The Torsional Behavior of Transversely Opened Reinforced Concrete Beams Strengthened by Steel Pipe

One way to strengthen beams with transverse openings is by adding material, such as steel plates or braces, around the openings. This addition helps distribute the load more evenly and reduces stress concentration at the weak points. In this study, experimental investigations were conducted to evaluate the effectiveness of using steel pipes of different sizes and thicknesses to improve the torsional behavior of reinforced concrete beams with different sizes of transverse openings. Another goal is to investigate the impact of different steel pipe orientations on the final twisting moment and twist angle. The experiment involved casting and testing fifteen rectangular reinforced concrete beams under pure torsion. The dimensions and reinforcement of all beams were similar. The specimens were divided into four groups, the first of which had a control beam made of a single beam cast without any openings. Using 4 mm diagonal reinforcement applied to each face of the beam and rounding the opening with PVC pipe from the second group, two beams with varying opening diameters (75 and 100) mm were strengthened. The third group consists of four beams that were strengthened using steel pipe welding at a double angle (32×32×3) mm to form a T-section with two orientations (45o and 90o). These beams were cast with transverse apertures. Six beams were cast as the fourth group to study the thickness effect on steel pipe (2, 3, and 4) mm, representing 50%, 75%, and 100% of stirrups’ nominal diameter. The results revealed that diagonal reinforcement with small openings did not affect torsional behavior. On the other hand, the diagonal reinforcement did not substitute for the missing torsional strength of the large opening in the beam. The ultimate torsional loads that result from the two orientations of steel pipes (450 and 900) were almost identical. Also, internal pipe deformation is prevented by utilizing a steel pipe at least 3 mm thick (0.75 of the stirrups' diameter), increasing protection for this area. Hence, beams with small openings and beams with a pipe thickness of 4 mm (1.0 of the stirrups diameter) are similar in toughness and initial stiffness.