الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
In current practice, moment resisting RC frame structures are designed based on the capacity design philosophy by introducing the weak beam-strong column hierarchy of strength to prevent soft-story and global collapse due to the seismic actions. Capacity design succeeded to prevent building collapse, and allow buildings to sway and stand, and allow people to evacuate during any seismic event. Due to the weak beam-strong column hierarchy of strength, beam ends, and base columns are identified to form plastic hinges. Several undesirable consequences are associated with plastic hinges formation. The first is damage of the beams at the plastic hinge zones, and the second is beams elongation. According to the literature, after many seismic events, many buildings designed according to the capacity design philosophy and meet the life-safety performance level, were deemed too expensive to be repaired and were consequently demolished. These and other unanticipated consequences of severe earthquakes have led to an increased concern over the repair ease and cost, raising the awareness over the need for new, more stringent, design requirements that go beyond collapse prevention and guarantee low damage to the structural elements. Beam-column connection plays a key role for maintaining the integrity and stability of the moment resisting RC frame structures. Due to the associated undesirable consequences due to plastic hinge formation, the slotted RC beam-column connection was introduced as a successful low damage substitution of the conventional RC beam-column connection. It consists of a conventional reinforced concrete beam, modified with a narrow vertical slot at the column face, running approximately three quarters of the beam 194 depth. It was first introduced in 1999 and went through many developments since that time. Indeed, its ability to resist earthquake demands with low damage and low beam elongation compared to the conventional RC beam-column connection has been proven. Unfortunately, despite the good performance of the slotted connection in reducing beam elongation and damage to the plastic hinge zones at the beam ends, a premature mode of failure of such connection due low-cyclic fatigue of the beam longitudinal bottom reinforcement bars was recorded in the literature. These issues have been reviewed in Chapter 2. In this contribution, enhancement of the cyclic behavior of the slotted RC beam-column connection by improving the low-cyclic fatigue life has been achieved through an extensive experimental program followed by a finite element micro modelling. Then, deep investigate the findings of the experimental program was conducted. Two different parameters were investigated experimentally. The first parameter worked to enhance the low cyclic fatigue life based on reducing the strain amplitude during the fully reversed cyclic loading, this was achieved by increasing the unbonded length of the beam bottom longitudinal rebars gradually from 120mm, 180mm, and up to 240mm. The second parameter worked to enhance the low cyclic fatigue life by applying a compressive mean strain during the cyclic loading. This was achieved by applying a post-compression force to the beam bottom longitudinal rebars using post-tensioning technique. Five different test specimens were investigated experimentally. The first specimen investigates the behavior of an exterior RC moment resisting monolithic beam-column connection “RCB” as a benchmark specimen 195 designed according to Chapter 21 of ACI 318-11 [17]. The next three test specimens were slotted RC beam-column connections with different unbonded length 120mm, 180mm, and 240mm and were designed to get the same flexural capacity of RCB. The last test specimen was identical to slotted connection with 180mm unbonded length in addition to adding an unbonded post tensioned rods attached to beam. This experimental program has been extensively described in Chapter 3. DIANA 10.3 [3] was used for constructing a detailed 2D finite element micro model for the current study. In Chapter 4, the numerical micro modelling was first described in terms of the appropriate constitutive models that are available in the program to simulate the behavior of RC beam-column connections under cyclic loading, elements, and nonlinear analysis procedure. 2D finite element micro models for the different experimental test specimens were constructed. The results of the FEM were verified against the experimental program results in terms of general behavior and hysteresis response, crack pattern and stress-strain over the unbonded length. A good agreement was achieved in predicting the actual behavior of the experimental test specimens. Chapter 5 presents a parametric study based on the findings of the experimental program and incorporating the capabilities of the verified finite element micro models. A more in-depth investigation of the unbonded length parameter that affect the low cyclic fatigue life of the slotted connection was conducted. A method to predict the low cyclic fatigue life of the slotted beam-column connections was proposed by incorporating the low cyclic fatigue strain energy-based theories with the stress-strain results obtained from the finite 196 element model and a good agreement was achieved in predicting the low cyclic fatigue failure. Then, the consequences of increasing the unbonded length of the beam longitudinal bottom rebars on stiffness, strength, and crack pattern were investigated. The verified finite element micro models were used to apply more unbonded lengths parameters, Accordingly, several conclusions were drawn in this regard. Then, the proposed method was used to find a recommendation for the optimum unbonded length to satisfy a specific low cyclic fatigue damage level.