الفهرس 
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Abstract
Strengthening and rehabilitation of existing structures are becoming the main part of the construction activities. Different strengthening and rehabilitation techniques are used to improve the column strength under different load conditions like eccentric loadings. In the last decade, a novel technique has been used in strengthening RC structural elements is ultra-high performance fiber reinforced concrete (UHPFRC).
This study involves an experimental investigation on the structural behavior of RC columns strengthened with UHPFRC under concentric and eccentric loadings. Sixteen rectangular R.C. columns were cast and tested; each (120 x150-mm2) cross-section and 1000 mm clear height. Four columns were tested under concentric and twelve columns were tested under eccentric loading with an eccentricity ratio of (0.25 and 0.50). Several parameters such as load eccentricity ratio (e/t), the thickness of UHPFRC, the volume fraction of steel fiber, and strengthening schemes were considered.
The experimental results showed that the UHPFRC is an effective strengthening technique to improve the strength, moment capacity, stiffness, and toughness of RC columns under concentric and eccentric loadings. The gain in axial load capacity, moment capacity and stiffness is proportional to thickness of UHPFRC jacket and inversely proportional to the eccentricity ratio. In specific, the full casting scheme of UHPFRC jacket was more effective than bonding laminates scheme.
Finally, P-M interaction diagrams of the tested columns were generated analytically to predict columns capacities; the comparisons between the experimental results and analytical calculations revealed that a good agreement can be achieved by the analytical model.