الفهرس 
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Abstract
Confinement effectiveness of externally bonded FRP jackets depends on different parameters including strength of concrete, steel reinforcement, FRP jacket stiffness, shape of cross section, aspect ratio (h/b) for non-circular sections and loading conditions. In case of FRP-confined rectangular columns, the cross-sectional aspect ratio affects significantly on the efficiency of this strengthening technique, whereas the effectively confined area of FRP-confined rectangular columns is a function of the dimensions of the rectangular columns and the radius of the corners. Therefore, in the updated version of the ACI 440.2R-08, the limitation of the aspect ratio of FRP- confined rectangular columns is extended from 1.5 to 2.0 as a limit to apply this strengthening technique, and the effect of the cross-sectionalaspect ratio (h/b) was added as a shape factor for noncircular cross sections columns confined by FRP.
A limited number of experimental studies have been performed on large-scale FRP-confined reinforced concrete columns having a rectangular cross section with a higher aspect ratio. Most experiments reported in the literature are focused on small-scale FRP-confined circular concrete column specimens or rectangular specimens with cross sectional aspect ratios less than 1.5. On the other side, few researchers investigated the behavior of large-scale FRP-confined and anchorage RC columns with higher aspect ratio.
It is necessary to the study of FRP-confined rectangular columns is the issue of effectiveness of FRP confinement, which may significantly decrease due to the presence of 90° comers or abrupt change of direction around the perimeter FRP tends to rupture at the sharp corners-square and rectangular due to the cutting effect of the concrete corner. In general, the effectiveness of confinement increases with the increase corner radius. Therefore, in the strengthening of non-circular columns, the sharp corners of the columns should be rounded to reduce the detrimental effect of the sharp corners on the tensile strength of the FRP, and to enhance the effectiveness of confinement. On other words, the cross section of rectangular shape columns,shape modification should be modified before applying FRP-confined strengthening system.
The Problem Statement:-
The previous studies have shown that the best performances of FRP-confined columns are obtained in members with circular cross-sections compared to members with square or rectangular cross-sections. Confinement of square and rectangular columns is not as effective as confinement of circular columns. Shape of cross-sections of columns can directly affect the confinement effectiveness of externally bonded FRP jackets.
This study investigates the technique of modifying the cross section by shape modification method to change the column’s shape cross section of square or rectangular column by rounded the sharp corners and the other method is performedbyusing anchorages at the long sides of RC rectangular column with different aspect ratios ≥ 1.5.
Research Significance and Main Objectives:-
This study investigatesexperimentally and analytically, the axially loaded behavior of RC modified non-circular columns with large-scale and high-aspect ratio (h/b) confined with carbon fiber-reinforced polymer (CFRP) sheets.Thirty-two normal strength reinforced concrete (RC) rectangular columns with different aspect ratios (h/b) were castto study the various parameters of RC short columns, externally confined with CFRP under axial static load. The experimental program was divided into threemain Groups of column specimens. group (A) for rectangular and square column specimens with rounded corners and two Groups (B and C) using the anchorage system for rectangular column specimens.For group A, sixteen RC rectangular columns with rounded comers were castwith different cross-sectional aspect ratios (h/b=l, 1.5, 2, and 3) and fully confined transversely with CFRP sheets with one layer, two layers and partially confined, where b is the smallest dimension of the column and h is the longest dimension of the column.Other additional sixteen RC rectangular columns with rounded corners and using the CFRP anchorages (B and C) with different cross-sectional aspect ratios (h/b= 1.5, 2, and 3), where (h) is the length of the straight portion of the longer side, (b) is the smallest dimension of the column of the original section, and then each column was fully confined transversely with CFRP sheets with one layer, two layers and partially confined.
The experiment results showed that the behavior of an axially loaded FRP- confined rectangular and anchorage reinforced concrete column is dependent on several parameters such as the number of layers, the cross sectional aspect ratio (h/b) also the shape of specimens, the mechanical properties of the confining material and confinement system. It is noted that with approximately the same FRP jacket thickness and certain aspect ratio, anchorage columns can provide higher axial strength and more ductility than rounded corner rectangular columns of CFRP- confined columns. The shape modification technique by using the CFRP anchorage has proven to be a very effective technique, method to significantly increase the compressive behavior for rectangular columns either by using rounded corners regardless the cross sectional aspect ratio and system type of confinement. The efficiency of FRP-confined system was proven to be lower with higher aspect ratio than that with the lower aspect ratio. In addition, increasing in the thickness of CFRP increases the gain in compressive strength, axial strain and ductility of FRP-confined columns with respect to unconfined columns.
Analytical models were proposed to predict compressive strength of FRP-confined and unconfined concrete strength for non-circular columns (square, rectangular and using the anchorage system).The Egyptian code ECP 208 [2005], ACI440 [2008], Triantafillou et. al. (2016) and Lix.et.al (2017).Different codes and analytical model not allowed to use partial wrapping of FRP to strengthen non-circular column, and gives limitation for use FRP wraps when strengthen non-circular column sections as rounded the edge of sections before fully wrapping.So, this study suggested proposed analytical models predicted compressive strength of FRP-confined and unconfined concrete strength for non-circular columns.The confining pressure depends mainly on the shape of cross-section, the type of confinement (Full and Partial wrapping) and mechanical properties of FRP composites.
The Proposed analytical models were assessed by comparing analytical values with corresponding experimental results, and the average ratios between theoretical and experimental strength, the coefficients of variation and the correlation factor was calculated to evaluate the performance of the analytical models. The proposed models are compared with existing models and showing good agreement with the experimental results and improved performance; it gives reasonable predictions of the test results.
The analytical model (1) is proposed in this research to predict the strength of fully and partially FRP-confined and anchorages of concrete columns showed a good estimation and approaches considerably to results obtained experimentally, with correlation factor and the coefficient of variation equal to 0.97 and 7.31%, respectively.
Both of the analytical models, proposed in this work and (ACI-2008, ECP-2005),Triantafillou et al. (2016) and Lix.et. al (2017)predicted the axial strength for fully and partially FRP-confined and anchorages of confinement concrete columns reasonably well, particularly, in case of that proposed in this work, which showed a better estimation approaching considerably to the experimental results.The proposed model (2) for rounded corners rectangular FRP-confined columns gives reasonable predictions of the obtained experimental results, with a good correlation factor equal to 0•98 and the lower coefficient of variation equal to 6.35%.
This study consists of five main chaptersas follows.
Chapter 1
This chapter presents a literature review for both theoretical and experimental works that have studied the parameters affecting the behavior of CFRP wrapped RC columns. Review for the main research about the constitutive relationship of concrete confined by transverse steel or FRP and both steel and FRP jackets are introduced.
Chapter 2
Thirty-two normal strength RC rectangular columns, were cast to study The newly conducted experiments 16 wrapped rectangular, square cross-sections of RC columns and 16 wrapped rectangular cross-section of RC columnswith CFRP anchorage are introduced in this chapter.Thischapter also includes the properties of materials, configuration of specimens, construction process, instrumentation, test setup, and testing procedures.
Chapter 3
The experimental results and data analysis are presented in this chapter. The effects of different variables on behavior of columns and the important observationsare also presented.
Chapter 4
This chapter contains the available analytical model, the suggested analytical model and the verification of the analytical model and via comparison with the experimental results
Chapter 5
This chapter includes the main conclusions and recommendations for