Torsional improvement of reinforced concrete beams using ultra high-performance fiber reinforced concrete (UHPFC) jackets – Experimental study

• Torsional upgrading of deficient RC beams without transverse reinforcement using UHPFC jacketing technique (4-sided, 3-sided and 2-sided) was evaluated.
• Torsional performances of strengthened beams were compared experimentally and numerically.
• UHPFC jackets enhanced the torsional performance of RC beams.

The efficiency of using ultra high-performance fiber reinforced concrete (UHPFC) to strengthen reinforced concrete (RC) beams under torsion is investigated. The significant advantages of the applied UHPFC jackets are (i) its high compressive and tensile strength and (ii) its excellent rheological properties led to facilitate concrete casting in strengthening works, and that is of high interest to the researchers and practice engineers. This study includes experimental results of all specimens with different types of configurations and thickness of UHPFC. Ten beams with only longitudinal reinforcement (i.e., without transverse reinforcement) are strengthened with UHPFC on two, three, and four sides. One beam with the same reinforcement ratio but without UHPFC is used as the control beam. As well as, finite element analysis was conducted in tandem with experimental work to compare and justify the effective of repair technique. Results show the effectiveness of the proposed technique at ultimate torque for different beam strengthening configurations, crack patterns, and behavioral curves. Strengthened RC beams four sides with a thin layer of UHPFC exhibit an enhanced torsional behavior and higher capacity than strengthened beams three and two sides. The UHPFC can generally be used as an effective external torsional reinforcement for RC beams without stirrups. It was noted that the behavior of the beams strengthen with UHPFC jackets are better than the control beams. The use of UHPFC had effect in delaying the growth of crack formation. The finite element analysis is a good agreement with the experimental data.