an effective alternative to reinforcing soft soils. In this paper, a series of centrifuge model tests were conducted to investigate the performance of GESC-supported embankment over soft clay by varying the stiffness of encasement material. The enhancement in the performance of stone columns encased with geosynthetic materials was quantified by comparing the test with ordinary stone columns (OSCs) under identical test conditions. The test results reveal that by encasing stone columns with geosynthetic material, a significant reduction in the ground settlement, relatively faster dissipation of excess pore pressure and enhanced stress concentration ratio was noticed. Moreover, with the increase in the encasement stiffness from 450 kN/m to 3300 kN/m, the stress concentration ratio increased from 4 to 6.5, which signifies the importance of encasement stiffness. In addition, a relatively lower value of soil arching ratio observed for GESCs compared to OSCs indicate the formation of a relatively strong soil arch in the GESC-supported embankment. Interestingly, under embankment loading, GESCs fail by bending while OSCs fail by bulging. The stress reduction method can be used to calculate the settlement of GESC-supported embankment with larger stress reduction factor than that in the OSC-supported embankment. Finally, the limitation of the construction of the embankment at 1 g was addressed.