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- 저자 : Ahmed Mohammed Youssef Mohammed (검색결과 19 건)
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Comparative Nonlinear Behavior of Corroded Circular and Square RC Columns
Ahmed Mohammed Youssef Mohammed,Ali Ahmed,Koichi Maekawa 대한토목학회 2020 KSCE Journal of Civil Engineering Vol.24 No.7
This paper discusses performance of the reinforced concrete structures deteriorated by corrosion on basis of numerical simulation analysis. The purpose is to preliminarily investigate the idea of performance comparison of circular and square reinforced concrete columns under corroded conditions. Previous research carried out by the authors shows that equivalent area reinforced concrete (RC) columns exhibit similar load-displacement behavior under flexural and shear controlled conditions. The two types of columns deviate from this similarity after the corrosion of steel reinforcement present in the concrete. The change in the load-displacement behavior is highly dependent upon factors including the corrosion ratio, axial load, presence of web reinforcement etc., The experimentally verified 3D finite element modelling (FEM) program (COM3D) was used to investigate the seismic performance of the circular shaped and its equivalent area square shaped RC columns. The results show that the effect of mild corrosion (around 2% corrosion) on the load-displacement behavior of square RC columns is more significant as compared to circular RC columns at without axial load and at lesser main reinforcement ratio while a similar behavior or reverse trend is observed at higher main reinforcement ratios and for cases with 10% axial load. The effect of corrosion on the web reinforcement present in square columns is more pronounced as compared to circular columns at low main reinforcement ratios.
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Performance Comparison of Circular and Square RC Columns under Monotonic Loading Conditions
Ahmed Mohammed Youssef Mohammed,Ali Ahmed,Koichi Maekawa 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.1
Current flexural and shear design methods for reinforced concrete members are mainly based upon the rectangular cross-sectional shape. A simplified new approach for designing circular cross sectional Reinforced Concrete (RC) members might be to convert them to equivalent area, square shapes. An experimental study was performed on reinforced concrete circular cross sections and equivalent area, rectangular cross sectional members. The RC members were tested under non linear monotonic loading conditions, under both flexural and shear controlled conditions. Furthermore, the 3D FEM package COM3D was used to simulate the nonlinear performance of circular and its equivalent area, square members. Experimental and analytical results show that the circular RC members and its equivalent square have similar nonlinear performance (load-deflection behavior) in both flexural and shear controlled failure conditions. A good agreement was found in nonlinear performance of main design criteria; initial stiffness, flexural capacity, and shear capacity of both types. Based upon these results, the proposed approach can be considered satisfactory.
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Ali Ahmed,Ahmed Mohammed Youssef Mohammed,Koichi Maekawa 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.5
In current design practice, mostly architectural needs govern the shape of reinforced concrete columns. There is a need to study and compare the load-deflection behavior and failure pattern of high strength reinforced concrete columns of different shapes. This paper presents a correlation between the performance of equivalent area circular and square columns subjected to shear controlled cyclic loading. Square and circular columns with equal cross-sectional area were experimentally tested in this research. Experimental results show that the maximum load, number of loading cycles and maximum deflection in case of square and circular columns were found to be close however, the final failure pattern was different. In case of columns without shear stirrups, the square column resisted 6.7% more loading cycles as compared to the circular column. However, the square column showed 19% lesser deflection at ultimate stage. In case of columns with shear stirrups, square column resisted only 9% more loading cycles as compared to circular column and exhibited similar ultimate deflection. The fatigue performance of equivalent area circular and square columns was found to be comparable in shear controlled conditions. However, the final failure pattern of circular columns shifted from shear to flexure near final failure.
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Load Balancing in Cloud Computing Using Meta-Heuristic Algorithm
Youssef Fahim,Hamza Rahhali,Mohamed Hanine,El-Habib Benlahmar,El-Houssine Labriji,Mostafa Hanoune,Ahmed Eddaoui 한국정보처리학회 2018 Journal of information processing systems Vol.14 No.3
Cloud computing, also known as “country as you go”, is used to turn any computer into a dematerializedarchitecture in which users can access different services. In addition to the daily evolution of stakeholders’number and beneficiaries, the imbalance between the virtual machines of data centers in a cloud environmentimpacts the performance as it decreases the hardware resources and the software’s profitability. Our axis ofresearch is the load balancing between a data center’s virtual machines. It is used for reducing the degree ofload imbalance between those machines in order to solve the problems caused by this technological evolutionand ensure a greater quality of service. Our article focuses on two main phases: the pre-classification of tasks,according to the requested resources; and the classification of tasks into levels (‘odd levels’ or ‘even levels’) inascending order based on the meta-heuristic “Bat-algorithm”. The task allocation is based on levels providedby the bat-algorithm and through our mathematical functions, and we will divide our system into a numberof virtual machines with nearly equal performance. Otherwise, we suggest different classes of virtualmachines, but the condition is that each class should contain machines with similar characteristics comparedto the existing binary search scheme.
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Ahmed M. Youssef,Mohamed Al-Kathery,Biswajeet Pradhan 한국지질과학협의회 2015 Geosciences Journal Vol.19 No.1
Mountain areas in the southern western corner ofthe Kingdom of Saudi Arabia frequently suffer from various typesof landslides due to rain storms and anthropogenic activities. Toresolve the problem related to landslides, landslide susceptibilitymap is important as a quick and safe mitigation measure and tohelp making strategic planning by identifying the most vulnerableareas. This paper summarizes findings of landslide susceptibilityanalysis at Al-Hasher area, Jizan, KSA, using two statistical models:frequency ratio and index of entropy models with the aid ofGIS tools and remote sensing data. The landslide locations (inventorymap) were identified in the study area using historical records,interpretation of high-resolution satellite images that include Geo-Eye in 2.5 m and Quickbird in 0.6m resolution, topographic mapsof 1:10,000 scale, and multiple field investigations. A total of 207landslides (80% out of 257 detected landslides) were randomlyselected for model training, and the remaining 50 landslides (19%)were used for the model validation. Ten landslide conditioning factorsincluding slope angle, slope-aspect, altitude, curvature, lithology,distance to lineaments, normalized difference vegetation index (NDVI),distance to roads, precipitation, and distance to streams, were extractedfrom spatial database. Using these conditioning factors and landslidelocations, landslide susceptibility and weights of each factorwere analyzed by using frequency ratio and index of entropy models. Our findings showed that the existing landslides of high and very highsusceptibility classes cover nearly 80.4% and 79.1% of the susceptibilitymaps produced by frequency ratio and index of entropy modelsrespectively. For verification, receiver operating characteristic (ROC)curves were drawn and the areas under the curve (AUC) were calculatedfor success and prediction rates. For success rate the resultsrevealed that for the index of entropy model (AUC = 77.9%) is slightlylower than frequency ratio model (AUC = 78.8%). For the predictionrate, it was found that the index of entropy model (AUC = 74.9%)is slightly lower than the frequency ratio model (AUC = 76.7%). The landslide susceptibility maps produced from this study couldhelp decision makers, planners, engineers, and urban areas developersto make suitable decisions.
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Ahmed Mohamed Youssef,Biswajeet Pradhan,Hamid Reza Pourghasemi,Saleh Abdullahi 한국지질과학협의회 2015 Geosciences Journal Vol.19 No.3
This paper presents an evaluation of two bivariate statistical approaches, frequency ratio (FR) and weights-of-evidence (WoE) for landslide susceptibility mapping (LSM) at south-western part of Saudi Arabia, Jizan region. Landslide locations were identified and mapped from interpretation of high resolution satellite images (GeoEye 0.5 m and QuikeBird 0.6m), topographic maps (scale of 1:10,000), historical records, and extensive field surveys. A total of 106 landslide locations were mapped using Arc- GIS software and divided into two groups, 75% and 25% of landslide locations were used for training and validation of models, respectively. Eleven landslide conditioning factors such as elevation, slope, curvature, aspect, lithology, topographic wetness index (TWI), normalized difference vegetation index (NDVI), proximity to lineament, roads and rivers were considered in this evaluation. The effects of these factors on landslide occurrence were assessed using aforementioned bivariate statistical approaches. For validation, the models results were compared with landslide locations which were not used during the models building. Subsequently, the receiver operating characteristic (ROC) curves were established and area under the curves (AUC) was calculated for the landslide susceptibility maps using the success (training data) and prediction (validation data) rates. The results showed that the area under the curve for success rates are 0.861 (86.1%) and 0.839 (83.9%) and for prediction rates are 0.796 (79.6%) and 0.791 (79.1%), respectively for frequency ratio and weight-of-evidence models. The resulting landslide susceptibility maps showed five classes of susceptibility such as very high, high, moderate, low, and very low. The percentage of existing training and validating landslides data in high and very high zones of the susceptibility maps were calculated to be 90.02% and 76.03% for frequency ratio model and 88.33% and 79.3% for weight-of-evidence model, respectively. The results revealed that the frequency ratio and weights-of-evidence models produced reasonable accuracy. The resultant maps would be useful and can also help planners for general choosing favorable locations for development schemes, such as infrastructural, buildings, road constructions, and environmental protection.
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Mohamed Abdelkhalek,Ahmed Setit,Francesco Bianco,Andrea Belli,Adel Denewer,Tamer Fady Youssef,Armando Falato,Giovanni Maria Romano 대한대장항문학회 2018 Annals of Coloproctolgy Vol.34 No.4
Purpose: Revolutions have occurred over the last 3 decades in the management of patients with colorectal cancer. Most advances were in rectal cancer surgery, especially after the introduction of the total mesorectal excision (TME) by Heald. However, no parallel advances regarding colon cancer surgeries have occurred. In 2009, Hohenberger introduced a new concept trying to translate the survival advantages of TME to patients with colon cancer. This relatively new concept of a complete mesocolic excision (CME) with central vascular ligation (CVL) in the management of patients with colon cancer represents an evolution in operative technique. We performed a comparative study between CME with CVL and conventional surgery for patients with colon cancer at Italian and Egyptian cancer centers, considering surgical quality and clinical outcome. Methods: Seventy-nine Egyptian patients underwent conventional surgery (non-CME group) while 52 Italian patients underwent CME with sharp dissection between the embryological planes and CVL of the supplying vessels (CME group). Results: Significantly better results were observed in terms of lymph node yield (CME group: 22.5 vs. non-CME group: 12; P < 0.0001) and lymph node ratio (CME group: 0.03 vs. non-CME group: 0.22; P < 0.0001). Regarding surgical morbidity, no significant difference was noted (CME group: 2 vs. non-CME group: 5; P < 0.702). Conclusion: CME appears to be a safe procedure when performed by experienced hands through proper embryological planes. It also provides a superior specimen, with a higher lymph node yield, which consequently affects the lymph node ratio. Eventually, CME with CVL should be increasingly adopted and studied more deeply.
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Ahmed Youssef Altonbary,Hazem Hakim,Ahmed Mohamed El-Shamy 대한소화기내시경학회 2019 Clinical Endoscopy Vol.52 No.4
Background/Aims: Endoscopic ultrasound (EUS) has a limited ability to determine the nature of solid pancreatic lesions (SPLs). Mostrecent ultrasound processors are provided with elastography software, which allows quantification of the tissue hardness. The aim ofthis study is to evaluate the effectiveness of the elasticity score (ES) and strain ratio (SR) in the differentiation of benign pancreaticlesions from malignant pancreatic lesions. Methods: The study had a retrospective design; it included 97 patients with SPLs and 19 patients with inflammatory lesions. The ES andSR were determined during the examination; finally, EUS-guided fine needle aspiration was performed. Results: In this 2-year study, 116 patients were enrolled (97 with malignant lesions and 19 with benign lesions). There were 69 men and47 women. Their median age was 55.9 years. A cut-off point was detected at SR of 7.75 with a specificity of 99.9%, sensitivity of 90.7%,positive predictive value (PPV) of 99.9%, negative predictive value (NPV) of 67.9%, and accuracy of 92.2%. After adding the ES to theSR, the cut-off point at 7.75 resulted in a specificity of 94.6%, sensitivity of 99%, PPV of 98%, NPV of 98.5%, and accuracy of 97%. Conclusions: The use of the ES combined with the SR increases the accuracy of differentiation between benign and malignant SPLsand is an effective method for the evaluation of pancreatic masses.
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