Sustained Load Research Articles

Effect of Testing Mechanisms on the Load-Strain-Time Behavior of Geosynthetic Reinforcements

Abstract This study compares how geosynthetics behave under load, under strain, and over time when subjected to confined tensile tests in soil, employing two commonly used mechanisms in research. One test type simulates a reinforced layer, where tensile loads are indirectly applied to the geosynthetic via stresses transferred from the soil. In contrast, the other test applies tensile loads directly to the geosynthetic material using clamps while under soil confinement. The objective is to elucidate how these testing mechanisms might yield differing in-soil tensile characteristics for different geosynthetics. The study involved conducting load-strain-time tests on samples of nonwoven and woven geotextiles, as well as a geogrid, under varying sustained loads over a 120-h period within a sand clay soil providing soil confinement to geosynthetics at different surcharge levels. The results suggest that soil confinement plays a significant role in shaping the load-strain-time behavior of geosynthetics. Furthermore, it was noted that the impact of testing mechanisms on this behavior is contingent upon the type and stiffness of the geosynthetics, as well as their interaction with the confining soil. In general, in-soil tests in which tensile loads are mobilized by geosynthetics and transferred from the soil provide more confident results for better simulating operation conditions. Tests that directly apply tensile loads to the geosynthetic while maintaining stationary soil confinement may yield misleading results, especially for geosynthetics that have poor interaction with the soil.

Creep behavior of BFRP-confined coal gangue concrete under sulfate and high stress conditions

To recycle the coal gangue more economically and effectively, the basalt fiber reinforced polymer (BFRP) and coal gangue concrete (CGC) are combined to form a novel supporting structure in the underground mines, BFRP-confined CGC (FCGC). However, the underground mine environment is rich in sulfate corrosive ions, and meanwhile, the structure is subjected to a high sustained load. Thus, this paper presents an experimental and theoretical investigation on the long-term deformation properties of FCGC under sulfate and high stress conditions. The effects of inner concrete, FRP layer, stress-to-strength ratio, sulfate concentration and load duration time on the shrinkage and creep behavior were clarified in detail. The findings indicate that the shrinkage of FCGC is relatively lower as the BFRP confinement weakens the moisture exchange between inner CGC and external environment. In addition, under sulfate and high stress conditions, the creep strain and specific creep increase continuously in the early stage, while the growth rate gradually slows down in the later stage, where the high stress-to-strength ratio is the key factor. Moreover, when compared with a single high stress condition, the creep strain of FCGC is relatively larger under sulfate and high stress coupling conditions, attributed to the sulfate corrosion on the BFRP wraps. Theoretically, the ACI 209 was modified to predict the nonlinear creep of CGC, by introducing the coal gangue influence coefficient and the increasing coefficient of nonlinear creep. Furthermore, based on the creep model of CGC and BFRP, the nonlinear calculation model of FCGC was developed considering the creep of CGC under a triaxial-stress state and the interaction between inner CGC and BFRP confinement. Validations against the experimental results show that the nonlinear creep model of FCGC works well.

Factual observations of dynamic bone crushing

Dynamic bone-crushing, exemplified by the pig bone rib, is characterized thermo-mechanically in relation to the bone’s microstructural characteristics. The cortical bone’s dominant role consists of shielding the trabecular component by resisting deformation, sustaining high load levels, and ultimately cracking. Here we present a qualitative factual study to show that this behavior is the absolute opposite of its quasi-static counterpart in which the trabecular bone was found to play the dominant role. Using infrared thermography, we observed for the first time a significant localized temperature rise of up to 11 degrees Celsius in both cortical and trabecular damaging regions. Such observations call for additional clinically oriented research. Such a high contrast between static and dynamic failure mechanisms was not reported previously, and it paves the way for forensic-oriented studies in which the nature of the sustained load must be determined.

Post-fire performance of hybrid GFRP-steel reinforced concrete columns

The fire safety requirements and knowledge on the use of Glass Fiber Reinforced Polymer (GFRP) bars as an alternative to conventional steel in reinforced concrete structures have been progressively evolving. This study investigates the post-fire axial performance of square GFRP reinforced concrete (RC) columns, addressing a significant gap in current knowledge. Five column specimens of the same cross-section and length were tested, where the main parameters considered are the clear cover depths (40, 50, and 65 mm) and the use of a 40-mm insulation on one column. The columns were subjected to a long 3-hour fire exposure per ASTM E119 standard without sustained loading. The columns were tested upon cooling under concentric axial loading. Despite the notable temperature differences between columns with 40 and 65 mm concrete cover (300 and 500 °C after 3 hours), the post-fire residual axial capacity appeared unaffected. This is primarily attributed to the minimal differences in the retained mechanical properties of GFRP bars at temperatures exceeding 200 °C. The study's findings indicate that GFRP longitudinal bars do not significantly influence the performance of columns in fires. Consequently, future research should focus on columns reinforced with GFRP ties as well. The predicted values of post-fire axial capacity closely match the experimental data for non-insulated columns, indicating a high degree of accuracy. The study provides design recommendations to enhance the fire performance of such elements. The use of insulation results in a substantial reduction of temperature at various depths of the column. Post-fire residual capacities for non-insulated columns were approximately 30 %, whereas insulated columns demonstrated a 60 % residual capacity.

New US DHHS Guidelines for Feeding of HIV Exposed Infants: Uptake, Practice Variability and Concerns

Abstract Background Approximately 5000 infants are born to mothers living with HIV annually in the US. In the past, the Center for Disease Control (CDC), American Academy of Pediatrics (AAP), and US Department of Health and Human Services (DHHS) have recommended that people living with HIV (PWH) not breast/chest feed their infants. Recent changes published in January 2023 in the “Section on Infant Feeding for Individuals Living with HIV” in the US DHHS HIV Guidelines, now include that individuals with HIV who are on antiretroviral therapy (ART) with a sustained undetectable viral load (VL) and who choose to breastfeed should be supported in this decision. We evaluated the uptake of these guidelines, and practice variability across providers who care for such mothers and infants. Methods We surveyed Pediatric Infectious Diseases Society members who practice clinically in the US, via an internal email list serve. The ten-question survey assessed uptake of the updated DHHS guidelines and respondents’ clinical practice in three key areas that are subject to interpretation in the guidelines: VL control, mixed feeding, and ART prophylaxis. We used descriptive statistics to examine guideline uptake and variability in practice. We used inductive qualitative thematic analysis to identify themes in open-ended survey responses. Results Of 915 individuals who opened the survey, 165 responded and 129 were included in the final analysis. Respondents represented 86 US clinical centers. Uptake varied: 14 respondents (10.8%) were unaware of the new guidelines, 103 (79.8%) had implemented or were planning to implement the new guidelines, and 12 (9.3%) were not planning to implement the guidelines. The table summarizes variability in pre-delivery VL suppression and mixed feeding criteria used by 117 respondents who are either planning/already implementing guidelines or who are unaware of guidelines. Areas of concern revealed by thematic analysis included insufficient data to support guidelines and lack of specific criteria for implementation. Conclusion We identified substantial heterogeneity in provider uptake and comfort with new breastfeeding guidelines among US pediatric infectious diseases practitioners, and variability in assessment of safety to breastfeed. Further research is essential to explore patient preferences, define necessary follow-up, and address provider concerns regarding insufficient data to support guidelines and lack of specific criteria for implementation.

Regional changes in the free Achilles tendon volume in response to repeated submaximal contractions

IntroductionThe Achilles tendon (AT) may become smaller in volume following acute bouts of heavy and sustained loading likely because of transient fluid exudation to the periphery and this could augment cellular mechanotransduction and tendon adaptation. Given the structure of the AT is distinct across its length, regional changes in the free AT volume may occur in response to loading. This study aimed to investigate whether the change in tendon volume in response to repeated submaximal loading is distinct across the free AT length. MethodsSixteen ATs of healthy males and females (age 24.4 ± 9.4 years, body mass 70.9 ± 16.1 kg, height 1.7 ± 0.1 m) were scanned at rest using freehand 3D ultrasound. Scanning was done before and immediately after submaximal (75 %) voluntary isometric plantarflexion contractions (8 s) involving four sets of ten repetitions. Regional volumetric changes were assessed across the free AT length by dividing the tendon into distal, mid, and proximal regions. ResultsSignificant reduction in the free AT volume occurred across all tendon regions in response to the intervention, however, the mid- region exhibited the greatest reduction in volume compared to the proximal region (P = 0.025). DiscussionThe fact that volume reduction was greatest in the mid-region compared to the proximal region of the free AT may suggest greater tendon adaptation, via mechanotransduction pathways, in the mid-region and this may be important for tendon health and injury prevention.

Single-center retrospective review of standard versus minimal monitoring for hepatitis C direct-acting antiviral therapy

BackgroundHighly effective direct-acting antiviral (DAA) therapies have transformed the landscape of hepatitis C virus (HCV) treatment. However, there continues to be limited data regarding the efficacy and safety of required in-person clinic visits (standard monitoring) versus completely telehealth clinic visits (minimal monitoring) during HCV therapy, which could delay practice adoption. ObjectivesThis study aimed to assess the rates of undetectable HCV ribonucleic acid (RNA) in sustained viral load 12 weeks after therapy (SVR12) in standard versus minimal monitoring approaches during DAA. MethodsA 12-month, single-center retrospective cohort study was conducted in treatment-naïve HCV-infected adults who received DAA therapy between May 1, 2020, and April 30, 2021. The standard monitoring group had ≥1 in-person clinic visit with HCV RNA laboratory monitoring during DAA treatment. The minimal monitoring group had entirely telehealth visits without HCV RNA laboratory monitoring during treatment. Both groups received telephonic touchpoints throughout DAA treatment from a clinical pharmacist practitioner and a nurse care coordinator. The primary outcome was SVR12. ResultsFrom May 2020 to April 2021, 133 patients with HCV met inclusion criteria and were treated with DAA (standard, n = 56; minimal, n = 77), with no differences in baseline demographics. Overall, total encounters during DAA treatment remained significantly higher in the standard than minimal monitoring group (standard, 2.1 ± 0.8, vs. minimal, 1.7 ± 0.9; P < .01). Although minimal monitoring had higher loss to follow-up rates (standard, 7.1%, vs. minimal, 18.2%; P = 0.06), the modified intention-to-treat analysis showed no differences in sustained virologic response (SVR) between standard and minimal monitoring approaches (standard, 98.1%, n = 51, vs. minimal, 95.3%, n = 60; P = 0.41). ConclusionsThis single-center retrospective cohort study demonstrated that minimal monitoring during HCV treatment was as effective in achieving SVR cure rates as standard monitoring. Eliminating required in-person clinic visits during DAA therapy alongside a collaborative approach may play a major role in overcoming barriers to HCV care in select patients.

Performance of UHP-SWSSC-Filled CFRP and GFRP Tubes under Combined Sustained Load and Seawater Exposure

Performance of UHP-SWSSC-Filled CFRP and GFRP Tubes under Combined Sustained Load and Seawater Exposure

Distributed battery energy storage systems for deferring distribution network reinforcements under sustained load growth scenarios

Energy storage systems can be leveraged in electricity distribution network planning as mitigation alternatives to traditional grid reinforcements if they are strategically installed and operated to reduce congestion and voltage limit violations. This paper examines the technical and economic viability of distributed battery energy storage systems owned by the system operator as an alternative to distribution network reinforcements. The case study analyzes the installation of battery energy storage systems in a real 500-bus Spanish medium voltage grid under sustained load growth scenarios. The results show that, in general, dedicated battery energy storage systems are only a cost-efficient alternative in distribution system planning under very specific conditions, such as when low load growth rates are expected. Nevertheless, they are only required for peak shaving a few days per year. For the analyzed case study, the recoverable portion of their total cost through deferral of distribution system upgrades is higher than the fraction of cycles required for peak shaving under all sustained load growth scenarios. Therefore, it is also explored if mobile battery energy storage systems, capital grants, and revenue stacking can enable battery energy storage systems to become an efficient distribution system planning alternative.

Experimental study on the residual strength of butt adhesive joints subjected to systematic creep damage

AbstractUsing adhesively bonded joints is an effective strategy for achieving lightweight designs. However, understanding the long‐term performance of these bonded joints remains a critical concern. Creep is a time‐dependent phenomenon induced by sustained mechanical loads, which can lead to viscous strain in adhesive materials. This strain has the potential to cause cracking in bonded structures over time. This study aims to investigate the creep and post‐creep behaviors of adhesively bonded aluminum joints, focusing on two crucial parameters: creep load level and creep duration. Butt adhesive joint (BAJ) specimens were fabricated and exposed to varying creep loads and times. Subsequently, quasi‐static tensile tests were conducted to assess the residual mechanical properties. The results indicated that higher creep loads resulted in increased creep deformations at constant creep durations. Furthermore, a downward trend was observed in the residual tensile mechanical properties of BAJ specimens following creep. Specifically, higher creep load levels and longer times led to more pronounced reductions in joint strength, strain, and stiffness. These reductions in joint mechanical properties were corroborated through joint fracture surface analysis. Additionally, mathematical models were developed using response surface methodology (RSM) to predict the experimental joint residual mechanical properties under different creep loads and times.Highlights Investigation of creep and post‐creep behaviors in adhesive joints. Higher creep load levels result in greater joint permanent deformations. Impact of higher creep load levels and durations on joint failure strength. Decreasing in the joint deformability and stiffness after creep.

Changes in memory and cognition during the SARS-CoV-2 human challenge study

Patient-reported outcomes and cross-sectional evidence show an association between COVID-19 and persistent cognitive problems. The causal basis, longevity and domain specificity of this association is unclear due to population variability in baseline cognitive abilities, vulnerabilities, virus variants, vaccination status and treatment. Thirty-four young, healthy, seronegative volunteers were inoculated with Wildtype SARS-CoV-2 under prospectively controlled conditions. Volunteers completed daily physiological measurements and computerised cognitive tasks during quarantine and follow-up at 30, 90, 180, 270, and 360 days. Linear modelling examined differences between 'infected' and 'inoculated but uninfected' individuals. The main cognitive endpoint was the baseline corrected global cognitive composite score across the battery of tasks administered to the volunteers. Exploratory cognitive endpoints included baseline corrected scores from individual tasks. The study was registered on ClinicalTrials.gov with the identifier NCT04865237 and took place between March 2021 and July2022. Eighteen volunteers developed infection by qPCR criteria of sustained viral load, one without symptoms and the remainder with mild illness. Infected volunteers showed statistically lower baseline-corrected global composite cognitive scores than uninfected volunteers, both acutely and during follow up (mean difference over all time points=-0.8631, 95% CI=-1.3613,-0.3766) with significant main effect of group in repeated measures ANOVA (F (1,34)=7.58, p=0.009). Sensitivity analysis replicated this cross-group difference after controlling for community upper respiratory tract infection, task-learning, remdesivir treatment, baseline reference and model structure. Memory and executive function tasks showed the largest between-group differences. No volunteers reported persistent subjective cognitive symptoms. These results support larger cross sectional findings indicating that mild Wildtype SARS-CoV-2 infection can be followed by small changes in cognition and memory that persist for at least a year. The mechanistic basis and clinical implications of these small changes remain unclear. This study was funded through the UK Vaccine Taskforce of the Department for Business, Energy and Industrial Strategy (BEIS) of Her Majesty's Government. WT was funded by the EPSRC through the CDT for Neurotechnology Imperial College London.

Financial incentives to increase engagement across the hepatitis C care cascade among people at risk of or diagnosed with hepatitis C: A systematic review

BackgroundReversing declining rates of people initiating and completing hepatitis C (HCV) treatment, observed in many countries, is needed to achieve global HCV elimination goals. Providing financial incentives to increase HCV testing and treatment uptake among people at-risk of or living with HCV infection could be an effective intervention. We conducted a systematic review to assess evidence regarding the effectiveness of financial incentives to improve engagement and progression through the HCV care cascade. MethodsWe searched MEDLINE, PubMed and EMBASE for studies published from January 2013 to January 2023 that evaluated financial incentives offered to people living with and at-risk of HCV to increase HCV antibody and or RNA testing, linkage to care, treatment initiation, treatment adherence, treatment completion, and sustained viral load (SVR) testing. Open-label randomised controlled trials (RCTs), controlled non-randomised studies, cohort or observation studies and mixed-methods studies were included, whereas literature reviews, case series and studies which did not report data were excluded. ResultsWe identified 1,278 studies, with 21 included after full-text screening (14,913 participants); three randomised controlled trials and 18 non-randomised studies. Studies evaluated incentives aimed at improving test uptake (n = 11), engagement in care (n = 13), treatment initiation (n = 8), adherence (n = 3), completion (n = 3) and attainment of SVR (n = 5). Findings provided inconclusive evidence for the effectiveness of incentives in improving engagement in the HCV cascade of care. Determining incentive effectiveness to improve care cascade engagement was limited by low quality study designs, heterogeneity in type (cash or voucher), value (US$5 to $600) and cascade stage being incentivised. No randomised controlled trials assessed the effectiveness of incentives to promote HCV testing, and none showed an impact on treatment uptake. In non-randomised studies (observational comparative), some evidence suggested that incentives promoted HCV testing, but evidence of their role in promoting linkage to care, HCV treatment adherence and treatment completion were mixed. ConclusionCurrently, there lacks high-quality evidence evaluating whether financial incentives improve HCV testing and treatment outcomes. Future research should seek to standardise methodologies, compare incentive types and values to enhance engagement in HCV care, and determine factors that support incentives effectiveness.

Frost resistance of recycled aggregate concrete subjected to coupling sustained compressive load and freeze-thaw cycles

Recycled aggregate concrete (RAC) structures situated in cold regions are required to withstand the combined effects of mechanical load and environmental factors throughout their operational lifespan. The influence of sustained load introduces complexity to the degradation mechanism of RAC. This research examines the frost resistance of RAC across varying levels of recycled coarse aggregate (RCA) replacement (0, 50 %, 100 %) and sustained compressive loading (0, 0.3 fc, 0.5 fc). The frost resistance was quantified by the indices of macroscopic morphology change, mass loss, relative dynamic modulus of elasticity, and mechanical properties. Results show that 0.3 fc can effectively improve the frost resistance of RAC, a trend that becomes more pronounced with increasing replacement rates of RCA. Excessive stress (0.5 fc) was found to be unfavorable to the frost resistance of RAC and increase the compressive strength variability of RAC after freeze-thaw cycles. Analysis of meso/micro-structure characteristics using optical and scanning electron microscopes, along with the mercury intrusion porosimetry, reveals that optimal compressive loading (0.3 fc) enhances mortar integrity, reduces porosity, and improves compactness, thereby bolstering RAC’s frost resistance.

Sustained Ampicillin Loading and Releasing Ability of Novel In-Situ Ca2+ Functionalized Ternary GO/PVP/CMC Nanocomposite Hydrogel

Sustained Ampicillin Loading and Releasing Ability of Novel In-Situ Ca2+ Functionalized Ternary GO/PVP/CMC Nanocomposite Hydrogel

Experimental Study on Long-Term Performance of Tiered Geogrid-Reinforced Soil Walls under Sustained Loading

Experimental Study on Long-Term Performance of Tiered Geogrid-Reinforced Soil Walls under Sustained Loading

Experimental study on the impact of sulfate attack on the performance of shaft lining concrete under sustained compressive load

To investigate the impact of sulfate corrosion on the performance of shaft lining concrete under sustained compressive loads, this study immersed samples in a 10 % sodium sulfate solution after subjecting to sustained compressive loads of 0.2fcand 0.4fc. The variation in compressive strength, ultrasonic velocity, and dynamic elasticity modulus with corrosion age were examined. The corrosion mechanisms were analyzed using field emission scanning electron microscope and energy dispersive spectrometer. The impact tendency of concrete was also evaluated. The results indicated that under sustained compressive loads of 0.2fcand 0.4fc, the compressive strength, ultrasonic velocity, and dynamic elasticity modulus are all increased with age, in the order of 0.2fc> 0.4fc>no-load. When exposed to a 10 % sodium sulfate solution under sustained compressive loads, these properties initially increased and then decreased, peaking at 90 days of corrosion age, and the order was 0.2fc> no-load > 0.4fc when the corrosion age was longer than 240 days.The shaft lining concrete exhibited weak impact tendency, with the brittleness index increasing as the corrosion age progressed. The outcome of this work might provide a reference for the further research on the design of shaft lining concrete materials.

Association between different levels of suppressed viral load and the risk of sexual transmission of HIV among serodiscordant couples on antiretroviral therapy: a protocol for a two-step systematic review and individual participant data meta-analysis

IntroductionHIV is a major global public health issue. The risk of sexual transmission of HIV in serodiscordant couples when the partner living with HIV maintains a suppressed viral load of...

Factors affecting the tensile strength of bituminous geomembrane seams

The tensile shear strength, break location, and constant tensile load failure times are examined for seams made from one 4 mm-thick bituminous geomembrane (BGM) product, with corresponding observations specific to that material. In short-term tests, failure is observed within the sheet material once the seam strength exceeded 0.8 times that of the sheet material. The effects of seam thickness reduction and overlap width on seam strength are examined for two methods of seaming. Seams with a short-term strength meeting or exceeding 80% of the sheet strength are subjected to constant tensile loads between 18 and 55% of sheet ultimate strength and the time to failure is reported. The relationship between short-term seam strength and time to failure under sustained load and thickness reduction and squeeze-out is investigated. Constant tensile load testing is proposed as a construction quality assurance procedure to assess the degree of geotextile engagement of field seams.

Shear behavior of pre-damaged RC beams strengthened with UHPFRC-CFRP grid layer

Ultra-high performance fiber reinforced concrete (UHPFRC), incorporating recycled tyre fibers, and carbon fiber-reinforced polymer (CFRP) grid were utilized to strengthen the pre-damaged reinforced concrete beams caused by coupling action of sustained loads and marine environment. The failure modes, characteristic loads, deflection features, and strain behavior of the strengthened beams with various types of UHPFRC, thicknesses of UHPFRC layers, CFRP grid ratios, and CFRP grid layout angles were investigated. The results indicated that they exhibited the typical shear failure, and their characteristic loads increased by 102 %–205 % compared to the undamaged beam. By increasing the thickness of the UHPFRC layer and the CFRP grid ratio, and adopting 45° CFRP layout angle, the cracking stiffness, energy absorption capacity, and shear force sharing ability would be further improved, while adopting the UHPFRC incorporating recycled tyre fibers would decrease the ductility. Moreover, analytical models were developed to calculate the ultimate loads, manifesting reasonable accuracy.

Time-dependent behaviour of 3D printed fibre-reinforced limestone calcined clay cement concrete under sustained loadings

The evolution of 3D-printed concrete (3DPC) structures has made remarkable impacts in the construction industry and academia for prospective engineering practice globally. This is due to promising outcomes of various investigations on its construction coupled with several advantages it offers over conventional cast concrete. However, the time-dependent deformation of 3DPC under sustained loading is still unknown and requires extensive research. Quasi-static studies have also shown that creep could be of great concern due to its production technique involving layer stacking, which eventually leads to weak interlayer bond strength. This paper experimentally investigates the time-dependent behaviour of fibre-reinforced printed concrete (FRPC) containing limestone calcined clay cement (LC3) under sustained tensile and flexural loadings. The experimental tests conducted on LC3-FRPC specimens in two orthogonal directions were individual creep and shrinkage to determine other parameters associated with creep responses, including creep fracture. The specimens for tensile and flexural creep were subjected to sustained stresses of 40, 60 and 80 % of the tensile and 40 % flexural strength results obtained from quasi-static tests. The quantified creep is compared in terms of the difference in stress levels, as the results revealed that none of the specimens fractured under sustained loadings. Instead, higher direct tensile strengths were recorded for the creep specimens after 225 days loaded at different stress levels. Then, it is postulated that direct tensile tests on similar LC3-FRPC specimens without creep loading may confirm that the monotonic stress-strain response at the age at which the tests are terminated forms an envelope for creep fracture.