المستودع الرقمي لـكلية الهندسة

This paper presents valuable potential savings from fuel and financial expenses of a steam boiler being studied at Elkhmus power plant, Libya. For this research, a visual basic program was developed and being applied for analyzing the gathered data. Key findings pointed to an acceptable level of savings throughout the entire operations within the studied section of the power plant. The highest level of findings was found to be the increasing of thermal gain along with the total efficiency of the boiler as a result of using the exhaust temperature for heating-up the feed water to the boiler. It was clearly found that the increase of the total efficiency has a direct impact on saving the amount of consumed fuel, and thereby the financial expenses were saved by an average of about 11.6% arabic 16 English 78
Rajab HOKOMA, Nabil M. Muhaisen, Omran Alshogi(1-2014)

This paper is concerned with calculating boiler efficiency as one of the most important types of performance measurements in any steam power plant. That has a key role in determining the overall effectiveness of the whole system within the power station. For this calculation, a Visual-Basic program was developed, and a steam power plant known as El-Khmus power plant, Libya was selected as a case study. The calculation of the boiler efficiency was applied by using heating balance method. The findings showed how the maximum heat energy which produced from the boiler increases the boiler efficiency through increasing the temperature of the feed water, and decreasing the exhaust temperature along with humidity levels of the of fuel used within the boiler. arabic 15 English 78
Rajab HOKOMA, Nabil M. Muhaisen(1-2012)

The behaviour of concrete, whether fresh or hardened, depends basically on the behaviour of its components and the relationship between them, therefore, obtaining a concrete with certain properties depends fundamentally on the concrete mix design. Concrete mix design generally includes two main steps: 1-Selection of the main components suitable for the concrete (cement, aggregate, water, and additives); 2-Determination of more economical mix ratios to fulfil the workability, strength and efficiency requirements. Currently, there are many international methods locally approved for mix designs. They are all related to each other, they give relatively the same quantities of the mix components and they are all capable of providing a good concrete mix. It is important to consider that these methods give approximate quantities which should be checked by experimental mixes in order to obtain results suitable for the requirements of the local environment and local materials. The ACI and BS methods are the most commonly used. Both of these methods depend on graphs and standard tables derived from previous research experience and actual concrete production as well as studies of the properties of the materials used. This paper illustrates a new approach for concrete mix design named as: “Double Coating Method”, which is currently used in some research centers in the republic of Poland and was recently applied in the laboratories of the Civil Engineering Departments in the Universities of Tripoli and Benghazi in Libya. This paper describes experiment in which 24 mixtures were used to assess the usefulness of this technique for problem of proportioning concrete mixtures in general. arabic 5 English 37
Hakim S. Abdelgader (12-2020)

Two-layered Grouted Aggregates Fibrous Concrete Composite (TGAFCC) is a new category concrete which became popular recently and attracted the attention of researchers globally. Recent studies indicated that TGAFCC has notable improvement in mechanical properties, which has been sufficiently documented. However, the impact behaviour of TGAFCC when combined with Glass Fibre Mesh (GFM) and Textile Fibre Mesh (TFM) is still unexplored. The research objective is to study the effect of GFM and TFM inser- tion in TGAFCC against the drop hammer impact. Twenty one TGAFCC mixtures were prepared and divided into two series; non-fibrous concrete and fibrous concrete. The combined action of GFM and TFM of various diameters were inserted between the two layers and tested experimentally against drop mass impact. Additionally, all fibrous specimens were reinforced with a constant 3% dosage of 5D hooked end fibre. All specimens were tested under repeated drop mass impact as per ACI Committee 544. The impacts number or number of blows till the first visible crack and failure, impact energy at the first vis- ible crack and failure, impact ductility index and cracking configuration were examined. Besides, Weibull distribution was used to examine the variations in the test results, where impact numbers were pre- sented using the reliability function. The research findings indicate that inserting GFM and TFM between the two layers combined with 5D hooked end steel fibres, provided high impact resistance, higher absorbed energy and prolonged failure duration. Increasing the diameters of the GFM and TFM insertions, in both non-fibrous and fibrous concrete resulted in increasing the impact numbers till the first visible crack and failure. The experimental findings confirm that the major contribution of impact resistance comes from the 5D hooked end steel fibres, while the share of the intermediate meshes was significantly lower. arabic 13 English 88
Hakim S. Abdelgader (12-2020)

As we known the traditional concrete (TC) is primarily composed of a mixture of cement, fine and coarse aggregates, and water. TC is made by mixing together all the components before placing them. Using two-stage concrete to solve and to eliminate the problem of the aggregate segregation which appears in TC and in the self-compacting concrete. Two-stage concrete (TSC) is a type of concrete that is placed in two stages where the coarse aggregates are first placed inside the formworks and then the grout is pumped from underneath through a manual pump. The main difference between TC and TSC is the method of preparation and size of aggregates. The described above technology is unique as it allows us to prevent aggregate segregation in a ready mixture. The results presented in this paper indicate that this technology is promising for any kind of concrete applications. arabic 7 English 48
Hakim S. Abdelgader(1-2020)

Two-stage concretes, despite the fact that they have proven themselves in various types of construction, have not been studied to the same extent as traditional heavy concretes. Therefore, the article developed the composition of frame concrete with various additives in the composition of the cement-sand mortar. A comparison of the mechanical characteristics of the developed compositions with the addition of silica fume (SF) and superplasticizer (SP) in various combinations. In addition, test specimens were prepared with combinations of water/cement ratios of 0.45, 0.55, and 0.85, and cement/sand ratios of 0.5, 1, and 1.5. A total of 36 mixtures were prepared, silica fume was introduced as a partial replacement of cement in the amount of 6 wt.%. And a superplasticizer equal to 1.2 % of the cement content was added to the water. Compressive strength tests on two-stage concrete cylinders were carried out in accordance with ASTM-C873 and ASTM-C943. Tensile strength was also tested on 3 samples of each composition in accordance with the procedure described in ASTM-C496/C496M. As a result, the development of the strength of two-stage concrete for 7, 28 and 120 days was studied. It was found that the overall compressive strength of the two-stage concrete based on SF, SP and SF + SP was higher than in concrete without any additives. At the same time, the modified concrete has higher strength properties, because it provides better contact due to expansion, as well as by reducing the water-cement ratio in grout. The results obtained allow to design a cement-sand mortar capable of filling all the voids between the coarse aggregate, thereby creating a dense structure of two-stage concrete. arabic 9 English 58
Hakim S. Abdelgader(5-2019)

Since its invention by the Romans, concrete has been cast into all manner of formworks. Whether temporary or permanent, however, rigid formwork has been the traditional standard. Because concrete is the most widely used construction material, improvements in the economy of erecting concrete structures will have significant implications. One of the best opportunities for cost reduction is minimizing formwork costs—expenses that can represent about half the total cost of a concrete structure.1,2 Fabric formwork is a potential solution toward this goal. As a compounding benefit, fabric formwork can also enable the casting of structurally efficient, variable section building components.3 Taking advantage of fabric forms, however, is a joint task of concrete technology specialists, structural engineers, and architects. Fabric structures exhibit material and geometric nonlinearities when loaded, so forms must be designed based on experimentation or structural analysis using software capable of shape-finding.4,5 Education and research must focus on this barrier before the full potential of this formwork type can be realized. arabic 5 English 31
Hakim S. Abdelgader(7-2018)

تناولت هذه الورقة دراسة للوضع الحالي لأعمال الصيانة بشركة الواحة للنفط بغرض التحقق من مستوى التطبيق الفعلي لأساليب الصيانة الإنتاجية الشاملة في الشركة، هدفت الدراسة للتعرف على أوجه القصور في تنفيذ أعمال الصيانة الحالية لاقتراح ما يلزم استخدامه من مفاهيم حديثة لأعمال الصيانة، بغرض تحقيق النجاح والرفع من مستويات الأداء لكافة الاعمال المنفذة في الشركة. اعتمدت الدراسة استخدام استمارة استبيان تم تصميمها خصيصاً لهذا الغرض، بالإضافة إلى إجراء بعض المقابلات الشخصية مع من لهم علاقة بأعمال الصيانة في الحقول التابعة للشركة، اضافة الى استخدام أسلوب الملاحظة المباشرة لكشف بعض المعوقات والاخطاء في تخطيط وتنفيذ العمليات بالشركة. تمثلت المساهمة العلمية لهذه الورقة في تقديم حقيقة من أرض الواقع على مدى الفهم والدراية للأساليب الحديثة لأعمال الصيانة، واستناداً على ما تم تحليله من بيانات أوضحت النتائج وجود انخفاض في مستويات الأداء لأعمال الصيانة، وضعف ملحوظ في برامج التدريب والتطوير، وعدم وضع استراتيجيات مناسبة لبرامج الصيانة المخططة، وانخفاض مستوى السيطرة والتحكم في تنفيذ العمليات، كذلك وجود تدني في مستوى الجودة في عمليات الصيانة والإنتاج. كما اقترحت الدراسة على متخذي القرار ضرورة اتخاذ إجراءات فورية فعالة، ووضع استراتيجية لتنفيذ نظام الصيانة الإنتاجية الشاملة، والاهتمام أكثر ببرامج التدريب والتطوير، كما أشارت الدراسة الى ضرورة إدخال ثقافة التحسين والتطوير المستمر والتعريف بها لكل العاملين.
أ.د. رجب عبدالله حكومة, المعتصم بالله المبروك أحمد العكاري(1-2019)