Effect of active confinement on the local bond stress-slip behavior of steel bars embedded in plain concrete with variable covers : experimental investigation and analytical modeling -

Thesis. M.E. American University of Beirut. Department of Civil and Environmental Engineering, 2015. ET:6301Advisor : Dr. Mohamed Harajli, Professor, Civil and Environmental Engineering ; Co-Advisor : Dr. Elie Hantouche, Assistant Professor, Civil and Environmental Engineering ; Committee Member : Dr. Shadi Najjar, Associate Professor, Civil and Environmental Engineering.Includes bibliographical references (leaves 34-36)Reinforced concrete structures are mainly designed for the concrete to carry compressive stresses and the steel to resist tensile stresses. Therefore, a composite interaction between concrete and reinforcing steel bars is necessary to achieve a good performance. This interaction depends on the local bond and slip behavior between the two materials. In the past, various experiments investigated the composite action between the concrete and reinforcing bars to examine the performance of reinforced concrete structures. Under monotonic increasing load, the influence of numerous parameters on the bond behavior were studied and it mainly includes the concrete compressive strength f'c, addition of fibers to concrete, bar diameter and geometry of the ribs, concrete cover, confining reinforcements, and transverse pressure. This study summarizes the results of a series of experimental and analytical studies on the effect of active confinement on the local bond stress-slip characteristics of steel bars embedded in plain concrete. Twenty specimens representing the confined region of a beam-column connection were tested under monotonic increasing load in tension. Different types of confinement and their effect on the local bond stress-slip response of reinforcing bars were investigated and compared. These include concrete cover-steel bar diameter ratio, and transverse applied pressure or active confinement. Based on the parameters that influence the bond strength, splitting, pull-out, and mixed mode failures were identified. A comprehensive analytical model predicting the local bond stress-slip response for steel bars embedded in plain concrete subjected to active confinement (transverse pressure) was developed. The model accounts for most of the important parameters that influence the behavior as observed in the experiment. The proposed analytical model shows acceptable agreement when compared against experimental results conducted as a part of this research

QTc prolongation during levofloxacin and triazole combination chemoprophylaxis: Prevalence and predisposing risk factors in a cohort of hematopoietic cell transplantation recipients

Background: QTc interval prolongation has been reported when combining fluoroquinolones and triazoles for chemoprophylaxis in cancer patients. Herein, we aimed to identify the prevalence and contributing factors to QTc prolongation in hematopoietic cell transplantation (HCT) recipients who received these agents during the neutropenic phase. Methods: This is a retrospective medical chart review conducted at a university hospital in Lebanon from 2017 to 2020. It included all adult HCT inpatients on antimicrobial prophylaxis with fluoroquinolones and triazoles and whose baseline ECG monitoring done prior to chemoprophylaxis administration, then on day-3 and day-6 of therapy, were available. Results: Overall, 68 HCT recipients met our inclusion criteria, of which 22% developed QTc prolongation. Based on bivariate analysis, female gender contributed to QTc prolongation (P = 0.001). There was a trend to QTc prolongation in patients with predisposing thyroid disease (P = 0.12), grade 2 vomiting and diarrhea (P = 0.16, P = 0.46, respectively), baseline hypokalemia (P = 0.18) and hypocalcemia (P = 0.3), hypomagnesemia on day-3 (P = 0.21) and day-6 hyponatremia (P = 0.36). Patients receiving two or more drugs with a known or probable risk of QTc prolongation (other than the fluoroquinolone/ triazole combination) were more prone to experience a prolonged QTc interval (P = 0.09). None of the patients that had QTc prolongation died or developed serious arrhythmias. Conclusion: The prevalence of QTc prolongation was 22% among HCT recipients on fluoroquinolone and triazole prophylaxis, yet we did not identify any independent risk factors for this issue. None of the patients that had QTc interval prolongation died or developed serious arrhythmias. © The Author(s) 2022

Modélisation multi-échelle de l'orientation des fibres dans des systèmes polymères visqueux renforcés de fibres

Thermoplastics reinforced with short fibers have gained prominence in engineering, notably in automotive applications. Accurate prediction of fiber orientation is crucial, as it profoundly influences mechanical characteristics. Previous research in this field has highlighted the complexity of fiber orientation within a flow. Most industrial simulations rely on macroscopic models that use pre-averaged quantities and closure approximations, often resulting in inaccuracies in predicting fiber orientation. To address this challenge and enhance accuracy, this study presents a novel approach based on resolving the Fokker-Planck equation at the meso-scale level, offering a more detailed and accurate model for predicting fiber orientation.In this work, the finite element method (FEM) is used to compute fiber orientation, providing a more precise representation of fiber behavior. Subsequently, the computed orientation tensor is integrated into the Stokes equations, creating a multi-scale fiber-flow model which enhances our understanding of the dynamic interaction between fibers and the surrounding flow. Furthermore, the research extends its scope to develop a two-phase flow model, reflecting real-world scenarios such as overmolding process. By leveraging the multi-scale model, this work aims to improve the accuracy of simulations in industrial applications, providing valuable insights for process optimization and design.Les thermoplastiques renforcés par des fibres courtes ont acquis une notoriété croissante en ingénierie, notamment dans les applications automobiles. La prédiction précise de l'orientation des fibres est cruciale car elle influence les caractéristiques mécaniques. Les travaux de recherche antérieurs dans ce domaine ont mis en exergue la complexité inhérente à l'orientation des fibres au sein d'un écoulement. La majorité des simulations industrielles s'appuient sur des modèles macroscopiques qui font usage de quantités préalablement moyennées et d'approximations de fermeture, engendrant fréquemment des inexactitudes dans la prédiction de l'orientation des fibres. Afin de relever ce défi, la présente étude propose une nouvelle approche reposant sur la résolution de l'équation de Fokker-Planck à l'échelle mésoscopique.La méthode des éléments finis (MEF) est utilisée pour calculer l'orientation des fibres, permettant une représentation plus précise du comportement des fibres. Le tenseur d'orientation ainsi calculé est intégré aux équations de Stokes, engendrant un modèle multi-échelle de l'interaction entre les fibres et l'écoulement environnant, ce qui enrichit considérablement notre compréhension de cette dynamique complexe. Finalement, un modèle d'écoulement à deux phases est étudié, reproduisant fidèlement des situations réelles telles que le processus de surmoulage. En exploitant ce modèle multi-échelle, cette étude vise à améliorer la précision des simulations dans les applications industrielles, offrant de nouvelles perspectives pour l'optimisation des processus et la conceptio

Modélisation multi-échelle de l'orientation des fibres dans des systèmes polymères visqueux renforcés de fibres

Les thermoplastiques renforcés par des fibres courtes ont acquis une notoriété croissante en ingénierie, notamment dans les applications automobiles. La prédiction précise de l'orientation des fibres est cruciale car elle influence les caractéristiques mécaniques. Les travaux de recherche antérieurs dans ce domaine ont mis en exergue la complexité inhérente à l'orientation des fibres au sein d'un écoulement. La majorité des simulations industrielles s'appuient sur des modèles macroscopiques qui font usage de quantités préalablement moyennées et d'approximations de fermeture, engendrant fréquemment des inexactitudes dans la prédiction de l'orientation des fibres. Afin de relever ce défi, la présente étude propose une nouvelle approche reposant sur la résolution de l'équation de Fokker-Planck à l'échelle mésoscopique.La méthode des éléments finis (MEF) est utilisée pour calculer l'orientation des fibres, permettant une représentation plus précise du comportement des fibres. Le tenseur d'orientation ainsi calculé est intégré aux équations de Stokes, engendrant un modèle multi-échelle de l'interaction entre les fibres et l'écoulement environnant, ce qui enrichit considérablement notre compréhension de cette dynamique complexe. Finalement, un modèle d'écoulement à deux phases est étudié, reproduisant fidèlement des situations réelles telles que le processus de surmoulage. En exploitant ce modèle multi-échelle, cette étude vise à améliorer la précision des simulations dans les applications industrielles, offrant de nouvelles perspectives pour l'optimisation des processus et la conceptionThermoplastics reinforced with short fibers have gained prominence in engineering, notably in automotive applications. Accurate prediction of fiber orientation is crucial, as it profoundly influences mechanical characteristics. Previous research in this field has highlighted the complexity of fiber orientation within a flow. Most industrial simulations rely on macroscopic models that use pre-averaged quantities and closure approximations, often resulting in inaccuracies in predicting fiber orientation. To address this challenge and enhance accuracy, this study presents a novel approach based on resolving the Fokker-Planck equation at the meso-scale level, offering a more detailed and accurate model for predicting fiber orientation.In this work, the finite element method (FEM) is used to compute fiber orientation, providing a more precise representation of fiber behavior. Subsequently, the computed orientation tensor is integrated into the Stokes equations, creating a multi-scale fiber-flow model which enhances our understanding of the dynamic interaction between fibers and the surrounding flow. Furthermore, the research extends its scope to develop a two-phase flow model, reflecting real-world scenarios such as overmolding process. By leveraging the multi-scale model, this work aims to improve the accuracy of simulations in industrial applications, providing valuable insights for process optimization and design

Surgery for unruptured Spetzler-Martin grade 3 brain arteriovenous malformations : a prospective surgical cohort

Background: There is uncertainty regarding the management of unruptured Spetzler-Martin grade 3 brain arteriovenous malformations (SMG3 ubAVM). Objective: To analyze our series of patients treated by surgery. Methods: A single-surgeon database of consecutively enrolled bAVMs (between 1989 and 2014) was analyzed. Adverse outcomes due to surgery were assigned within the first 6 weeks following surgery and outcome was prospectively recorded and assigned at the last follow-up visit by using modified Rankin Scale (mRS) score. Results: Of the 137 reviewed patients, 112 (82%) were treated by surgery, 15 (11%) were treated elsewhere or by radiosurgery, and 10 (7%) were recommended for conservative management. Surgery for SMG3 ubAVM was associated with adverse outcomes with a new permanent neurological deficit of mRS >1 in 23 of 112 (21%) patients. Permanent neurological deficit leading to a mRS >2 from surgery was 3.6% (95% confidence interval, 1.1%-9.1%). Late recurrence of a bAVM occurred in 3 of 103 (2.9%) patients who had complete obliteration of bAVM confirmed immediately after surgery and who were subsequently later followed with radiological studies during the mean follow-up period of 3.0 years (range, 6 days to 18.8 years). Conclusion: When discussing surgical options for SMG3 ubAVM, a thorough understanding of the significance and incidence of adverse events and outcomes is required to fully inform patients. For our series, the additional subclassification of SMG ubAVM (based on variables contributing to the SMG or age) would not have been of use.9 page(s

How does the participation of a resident surgeon in procedures for small intracranial aneurysms impact patient outcome?

Object. In this paper the authors' goal was to evaluate whether resident neurosurgeons participating in entry-level aneurysm surgery have a negative impact on patient outcomes. Methods. The authors searched the database for entry-level aneurysm surgeries (that is, those # 10 mm and located in the internal carotid artery [beyond the paraclinoid segment] and middle cerebral artery) performed in 1991 through 2005. The presence or absence of an advanced resident (in his/her last 3 years of residency) was noted. The analysis was examined in 3-year quintiles. A total of 355 cases (196 with resident participation and 159 without) were evaluated. Permanent adverse outcomes were seen in 11 patients (3.1% of the total study population), all due to branch artery occlusion. The incidence of permanent adverse outcomes in the first 3 years was 10.7% and 2.4% thereafter. This difference was statistically significant (p = 0.015). There was no difference in the incidence of adverse outcomes when comparing surgery performed with and without participation of an advanced resident. Conclusions. In this study the authors have demonstrated a learning curve in this series of patients. This study also suggests that involving residents in the repair of small unruptured aneurysms will not compromise patient care. In addition, patients can be informed that the team approach to their surgery is at least as good as having the experienced surgeon performing all aspects of the surgery.4 page(s

Quality of life and disability 12-months after surgery vs. conservative management for unruptured brain arteriovenous malformations: Scottish population-based and Australian hospital-based studies

Background Few data are available on disability and quality of life (QOL) after surgery versus conservative management for unruptured brain arteriovenous malformations (uAVMs). Objective The aim of this study was to test the hypothesis that QOL and disability are worse after surgery ± preoperative embolisation for uAVM compared with conservative management. Methods We included consecutive patients diagnosed with uAVM from a prospective population-based study in Scotland (1999–2003; 2006–2010) and a prospective hospital-based series in Australia (2011–2015). We assessed outcomes on the modified Rankin Scale (mRS) and the Short Form (SF)-36 at ~ 12 months after surgery or conservative treatment and compared these groups using continuous ordinal regression in the two cohorts separately. Results Surgery was performed for 29% of all uAVM cases diagnosed in Scotland and 84% of all uAVM referred in Australia. There was no statistically significant difference between surgery and conservative management at 12 months among 79 patients in Scotland (mean SF-36 Physical Component Score (PCS) 39 [SD 14] vs. 39 [SD 13]; mean SF-36 Mental Component Score (MCS) 38 [SD 14] vs. 39 [SD 14]; mRS > 1, 24 vs. 9%), nor among 37 patients in Australia (PCS 51 [SD 10] vs. 49 [SD 6]; MCS 48 [SD 12] vs. 49 [SD 10]; mRS > 1, 19 vs. 30%). In the Australian series, there was no statistically significant change in the MCS and PCS between baseline before surgery or conservative management and 12 months. Conclusions We did not find a statistically significant difference between surgery ± preoperative embolisation and conservative management in disability or QOL at 12 months

Do prophylactic steroids prevent chemical meningitis in surgery for epidermoid cysts? Case report and literature review

Background: Cranial and spinal epidermoid cysts (ECs) are rare and surgical resection can be complicated by chemical meningitis. Here, we treated a patient undergoing surgical resection of an intramedullary spinal EC with prophylactic steroids to help prevent postoperative chemical meningitis. Notably, we found a paucity of evidence regarding the efficacy of steroids used for this purpose. Case Description: A 44-year-old male presented with a rare intramedullary thoracic EC. He was given oral dexamethasone postoperatively and did not subsequently develop chemical meningitis. Here, we reviewed the current literature regarding the efficacy of steroid use for this purpose, utilizing multiple electronic databases (Ovid MEDLINE, Ovid EMBASE, and Scopus). We found only three studies (one case report, one case series, and a randomized controlled trial), that involved patients who received steroids. Of the 24 patients given prophylactic steroids, none developed fever or meningismus. One patient received 8 days of oral dexamethasone. Eleven patients received intraoperative hydrocortisone irrigation alone, while final 12 patients received intraoperative hydrocortisone irrigation plus a 3 week postoperative tapering course of oral steroids. Notably, all of the nine patients who did not receive any steroids developed postoperative fever, with 78% demonstrating meningismus. Conclusion: Here is level II evidence that establishes the efficacy of prophylactic steroids utilized in patients undergoing surgery for ECs to prevent postoperative chemical meningitis. Nevertheless, there is still no current consensus regarding either the type of steroid utilized, or the route of administration. </jats:sec

Complication-effectiveness analysis for brain arteriovenous malformation surgery : a prospective cohort study

Background: Intervention for brain arteriovenous malformations (bAVMs) should aim at treatment that is safe and effective. Objective: To analyze a prospective database to derive the probability of neurological deficit and adjust this risk for effectively treated bAVMs (complication-effectiveness analysis [CEA]). Methods: First, we calculated the percentage of surgical complications leading to a modified Rankin Scale >1 at 12 months after surgery for each Spetzler-Ponce class (SPC). Second, we performed a sensitivity analysis of these results by including bAVMs not undergoing surgery, to correct for bias. Third, we established the long-term cumulative incidence of freedom from recurrence from Kaplan-Meier analysis. Finally, we combined the results to calculate the risk of surgery per effective treatment in a complication-effectiveness analysis. Results: Seven hundred seventy-nine patients underwent 641 microsurgical resections. Complications of surgery leading to a modified Rankin Scale >1 at 12 months occurred in 1.4% (95% confidence interval [CI]: 0.5-3.3), 20% (95% CI: 15-26), and 41% (95% CI: 30-52) of SPC A, SPC B, and SPC C, respectively. The cumulative 9-year freedom from recurrence was 97% for SPC A and 92% for other bAVMs. The 9-year CEA risk was 1.4% (credible range: 0.5%-3.4%) for SPC A, 22% to 24% (credible range: 16%-31%) for SPC B, and 45% to 63% (credible range: 33%-73%) for SPC C bAVM. Conclusion: CEA presents the treatment outcome in the context of efficacy and provides a basis for comparing outcomes from techniques with different times to elimination of the bAVM.11 page(s