Cyclic behaviour of infilled steel frames with different beam-to-column connection types

Mohammed A. Sakr,Mohammed M. Eladly,Tarek Khalifa,Saher El-Khoriby 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.30 No.5

Although numerous researchers demonstrated the significant difference in performance between the various beam-to-column connection types, most of the previous studies in the area of infilled steel frames focused on the behaviour of frames with welded connections. Therefore, there is a need for conducting studies on infilled steel frames with other common connection types (extended endplate with and without rib stiffeners, flush endplate and shear connections). In this paper, firstly, a two-dimensional finite-element model simulating the cyclic response of infilled steel frames was presented. The infill-frame interaction, as well as the interactions between connections’ components, were properly modelled. Using the previously-validated model, a parametric study on infilled steel frames with five different beam-to-column connection types, under cyclic loading, was carried out. Several parameters, including infill material, fracture energy of masonry and infill thickness, were investigated. The results showed that the infilled frames with welded connections had the highest initial stiffness and load-carrying capacity. However, the infilled frames with extended endplate connections (without rib stiffeners) showed the greatest energy dissipation capacity and about 96% of the load-carrying capacity of frames with welded connections which indicates that this type of connection could have the best performance among the studied connection types. Finally, a simplified analytical model for estimating the stiffness and strength of infilled steel frames (with different beam-to-column connection types) subjected to lateral cyclic loading, was suggested.

Evaluation of the role of ischemia modified albumin in neonatal hypoxic-ischemic encephalopathy

Talat, Mohamed A.,Saleh, Rabab M.,Shehab, Mohammed M.,Khalifa, Naglaa A.,Sakr, Maha Mahmoud Hamed,Elmesalamy, Walaa M. The Korean Pediatric Society 2020 Clinical and Experimental Pediatrics (CEP) Vol.63 No.8

Background: Birth asphyxia is a leading cause of neonatal mortality. Ischemia-modified albumin (IMA) levels may have a predictive role in the identification and prevention of hypoxic disorders, as they increase in cases of ischemia of the liver, heart, brain, bowel, and kidney. Purpose: This study aimed to assess the value of IMA levels as a diagnostic marker for neonatal hypoxic-ischemic encephalopathy (HIE). Methods: Sixty newborns who fulfilled 3 or more of the clinical and biochemical criteria and developed HIE as defined by Levene staging were included in our study as the asphyxia group. Neonates with congenital malformation, systemic infection, intrauterine growth retardation, low-birth weight, cardiac or hemolytic disease, family history of neurological diseases, congenital or perinatal infections, preeclampsia, diabetes, and renal diseases were excluded from the study. Sixty healthy neonates matched for gestational age and with no maternal history of illness, established respiration at birth, and an Apgar score ≥7 at 1 and 5 minutes were included as the control group. IMA was determined by double-antibody enzyme-linked immunosorbent assay of a cord blood sample collected within 30 minutes after birth. Results: Cord blood IMA levels were higher in asphyxiated newborns than in controls (250.83±36.07 pmol/mL vs. 120.24±38.9 pmol/mL). Comparison of IMA levels by HIE stage revealed a highly significant difference among them (207.3±26.65, 259.28±11.68, 294.99±4.41 pmol/mL for mild, moderate, and severe, respectively). At a cutoff of 197.6 pmol/mL, the sensitivity was 84.5%, specificity was 86%, positive predictive value was 82.8%, negative predictive value was 88.3%, and area under the curve was 0.963 (P<0.001). Conclusion: IMA levels can be a reliable marker for the early diagnosis of neonatal HIE and can be a predictor of injury severity.

Modeling of RC shear walls strengthened by FRP composites

Mohammed A. Sakr,Saher R. El-khoriby,Tarek M. Khalifa,Mohammed T. Nagib 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.61 No.3

RC shear walls are considered one of the main lateral resisting members in buildings. In recent years, FRP has been widely utilized in order to strengthen and retrofit concrete structures. A number of experimental studies used CFRP sheets as an external bracing system for retrofitting of RC shear walls. It has been found that the common mode of failure is the debonding of the CFRP-concrete adhesive material. In this study, behavior of RC shear wall was investigated with three different micro models. The analysis included 2D model using plane stress element, 3D model using shell element and 3D model using solid element. To allow for the debonding mode of failure, the adhesive layer was modeled using cohesive surface-to-surface interaction model at 3D analysis model and node-to-node interaction method using Cartesian elastic-plastic connector element at 2D analysis model. The FE model results are validated comparing the experimental results in the literature. It is shown that the proposed FE model can predict the modes of failure due to debonding of CFRP and behavior of CFRP strengthened RC shear wall reasonably well. Additionally, using 2D plane stress model, many parameters on the behavior of the cohesive surfaces are investigated such as fracture energy, interfacial shear stress, partial bonding, proposed CFRP anchor location and using different bracing of CFRP strips. Using two anchors near end of each diagonal CFRP strips delay the end debonding and increase the ductility for RC shear walls.

Physical characterization and radiation shielding features of B2O3-As2O3 glass ceramic

Mohamed Y. Hanfi,Ahmed K. Sakr,A.M. Ismail,Bahig M. Atia,Mohammed S. Alqahtani,K.A. Mahmoud 한국원자력학회 2023 Nuclear Engineering and Technology Vol.55 No.1

The synthetic B2O3eAs2O3 glass ceramic are prepared to investigate the physical properties and the radiation shielding capabilities with the variation of concentration of the As2O3 with 10, 20, 30, and 40%, respectively. XRD analyses are performed on the fabricated glasseceramic and depicted the improvement of crystallinity by adding As2O3. The radiation shielding properties are studied for the B2O3eAs2O3 glass ceramic. The values of linear attenuation coefficient (LAC) are varied with the variation of incident photon gamma energy (23.1e103 keV). The LAC values enhanced from 12.19 cm1e37.75 cm1 by raising the As2O3 concentration from 10 to 40 mol% at low gamma energy (23.1 keV) for BAs10 and BAs40, respectively. Among the shielding parameters, the halfevalue layer, transmission factor, and radiation protection efficiency are estimated. Furthermore, the fabricated samples of glass ceramic have low manufacturing costs and good shielding features compared to the previous work. It can be concluded the B2O3eAs2O3 glass ceramic is appropriate to apply in X-ray or low-energy gamma-ray shielding applications.

Effect of saffron (Crocus sativus L.) on sodium valporate induced cytogenetic and testicular alterations in albino rats

Saber A Sakr,Mohamed E Zowail,Amera M Marzouk 대한해부학회 2014 Anatomy & Cell Biology Vol.47 No.3

The present study investigated the cytogenetic and testicular damage induced by the antiepileptic drug, sodium valporate (SVP) in albino rats and the effect of saffron aqueous extracts. Treating rats with SVP caused a significant increase in the chromosomal aberrations either structural or numerical and decreased the mitotic index. Besides, animals administered SVP showed DNA damage appeared in the single strand breaks (comet assay). Testis of SVP-treated rats showed many histopathological changes. A significant decrease in seminiferous tubules and their epithelial heights diameters and inhibition of spermatogenesis was recorded. In addition, the number of sperm head abnormalities was increased. Biochemical results revealed an increase in malondialdhyde (MDA) which is lipid peroxidation marker and a significant decrease in the level of serum antioxidant enzyme, catalase (CAT) and reducing antioxidant power (RAP). Animals given SVP and saffron showed an improvement in chromosomal aberrations, mitotic index, DNA damage and testicular alterations caused by SVP. Moreover, MDA decreased and CAT and RAP increased. It is concluded from the present results that the ameliorative effects of saffron extract against SVP-induced cytogenetic and testicular damage in albino rats may be due to the presence of one or more antioxidant components of saffron.

Bond behavior between concrete and prefabricated Ultra High-Performance Fiber-Reinforced Concrete (UHPFRC) plates

Walid Mansour,Mohammed A. Sakr,Ayman A. Seleemah,Bassam A. Tayeh,Tarek M. Khalifa 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.81 No.3

Externally bonded ultrahigh performance fiber-reinforced concrete (UHPFRC) is commonly used as a strengthening material for reinforced concrete (RC) structures. This study reports the results of an experimental program investigating the bonding behavior between concrete and prefabricated UHPFRC plates. The overall experimental program is consisting of five RC specimens, which are strengthened using the different lengths and widths of prefabricated UHPFRC plates. These specimens were analyzed using the pull-pull double-shear test. The performance of each strengthened specimen is presented, discussed and compared in terms of failure mode, maximum load, load-slip relationship, fracture energy and strain distribution. Specimen C- 25-160-300 which bonded along the whole width of 160 mm recorded the highest maximum load (109.2 kN) among all the analysed specimens. Moreover, a 3D numerical finite element model (FEM) is proposed to simulate the bond behavior between concrete and UHPFRC plates. Moreover, this study reviews the analytical models that can predict the relationship between the maximum bond stress and slip for strengthened concrete elements. The proposed FEM is verified against the experimental program and then used to test 36 RC specimens strengthened with prefabricated UHPFRC plates with different concrete grades and UHPFRC plate widths. The obtained results together with the review of analytical models helped in the formation of a design equation for estimating the bond stress between concrete and prefabricated UHPFRC plates.

Effect of Intermittent Fasting on Glucose Homeostasis and Bone Remodeling in Glucocorticoid-Induced Osteoporosis Rat Model

Majed G. Alrowaili,Abdelaziz M. Hussein,Elsayed A. Eid,Mohamed S. Serria,Hussein Abdellatif,Hussein F Sakr 대한골대사학회 2021 대한골대사학회지 Vol.28 No.4

Background: The present study examined the effect of intermittent fasting (IF) on bone mineral content (BMC) and bone mineral density (BMD) and the markers of bone remodeling in a glucocorticoid-induced osteoporosis (GIO) rat model. Methods: Forty male rats were allocated to 4 groups (N=10 per group): control group of normal rats; control+IF group (normal rats subjected to IF for 16-18 hr daily for 90 days); dexamethasone (DEX) group: (DEX [0.5 mg i.p.] for 90 days); and DEX+IF group (DEX and IF for 90 days). By the end of the experiment, BMD and BMC in the right tibia were measured. Serum levels of the following were measured: glucose; insulin; triglycerides (TGs); total cholesterol; parathyroid hormone (PTH); osteoprotegerin (OPG); receptor activator of nuclear factor-κB (RANK); bone-resorbing cytokines, including bone deoxypyridinoline (DPD), N-terminal telopeptide of collagen type I (NTX-1), and tartrate-resistant acid phosphatase 5b (TRAP-5b); and bone-forming cytokines, including alkaline phosphatase (ALP) and osteocalcin (OC). Results: DEX administration for 90 days resulted in significantly increased serum levels of glucose, insulin, TGs, cholesterol, PTH, OPG, DPD, NTX-1, and TRAP-5b and significantly decreased BMD, BMC, and serum levels of RANK, OC, and ALP (all P<0.05). IF for 90 days significantly improved all these parameters (all P<0.05). Conclusions: IF corrected GIO in rats by inhibiting osteoclastogenesis and PTH secretion and stimulating osteoblast activity.