الفهرس 
Chapter One IntroductionOnly 14 pages are availabe for public view
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Abstract
”The behavior of reinforced concrete (RC) frames depends on the properties of their components; beams, columns, and joints. A robust and safe frame performance can be achieved by the proper design and well reinforcement detailing of its components. Beam-column connections are the most critical region that plays a major role in the behavior of reinforced concrete frames. The proper reinforcement detailing of both the beam bars and the joint stirrups is essential for developing the maximum framing action of the connected beams and columns and ensuring a ductile response of the frame. Most recent codes specify requirements for ensuring the relevant detailing for both the beam bars and the joint reinforcement. Especially in exterior beam-column connection, the codes recommended that the beam bars terminated into the joint core must be fully anchored using standard 90-degrees hooks. These codes required the provision of sufficient column depth and a minimum vertical tail length of the hook. On the other side, the proper detailing for the joint reinforcement is achieved by providing a minimum stirrups area and a maximum spacing between the stirrups. The current study aimed to numerically investigate, using ABAQUS software, the effect of the vertical tail length of the 90-degrees hook, used for the beam bars, on the performance of exterior beam-column connection and to assess the optimum tail length needed for full anchorage and to develop a measure of the joint strength for different values of tail length. Furthermore, based on a parametric study on different sets of exterior joints considering the tail length, joint aspect ratio, column axial stress, and the concrete uniaxial strength, an accurate equation for the prediction of the joint shear strength has been developed. In addition, the study also investigated the influence of different joint stirrups configurations with greater spacing on the joint strength and deformation capacity. A wide range of vertical tail lengths, varied from 10 to 45 times the diameter of beam bars, have been examined. It has been found that joints with a vertical tail length of 30 times the bar diameter or greater give superior performance, which is attributed to the better bond condition in the joint region. This study reveals that the limits of tail length given by some international codes; e.g., ACI 318-19, ACI 352R-02, and EC-8, are inadequate. Moreover, the proposed equation for predicting the joint strength considering the vertical tail length, joint aspect ratio, column axial stress level, and the concrete uniaxial strength gives an accurate prediction when compared to the reference experimental results. Different sets of beam-column connections with different joint stirrups configurations have been modeled with greater spacing between the stirrups. This study reveals that achieving the codes minimum joint reinforcement ratio using both internal cross ties and outer stirrups with greater spacing between the stirrups instead of outer stirrups only is more efficient in terms of joint strength and deformation capacity, which indicates that the contribution of the cross ties considering its shape and location in the shear strength resistance should be considered. As a result, the key role of the joint stirrups should be considered as a tension tie and a crack-controlled reinforcement that requires less steel and wider spacing for the joint details rather than the confinement of the concrete. Consequently, the ACI 352R-02 requirements for the number of joint stirrups are superfluous. Furthermore, it has been observed that both the joint strength and deformation capacity have been significantly improved with the use of three layers of stirrups with two closed rectangular cross ties or one polygon cross tie within the joint region located at the top, the middle, and bottom of the joint core. However, the employment of only two layers of stirrups with two closed rectangular cross ties located at the middle third of the joint as well as diagonal bars at the joint corners between the beam and column successfully controlled the joint cracks as well as achieving satisfactory performance of the connection. Thus, the latter approach is highly recommended for achieving proper detailing for the joint reinforcement with great spacing between the stirrups so that it does not exceed 70 percent of the minimum width of the column nor the distance required to prevent buckling of the bars according to the codes. The results also proved that the induced stress in the joint stirrups does not necessarily reach their yield strength even at the instant of joint failure. Hence, the yielding assumption of joint reinforcement in some analytical models and different international codes is unsafe and needs some revision.