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Register a new userThe Effect of Fiber Reinforced Polymer Strengthened RC Beams on cracks width
تأثير تقوية الجيزان البيتونية المسلحة بالبوليميرات المسلحة بالالياف الكربونية في ضبط عرض الشقوق
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Tishreen University ورقة بحثية
Publication date
2015
fields
Structural Engineering
and research's language is
العربية
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Shamra Editor
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تطرح هذه الورقة دراسة تجريبية و تحليلية لتعيين عرض الشقوق في الجيزان البيتونية المسلحة المقواة بالبوليميرات المسلحة بالالياف الكربونية تحت تأثير الحمولات الدائمة و بسويات تحميل مختلفة و بنسب تقوية مختلفة. بما أن العلاقات المتوفرة لحساب عرض الشق الآني في حالة الجيزان البيتونية لا تلائم حالة الجيزان البيتونية المسلحة المقواة بالبوليميرات المسلحة بالالياف الكربونية[8] . تم اعتماد التحليل الإحصائي لبيانات نتائج تجارب من مصادر عالمية [6-9-10] و نتائج التجربة المجراة في مخبر البيتون في كلية الهندسة المدنية في جامعة دمشق (عام 2014) من أجل التوصل إلى علاقة رياضية تجريبية جديدة لحساب عرض الشقوق الآنية في الجيزان البيتونية المسلحة المقواة بالبوليميرات المسلحة بالالياف الكربونية و هذه العلاقة هي عبارة عن تابع للاجهاد في قضبان الفولاذ و مساحة البيتون المشدودة الفعالة و مسافة التغطية السفلية. كما تم التوصل إلى علاقة رياضية تجريبية تحسب عرض الشقوق طويلة الأمد في الجيزان الخرسانية المسلحة مقواة بالـ FRP تحت تأثير الحمولات الدائمة باعتماد نتائج التجربة المجراة من أجل هذا البحث (دمشق،2014).
This paper makes an experimental and analytical investigation of cracks characteristics in Fiber Reinforced Polymer strengthened RC beams under different levels of sustained load and Reinforced ratio. As the equations available for conventional RC beams are inappropriate for the calculation of the short-term crack width in FRP-strengthened RC beams[8], a statistical analysis is carried out on available test data from international sources [6-9-10] and from the test results obtained in the current study (Concrete Labor- Civil engineering Department- Damascus University-2014) to establish a new equation that considers the effect of the FRP laminates. This equation is a correlation of stress in steel bars, concrete surface tension , and effective side cover. The long-term crack width is then related to the instantaneous crack width by empirical equations which are derived from the test results obtained in the current study.
References used
ACI Committee 224R, ACI Manual of Concrete Practice Part 2, USA, 2004, pp.17-21
Broms, B., Crack Width and Crack Spacing in Reinforced Concrete Members, ACI Journal, 1965, pp.1237-1256
CEB-FIP Model Code, Comite Euro International Du Beton – London, 1990, pp.246-253
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In the last two decades, the use of advanced composite materials such
as Fiber Reinforced Polymers (FRP) in strengthening reinforced
concrete (RC) structural elements has been increasing. Research and
design guidelines concluded that externally bo
nded FRP could increase
the capacity of RC elements efficiently. However, the linear stressstrain
characteristics of FRP up to failure and lack of yield plateau have
a negative impact on the overall ductility of the strengthened RC
elements. Use of hybrid FRP laminates, which consist of a
combination of either carbon and glass fibers, or glass and aramid
fibers, changes the behavior of the material to a non-linear behavior.
This paper aims to study the performance of reinforced concrete beams
strengthened by hybrid FRP laminates.
This research aims to study the efficiency of flexural strengthening of RC beams with different lengths of CFRP strips by using (NSM) technique. The study is carried out experimentally on (14) concrete beams; the variables considered are (the length
and number of CFRP strips). This is established by dividing the work into two groups: the first one includes (6) beams strengthened by variable carbon fiber strip lengths and one strip, The second group includes (6) beams strengthened by variable carbon fiber strip lengths and two strips, as well as two control beams. The results indicate that carbon fibers have a noticeable effect on increasing the bearing capacity of (NSM) strengthened beams. The results also show that strengthening the beams by CFRP and not along the length of the beam and in one layer does not contribute to increasing beam strength, but when the number of layers increases, an increase in beam strength is noticed at a rate range (40%-72%).
Fiber reinforced polymer (FRP) plates have gained popularity in the strengthening of reinforced concrete (RC) members due to the high strength to weight ratio, the ease of installation and low maintenance costs compared to other systems such as steel
plates. Also, external bonding of fiber reinforced polymer (FRP) plate has been proven to be an effective method to strengthen and damage RC structures. However, not much attention has been given to the long-term behavioral aspects of FRP-strengthened RC members. It is difficult to accurately predict the long-term deflection, crack width and behavior of FRP-strengthened RC members.
This study presents a method for predicting the deflections at any time of the service life of normal and high strength concrete structures, loaded at any age, creep coefficient and shrinkage strain and the participation of the compressive steel for RC beams, and for RC beams strengthened with FRP plates.
The accurate prediction of deflections is a complex problem which requires the use of non-linear and time-dependent analytical methods. These methods are, in general, time consuming and require great effort[6-13]. However, at the design stage, simple but reliable methods which take into account the most important parameters influencing the long-term deflections may be very useful to adequately design the structure. For that purpose, many simplified methods have been developed [1-2-3-4-14]. Equations have been programmed to access the method combines the simplicity and accuracy and provides valuable information about the influence of each parameter on the increasing deflections with time.
The analytical values are compared to the experimental results from some existing papers [8-9], and to the results obtained from ACI code [1]. It is found that the analytical method is in a good agreement with the experimental results from some existing papers
[8-9].
Cracks are considered important defects in concrete elements, it was noticed after constructing the reinforced concrete walls related to the Foundation, that after a short time after the hardening of concrete and without any overloading on the wall,
there have been vertical cracks of regular distances along each wall we noticed this phenomenon it had happened in many construction projects. We have described the situation, we have also explained, analyzed it by examining its reasons. By a thorough study of three projects carried out in lattakia including scale decanter, building of a tourist hotel and a trade centre, which crack width ranging from 1.25 mm to 3 mm, the height differed in each case studied. Ultimately we have found the practical solutions to avoid this phenomenon including adoption of longitudinal joints for reinforced concrete walls, spacing is about thirty times the wall thickness in order to avoid cracks caused by shrinkage and thermal stress where the depth of joint about 20 mm and the width ranging between 15 mm to 20 mm implemented on both sides of the wall internal and external. After hardening of concrete and lifting the wooden template fill the joints with filler flexible materials.
The mixed use of steel bars and carbon rods in concrete beams can offer beams with different behaviour from that of steel reinforcement only. This paper studies the case of reinforcing concrete beams with two layers of bars, and the main parameters
investigated are the proportion and the distribution of carbon rods in the cross-section. Four groups containing 12 beams are tested, and each is reinforced with 4 bars located in two layers. The first group includes three control beams reinforced with steel bars, while the second includes three beams reinforced with carbon bars. Each of the third and fourth groups includes three beams reinforced with two steel bars and two carbon bars, whereas in the third group, steel bars are located above carbon ones, but in the fourth group, steel bars are located under carbon ones. Concrete beams reinforced with carbon rods in the second group exhibit a higher load carrying capacity and deflections, compared with other beams. However, the beams in the third and fourth groups have approximately the same load carrying capacity and the same behaviour up to the load level equal to 75% of their load carrying capacity. But after that, the beams in the fourth group become more deformed, compared with those of the third group.
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