flexural strengthening of deficient reinforced concrete beams with post-tensioned carbon composites using finite element modelling

The application of external posttensioned steel bars as an effective way to strengthen an existing bridge has been so far used in many different countries. in recent decades, however, they have been replaced by bars made from carbon fiber reinforced polymer (cfrp), as a material with high tensile strength and corrosion resistance, to address several concerns with steel bars such as their application costs and difficulties, and also their durability.  posttensioning these sheets can be a new efficient method in strengthening the beams and utilizing the high strength of these material.this study has focused on the flexural behavior of beams reinforced by posttensioned nonbonded cfrp sheets. 15 beams were categorized in 3 groups of 5m-, 10m-, and 15m-span in order to evaluate the effect of some parameters such as level of posttensioning, sheet length, and beam span on its load capacity, failure mode, ductility, and cracks behavior. the results indicate that even though the increase in posttensioning levels improves the effectiveness of the method, but this capacity improvement is much more for small span beams especially when cfrp sheets are 90% of the beam span, compared to long span beams. there has been a noticeable capacity increase around 50% in the beams when decreasing the sheet length from 90% to 45% of the beam span and also causing 11-14% increase in ductility in various conditions.