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شهدت مدينة طرابلس الكبرى قفزة نوعية في العديد من التعاقدات لتنفيذ مشاريع تنموية في البنى التحتية والاسكان وما يتطلب من مشاريع مرافقة إلا أنها في الآونة الاخيرة ومع بداية هذا العقد عانت أغلب تلك المشاريع من العديد من المشاكل، مما انعكس سلباً على كافة مراحل التنفيذ، لذلك تم القيام بهذه الدراسة هذه الدراسة للوقوف على أسباب التأخير في تلك المشاريع، وبالتالي العمل على إثراء المكتبة الليبية بالبحوث الميدانية التي تتناول موضوع أسباب التأخير في إكمال المشاريع الإنشائية، ويمكن أن تلفت الدراسة الحالية اهتمام الباحثين إلى معرفة الاسباب والتي أدت إلى التأخير في المشاريع، ودراسة كل سبب من ناحية ظروف حدوثه، وأهم النتائج المؤثرة سلبا على المشروعات، ونسق مساهمتها في التأخير، ومن خلال هذه الدراسة تم التعرف على الأسباب التي أدت للمساهمة في عرقلة تنفيذ المشاريع ببلدية طرابلس الكبرى، لأجل التركيز عليها مستقبلاً بهدف تفادي حدوثها. arabic 177 English 0
رجب عبدالله عبدالقادر حكومة, عبدالوهاب احمد دريبيكة(1-2019)

In reinforced concrete design, the concrete in the tensile zone is assumed to be ineffective and increase the dead load of the structural elements. In order to reduce the self-weight, this paper examines the structural behavior of reinforced concrete beams containing lightweight concrete in the tensile region and normal weight concrete in the rest of the beam. The lightweight concrete was made from waste polystyrene. Four reinforced concrete beams were prepared with different depth of lightweight concrete. The control beam B1 consists of normal concrete. In Beams B2, B3 and B4, the depth of lightweight concrete was 25%, 50% and 75% of the total depth of the beam measured from the bottom surface respectively. A four-point bending test was conducted on all beams. The beams were loaded in increments until failure. At each load increment, the central deflection was determined. Cracks initiation and the mode of failure were observed during the experiment. The failure load was found to decreases with the increase of depth of lightweight concrete. The presence of lightweight aggregate tends to cause brittle failure. In addition, the mode of failure for reinforced concrete beams containing lightweight concrete was a shear failure. arabic 11 English 79
Hakim S. Abdelgader(6-2020)

The behavior of reinforced concrete beams containing fibers made of waste plastic straws (WPSs) under the three point bending test is examined. The eect of WPS fiber addition on the compressive and split tensile strength is reported. Four concrete mixes were prepared. The control mix PS-0 had a proportion of 1 cement: 1 sand: 2 coarse aggregate and a water cement ratio of 0.4. In the other three mixes PS-0.5, PS-1.5 and PS-3, 0%, 0.5%, 1.5% and 3% of WPS fiber (by volume) was added respectively. The results show that at 0.5% WPS, there is slight increase in compressive strength. However, beyond 0.5% addition, a decrease in compressive strength is observed. The split tensile strength shows a systematic increase with the addition of WPS fibers. The reinforced concrete beams containing WPS fibers show higher ductility as demonstrated by the larger ultimate tensile strain and ductility index (Du/Dy). There is a tendency to have more fine cracks with the presence of WPS fibers. arabic 9 English 76
Hakim S. Abdelgader(10-2020)

The performance of novel Layered Two Stage Fibrous Composite slabs (LTSFC) was pioneered under falling mass collisions using a combined experimental and numerical study. Such LTSFC slabs consist of three layers with and without the insertion of glass fibre mesh between the layers. LTSFC techniques were used to fabricate the composite slabs with three layers including 3%, 1.5%, and 3% of fibre content for the top, middle, and bottom layers respectively. Sixteen MLPAFC square slabs were cast with only short hooked end fibres and tested under falling mass collisions by amending two parameters namely the type of support (fixed and hinge) and support layout. Two distinct support layouts on two types of support were considered and tested with and without the glass fibre mesh between layers of LTSFC. A glass fibre mesh was introduced between the three layers to block crack growth propagation and absorb additional collision energy. The glass fibre mesh insertion between the layers and the LTSFC production technique were considered as novel modifications. A numerical study using Auto desk Fusion 360 was conducted and compared with experimental results. The numerical results showed fair agreement with the experimental test results. Based on the validated numerical models, collision energy and cracking pattern evolution were studied. The findings indicated that the glass fibre mesh insertion between the layers combined with steel fibres disrupted crack proliferation, thus exhibiting superior engrossed collision energy and postponing crack growth. Additionally, the engrossed collision energy at crack initiation and ultimate crack for the slabs with four sides fixed and hinged support were greater with respect to two opposite sides fixed and hinged support. Numerical values were in reasonable agreement with the experimental values in terms of collision energy and cracking patterns. arabic 13 English 81
Hakim S. Abdelgader(2-2021)

Multi-layered Prepacked aggregate fibrous composite (MLPAFC) is a new type of concrete, which is prepared in two subsequent stages of aggregate-fibre skeleton prepacking and cementitious grouting. In this study, ten MLPAFC mixtures were prepared in three subsequent layers incorporating different contents of four different types of steel fibres. Long and short hooked-end and crimped steel fibers were adopted with 3.0 and 1.5% dosages for the outer and interior layers, respectively. In-between the three MLPAFC layers, two layers of Glass Fiber Mesh (GFM) were inserted in five of the ten mixtures. The impact response of the MLPAFC mixtures was evaluated using two test methods. In the first, the ACI 544-2R repeated free-falling weight test was followed using disk specimens, while flexural free-falling weight on prism specimens was the second adopted impact test. Moreover, Weibull distribution was used to statistically analyse the discrepancies of the obtained experimental impact records. The impact tests results revealed that MLPAFC can absorb significantly high energy under falling weight impact due to its structure and the dual crack arresting activity of both steel fibers and GFM. The cracking number of impacts of MLPAFC cylindrical specimens without GFM was increased by approximately 530–870% compared reference specimens, while increment percentages reaching 1350% were recorded at failure stage. The impact resistance of MLPAFC prisms under flexural impact was noticeably improved, yet with lower percentages than cylindrical specimens. The insertion of intermediate GFMs let to additional developments in the impact strength of both cylindrical and prism specimens. arabic 14 English 97
Hakim S. Abdelgader (12-2020)

An efficient way to reduce the energy required for conditioning buildings and therefore to reduce CO2 emission is the use of proper thermal insulation in buildings' external walls. This measure requires data from metrological stations that can be used in the optimization of the thermal insulation. The main objectives of this study are to construct thermal climatic zones for Libya and to specify the optimum insulation thickness for external walls for the different zones. This work is comprehensive as the metrological data from all existing 33 weather stations has been collected and used for identifying thermal zones. For the optimization of the construction of external walls, the most commonly used local wall structures are investigated: hollow concrete block, limestone block and hollow brick. In addition, four thermal insulation materials: extruded polystyrene, expanded polystyrene, rock wool and foamed polyurethane are used with every wall type. Optimum insulation thickness, energy savings, energy cost and payback periods were estimated for the 33 locations using life cycle cost analysis. A map is constructed for the thermal zones based on degree-day values for the entire country. The results show that limestone blocks with expanded polystyrene insulation form the optimum wall construction as it provides the minimum total cost for all locations. Depending on the Degree-day values, the optimum insulation thickness varies between 5.4 and 15.3 cm across the country with energy saving varies between 28 and 178 $/m2. Using the optimum thickness, the average CO2 emissions can potentially be reduced by about 85%. Finally, a contour map represents the optimum thickness of expanded polystyrene is presented in this work. arabic 12 English 80
Samah Khlifa Otman Alghoul, (1-2021)

Prediction of the present and future state of Reinforced Concrete (RC) structures suffering from chloride-induced corrosion is important if proper planning for inspection and maintenance is to be made. The majority of research studies have thus far focused on the diffusion process of chloride ions through the concrete cover, the time to corrosion initiation and on the prediction of the surface condition of the structure. However; practical evidence and theoretical analysis suggests that many structures can tolerate considerable corrosion damage without serious reduction to their load carrying capacity. Therefore, visual impression-based maintenance is not an optimum solution particularly when financial resources are limited. To support this notion, accurate models are needed to predict the deterioration rate of the structural load carrying capacity over time. This paper uses existing empirical RC deterioration models to predict the loss in the load carrying capacity of a typical RC T-beam using a reliability based approach. The approach takes into consideration the spatial variability of the deterioration parameters, thereby demonstrating the importance of its inclusion in any such analysis. arabic 13 English 97
Omran Kenshel(1-2009)

This paper provides experimentally determined estimates of the scale of fluctuation of the principal variables employed in modeling chloride-induced corrosion for reinforced concrete; i.e., the surface chloride content (Cs) and apparent diffusion coefficient (Dapp). The estimation of the scale of fluctuation, θ, is based on the analysis of experimental data recorded on a bridge in South East Ireland prior to its extensive rehabilitation in 2007. In determining the scale of fluctuation the paper considers two commonly used methods; i.e., the maximum likelihood method and the autocorrelation curve-fitting method. The reliability of both methods is discussed. Introduction of the kriging statistical interpolation method is demonstrated to improve the reliability of the estimates of the scale of fluctuation. The results obtained from the analysis are compared with values in the literature proffered by other researchers. arabic 16 English 119
Omran Kenshel(1-2013)