الفهرس 
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Abstract
he external confinement of reinforced concrete columns to improve their capacity and ductility has attracted many researchers. The application of casting concrete through UPVC tubes has been used as a new technique for external confinement of reinforced concrete columns. This investigation aims to study the effectiveness of unplasticised poly vinyl chloride (UPVC) tube as outer confining layer in order to increase the load carrying capacity, ductility and fracture toughness of the column. Several parameters are considered in the research program. These parameters are concrete grade level (20 MPa, 30 MPa and 40 MPa), column aspect ratio (4.55, 6.36 and 9.09), column diameter to thickness ratio (16.1, 20.8 and 50.0), adding polypropylene fiber volume fraction to concrete (0.15% and 0.30%) and internal surface configurations of UPVC tube. To study the effect of using UPVC tube as external reinforcement for repairing process, four strengthening configurations are applied. The columns are tested under uni-axial compression loads and the load carrying capacity, ductility and fracture toughness are determined. from the experimental results, the load carrying capacity increases due to UPVC confinement in range of 30%:45% depending on concrete grade level. Also, the increase in concrete grade level decreases the column ductility by 26% and 56% for the concrete grade level of 30 MPa and 40 MPa, respectively compared with that of 20 MPa concrete grade level. The increasing in H/D and D/T ratios decreases the load carrying capacity. The vertical stiffeners enhance the load carrying capacity while the horizontal stiffeners enhance the ductility. Finally, the strengthening applications, it was found that using both single cut and double cuts techniques enhance the load carrying capacity, the ductility and the fracture toughness of reinforced concrete columns. The corresponding experimental results are compared with developed models on confinement theory and presented in this research work